I've got this 8TS30 on the bench, and I should start by saying that this is the 2nd 8TS30 I've done, and about the 8th 630 chassis set....so I'm very familiar with them.....but I've run into an issue that I can't seem to get a handle on.

Started with a recap, and replaced the wirewound resistor and bad sections of the candohm in the metal box behind the transformer. Powered it up, got perfect sound but no HV. The only thing that I didn't check was the large wirewound in the HV cage. Sure enough, it was open. Now here's where things get interesting:

http://www.earlytelevision.org/pdf/rca-630ts-sams-54.pdf

Third page, illustrated about 10:00 to the 5V4 in the diagram, is R123....which was the open resistor. I replaced it, and variac'd it up. About 5 seconds after I hit the power at about 78 volts or so, R127B started arcing and smoking (shown on page 2, lower right). I replaced R127B with a Dale chassis mounted resistor of the correct resistance and wattage.

The first thing I thought of was that I wired the resistors incorrectly. I then stuck an untouched 8TS30 on the bench next to it, and traced out the wiring. Everything looks correct. Next, I pulled the chassis out of a restored 8TS30 to triple check my work. Again, everything I did is correct from what I can see.

Kind of at a loss as to how to proceed. Ideas/thoughts? I'm thinking there's another issue that this set has, as there's a lot of circuitry between R127B and R123....but since R123 comes right off the flyback, being open it wasn't engaging any of the HV.

If R123 is now a chassis mount dale, then what are the odds that the yoke voltage on it is enough to short thru the dale to it's chassis mounting and load the heck out of the fly?

Yeah, but he said he replaced 127B with a Dale chassis mount,which should have no connection to the yoke?

I can't see that R127B supplies any source voltages to the horizontal or vertical circuitry. Looks like it supplies negative bias to the video and sync circuits. R127B is in series with the negative voltage on the center tap of the 5U4 transformer winding - that feeds the focus coil and Ion trap, which is also in series with R128B-C and continues to ground. So basically you have a negative voltage source being divided across several resistors all in series to ground, negative bias voltages picked off to bias the video and sync circuits. Have you slowly powered back up since you replaced R127B?

I just noticed that R127B also feeds a negative bias voltage to the grid of the 6K6 audio output, but that should be isolated through a 270k resistor in series with the 6K6 grid. However the 270K(R76) may be worth investigating.

Yeah, but he said he replaced 127B with a Dale chassis mount,which should have no connection to the yoke?


I never mentioned 127B. I was talking about R123. I think you misread my post....Though Kamakiri did not say what he replaced R123 with so perhaps I misread his post.

Sorry. I lumped R127B and chassis mount Dale together. And I took it he was now concerned with why R127B smoked. We may be missing information.

I replaced R123 with a wirewound of the same spec. That's why the set had no HV, it was open. I replaced R127B with a chassis mounted Dale resistor, but now that I think about it, I dressed the lead at a 90 degree angle, and there was *maybe* 1/4" clearance between the chassis and the resistor. Is it possible that all I did was create a gap just large enough for spark to jump to chassis ground?

I haven't replaced the resistor and powered it up since. Figured I'd verify all my work before I did.

When that thing sparked, it was like a welding arc......

The source of voltage across that group of series resistors that forms the focus coil, Ion trap, and bias network( includes R127B) , comes from the center tap of the 5U4 low voltage rectifier winding. Measuring across C1C to ground, you should have a negative voltage of less than 150.

FWIW, I would first suspect a hard B+ short-to-ground (possibly from the H.centering control or V.centering control to ground).
A hard short on the B+ line would throw a huge current draw on the 5U4 and its centertapped HV winding, and cause a large overcurrent through the resistor chain off the centertap, which includes R127B (it's the highest resistance in the chain, so it will run the hottest).

I think you probably nailed it there old-coot88. But I was sort of hoping we could at least fire up the dim bulb tester, maybe get a few voltage measurements. At least for me, most of the fun is learning how to walk through the circuit and do some basic DC troubleshooting. But I also understand that time is money. :D

Well, it's also an opportunity for a noob to see how the back-bias system works to supply negative voltages. The centertap of the HV winding, instead of going directly to ground as it normally would, goes through a resistance that's tapped for the different (-) voltages.

Troubleshooting without understanding the back-bias thing would be confusing, as evidenced in the thread.
(Of course in this case, there's also a focus circuit and ion trap whose summed resistance forms part of the resistor chain.)

Well, you've given me a place to start, appreciate that!

The set that I restored that was working fine (not this one obviously), all I did was remove and reinstall the resistor cover and look at my wiring that I did. That's IT.

Decided to watch that set for a little while, turned it on, and guess what? No raster. Removed the cover, and everything looked as it was. I didn't even pull the chassis. So now I have to figure that one out too.

#&%@ televisions. :rant:

I think you probably nailed it there old-coot88. But I was sort of hoping we could at least fire up the dim bulb tester, maybe get a few voltage measurements. At least for me, most of the fun is learning how to walk through the circuit and do some basic DC troubleshooting. But I also understand that time is money. :D

For me, it's difficult because I've never had any formal electronics training whatsoever. Heck, I've never even had the benefit of someone in person walking me through a set step by step. It was just something that I wanted to do ever since I was a boy, so I pick it up as I go and have been doing that for the last decade or so.

I've restored close to 100 sets over the years, but every one of them was done by either recapping and getting lucky, or working through electronic principles and developing a rudimentary understanding of how things work along with problems associated with different circuits and how to resolve them.

I can recap a 630 chassis in 2-3 weeks, and my work is very precise. Hands, I've got. Diagnostic skills, not so much. Doesn't stop me from trying and learning though.

Well, you've given me a place to start, appreciate that!

The set that I restored that was working fine (not this one obviously), all I did was remove and reinstall the resistor cover and look at my wiring that I did. That's IT.

Decided to watch that set for a little while, turned it on, and guess what? No raster. Removed the cover, and everything looked as it was. I didn't even pull the chassis. So now I have to figure that one out too.

#&%@ televisions. :rant:

Everything with my restored 8TS30 (mentioned above) is now okay.

