:banana:
Well I got that 1966 Magnavox combo powered up tonight.. I recapped the entire electrolytic plethora on this chassis the last 2 days. What A PaIn In The ***!!! Who were the elves that wired this chassis, the filters in this set are buried! And the chassis is totally compact compared to the RCA chassis im familliar with. But anyway this set is full of gremlins!

First and foremost (the concerning part), when the raster comes up upon startup the horiz hold is way off and the left side of the screen is shrunk in an inch. Will stay this way until I start adjusting the horiz hold a little, then you can hear the set come in and the left comes back out, raster gets brighter and then I can stabilize it. Good bright raster and plenty of contrast and focus. If I turn the set off and right back on, same scenerio, horiz way off and left side shrunk. I move the horiz hold dial far left and back to where it was and problem solved..

That may or may not be related to the 2nd issue. The Raster after 10 minutes of use gradually darkens, goes out of focus, shrinks on both sides and a little on the top and bottom. If I turn the brightness up picture blooms bad and shrinks worse. If I turn the set off and back on over a minute period, problem solved except the movement of the horiz hold dial to get the pic back into sync.

3rd issue. really bad pincushion top, bottom and sides of the screen.

4th and last issue, Colors way off, but im sure this is due to a flaky demod and agc sync seperator tubes. I should have this fixed soon, (also completely deteriorated bakelite sockets on the x and z demod tube locations.

Any help is greatly appreciated, and you guys are always the best!
Thanks!
Shawn

Blooming and shrinkage at the same time? wow, that's an odd one. However I may be able to help out by splitting the symptoms up for you.

First, check out the damper and HO section. Low voltage could be the cause for the oscillator drift and shrunken raster. Shrinking on the sides is almost always attributed to B+ boost problems with the Damper tube or HO tube. Check the tubes.

Poor focus, blooming, and dimming are caused by weak HV, bad HV rectifiers, poor or NO HV regulation. However if you are getting this symptom along with a 4 sided shrink, then I might go back to the power supply and check for bad solder joints. If this set has an inrush limiter in series with the transformer primary, it may going up in resistance. You can check by measuring the voltage at the primary of the transformer. If its less than the voltage coming out of the wall then trace it back from the transformer and see where the voltage drop is.

Another problem is the use of Fuseistors, or fuseable resistors. These were often used in place of circuit breakers or fuses in the B+ circuits of some color sets. They will usually be 7 ohms at 5 watts or something like that. They will sometimes increase in value as they warm up, killing the B+ voltage.

Measure the B+ after the rectifier(s), and see if it changes after the set warms up. Then you can get somewhat of an idea of where to proceed from there. Follow the B+ line and see if there is anything like a dropping resistor that might cause voltage problems.

And check ALL the tube sockets! They may not be making good contact. I've seen it a lot in 5 tube radios from the '60's.

And yes, those filter cans are the devil to change. My T933 has one behind the power transformer and two behind the HV cage. Those are certainly not ones that you will change in 10 minutes!

That sounds exactly how my chassis is too, everyone that has a maggie chassis seems to start with a T, mine is a U, but none the less im sure these chassis are the same. On the topic JPDylon brings up a great point, (Bad HV regulation), If i have a 3A3 that reads into the question mark area, althought AK'rs tell me that this tube is like a diode, Im going to start with replacing that 3A3, just seems to me that I should start there, then start checking voltages and rectifiers along with those flake fusistors. Do you guys think that the 3A3 could be a culprit here, at least to the loss of HV regulation?


And check ALL the tube sockets! They may not be making good contact. I've seen it a lot in 5 tube radios from the '60's.

And yes, those filter cans are the devil to change. My T933 has one behind the power transformer and two behind the HV cage. Those are certainly not ones that you will change in 10 minutes!

I was advised by a member of AK to use a 3CU3 in place of the 3A3 in my Magnavox. The reason is that the internal structure of a 3CU3 is fixed so the filament can't sag and short like a 3A3 can.

If you are having trouble with HV regulation, I'd check the 6BK4 tube and it's associated parts.

The "U" was on older prefix used before the "T" chassis. I think all the tube color Magnavox chassis were very similar. The "T" series chassis were used up to the early '80's. I think the T809 was the last 19" color set and the T815 was the last console.

