My first powerup after the recap revealed a hum in the sound, and no raster. HO tube was dead, so I got another.

Second powerup reveals hum in sound, no raster, but I can hear singing, so at least the oscillator is working....


and then...

it all stops working, leaving nothing but the tubes lit. I power down, check the underside for failed components, overheated parts, etc. All fuses intact. LV rectifier checks good on my tester.

Power back up, and the 5u4 lights up in a shower of sparks for a second. Pulled rectifier and replaced it. Powered up again. Same dead set symptom with tubes lit, but the rectifier is making this buzzing rattle, like internal elements are loose or something. Again, no fuses are blown, transformer is cool, and no excessive current draw from the variac.

WTF happened? I was getting so close to first light...now nothing. I hope the transformer didn't crap out :sigh:

Right now its down in the mid 30s and my workshop has little to no heat. When I do get a chance to get back out there to tinker, where should I start looking to resolve this problem?

Jordan -

Heater winding for the 5U4 shorted to transformer case or other windings?

I would remove the rectifier from the socket and check the voltage(s) from socket pins 4 and 6 to the center tap of the transformer. Don't know what they should be on that particular set (maybe in the neighborhood of 400-450 VAC) but they should be close to each other.

Another thing you could try - check with an ohmmeter between B+ and center tap to see if anything is pulling the B+ down.

Hope this gives you somewhere to start - I know how much fun it is working on sets in unheated spaces... :)

Jim

THanks for the advice Jim. I'll have to pull the scat and check all the transformer windings and voltages.

The problem was a cruddy rectifier socket. Some deoxit and pipe cleaners solved that problem. Now I've got good B+, sound, and vertical sweep, but still no raster.

Damper HO tube and HV rectifier are all new. HO cathode fuse is not blown. I tried adjusting the horizontal drive slightly, but it has no effect. Don't want to adjust it too far, as I believe it controls bias for the HO?

any thoughts?

Well, I'm no expert at these things, seeing as how a defective damper tube led me on a wild goose chase through the innards of the Admiral in a recent thread, but here goes:

1. Do you have drive at the grid of the horizontal output tube? You can check with a meter or a scope; you should see maybe -10 to -20 volts at the grid, or a somewhat sawtooth/square wave combination on the scope.

2. Check the plate cap of the HO tube by holding a neon test light close to the insulated plate lead. If it lights, AC is being produced at the flyback primary.

3. Do you have any cathode current on the HO tube?

Hope this helps; maybe someone else has some ideas.

Jim

Also, if the neon test lamp does not indicate HV when held near the plate lead, check whether you have B+ through the flyback: Remove the plate cap from the horizontal output tube and connect a voltmeter to the disconnected plate lead. If there is B+ the damper and flyback primary winding is working.

damper circuits are working, and the fly is conducting. I get 265vdc at pin 5 of the 6w4 and 249 at pin 3 --just about spot on with the test points in the sams. I also get 265vdc at the disconnected HO plate connector.

Next time I get a break I'll look at the HO circuits.

Jordan -

It looks like excellent work so far!

I like your idea of mounting a terminal strip inside the chassis, then using it as a common for all your under-chassis caps. A neat arrangement and excellent physical mounting stability. If you recall, I chose exactly the same spot for my electrolytics, but mounted them tranversely in gobs of electrical tape, and tied all the negs together and soldered the common bunch of leads to the voltage-divider-resistor lug, using the lug as support. It's solid enough, but not great. Your solution is superior.

As far as the horizontal-drive control setting, yeah, cranking it all the way up might be a little hard on the 6BG6, but probably not catastrophically so. Turn it all the way down and you should have nothing at the plate of V20. As you turn the control up, there'll be a go/nogo point at which V20 starts conducting. Just leave it there, that should be enough to give you a bright screen. The only penalty I'm aware of for having it too high is a series of one or more "drive lines" will appear vertically on the left half of the picture, which is annoying but not dangerous, and at this point since you still have no picture, unnoticeable as well. Wouldn't hurt to turn it all the way up, just once, to see if there's any effect on the CRT screen.

It would appear from your photos that you do have a different tuner than the rest of the CX-33's on AK. At least the metal cover hints in that direction. Compare it to retrohacker's photo here:
http://audiokarma.org/forums/attachment.php?attachmentid=14508&d=1146310262

and mine:
http://audiokarma.org/forums/attachment.php?attachmentid=15706&d=1147575217

and notice the big brown bakelite drum turret with contact points distributed about the curcumference. I've never seen this drum turret covered by a metal plate before, either in actual TV pics or in service documents. I think if you pull the metal cover on yours, you'll see a bunch of parallel wafers instead of the brown drum. Page 7 of your Sams 112 vs. Page 10 of your Sams 160, to be more precise.