I disassembled and tested each resistor in the network, the wirewound in the HV cage, the resistor at the bottom of the 1B3, the doorknob cap, all of the tubes in the HV section, even the picture tube. Found not a damn thing wrong. Put it back together, and for some reason now it works.

Now back on to the problem child at hand :)

For me, it's difficult because I've never had any formal electronics training whatsoever. Heck, I've never even had the benefit of someone in person walking me through a set step by step. It was just something that I wanted to do ever since I was a boy, so I pick it up as I go and have been doing that for the last decade or so.

I've restored close to 100 sets over the years, but every one of them was done by either recapping and getting lucky, or working through electronic principles and developing a rudimentary understanding of how things work along with problems associated with different circuits and how to resolve them.

I can recap a 630 chassis in 2-3 weeks, and my work is very precise. Hands, I've got. Diagnostic skills, not so much. Doesn't stop me from trying and learning though.

Well I hope my remarks didn't come off as sounding harsh or criticizing, that surely is never my intention here. I suppose I'm guilty of being a little too sarcastic some days. :)

I went to electronic servicing school way to late in the consumer electronics game to make any career out of it. So I ended up working many years for an industrial supplier to the weighing industry. Therefore most of my professional experience has been with DC circuits and analog to digital conversion. But in my opinion, understanding the very basics of DC and AC circuits is the key to efficiently troubleshooting these TV's, or for that matter any AC/DC electronic circuit - being able to apply Ohms law, and understanding how current flows through a circuit branch, and how that current flow creates voltage drops across the various components. In my case, seeing is believing, and so very early on I got hooked on using a scope, even when looking at simple things like power supply voltages. Where I have a major weakness is in understanding RF flow through capacitors,coils, and tuned circuits, and it's because I never really took a liking to the math involved in AC circuits. I can still look at the signals, but the results often don't make sense to me. Major stumbling block for me, that I didn't focus more on that math in my younger days.

Nah, not at all. You've helped me through a lot, as well as a lot of others, and I appreciate the patience you guys take to take concepts that you know, and "dumb them down" :)

When it comes to repair of anything, there are those who are perfectionists, those who are mechanics, and those who are just plain hacks. I'm a darn good mechanic.

For me, it's difficult because I've never had any formal electronics training whatsoever . . . . . . Hands, I've got. Diagnostic skills, not so much. Doesn't stop me from trying and learning though.


One of the hardest TV repair jobs that I've ever undertaken was late 1940s TV with a stacked power supply circuit, with a humongous candohm that balanced the load between two different DC plus voltage power supplies and one DC negative voltage.

The monster candohm was open when I got the set and it was quickly located and changed out with a NOS candohm. On power-up, all three voltages were still all messed up, but in a new way. It turns out that the NOS candohm was pinched too hard in manufacture and it had a short to ground in the center.

Not hard to find, but so damned unexpected, that it was the last place I checked because I'd already changed out that bleeder network. Duh!

So, if I were you, the first thing I'd check is to verify that neither of the two resistors you replaced have a direct short to ground on either end.

The second thing I would check, would be the ohms readings on the 5V4 damper, that are in Sams. Note the '*' listing, which tells where you are to park your ground for this tube.

The final check would be to open the R123 connections to recreate the original conditions, replace the R127B, power up and see if the newest R127B gets hot. Purpose: Something else could have happened at the same time that you put in the Horiz Linearity resistor.

Since ETF also has a factory single set RCA manual for this TV, why would one use a maybe "schematic" that covers two sets that were built two years apart when the exact is available.
Sams R123 = RCA R209 and Sams R127B = RCA R232.


For the record: My nearest to formal education in electronics was the Progressive Edu-Kit in 1952:

http://www.ohio.edu/people/postr/bapix/edukit.htm

The one mentioned, along a more advanced one and with every book on electronics in the local County Library.

Hope this helps.
Jas.

For me, it's difficult because I've never had any formal electronics training whatsoever. Heck, I've never even had the benefit of someone in person walking me through a set step by step. It was just something that I wanted to do ever since I was a boy, so I pick it up as I go and have been doing that for the last decade or so.

I have a degree in electronics and I took it as a trade in high school. I sometimes think that I got more useful training in high school than I did in college. I only took the first year in h.s. and I remember it being all about the math of Ohm's Law and Kirchoff's Law, the use of a Simspon ANALOG meter, and logical use of your God given senses which could be nearly as important as the former(s).

By the time I found a way to make it through college consumer electronics repair was all but done with. Even component level troubleshooting with scopes and such was reduced to nearly nothing beyond power supplies. Schools are set up to help people start careers and find jobs and that dictates the curriculm's content. Thank God that both my h.s. and college teachers were "old school" guys who were around when electronics was a true science as opposed to a digital mess of plug and play stuff called electronics. An "electronics tech" of years ago bore knowledge that makes today's "electronics tech" seem like a kindergarten student in many ways.

Just take a look at the old textbooks (which by the way we all should have) and compare to something of late. No comparison. Enough to cover what is needed to unlesah the potential graduate on industrial applications which are what most schools elaborate on these days. At least community colleges or junior colleges. I unfortunately can't say what a university electronics engineering student might go experience. Probably the equivalent of what the junior college or trade school student of the 40s or 50s experienced only up to date.

Nothing at all wrong with taking a natural interest and building on it through real world experience all while having a lot of fun. And trust me, this pool of knowledge that we all are lucky to be a part of here is used by me a lot on what often is rudimentary electronics troubleshooting. We all have strengths and weaknesses. What I love about electronics is that you never stop learing. Even with backdated technology it is a constant learning experience! :thmbsp:

So, if I were you, the first thing I'd check is to verify that neither of the two resistors you replaced have a direct short to ground on either end.

The second thing I would check, would be the ohms readings on the 5V4 damper, that are in Sams. Note the '*' listing, which tells where you are to park your ground for this tube.

The final check would be to open the R123 connections to recreate the original conditions, replace the R127B, power up and see if the newest R127B gets hot. Purpose: Something else could have happened at the same time that you put in the Horiz Linearity resistor.

Brilliant :)

First check: nothing has a direct short to ground.

Second check: readings on the 5V4 are dead on.

Final check: that's next.....exactly what I had planned on doing.

Final check: that's next.....exactly what I had planned on doing.