Hey guys, where can I get tube sockets to replace for the demod tubes in this chassis? The ones in there are completely deteriorted. I need 2 of them. These sockets are for the smaller tubes, the tube type is 6GY6.. Thanks!

check out tubesandmore.com

just search for "9 pin socket" or "7 pin socket"

dunno how many pins that tubes uses. i'm guessing 7

Coool, thanks man, got 'em ordered...

Well, I checked the 6JE6 yesterday, upon startup, it's reading 208ma. After 10 minutt will drop all the way to 145ma. As it slowly drops down, crt starts to lose focus and a little shrinking on the left side of raster at 184ma. It will start geting wonky and horiz will start to flutter after it's been on for a while. Now whats interesting, it will drop quick if I turn up the brightness, but it can stabalize and eventually it will come back up and stay around 190ma and the raster looks good, although the horiz flutters a bit. Upon startup I have to turn the horiz hold all the way over and back to get a raster or it's way off. Haven't checked line voltage at the trans taps yet. Im stumped though, why would the b+ come back up after it drops way down? When I check this and attach my meter and disconnect the lead to ground and run my meter in series, this is checking B+ right?

Also I forgot to add that the vertical takes a bit to stabilize too, and is touchy. The horiz when I say is wonky, it has a tenency to flutter a bit back and forth like im barely turning the knob.

Hey Guys, just wanted to update.. I had my suspiciouns about the HO tube, on the meter, it would read great (115%), after a minute of being on the meter it kept dropping, so I replaced it with NOS. The srunken rater thing went away upon startup, horiz is correct now. The only deal is that after 10 minutes of being on the horiz wants to flutter and come in and out of phase a little. After 30 minutes, it's hard to lock, and gets really touchy. Cathode current is staying at an even 214ma to 210ma. The grid voltage stays at -54 vdc. At the transformer tap on the pc board is labeled 120v, i read 88vdc from the trans. Now this reading is taken before I power up the set, powering it up oes not change that voltage reading. Another tap going to the board is labeled 128v, I get nothing, ever... (and the set runs).. Any ideas? Also vertical hold flips like crazy upon startup and stabizizes after a couple minutes, if I stabilize it upon startup, it will start rolling when the set warms up..
Thanks

You need to set the meter to read ac voltage not vdc when checking the voltage on the primary side of the transformer. Voltages on the primary side of the transformer should be at or near line voltage. The B+ supplies are usually checked at the positive terminals of the main filter capacitors. There will be several B+ supplies. Usually 400V, 395V, 260V, 195V 130V. Something like that anyway. Set the meter to read DC voltage and connect the - lead to chassis ground, then you can touch the + lead to the power supply sources and check the readings. I do not know the chassis number of your set, but the U904 also uses a 6GC5 tube for a voltage divider to derive the 130 volt supply from the 260 volt source. The 395, 260, and 130 volt sources are all used in the sweep section. It would help to know what the chassis number is. I should have the schematic if you can post the chassis number. Check the voltages and componants in the Horiz afc and oscillator circuit for thermal faults. Before it gets hot use a soldering iron to heat the componants and see if that causes it to fail sooner. Be sure to check any high value or high wattage resistors in the sync circuits as well as the HV regulator circuit.

Bill R

Does this set have have a pincushion adj for the vertical circuit? The chassis is a U9109BB chassis. Thanks guys. BTW I am getting steady 391 vdc at the horiz sweep so not thinking b+ is an issue now...

what is the grid voltage on the Horizontal output when the failure starts occurring? If the HO is loosing bias it will greatly effect the sweep and size. The oscillator is responsible for biasing the HO tube, so you might see if the HO oscillator is ok. If you have a scope, look at the waveform at the output of the oscillator for a clean looking sawtooth around 17.5 khz

In some cases like this its sometimes best to simply sub out the HO and damper to make sure its not either of those two tubes. tube testers will test basic emission and shorts. Most don't have enough supply voltage to test sufficiently for leakage. It may show as good, but after the tube heats up driving the Horizontal sweep and HV section, it can be bad in circuit.

What HO and damper does it use? I may have them kicking around here somewhere.

Sounds interesting, The grid voltage of the 6JE6 HO is -54vdc constant, no change as opposed to heat.. The damper is a 6DW4.. There is a small sprague wax cap next to the horiz effenciency coil, Im thinking it's prob a good time to change it..

