looking for a schmatic for a '72 GE color set - Videokarma.org TV - Video

drh4683 · #1 06-19-2008, 07:55 PM

Ive been working on this '72 GE 19" color set I picked up a few months back from the estates. I found a couple bad tubes and one of them is the video output tube. The shorted tube must have caused some other part to either short or open in the video circuit. I cannot get the brightness to cutoff. This is the most diabolical TV I've ever worked on. the designers of this chassis must have been inspired by a rats nest. According to my sams index, this set should be in folder #1231 from sometime in 1972. Any help is greatly appriciated.
Thanks

Chad Hauris · #2 06-19-2008, 08:00 PM

How about the brightness limiter control, I had this kind of problem on a '75 GE tube type set and it turned out to be a short in the brightness limiter pot (bad pot).

drh4683 · #3 06-19-2008, 08:24 PM

Thanks for the tip. the brightness limiter did have some effect, but very little, so I figured it was OK. I'll check it out.

Findm-Keepm · #4 06-19-2008, 10:38 PM

Doug,

I'll check my new stash of Sams - I should have it. Also, I have quite a stash of GE parts, and might be able to help if it is something unique. What chassis? I may also have it in Tekfax - if so, I'll send you the Tekfax. I still have a PM with your address, I think.

Also - got a complete Zenith VDR kit - compliments of my Dad. He had it put away in some stuff he had stored in his garage at home, so if you ever need another Zenith VDR...

Dad finally closed shop in May after 52 years of fixin' TVs. I got all of his early Sams (17-2399) and most of his older parts stash. He sold all of the newer Sams (2400-current, complete!) for 2K to another repair shop. Now to sort all of the stuff - most of it was organized, but got kinda mixed up, as we had a shortage of boxes.

There's nothing sadder than the end of a repair shop. Dad has his own shop for 30 years and 4 days - first set was an early Xl-100 and his last was a CTC-185 set, so RCA was his first and last repair. Oddly, the CTC-185 set was a callback for a tuner problem, not the original gripe.

I'll check the Sams tomorrow and get back with you via PM. Meanwhile, a chassis would help me see if I have it in Tekfax.

Cheers,

Findm-Keepm · #5 06-20-2008, 04:47 PM

Doug, I have both the Sams and Tekfax (copy of the original GE factory schematic) at hand.

One note - there is a 50uF electrolytic (C179) in the 8AL9 circuit that causes poor contrast if it fails.

The only other tip is to replace C278 - they have a tendency to short, causing the focus circuit to arc. Its a 3900 pf HV Ceramic disc.

Also, the three drive controls are in parallel (9K ohms each, for a B+ load of 3K ohms) - if any of them were to open up, you'll get too much drive voltage to the cathodes. Real common problem, apparently - there is a Symcure in a 1974 Electronic Technician Dealer for the problem, as reported by GE. Replacement of the multi-pot assembly fixes it.

Key voltages:
GE defines on and off signal as antenna connected or disconnected.

8AL9:
Pin 2: 200V (on signal) 180V (off signal)
Pin 11: 3.8V(on signal)-5.4V(off signal)
Pin 4: 5.7V (on signal) - 6.6V (off signal) - this is tied to the brightness and brightness limiter controls.
Pin 10: 140V

6AC10:
Pins 2/5/10 - 165V

CRT:
G1: 90V (pins 3/7/12)
Screen controls are fed by boost voltages on one side and 280V source through R557 ( a 270K resistor) on the other side

Hope this helps,

Findm-Keepm · #6 06-20-2008, 04:51 PM

Doug,

One last note:

Pots - Briteness pot is 400 ohms, Brite limit is 150 ohms, and Contrast control os 500 ohms as well. I wasn't sure if they are marked on the pot. R195 ( a 270 ohm resistor is in series with the brite and brite limit controls.

Cheers,

*zenithfan1* · #7 06-20-2008, 06:39 PM

MWahhHaahaa!! Your plans have again been foiled by the General! But seriously, Those things are crazy! I have two sets built like that, one is a '73 and the other is a '75. Do you still need the schematic, I can help you out with that if you need.

KentTeffeteller · #8 06-21-2008, 03:53 PM

Hi,

When I was learning to fix TV sets in my youth, we referred to repairing a GE as "Saluting The General". Most of them weren't service friendly and prone to repairs. GE Flambe Television!

drh4683 · #9 06-23-2008, 06:25 PM

Well,

I can now "salute" the general. Its fixed now. Loss of brightness control in this case was caused by R189 27K 2W carbon resistor went down in value to 8K ohms. R189 tied to the low side of all three G1 controls to ground. Keep this one in mind as there might be 3 or so of these sets in existance that might need the repair.