Always do the tests first that are least likely to damage something. :yes:

Refresh my memory. Did you check your focus coil for internal resistance? If not do it before powering up the set.

Also, before you fire the set up, clip a DC voltmeter across R127B with the negative lead on the focus coil side.

As you bring your Variac up, when it hits 24 volts across R127B, the resistor is pulling 5 watts current draw and at 48 volts it is 10 watts and if you stay there more than a few moments you will fry your brand new 10 watt wirewound.
___________________________________

One never sees their own mistakes and a prime example is the final statement in my previous post:

Sam's R127B should be RCA's R185A (and not R232 which is next to it.)

James

Welp, the set's got audio, and makes a raster. Sort of :)

No vertical deflection, but everything else is where it should be. I tested resistances of everything in the HV/horizontal before power up and everything is where it should be. Now, on to the vertical.

Centering control moves the line about an inch.

In retrospect, the ONLY thing I can think of was that resistor simply arcing to chassis. Might not have been enough clearance there.

Okay, the set's operational :)

Turns out that the resistor WAS too close to the chassis, and it arced over. Had to end up putting a vertical blocking transformer in it as well, but everything seems fine now....except for a couple things.

The set's got inadequate width, but only by about 3/8" on either side, so I'm not so worried about that right this second. What DOES worry me is that the resistor network in the back cover is getting hot. I mean HOT. As in, I was watching the set, and I *believe* the solder on one of the resistors just melted off and POP.....the resistor dropped from the wire and I lost picture.

The contrast/AGC control also barely does anything to the picture, which is somewhat on the weak side. My other 8TS30 has full range in that department.

I don't remember any of the other 630 chassis sets I've done run so bloody hot....but then again I can't remember how much heat's back there because I've never had an issue like this.....

You need to verify your B+ voltages are what they should be at the various check points, very similar to what you just went through with the Admiral. If that resistor is burning hot, there's got to be a circuit pulling excessive current, which will show up as a lower than normal voltage at some point along the PS resistance dividing network. Voltage checks generally come first, followed by looking for circuit abnormalities causing the incorrect voltage drop.

By the way, Kevin, I very much appreciate your patience and guidance in these sets I'm having issues with.

I've repaired or recapped 26 sets over the course of 2015. Twenty six, and that's not counting ones I've shelved with issues for the time being. But for me, restoring a TV is like having a butcher remove your appendix. He can probably do it well because he's got tons of experience with the needed tools, knows what all the parts are, and is fast and skilled with his hands. Just don't expect him to have a full understanding of what all the parts are doing.....

No problem, Tim. I enjoy trying to help out, when I'm able, so it's a win-win situation. Have to admit I've only a handful of TV restorations to my credit, so I'm no veteran of the trade. I really Really appreciate the vast pool of knowledge that visits these forums on a daily basis. Not too many future generations will be able to experience the same honor. And quite honestly, it's a humbling experience, just being here in their presence.

What DOES worry me is that the resistor network in the back cover is getting hot. I mean HOT. As in, I was watching the set, and I *believe* the solder on one of the resistors just melted off and POP.....the resistor dropped from the wire and I lost picture.


Here's where I'd start. Sams chose not to list any voltages in the power supply area, so here's Riders references for those chimney mounted resistors.

Keep in mind that those resistors with negative voltages listed are in series with the 5U4's center tap winding going to ground. Every circuit that gets B+ is drawing current through them, but in a negative direction- the higher the B+ load, the more negative those voltages will be. It's not shown in the pictorial, but there should be something in the neighborhood of neg 55v on the left terminal of R185A.

http://i452.photobucket.com/albums/qq245/Kuehn/VK%20Pictures/RCA%208TS30%20Chimney%20Resistors%20a_zpszxc1jyev. jpg

...It's not shown in the pictorial, but there should be something in the neighborhood of neg 55v on the left terminal of R185A.
Is R185a what's overheating?
And does R185a translate to R125 in Sams? If so, it's in parallel with the focus coil. If the focus coil were open, excessive voltage would appear across R185a, causing it to overheat.
Also the main B+ would drop some, likely causing insufficient width.

And does R185a translate to R125 in Sams? If so, it's in parallel with the focus coil. If the focus coil were open, excessive voltage would appear across R185a, causing it to overheat.
Also the main B+ would drop some, likely causing insufficient width.

Nope.
R185A was what I referenced from the Riders chimney wiring pictorial - it's equivalent to R127B(230 ohms) in Sams. Yeah, it's confusing as heck going back and forth between the two source materials, but I wanted to show the voltages as pictured on those resistors in Riders. The 1800 ohm resistor in parallel with the focus coil is not in the chimney. The resistors as shown in Sams that appear in the Chimney, are R127a,b and R128a,b,c. I went back and added the resistor values in red to the Riders pictorial.

So which resistor specifically is overheating?

No clue. I don't think he's spilled the beans. :D

Captain, if your sick of this one and nothing prevents either of us from going to the meet I'd be willing to take it off your hands....especially if it is the one with the blue tinted screen (that thing is wicked awesome looking).

It's R127B again, but R127A's getting pretty toasty too. And no, it's not the one with the blue screen....although I've been thinking of selling that one, actually ;) . This one belongs to Rodmonster, I'm doing him a gigantic favor.....

No, no, I didn't get sick of the set....we just had a rare couple of 60 degree December days in Buffalo, so I wanted to take full advantage of it to get some work done on the TV hauler.

This is the picture I got on the screen just before the "meltdown". The resistor itself looks okay, admittedly I didn't ohm it out yet. The raster is full width, but the picture is not.

It's R127B again, but R127A's getting pretty toasty too.
....... The resistor itself looks okay, admittedly I didn't ohm it out yet.
OK lessee if I got this right now.
R127B corresponds to Riders R185A (the right-hand section of the big honkin' chimneyed resistor shown in post# 26). If so, it should measure 230 ohms with one end disconnected.
If it's signifigantly higher than 230 ohms, it would definitely overheat as well as drop the main B+ a bit.
----
Is there any chance the replacement was swapped end-for-end when installed? If so, it would explain the overheating since the other section is 1360 ohms. (it would probably explain the width anomaly too)

About a 99% chance that's not the case. When I started having issues that prompted this thread, I checked the wiring against two other 8TS30s, one unrestored and one I restored about a year ago. Both were a match.