-54 volts is good as far as HO bias goes.

I'll check my tube stock this evening.

Sweet! Thanks Jordan:thmbsp:

BTW, ajdusting the effiency coil puts the sync lock in a different position on the horiz hold dial, and does not really change the cathode current reading in ma when relocked into sync.. still sits around 214ma, is that normal? I have the coil set so horiz lock is right in the middle of the dial.

Oh yeah, I also ruled out the horiz hold rheostat, I took a measurement, approx 35k ohms to lock horiz hold, so I soldered in a 35k resistor and took the rheostat out of circuit, still flutters and comes off sync and back into sync so it's not that..

damn, looks like I have neither.

lotsa 12DW4 and 17DW4 though :D

Well, thanks for lookin, im going to check a store up here that supplies all the tubes, caps and other parts I need. He's a nice guy and loves his work, he repairs vintage audio and guitar amps.

So to recap the problem now is that after the set has been on the horizontal sync is not stable, and on startup the vertical is out of sync? Raster is no longer shrinking and loosing focus and brightness?
Sounds like the horizontal oscillator is drifting, or the not locking when it is hot. I would start checking componants in the horiz. oscillator and sync seperator circuits looking for out of value resistors and caps. The fact that you still have more than one problem still could be in the power supply. Remember there are more than one B+ sources. I would check them all to be sure.
The chassis number should have one more number in it. the T or U will not matter. The first three numbers are the chassis series, then the last two numbers are the run number. The letters are production changes with the first letter indicating major electrical changes and the last letter indicating major mechanical changes. So it would be U91? 09 BB. U918 series was 1967 I think, and U911 was late 66 or 67 I think.

Bill R

I think you have a U919 chassis. 214ma is normal for that set. Sams shows the Horiz hold pot to be a 35K pot. So soldering in a 35K resistor would be like having the control set at one end not in the middle. The control is probably ok. The horiz osc and afc circuit is powered by the 390V source. In fact there is 390V at one end of the hold control. There is a 680 ohm 1 watt resistor connected to the 30mfd filter cap in the 390V source that could be increasing in value as the set heats up causing the voltage to drop just enough to affect the horiz lock.
Your vertical problem could be a weak 6gf7 tube. I also notice the sync seperator tube is a 6gh8 just change it.

Bill R

Ok cool! well I had my suspicions on that 6GH8 as well so I did change it, no difference, the 390v source is stable, I looked at that 680 ohm resistor, It doesn't look happy! Im going to change it out! This might be it!

I got another issue... I just replaced the 2 tube sockets that were cooked, they are the 7 pin sockets for the 6GY6 demods. Now one of the tube heaters will not light up, (possibly due to the old pin was bent over touching pin 2 or a resistor located next to it) Checked soldering with ohm meter and it's good, so I looked under the board and pin 3 solder trace looked bad and broken, so I bypassed it with a wire to the correct source, still wont light up. Im trying to find out where the power for the heater on pin 3 comes from... Any ideas what to look for? I havent done too much research yet...

I think you have a U919 chassis. 214ma is normal for that set. Sams shows the Horiz hold pot to be a 35K pot. So soldering in a 35K resistor would be like having the control set at one end not in the middle. The control is probably ok. The horiz osc and afc circuit is powered by the 390V source. In fact there is 390V at one end of the hold control. There is a 680 ohm 1 watt resistor connected to the 30mfd filter cap in the 390V source that could be increasing in value as the set heats up causing the voltage to drop just enough to affect the horiz lock.
Your vertical problem could be a weak 6gf7 tube. I also notice the sync seperator tube is a 6gh8 just change it.

Bill R

Well I spent all night on tracing down solder joints and paths and I found a burned trace on the board that controls the heater for the x demod down the board where the b+ splits up near a fuse, I don't have schematics for the set so I am bearing on just point and shoot alone, lol. Well that was the color issue. Man this set puts out the colors and the contrast and brightness! Im shocked on the quality of the picture on this set! The demod sockets were shot but on the bottom of the board there is no charing or burning, which is odd due to the replaced CRT, but as far as I can tell, All the tubes besides the rectifiier and HV and the 3CU3 are original, possibly a low hour set? I know the reputation for the 23EGP22 but it's new and hardly used and it looks and tests great! Pincushion is fixed now and so is the convergence, (that was a nightmare). Ill take pics today and post! Still have to change out that 680ohm 1 watt resistor on the 390v supply to fix the horiz fluttering, but looks like this set's a keeper!

