84 GE 25PM-C Color console problem

[jg6364]

You guys helped me so much with the Sylvania set now I have another problem. I just got this set and the first day it played beautifully. It is a 1984 GE color console with stereo and a bilingual adapter. It is using the same 25PM-C Chassis as another set I have.





I turned it on the next day and it clicked a few times and smoked. I found that it was a 5.6 uH choke coil or maybe its called an inductor I've heard it called both.



Here's the full schematic on the sweep board that has the problem.

I tried swapping the entire chassis with the other tv but it had the same problem and the same inductor started getting hot . I turned it off and put the chassis back in the other set. Fortunately it didn't hurt it. I'm thinking something in the stereo adapter or the connections for the bilingual adapter could be causing the problem.







I'm going to get the replacement part but I figured something caused this and I was wondering what to look for. The bilingual adapter on the back of the set was unplugged. Any suggestions is greatly appreciated.

Jeff

[zeno]

Not sure what the +36 feeds but prob vert or tuning voltage.
Most likely Y932 shorted, note there is not the usual low ohm
resistor used as a fuse. Also the 2 'lytics possible also.
I got the training manual at least & will pull it tomorrow
& have a look what it feeds.

73 Zeno

[jg6364]

Originally Posted by zeno

Not sure what the +36 feeds but prob vert or tuning voltage.
Most likely Y932 shorted, note there is not the usual low ohm
resistor used as a fuse. Also the 2 'lytics possible also.
I got the training manual at least & will pull it tomorrow
& have a look what it feeds.

73 Zeno

Yeah, My gut feeling is it's something in the tuner module. I swapped the entire chassis from the other TV. I used the same stereo board and tuner module. The problem was the same and the same part got really hot.
What about the relay driver in the tuner module?


Thanks

Jeff

[Findm-Keepm]

The 36V source feeds the tuner and the audio output. Your problem probably lies in one of three things - a shorted device at the powers supply, or a short in the tuner or audio amp. Very few components to check - I'd start with Y932, C937-939, and then pull the audio output to see if the audio is pulling the 36V down if not, it is most certainly the tuner.

Cheers,

[jg6364]

Originally Posted by Findm-Keepm

The 36V source feeds the tuner and the audio output. Your problem probably lies in one of three things - a shorted device at the powers supply, or a short in the tuner or audio amp. Very few components to check - I'd start with Y932, C937-939, and then pull the audio output to see if the audio is pulling the 36V down if not, it is most certainly the tuner.

Cheers,

thanks
I checked c937-939, all good. I will go back and check y932 , and then go from there.

Jeff

[zeno]

Originally Posted by jg6364

thanks
I checked c937-939, all good. I will go back and check y932 , and then go from there.

Jeff

If its the diode use the right one. ECG552 IIRC the regular
diodes overheat & short at 15khz.
For the tuner there will be a resistor then a 32V zener to ground.
Suspect that. If audio the output IC almost a sure thing.
I will pull the manual later..

73 Zeno

[jg6364]

OK, it looks like it the audio amp. I hooked everything back up and it did the same thing, I unplugged the amp and it came up with a perfect picture. Here is the pic of it unplugged.




from the schematic ic200 and ic201 is EP84X109. that crosses to NTE1376. if you guys know of something that will replace it that may be a little easier to find that would be great. How would you go about testing these to see if they are shorted?





Thanks for all of the help

Jeff

[zeno]

If shorted they usually read real low ohms ( pin5 -pin 3 )
or 5-4 etc. the zeners on the output (pin 4 ) could do it also.
If one is gone I would change both. ECG is same as NTE &
maybe easier to find. Also could back cross it to an
origional number ( not GE ) but dont know where to do it.
Any markings on them ???

73 Zeno

[jg6364]

Originally Posted by zeno

If shorted they usually read real low ohms ( pin5 -pin 3 )
or 5-4 etc. the zeners on the output (pin 4 ) could do it also.
If one is gone I would change both. ECG is same as NTE &
maybe easier to find. Also could back cross it to an
origional number ( not GE ) but dont know where to do it.
Any markings on them ???

73 Zeno

There are 2 numbers on it 143530-1
underneath is 88419 and a logo of SGS.
I tested them and one did have resistance of .5 ohms between 5 and 4 and 11 M- ohms between 5 and 3 the other had of 11M-ohms reading on either points. I ordered a lot of 3 NTE1376 new unopened from eBay for $12.99. That was the cheapest I could find. While I have it out I'm going to check all the caps too.
Thanks for all the info I will update you when I get the parts in.

Jeff

[Findm-Keepm]

The Audio ICs are LM1875T - GE used them in the PM/PC chassis. Digi-Key and others stock them. We sold the GE ones for ~12 bucks, the LM1875T was cheaper to source, and we sold lots of them.

CHeers,

[Findm-Keepm]

The Digi-Key part number LM1875T/NOPB-ND is now a lead-free (RoHS) part with the NOPB suffix (no lead), and works fine. Make sure you use some heat sink compound when you remount the new ones.

Cheers,

[jg6364]

Originally Posted by Findm-Keepm

The Digi-Key part number LM1875T/NOPB-ND is now a lead-free (RoHS) part with the NOPB suffix (no lead), and works fine. Make sure you use some heat sink compound when you remount the new ones.

Cheers,

I had printed a data sheet on that part number and was wondering if it would work. It's good to know. I tested all the capacitors on the audio board and found one 2200 uf 35V cap was reading only 1 uf. I will get it and the other parts in a few days. I hope to get it back going soon. The other GE set has the same chassis but it is mono. This has the stereo amplifier and the bilingual decoder on the back of the set. I like the fact that is has several antenna hookups as well has several rca inputs. That's kind of rare for this old of a set. I know after 1986 a lot of the sets had stereo as a standard feature.

[jg6364]

I replaced the 5.6uh inductor that was burned out in the chassis. I replaced both of the audio IC's and one 2200uf 35V cap on the audio board. It's back working great again. Its the TV on the right. the other set has a weak picture tube.



This TV will be replacing the set on the left to be used in the living room.

Thanks again everyone for your guidance.

[zeno]

Glad to see it running again. I always like the PM & PC
GE chassii, otherwise I dont miss GE.

73 Zeno

[dieseljeep]

Is that one of those Zinwell DTV adaptors. I picked one up at the G/W for 5 bucks. Brand new, in the box. I don't think it's very hot.
I'm 41 miles from the transmitter, using an amplified set-top antenna.