So.. have you physically disconnected one end of R127B and ohmed it for 230 ohms? And verified that circuit-wise it's connected correctly (i.e., one end going to the ion trap and the other end to the 93 ohm resistor R128C)?

OK lessee if I got this right now.
R127B corresponds to Riders R185A (the right-hand section of the big honkin' chimneyed resistor shown in post# 26). If so, it should measure 230 ohms with one end disconnected.


You got it. Now if we could only get our field representative to take a couple measurements...;)

:DSotta like gettin' Hannibal over the Alps.
Just Kidding!!!! :p:

I'm glad YOU said that. :D

Geeze louise....I gotta work for a living too, y'know! So nyah ;)

Since one end of the resistor's already disconnected, that made it easy. 234 ohms. I knew it would be because I replaced it earlier, unless it fried, which it didn't.

I'll do some wire tracing when I finish work for the day......

Sollder that puppy back up and lets get a voltage measurement acrost it. Plus it would be cool if you could make a video of solder melting off it's terminals. ;)

What range should it read? In an earlier post, earlyfilm was mentioning a slow power up, but I can't hit those low voltages with my variac. The lowest it will go is 75 VAC.

I'll keep my digital camera handy for your amusement should it reoccur ;)

Since you've replaced R127B with a chassis mount type, and verified its resistance, what is the actual wattage rating of the replacement?

What range should it read?

Based on Riders voltages I'm coming up with 39.4v across R127B, which would be about 6.77 watts. Or 57.4v from the left side terminal to ground. 9.84 watts dissipated between those three series resistors. Then another 9.323 watts across R127A and R128A. For a grand total of 19.16 watts in the chimney. Does that sound feasible?

So based on 40V max across R127B, it should be rated at at least 10W, preferably higher (I'd prefer much higher for cooler running).

So based on 40V max across R127B, it should be rated at at least 10W, preferably higher (I'd prefer much higher for cooler running). Sams lists it as a 10 watt. 17 watt for R127A. They're really banking on that chimney to draw cool air in.

R127B I have a 10 watt, R127A is a 20 watt. R127B is a chassis mount, but since the arcing issue a couple pages back, it's just floating loose in space at the moment.

So what's the actual DC voltage you have across R127B (at normal line voltage or whatever voltage you normally run the variac at)?

Based on Riders voltages I'm coming up with 39.4v across R127B, which would be about 6.77 watts.

I'm at 45.8v across R127B, running the set at 117 VAC.

I'm at 45.8v across R127B, running the set at 117 VAC.
Kinda high. The current will be 196 ma. @8.96 watts. A 10W resistor will run sizzling hot.
196 ma. is the total current of the entire B supply going thru that resistor
What does the voltage across it drop to when you pull the 6BG6?

(Edit)
In a darkened room, does the 6BG6 show any sign of red plating?

With the 6BG6 pulled, I'm at 48.9 VDC. Can't see any hot plating.....

With the 6BG6 pulled, I'm at 48.9 VDC. Can't see any hot plating.....
Holy makrel!:eek: That's over 10 watts. Try pulling the damper, and then the rest of the tubes one at a time, starting with the audio output, while watching the voltage across R127B. If the voltage stays up, it'll prove there's not a tube overconducting.

To save brutalizing R127B while troubleshooting, you could sub it with a couple of 100 ohm 10 watt resistors in series if you happen to have such.

Just so that I have this right, I'm gonna next pull the damper, power it up, then start powering up the chassis, each time yanking a tube and watching the meter, looking for a change in voltage? :headscrat

This is something I've never done before. I was always under the impression that I'd end up damaging something doing that if I yanked more than one out.

This is something I've never done before. I was always under the impression that I'd end up damaging something doing that if I yanked more than one out.
Ordinarily*, pulling tubes might allow B+ to go too high, stressing the filter caps. But in this case, there's already a huge draw on the B supply. And you have a variac to keep it under control.
Just so that I have this right, I'm gonna next pull the damper, power it up, then start powering up the chassis, each time yanking a tube and watching the meter, looking for a change in voltage? :headscrat
Basically yes, using your variac to bring it up each time. Actually, just do the damper> AF out> vert.out for now.
-------------
*One big no no would be pulling the H.osc tube while the H.out tube is still in place.

Wow, I don't understand how removing load from B+ can cause the voltage across R127B to go higher. :scratch2:

First verify that your rectifiers are 5U4's and the damper is a 5V4, which is a rather unusual choice for a damper.

Yes, pull both at the same time. A shorted damper can kill a new horizontal output tube and I normally yank both together. The multiple tube pull method won't work on stacked power supplies, but the stacking is limited in this set.

If the voltage across the resistor is as high as before, immediately kill the power and feel all electrolytic caps.

Don't worry about the HV, as it wont be working, but don't touch the chassis and an electrolytic at the same time as some might have lingering B+. If one is heating, check for incorrect wiring, ratings and polarity on the hot one(s).

If no electrolytic is heating, print out the RCA Factory Schematic and Wiring diagrams from the RCA 8TS30 PDF on ETF and give them to your son and offer him a reward if he can find your wiring error starting from the Power Supply and Reaction Scanning (damper) tubes. The wiring error could be something as simple as a tube in the wrong socket . . . . . or a grounded floating ground . . . . or an electrolytic with polarity inverted.

Jas.

With both the 5V4 and the 6BG6 removed, it dropped to 44.9 VDC. Continue pulling tubes and checking, or stop here?

Any chance you could show us a picture of the inside chimney wiring? Another very strange thing, is how you mentioned earlier that R127B was arcing to ground. There shouldn't be any voltage potential on that resistor high enough to arc to ground, unless you meant one of it's terminals was touching ground. Is R127B an aluminum cased or ceramic coated?

What's the voltage reading from either side of R127B to ground?

Bear in mind that this isn't the "finished product", as I'm moving things around, testing, etc. My finished work is much neater.

R127B is on the right, that's the gold chassis mount resistor. R127A is the enameled wirewound. You can see how the previous R127B just let loose. It wasn't touching ground, it had an arc jump TO ground on the right side. It was close to ground, but not touching. Probably 1/8" or so.