Thanks for the help again!

Ok cool! well I had my suspicions on that 6GH8 as well so I did change it, no difference, the 390v source is stable, I looked at that 680 ohm resistor, It doesn't look happy! Im going to change it out! This might be it!

I got another issue... I just replaced the 2 tube sockets that were cooked, they are the 7 pin sockets for the 6GY6 demods. Now one of the tube heaters will not light up, (possibly due to the old pin was bent over touching pin 2 or a resistor located next to it) Checked soldering with ohm meter and it's good, so I looked under the board and pin 3 solder trace looked bad and broken, so I bypassed it with a wire to the correct source, still wont light up. Im trying to find out where the power for the heater on pin 3 comes from... Any ideas what to look for? I havent done too much research yet...

What did you find was the problem with pincussion and convergance?

Bill R

Just some really off the wall adjustments. The CRT was replaced in 1977, and when that was done at the time, I dont believe the sercvice man put any time into readjusting convergence,, yoke attenuation or pincushion phase and trap settings at all! The colors were washy, really bad convergence, and alot of color purity blotching and crooked raster, due to he yoke being out of whack. But almost perfect now!

Bill do know how to adjust the horiz width in this set? I cant find that either and it's stretched a little too much.
Thanks!

Width is adjusted with the Horiz Linerity control. This is the same adjustment for the HO cathode current. Adjust it for minimum current. Than set the High voltage to 25KV with the brightness all the way down. The current should not exceed 240ma. You said you were at 214ma and that is good so you shouldnt need much adjustment. You could back it down a little. After you adjust the width you will need to adjust the vertical height and linerity for the correct picture geometry.

Bill R

ps: pictures?

I replaced that awful looking 380ohm 1 watt resistor on the filter cap for the 39pv supply. The set still has the same issue.. I am going to go in depth and replace all the resistors in the horiz sweep section that seem out of tolerance. I think one of these are the culprit. Funny thing is as the set is cold, it's doing it still.

Check the coupling cap in the Horizontal afc circuit. should be 820pf. This couples the oscilator back to the horizontal afc section. Ihave seen the Horizontal phase detector diodes be leaky causing marginal sync. The only high wattage resistor is the 150K resistor off the horiz hold control. Pay close attention to componants off pin 1, 2, and 3 of the 6FQ7 tube. This is the horizontal afc section.

Bill R

Cool thanks for the tip Bill, Ill check that out tonight!

Check the coupling cap in the Horizontal afc circuit. should be 820pf. This couples the oscilator back to the horizontal afc section. Ihave seen the Horizontal phase detector diodes be leaky causing marginal sync. The only high wattage resistor is the 150K resistor off the horiz hold control. Pay close attention to componants off pin 1, 2, and 3 of the 6FQ7 tube. This is the horizontal afc section.

Bill R

post pics of your combo working. i cant wait to see it in action!

Here are some shots of the Maggie in action, this is before the horiz glitching, as you can see the crt and the raster are nice, crisp, colorful, and full of contrast and bright! Despite the little quirks, this set was well worth restoring!

http://i236.photobucket.com/albums/ff144/freakaftr8/12-21-07_0040.jpg

http://i236.photobucket.com/albums/ff144/freakaftr8/12-21-07_0042.jpg

http://i236.photobucket.com/albums/ff144/freakaftr8/12-21-07_0041.jpg

Sienfeld.....one of the greatest TV shows ever in my opinion. And of course Family Guy. Anyway im really impressed with the RED in the first pic!!

If this is a 1977 year crt does this mean it's rare earth?

I think by the time the rectangular tubes came out, the rare earth red phosphor was in common use. It is likely a rebuild and the phosphors should be original...as if it was a brand new tube it likely would have been a more advanced type like a 23V type.
I don't think I have a tube manual at home but if you can find one or if someone else has one it will tell you the phosphor type.
The red looks really great! It always seems like that is the first color to go bad on weak CRT's.

now thats what i m talkin about! looks great! happy for your success and thanks for info on my combo. another one saved!!!!