If you can hear the 15.75 Khz "singing" of the horizontal oscillator, one would think you'd have raster. At this point I might urge you to consider the 16RP4 on eBay (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=190073211353). They don't show up often, new. Sylvania 85's are great tubes, and given it's in the original carton, it's packed in such a way that it won't bounce around. If you insist on having it double-boxed (which he ought to do anyway), I would expect it to arrive safely. I've gotten a few that way, shipped cross-country, in good shape. Given that you've already measured yours as very weak anyway, you'll want a fresh one at some point. Might as well be now, and you can rule out (probably) the pic tube you have.

But first, do some voltage checks of pin 2 of the CRT while adjusting the brightness control. It ought to go both positive and negative, with respect to ground, depending on where the pot is set -- around -80V at minimum, down to zero and then a little positive, maybe as high as +30V. Depending on how well toleranced R43 and R2 are. If not, your brightness pot or R43 could be bad, leaving you with a black screen, despite having plenty of HV.

Since you've already had one problem with dirty tube sockets, it wouldn't hurt to rock each of the tubes in the video strip around, just in case there's a similar problem there. If you're comfortable with doing this while power is on, you ought to see some flashes or sparkles on screen when you rock the tubes, assuming the CRT isn't shot, but be very careful reaching in there to rock the tubes. Wear gloves and all that.

You're definitely on track, and you should be enjoying your vintage Capehart any time now. As long as you're having fun, go for it!

- Kirk

Make sure you've got 400V at pin 10 of the CRT as well. It ought to vary a little with the width control too, 400 to 440 according to Sams. -k

Thanks for the advice Kirk. I'll post my findings when i can get to the capehart again. get to help a friend with a porthole tomorrow :)

here's what i have run into

pin 8
sams says 170vdc --I have 190v

Pin 5
sams says -70vdc --i have fluctuating voltage between -1 and -5

Pin 4
sams says -70vdc --i have 0v

pin 3
sams says -65vdc --i have 0v

Drive voltage at pot is 273v


R96 has jumped from 47 to 106 ohms --that's probably one fault. Pin 5 side is -2 volts, other side of R96 is -91 volts

Still can't figure out why I'm getting 0v at pin 3.

here's what i have run into

pin 8
sams says 170vdc --I have 190v

Pin 5
sams says -70vdc --i have fluctuating voltage between -1 and -5

Pin 4
sams says -70vdc --i have 0v


That looks suspicous, maybe a heater-cathode short either inside the tube, or in the tube socket? With the power off, take an ohmmeter measurement between the cathode pin and the chassis ground. Also check resistors R98 and R99, the parallel pair should measure 110 ohms. A short on pin 3 could overheat them and blow them up.

Do you have -90VDC (against chassis ground) at the far terminal of R109 (where you soldered the black wire for your terminal strip for the electrolytics)? All of the common negatives of your electrolytics should be there too, -90VDC. This is the -90VDC that feeds pin 3 of your HO tube (dropped to -65VDC thru the R98/R99 pair). If you can see -90VDC at the R109 tap-off, and at the terminals of your strip, then you ought to see it at one side of the R98/R99 pair. The other side of the R98/R99 pair connects to pin 3, where you see 0V. If you have 0V at pin 3 due to a short to ground, then (as WA2ISE says) you'd expect the resistor pair to smoke. If you have 0V there because you've got no -90VDC coming in, then it should be easy to track down from what I just said.

You should verify -90VDC at the R109 lug, as stated above, and also verify -43VDC at the center lug, and make sure the left lug is grounded. Verify the +3.8VDC, +115VDC, +205VDC, and +220VDC points as well, as shown in the sams schematic at R105, 106, 107, 108, and 109.

That's interesting that there is a -90 volt fixed bias at the grid of the horiz output tube...usually the set relies on grid leak bias only for the tube.

I would remove the tube from the socket and check the grid voltage, this will tell if there is a tube related short. 106 ohms instead of 47 is not good...I would replace the resistor feeding the grid.
Also would be good to take a scope and check for an AC signal at the grid.

If there really is only -2 volts at the 6BG6 grid this is hard on the tube, and I would check it after making repairs to the resistor circuit. I have observed lack of bias voltage destroy horizontal output tubes.

I have 136k ohms between cathode (pin 3) and ground. Should be sufficient enough right? This was with the HO in or out of the socket.