It's hard for me to see clearly what's connected to where, but is that a 10 ohm cement coated Dale, with the left end connected to chassis ground? And where is the other end of that same resistor going? Edit- I guess that 10 ohm Dale is in series with the 12 ohm(128B)?

Left end is to chassis ground, right end is connected to the 3rd terminal of the candohm. That section of the candohm was dead.

Something does not look right there. Am I correct that the cement Dale says 10 ohms on it? Compare your wiring to what Riders shows. I added the resistance values in red.

http://i452.photobucket.com/albums/qq245/Kuehn/VK%20Pictures/RCA%208TS30%20Chimney%20Resistors%20a_zpszxc1jyev. jpg

http://videokarma.org/attachment.php?attachmentid=189204&d=1450193991

Deleted. Posted too soon

If my eyes are not deceiving me, and that is a 10 ohm cement Dale resistor that's replacing the 6750 ohm candohm section, then there's one heck of a load on the B+. But I'm having a hard time seeing the connections.

No, the 10 ohm is replacing the 12 ohm R240, which was open on the candohm. But the ground is totally disconnected from the second pin of the 6750 ohm candohm section, and I relocated it to the Dale resistor rather than jumpering it across. The hell??? Before it all made sense to me, now I'm looking at this wondering what the devil I did here.....

And why would I use such a big resistor?? Okay, time to start from scratch on this candohm replacement. Now, none of it looks right.

Well what's confusing me, is that Riders only shows two resistors in that Candohm, but Sams lists sections A,B,C. Yet your picture seems to show a separate resistor for the 12 ohm?

Is there by chance a 12 ohm resistor between the two inside terminals of the Candohm, and the left side is no longer connected to ground?

That's what is getting me, too. I think that's where my confusion lied. Using the Sams, I'm assuming that between the 2nd and 3rd pins of the candohm, I should read 12 ohms, and I'm reading it open. I stuck a 10 ohm monster resistor in there for some reason.

It appears that at worst, all I did was miss a ground on the 6750 ohm section of the candohm. But aren't the two inside terminals of the candohm supposed to read 12 ohms as represented in the Riders diagram above, or no?

But aren't the two inside terminals of the candohm supposed to read 12 ohms as represented in the Riders diagram above, or no?

No, the Riders diagram shows only two resistors inside the Candohm, and then R240 is the 12 ohm resistor, which one end is connected to the 3rd terminal from the left, and it's other end heads over to chassis ground(what looks like a spade lug), along with the GND wire that grounds the 2nd terminal of the Candohm.


What is the resistor looking component that my red arrow is pointing to, is it a 12 ohm resistor, because I thought that was the same component that Riders is calling R240.
http://i452.photobucket.com/albums/qq245/Kuehn/VK%20Pictures/inside%20chimney_zpse4prmycg.jpg

That explains the whole damn thing. Got it. You're right, that IS the 12 ohm.

So, all I have to do is get rid of that 10 ohm resistor, and hook the ground back up to the 6750 ohm side of the candohm and I should be in business. It checked fine before, but now is reading about 14K ohm. I might have one here, but the Sams isn't specific about the wattage.

From what I see in the RCA service manual is the candohm is two separate resistors and R240 is a separate 12 ohm resistor going to ground so yes it can go between the two middle terminals.

Gregb

Riders says 3.2 watts on the 6750 ohmer.

By having the one end of the 6750 ohm resistor not grounded, you introduced higher than normal voltages to some circuits(haven't looked at which yet). That may explain why some circuits were pulling more than their normal load.

My next question- is the green wire end of the 12 ohm resistor connected to ground, so now you have both ends grounded? In other words, did you inadvertently connect the end to chassis ground that was suppose to be up on the 3 terminal from the left of the Candohm?

Is it possible the other green wire you have going to the left end terminal of the Candohm, is also grounded, and that should be on the right end of the 6750 ohm section? It would make some sense that those two green wires disappear to a ground lug under the chassis. Sorry about so many details, but it's just a little confusing in that chimney. :)

At this point, with the chassis still in fault mode, I would put an ohmmeter on the main B+ rail, to ground. A good place to find the B+ rail is the width coil or the top of filter caps C3A/C2B. (with the set off, of course.) Connect the positive lead to the B+ rail, negative lead to ground. What reading does it settle into after the initial charge-up spike?
Does it stop hard at a few K ohms, or drift up into the fractional-megohm range?

Is it possible the other green wire you have going to the left end terminal of the Candohm, is also grounded, and that should be on the right end of the 6750 ohm section? It would make some sense that those two green wires disappear to a ground lug under the chassis. Sorry about so many details, but it's just a little confusing in that chimney. :)

Hah, you're tellin' me!

No, in effect for some reason (read brain fart) I didn't realize at a glance that the funky cloth covered little inchworm was a 12 watt resistor, so I added a 10 watt resistor where it should have gone according to the Sams, thereby giving that part of the circuit a 22 ohm resistance instead of 12.

Then, that 6750 ohm section should have had the inner terminal going to chassis ground, and I believe I just got confused working from the schematic alone.

I'll order up some parts tonight, and double check them against another 8TS30 I have here.

I found this picture from another thread here. Looks like what I thought were green wires are not suppose to be grounds. Apparently the ground connections are to be soldered directly to the chassis below the chimney, as shown. Sorry for making things more confusing, I've never restored one of these RCA sets.

http://www.videokarma.org/attachment.php?attachmentid=172667&d=1325133764

Hah, you're tellin' me!

No, in effect for some reason (read brain fart) I didn't realize at a glance that the funky cloth covered little inchworm was a 12 watt resistor, so I added a 10 watt resistor where it should have gone according to the Sams, thereby giving that part of the circuit a 22 ohm resistance instead of 12.

Then, that 6750 ohm section should have had the inner terminal going to chassis ground, and I believe I just got confused working from the schematic alone.

I'll order up some parts tonight, and double check them against another 8TS30 I have here.


OK, you posted while I was out looking for another reference photo. Sounds like you've now got your head screwed back on straight. :thmbsp:

And I should really know better, too. This is the 2nd 8TS30 I've done, and before that I've got a Crosley 630 clone, a DeWald BT-100, and an RCA 9T246 under my belt.