Brian, thanks for your help and offerings. Thanks for mentioning tekfax. I completely forgot I had those! This set has the C-2 chassis, and I found the schematic in tekfax 112. Brightness now is controlable and can get the picture very dark to near total cut off upto a nice bright picture. I tacked in a crappy short lead 27K just to see if it did the trick as its the only one I could find. I need to stop at frys and pick up a new resistor to put in and call it a done deal. One resistor I'd like to find though is a 7.5K 7W green plate load resistor(R186). Its in the plate of the 8AL9 and I dont like the way it looks. Its also in a terrible spot all the way up in front of the chassis under the CRT. Basically impossible access without TV dissassembly.

I do give good credit to GE for one thing, they made a removable service plate under the chassis so I can solder under the board. There are alot of reinforcement ribs though so the probability of the part you need to replace being under a rib is quite high. I can be a hack tech and use a pair of snips to cut the rib out of my way so I can work, but I dont like doing things that way. This is a neat set and need to keep it working for a few more hours.

Findm-Keepm · #10 06-23-2008, 08:16 PM

Doug,

Glad to hear you got the set fixed. I'll check my stock - I probably have the 7W, 7.5K resistor in my stock of stuff. Those resistors are tough - I've seen them absolutely white from overload, but still check within 5% tolerance. Corning made them - basically metal film on a ceramic core with bronze crimps on the ends. I'll check tomorrow - short day for me, as I'm volunteering up some time at Bible School for the kids.

A-HEM..you owe us some pix - or a link when you post them to your gallery.

Cheers,

Findm-Keepm · #11 06-24-2008, 06:03 PM

Quote:

Originally Posted by drh4683

Well,
One resistor I'd like to find though is a 7.5K 7W green plate load resistor(R186).

Doug,

I gotcha one - it'll be on it's way in the morning. Spankin new one - green and all.....

Spent the day sorting through some stuff, hoping to find your resistor. Need any Belfuses? I could fill a shoebox with them - and I even have the sockets! Dad sure had some great stuff, the bulk of which is too new for 90% of the forum. Some day I'll get it all cataloged.

Your resistor is on it's way in the AM - I still have your address in Batavia.

Cheers,

drh4683 · #12 06-24-2008, 08:02 PM

Brian,

thanks a million for all your help. I really appriciate it. Its always good to have a nice stock of belfuses! Ive got a few myself. I have an old library card catalog cabinet that I keep alot of small compnents in. One of those drawers is belfuses of all sorts!

Once I get the new resistors installed, I'll get some photos of this set posted. I got this set back in february. Its been sitting on my "off to the side" tv bench with the back off since then awaiting the repairs! So many other projects took presedence. Im glad I finally made it important get to this one.
thanks again

drh4683 · #13 06-26-2008, 08:16 PM

There are yet more problems to deal with now. I noticed that there is quite a bit of corona discharge around the HV lead. So I decided to check the HV and its running high at 25KV. Supposed to be 22KV and HV control does absolutly nothing. This is one of those mint condition all original TVs that will have one problem after another. These are the worst ones. I'll be looking into the problem later on.

Findm-Keepm · #14 06-26-2008, 10:11 PM

Quote:

Originally Posted by drh4683

I noticed that there is quite a bit of corona discharge around the HV lead.

Doug,

Check C278 - GE had a bulletin about this very problem - corona discharge (arcing), too much HV, and short damper tube life. C278 is part of the focus tracking assembly, but can be replaced separately if the two 430K resistors check within tolerance. GE advises to replace the whole assembly if any sign of arcing has occured (carbon traces, bunr marks, etc). Real common problem on these sets.

Two other caveats, based on Dad's handwritten notes - R251, a 39K resistor, will go out of tolerance (high) and cause problems. It ties the horizontal osc/AFC circuit to the damper. Also check C268, a pulse coupling cap (.005uF) that feeds the HV adjust circuit. They tend to open/change value - if it shorts, you'll lose color keying or have color sync issues. Open, no pulse to rectify for HV regulation.

Hope these tips help, still digging. Dummy me passed on the GE service literature from another shop/GE service center that closed after 35+ years. But hey, I DID get the GE parts....

And according to the post office, your resistor has left Norfolk:

Your item was processed and left our NORFOLK, VA 23501 facility on June 25, 2008.

Cheers,

bgadow · #15 06-27-2008, 10:11 PM

I have a couple of those C2 sets and they are about the most miserable things...I've mentioned before about my copy of the Sams for these, which came from a longtime GE dealer. The whole thing is dog-eared, covered in coffee stains and solder burns and little notes all over the place. Mean. The older of my pair acted similiar to yours, with uncontrollable brightness. New drive pots fixed it, as I recall, though it still puts out a poor picture. I'll have to check that resistor when I crack it open again. (a long time in the future)

Findm, if you ever head north up 13 let me know...I'd give you one or both of those sets (if you wanted 'em) or maybe someday I'll save up enough gas money to go across the bridge/tunnel again.