I left the Ho tube out and took readings from the PS at the resistors Kirk mentioned. The voltages were higher with the tube out, I didn't take them with the tube in because I noticed that even when i left the set on for 30 seconds to take voltage measurements with the Ho tube in it got hot quickly

with the HO tube out i had -95vdc on pin5 and -99vdc on pin 3. OK, maybe the tube is bad? so i put in another 6BG6 and fire it up. Now I've got -84 on pin5 and -71 on pin3 and i can hear the oscillator singing again --but still no raster.

pin 10 of the CRT reads 270vdc. R103 is reading 300k in circuit, could be the reason for lack of G2 voltage. Good side of R103 is 420vdc, other side (pin 10 on CRT) is only reading 270VDC.

pin 2 of the CRT varies between -95vdc and 40vdc through the range of the brightness control.

Do you have a scope...it would be good to check the AC waveform at the horiz output grid and compare it to the sams.

Your power-supply readings are excellent, pretty much identical to mine when I was working on it, before I had the whole set going. The deviations are because the set isn't loading it down until it's working completely. The PS is done correctly. Good work.

Could get a little expensive, smoking 6BG6s. They normally do get very hot though. I guess just keep the tests short until you know it's all correct. Your -71VDC on pin 3 is excellent. Pin 4 isn't used on a 6BG6, so I assume the socket lug for pin 4 is just used as a soldering tab for some other circuit. Without pulling my chassis, I'm not certain what you ought to see there, except that the Sams spec says you're pretty much on track.

Your black screen certainly isn't the brightness control's fault, excellent readings there. The low voltage on pin 10 of the CRT is suspicious. Maybe focus there a bit...?

You're close though.

- Kirk

Sams wants you to have 1.5K Ohms between V20 pin3 and ground, not 136K. The path to ground is thru R98/99, R109A, and R109B, which add up to (roughly) the 1.5K. Because your PS voltages are correct, I have to assume R109 is in good shape. Your R98/99 pair must be smoked open from 110 ohms to more than 100K Ohms. Replace them. R97, at 1 meg, will likely have drifted high too. Check and replace if necessary. R96 you already know is bad. Replacing these ought to get you back to a safe grid bias voltage and you won't blow any more HO tubes. I assume the capacitors in this circuit, if paper, have already been replaced with orange drops. If not, do so. Hope this helps.

- Kirk

I am without a scope. The last one I had stopped working, so i sold the remains.

There is no width pot on this chassis. Its stamped on the rear of the chassis, but the hole has been plugged with some cap. It looks like it was factory, but I could be wrong. The last owner was an electronics technician. I have no idea what else he did to this set. If he wasn't dead, I would ask him!

Sams wants you to have 1.5K Ohms between V20 pin3 and ground, not 136K. - Kirk

OOPS. There was supposed to be a decimal point in there. its 1.36k. R98 and R99 are reading just under 115 ohms

Rats. Or I guess good. I'm still leaning towards your CRT is just bad and you really do have raster. I'd feel better if you had more V at CRT pin 10. I'll measure mine tomorrow, just to make sure.

I'll measure it with the socket off the CRT and see if I get better voltage --after changing the resistor. I figure the CRT is the culprit it registers near nothing on the tester. Good chance its the tube, but I won't know for sure until I try everything else and get voltages where they are supposed to be.

hope I win that 16KP4, crossin my fingers I can snipe it :banana:

You need to check whether you definitely have HV before suspecting bad CRT.....
Do you get a spark when discharging CRT anode after power is disconnected?

haven't tried discharging yet. I do notice a blue glow around the HV rectifier and HO tube with the lights out. Its gota be making some kinda HV...

I'll give that a shot tomorrow.

NO HV at the connector, hmmmm.

HV rectifier filament is not lighting. I pulled it and it tests great, so its either a bad socket, or open heater winding

The anode lead itself possibly shorting to the HV cage where it exits? or just open somewhere internally? Use standard precautions to discharge the HV at pin 2 or 7 of V22, or at the flyback secondary. Then test the anode lead for continuity, or short to ground.

Then do a continuity check from pin 3 of V21 to the top cap of V22. Ought to be the 500-600 Ohms of the flyback primary only, and will verify the wiring around it. With V22 removed, make sure there's continuitly in the flyback's secondary (socket pins 2 and 7 ought to be near 0 Ohms).

You should always be able to drag the back of your hand or forearm across the picture tube screen and feel the hairs raise from static electricity. Even if the tube is "dead" from lack of emission.