I think I tried really hard to forget about those spiders nests as soon as I finished the job :D

There's one more unrestored 8TS30 sitting here staring at me too :tongue:

If it is still acting up once you rewire it, check the candohm for shorts to chassis.

And I should really know better, too. This is the 2nd 8TS30 I've done, and before that I've got a Crosley 630 clone, a DeWald BT-100, and an RCA 9T246 under my belt.

I think I tried really hard to forget about those spiders nests as soon as I finished the job :D

There's one more unrestored 8TS30 sitting here staring at me too :tongue:

Sounds like too many caps ago, and too little time. :)

You're not kiddin'.....

There's got to be a 6.8K ohm resistor around here somewhere. Time to go dig through my wirewounds.

Okay, something's still very wrong. Here's where I'm at.....

I found a 7K ohm 10 watt in my stock. Close enough to give it a try. I'm getting 39.8 V across R127B, so we're right there in the correct range. Now, the horizontal linearity is WAY off, compressed on the left side (as I recall).

But everything's getting hot still. Really hot...to the point where something was starting to give a wisp of smoke. When I lifted the leads off R127B after the set was shut down for a couple minutes they were still extremely warm. The contrast/AGC control does almost nothing now, and the picture has slightly less width than it had.

Here's my work as it is now. The 12 ohm resistor to chassis ground checks out fine.

OK, now try the same power-up except with the 6BG6, damper, vert.output, and audio output tube removed, while monitoring voltage across R127B. It should drop 'waay down with those heavy-draw tubes removed.
If it doesn't, try the ohmmeter test suggested in post# 75.

I'll pick it up here tomorrow. Gotta go work the night shift on the railroad tonight :)

I'll pick it up here tomorrow. Gotta go work the night shift on the railroad tonight :)

Good ol' Lionel "O" scale model RR...Used to set up my father or grandfather's set 'round the tree most Christmases....The tracks liked to push apart when the train went over it and speed dropped a lot on the far side from the power connection to the tracks.....Until I tried tying the track sections together, then they did not come apart and power loss along the tracks dropped significantly.

At this point, with the chassis still in fault mode, I would put an ohmmeter on the main B+ rail, to ground. A good place to find the B+ rail is the width coil or the top of filter caps C3A/C2B. (with the set off, of course.) Connect the positive lead to the B+ rail, negative lead to ground. What reading does it settle into after the initial charge-up spike?
Does it stop hard at a few K ohms, or drift up into the fractional-megohm range?

Voltage test didn't change with all 4 tubes removed, so I went on to this. The meter stopped at almost exactly 6.8 K Ohms.

Voltage test didn't change with all 4 tubes removed, so I went on to this. The meter stopped at almost exactly 6.8 K Ohms.
Well, 6.8K is reasonable enough, considering that the B+ bleeder string to ground (R127A and R128A) add up to 8.1K. Current will only be around 45 ma., nowhere near the 175 or so ma. that's going thru poor R127B.

It almost looks like a B+ filter cap is breaking down under voltage, like maybe a cap has been replaced with one having too low a voltage rating. The most likely suspect would be C4A, which should be 40 mf and rated at 450V. Does the C4 can show evidence of heating?

Any progress on this?

I'm curious how much your B+ increased when you pulled those 4 tubes? Or if it didn't, I'd continue to pull tubes, one at a time, except leave the audio output tube in. Continue to check voltage across R127B and B+. Make sure B+ doesn't exceed your 450v cap ratings while doing this.

Good timing, I just pulled the chassis back out a couple minutes ago. Christmas stuff's delayed my work a bit.....stand by.

It almost looks like a B+ filter cap is breaking down under voltage, like maybe a cap has been replaced with one having too low a voltage rating. The most likely suspect would be C4A, which should be 40 mf and rated at 450V. Does the C4 can show evidence of heating?

C4's been replaced with all new Nichicons. C4A is now 47 uF @ 450v. Don't see any signs of anything under there.....

Any progress on this?

I'm curious how much your B+ increased when you pulled those 4 tubes?

No change. With all those tubes out and still that much of a current draw, are there any likely suspects at this point?

How bizarre. So with those tubes removed, what voltages do you measure across C1A,C3A and C1C? Measure directly across their + and - terminals, NOT from + to chassis.

Gonna have to do it with the picture tube pulled and the speaker disconnected because of the way everything's mounted in the cabinet on this set, or do I need to jig anything up? I assume that it would be fine, but I'm asking anyway, since I've got so many things pulled as it is.

Hmm, that sounds like a major pain, but I think it's come down to getting that chassis up on it's side for voltage measurements. I'm not sure why we'd need the picture tube installed at this point, anyone else have a better idea?

FWIW, I would first suspect a hard B+ short-to-ground (possibly from the H.centering control or V.centering control to ground).
A hard short on the B+ line would throw a huge current draw on the 5U4 and its centertapped HV winding, and cause a large overcurrent through the resistor chain off the centertap, which includes R127B (it's the highest resistance in the chain, so it will run the hottest).

Did you ever verify that these controls, or possibly one of the yoke windings are not shorted to chassis, or to each other?

One question. With those four tubes removed, is R127B still running severely hot like it was? If so, something else (besides the focus coil) somewhere in the chassis oughta be running overly hot also.

Or else... what kind of meter are you using, analog or digital? The fact is, I would not trust a digital meter on anything other than pure DC or pure sinewave AC (when measuring voltage or current). If there's any ripple component to voltage or current as there is here, a digital meter could be giving screwy readings.

If you were to disconnect one end of R127B and put an analog milliameter in series, it would give a bulletproof reading of the actual current. Do you have a Simpson 260 or anything of the like?

(Those main filter caps C1A, C1B, C1C, C3A and C2B would not be suspect as they are not in the current loop with R127B.)

(Those main filter caps C1A, C1B, C1C, C3A and C2B would not be suspect as they are not in the current loop with R127B.)

No, but the voltage across them could be revealing . And I think that chassis should come out of the cabinet to get any meaningful measurements, as we're beyond pulling tubes. As you mentioned way back, something besides a tube must be drawing major current on the B+.

At this point it might be well to consider that the replacement for R127B, although rated at 10 watts, is intended to be heat sinked by mounting to sheet metal. Its unmounted rating is gonna be considerably lower than 10W, and it will get overly hot even at normal current.

And if voltage and current readings are being taken with a digital meter, all bets are off. At the very least an analog milliameter should be used to verify that the current thru R127B is actually too high.

Well I'd have to agree. It would be a real shame to keep chasing ones tail, all over a underrated resistor that's overheating. A good rule of thumb is to have something at least as physically large as the original.

Yeah, the point was made earlier that a temporary sub for R127B could be strung together, something like a couple of 100 ohm 10 watters and a 33 ohm 2W in series, as a fill in during troubleshooting.

But at least get an analog reading of the actual current ('stead of computing it from a possibly-questionable voltage reading)

Welp.....I've been using a digital non auto ranging meter. I do have an old analog I can use to take new readings. At any rate though, the hot resistor was the problem before but now that the resistor network is straightened out I now have raster issues.

At any rate....I'll reassemble it, dig up the analog meter and verify the readings

A good rule of thumb is to have something at least as physically large as the original.

A better rule of thumb is to use a replacement at least double the power that the circuit is designed to dissipate in the resistor (using: Power in Watts=IV=(v^2)/R=(I^2)R ) for a cool operating part.

Do you happen to have a test CRT hanging around, like a 5AXP4 or an 8XP4? Life would be a lot easier if you could keep that chassis away from it's cabinet and up on it's side while troubleshooting.

Yeah, Tom, that works fine, but for the sake of simplicity, we know the original was designed conservatively. Also modern components may be able to withstand more heat, but there's still nothing like good old surface area to dissipate the heat away.

Shucks, for some reason I thought the chassis was already out of the cabinet. If you haven't pulled it yet, and while those tubes are still removed, try to get an analog current reading on R127B.

Another thought - Those resistors may actually run hotter if you're leaving the back cover off the chimney. Something about convection not being able to pull cool air up through the bottom opening, and the heat just sort of hangs around.

Chassis is out of the cabinet at the moment. Putting it back in is a 10 minute job....no big deal there. If the HV lead doesn't need to be connected I do have an adapter lead to hook up the socket so I can set the tube next to the chassis. I don't have a test tube here. And the cover is definitely off the chimney :)

Just tell me what's next. This set has a ride back home next weekend if we can get it figured out. If not no big deal.....it would just have to wait till the next time.

I've kinda lost track of what kuszactly the current state of affairs is?
Maybe there should be a live web camera aimed at the Kamakiri workbench. :D

With the chassis out, you don't need the CRT hooked up for troubleshooting this particular problem. It's not going to make HV anyway with those tubes removed.
If you've got an analog milliameter with a 0-500 ma (or 0-250 ma) range, just stick it in series with R127B, variac the chassis up to normal line voltage, and see what the current thru R127B is.

I've kinda lost track of what kuszactly the current state of affairs is?
Maybe there should be a live web camera aimed at the Kamakiri workbench. :D

Well, if a visual aid helps.... ;)

FYI, here's the meter I've been using.

I don't have an analog milliameter. I have two analog meters, a basic Micronta voltmeter, and a prehistoric Weston model 697 that works, but doesn't have the range.

Decided to power it up to get a reading on my digital meter. Started it off on the variac at 75v, and all of a sudden heard and saw a SNAP. Looked like the spark came from the area of the chassis ground lead below the chimney, but inside the chassis. The *only* thing in that area, but further down below, is the horizontal centering control.

:tears:

Y'know, I'm about ready to give up on this stupid thing......

Now let's back it up a sec. When I had missed the ground lead on R128A, everything was acceptable except the heat going to R127B. I'll say this out of frustration, but can't I just leave that ground lead off, and stick like a 50 watt wirewound in R127B?

Yeah, didn't think so.....

Wait, wait, wait wait. Careful study of the chassis just revealed something to me.

It seems that someone back in the day replaced C3 before I recapped the set, but didn't anchor it properly to the chassis. With the jostling of moving the chassis around, C3 must have knocked loose and the floating ground was very lightly touching chassis ground.

Odd thing is that I don't recall it being loose during the restoration, but there it is loose, with only one rivet hole drilled all the way through and one missing rivet.

Gonna fix that and try it again.

Got that all fixed, and powered it up. Now I've got no HV. Dammit.

Got that all fixed, and powered it up. Now I've got no HV. Dammit.

So now with that cap not shorting to ground, are things running any cooler? Did you re check the DC voltage across R127B?

Friggity frack, this thing is haunted.

I did NOTHING to it since the last power up, and now I have a picture.

:screwy: :wtf:

Here's what is on the screen, bear in mind I've made no adjustments because I didn't want to run it out too long. Contrast control does nothing, brightness past halfway causes the picture to bloom and lose focus.

Resistors R127A and B are pretty damn toasty, but measuring 40.3 V across R127B.

Well 40.3 volts DC across R127B is really close to where it's suppose to be, provided your voltage reading is accurate. I'd replace R127B with like a 20-25 watt unit, install the chimney back cover and let it run a while.

Well sunnava gun. Now, with that Micronta meter, you can get a reliable current reading using the analog voltage across R127B, per I=E/R (current=voltsXohms). Then for wattage, P=EI (watts=voltsXamps).
Be interesting to see if the voltage reading on the Micronta matches the digital's.

This has GOT to be the world's crappiest analog meter. The DC V scale only goes up to 15, and then a VERY coarse 0-1000 V. Ugh. Model 22-027U. I'll be honest in saying that I hate analog meters....had a couple Simpson 360s along the way that I really wanted to love.....but just couldn't. Guess it's all in what you're used to.

Time to take a Holiday break and order up some big honkin resistors for this sucker. I don't expect they'd be in any time before next week, so unless anyone has any other thoughts (which are always appeciated), we'll pick this one up after Christmas.

Meanwhile, I just might toss this Zenith roundie chassis on the bench and get going on it :)

You will get this set working, I am sure. Enjoy your holidays, and get back to this set when you have both time and desire. Lots of us here are ready and willing to offer help.

It needs to be installed in a airconditioner to be kept cool loll. If you have two 10 watt resistors of equal value you could put them together to get the 20watts but they must be equal and add to the ohms you want. Or put two parallel to decrease the ohms to the value you want.