The blue glow of the HV tube is normal (and quite lovely to look at). It's the easy way to set the horizontal drive control. When the control is set minimum the blue glow will not be there, turn it up just until the blue glow appears, and leave it there. that's what I called "conducting", although there's probably a better term. The go/nogo point is where the blue glow is either present, or not. Oscillator singing will appear at the same time.

The HV Rectifier has a very small, 1-volt filament, under a metal "bell" internally. You can't see it glow, over the other tube light in the set, and even on a tube tester, in pitch black darkness, it's hard to see. If it tests ok. it could be glowing in the set too, and you just can't see it.

Best of luck on the 16KP4.

- Kirk

C82 was bad on my set. Normally the micas and ceramics you don't have to worry about, but this one takes a beating. Check it with your Ohmmeter for infinity reading. Mine was about 500 Ohms and pretty smoked-looking. That would definitely drag your HV down...

pin3 of V21 to the top cap ov V22 is 531 ohms

resistance across pins 2 and 7 of V22 socket read .3 ohms

Fly looks good. however, i cannot find C82 anywhere on the chassis. Could you shoot me a pic of where its located? I'm not sure if someone pulled it out of the circuit, or where it is at all. I'm following the scat, but when I get to the tie point where C82 might be, its not there. The service notes say that not all models have this cap, and some models have it connected between V20 plate and chassis to increase width.

maybe mine was without C82 in production?

missed the 16KP4 :(

I clicked placed bid and confirmed, but my connection shat and it didn't go through. would have been 60 dollar max too :tears:

Pity. Oh, well, you're connected here for a used one I'm sure. Your flyback's fine, not much left! If you get HV and still dark screen, maybe toss in a tube brightener.

C82 on my set(s) is just sort of strung across the top of the HV cage. From Flyback primary to a pop-riveted solder tab on the left side of the cage. Can't miss it if it's there. Your (early) set, it probably isn't there.

Trace the lack of HV from the CRT anode cap back. Should be 0 Ohms from the cap to pin 2 of the 1B3GT. Fly is good. It really should be working.

- Kirk

From what I can tell everything should be working.

The oscillator is working. I can get a 15.74khz signal at the HO grid pin 5 and 3, and you can hear it singing.

After everything warms up, I can hear a faint fizz at the CRT anode and in the HV cage. It fizzes again when I turn the set off. If I pull the anode from the CRT it doesn't make the noise. I guess HV is there, but I still cannot feel it on the back of my arm and hand as I pass it by the tube face. I thought I had good continuity on my HV lead to the rectifier, but I'll double check again.

After replacing R96 CRT voltage at pin 10 is around 350v. There is very little change when I disconnect the CRT socket.

Other than that, I'm not sure what else to do here. Perhaps the near dead tube is to blame. I raised the filament voltage to 9 volts on my CRT tester but the emission didn't budge. Its just a cooked tube. I've tried rejuvenation but its just no use.

I guess for now its dead in the water...

Does your CRT need an ion trap? If it does need one, and it's missing or misadjusted, you won't get a picture on the screen.

I've tried moving the ion trap around, but I don't see any difference, even in a dim lit room

emission on this tube is next to nothing

I confirmed that its the CRT this morning.

I was curious to see if the chassis was working the way it should. I found a 70 to 110 degree adapter and connected the chassis to a 110 tube I had in another project set. The CRT tested like new, so I figured if the chassis works, we should see light. I made a crude HV extension, connect the tube and powered up. I had no way of properly connecting the deflection yoke, so i just waited for the spot. BINGO! we have light! So I turned off the chassis, discharged the tube and breathed a sigh of relief. The chassis is working fine.

I was contacted by a member who has a 16KP4 he would sell me. At the end of the month, i hope to purchase it and get this baby working right again!

I love this place. Thank you to all who helped me troubleshoot the chassis.

I had a tube like that once. No matter how many times I tried to re-juvinate it, it had no emission. No shorts, etc, just no emission.

I found a parts set with a re-built CRT. This worked fine.

Jordan -

Just wondering where you're at with the Capehart. Thought this thread deserved a bump.

- Kirk

Kirk,

I received a good CRT from Tim. The chassis is near complete except for a vertical blanking circuit that I would like to add.

My only problem now is finding the spare time to get to the set. Working 6+ days a week makes it difficult to find spare time.

I may also attempt some cabinet restoration. The top has seen better days.

Jordan -

I know what you mean. I can only work on my sets for a few hours on Sundays if I'm lucky. That's why projects like my soundless Admiral drag on so long.

I'm glad that Capehart is in good hands, and nearly restored. I haven't seen another one yet, or I'd own it. Definitely a tough get. Make sure to post a shot of it working, sometime.

- Kirk