Just a coupla thots for when you tackle the beastie again.
You mentioned R127A running "pretty damn toasty". That's interesting since it shares the same current loop with hot-running R127B.

According to Sams there should be 117V DC on the low end of R127A, at its junction with R128A.
See simplified diagram attached.

What voltage do you get at the junction? Is it signifigantly lower than 117V?

Filter cap C5B connects from that junction to ground. Sams lists it as 80 mf.@350v.

Is there any chance that cap coulda been replaced with one having too low a voltage rating? If so, it could be breaking down and pulling excess current.

But if the 117 V is OK, then there isn't a problem.

Nah. All of the bypass caps I stock are 630V and all of the electrolytics are always 450 V. But I'll poke around in there after Christmas :)

Well 40.3 volts DC across R127B is really close to where it's suppose to be, provided your voltage reading is accurate. I'd replace R127B with like a 20-25 watt unit, install the chimney back cover and let it run a while.

Okay....so here we are with the holidays behind us. I've got a 25 watt NTE ceramic resistor ready to go in. Just install it and let it run....?

I just got one outstanding question.. Does that large voltage drop still occur across that resistor with those four tubes removed, or not?
(H.out, damper, audio out, and vert out.)

No change at all when I pulled those 4 tubes.....

No change at all when I pulled those 4 tubes.....

That does seem almost impossible, that the voltage across that resistor wouldn't budge with those 4 tubes removed. After all, it's the load on the B+ that is pulling current through the high voltage winding center tap, and that same current has to pass through that resistor on it's return path to ground.

Okay....so here we are with the holidays behind us. I've got a 25 watt NTE ceramic resistor ready to go in. Just install it and let it run....?

Yeah, that's basically the plan. You might keep your volt meter clipped across it and monitor that your previous voltage reading doesn't increase dramatically over time . Wouldn't be a bad idea to pick up something like a Simpson 260, so you could take a average current measurement in series with a load. Considering the volume of set's your working on, it would be a good long term investment.

Referring back to post# 122, what voltage do you get at the R127A/R128A junction? It should be 117V according to Sams. (That's extrapolated from the 117V called for on pin 6 of V9 and pin 4 of V10, which are connected to that junction.)

Sometimes having a TV friend staring at something helps you to bring clarity...

Ed: "Okay, but you didn't replace one section of the candohm"

Me: "Right, but it ohms out perfectly"

Ed: "But did you ohm it to ground?"

Me: "Well, no. I usually replace all the sections, but this one tested fine. Wouldn't the value be off if it was shorted to ground?"

Ed: "Don't EVER trust a candohm. Replace that section and power it up and see where you are"

So I did, and now it's got a stable linear picture, and nothing's sizzling. Takes a few minutes of running to get decent AGC and there's some occasional snapping static in the audio (could be a tube socket that needs cleaning), but we'll see if that levels off with repeated 5 minute stints of usage. Have to tweak the adjustments too, of course.

The moral of the story: like Ed said, never trust a candohm......

So which section of what was bad? Was it open or shorted or...? :saywhat: (I'm guessing R128A.)

R128C. I replaced all but that one section which tested fine, and figured with it left in circuit that would be a good mounting point for the other stuff.

It bothered me the more I thought about it, so I tested it. It's not shorted to ground, and it's not open....in fact it's right on the money. Must have been doing something when the set was under load. Who knows, all I know is that it's approaching operational now....

I think I'd have to split that candohm open and see what was going on.

I'd be careful doing that, I think they were insulated with Asbestos.
The insulation can get damp and break down, especially after nearly 70 years.

I think I'd have to split that candohm open and see what was going on.

After the hell that this sucker's put me through I have lost any semblance of curiosity as to why it hasn't worked :D

That puppy was kickin' our collective keester for sure. Glad you finally nailed it to the wall. :beerchug:

The candohms I have taken apart were insulated with paper.

Still not enough contrast to the picture though. This thing should have amazing contrast, and it's too washed out for what I know this set should be doing.

Gonna have to yank the chassis for the 53rd time and start testing the resistors in the AGC. The contrast control is questionable too, as it has a dead spot and seems to not do a heck of a lot.

Well, in lookin' at the schematic, the contrast control appears to be a manual (not automatic) gain control, varying the negative grid bias on the IF tubes. Low gain would indicate the control voltage is too negative.

The control pot is supplied with a negative voltage thru R44 (2.7K), and the other end of the pot goes to ground thru R42 (680 ohms).

The control voltage being too high could be due to: R44 being too low in value, or R42 being too high in value. Those would be the first things I would check. Then disconnect one end of the pot, and connect an ohmmeter to that end and to the wiper. Rotate the control, looking for dead spots. Also be sure the control element (10K) is not open.

Then go ahead and check R40, R41, and R43 (whose purpose appears to be to make the control's action more linear).

On my 8TS30, the contrast control has a wide range of action, from no video to way overloaded. It is indeed a "manual (IF) gain control"; there is no AGC.

Compare to your DeWald BT-100, how does that set's contrast control behave? Both sets should be nearly the same, I would expect.

Well yeah.....I interchange the terms "contrast" and "AGC" on this set because they're one in the same.

It's definiitely washed out and has very little range.....from totally washed out to barely adequate. Plus, there's a dead spot on the control. The DeWald is the same as your 8TS30, which is the same as my 8TS30 (this isn't even my set!), so I know there's definitely something awry.

Gonna finally call this one done after I give the tuner a good cleaning :yes:

The screen shot is lousy, but the set regained contrast after I removed ALL the wires from the candohm, and used terminal strips to isolate everything. It looks like a bit of a train wreck, but hey, it works!

It's not *as* contrast-y as my 8TS30, but this set has zero horizontal or vertical lock drift....and mine does a little while it's warming up. I'll just chalk that up to their individual "personalities" :)

Well here's an ironic post-script to this thread!!!

I bought a restored 8TS30 at the ETF auction, and I remembered that I did the work to it, but it JUST dawned on me that it was THIS SET!! :lmao:

There it is, under the table:

https://www.flickr.com/photos/42002845@N02/27116094497/in/album-72157668760424818/

The contrast issue ended up being a couple micas, it now works as good as new. And now it's back here!!! :stupid: