RCA (Thomson) F20TF10 in a coma

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Thanks, that is what I've been doing, taking pics and tracing out on the computer screen, traces are too hard to see otherwise. That collector connection goes all over the place through jumpers galore.

You'll have to bear with me though, I have a 9 year old daughter who keeps swiping my camera. Plus I can only spend limited time looking as it hurts my old arthritic neck. I'll keep you updated as I find out.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Sorry for the delay. Here are some pics of that area that are clearer I think.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

I study photos. IP301 now is voltage on pins ?

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Yes, IP301 still has proper voltages; 9.2v on pin 1 and 5.9v on pin 3.

I've got some of the circuit traced out from pin 26 on the video chip but not completely. So far it goes nowhere near the flyback.

[Andrew F. Ali]

Re: RCA (Thomson) F20TF10 in a coma

Is that bulging cap opposite the crystal and just above to Main IC??? I see Qio2 next to it but that isn't the label it should be Cxxx.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Need actual voltage IP330, TP390 and TP391

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Andrew, the cap isn't bulging, it's the lighting and shadows. It's labeled CV28 on the other side of the cap.

Kasfamily, here are the voltages:
IP330
Pin 1 = 10.4v
Pin 2 = 0v
Pin 3 = 8.6v

TP390
E = 0v
B = .5v
C = 8.7v

TP391
E = -.01v
B = .67v
C = .03v

When measuring TP390 I accidentally shorted B to C which turned on HV to CRT anode.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

TP390 has already been tested ok out of circuit.
I just pulled TP931 and it tests ok as well.

My accidental short of B-C on TP390 turning on HV tells me something is not turning that transistor on.

Wish I had a schematic for this board.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

OK!TP391 controls the supply of 9 volts on pin 26 TA1268 through TP390. Enable signal is applied to the base TP391(may be to press POWER button). If not, need photo area board from N to R and 0 to Z, with two sides. What would follow the chain of signal control base TP391

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Yes! Pwr button now functions! WIth the set off though I can still hear quiet hissing but unable to pinpoint it yet.

I am able to test the CRT, turned screen control up enough for dimly lit screen, shorted pins 6, 8, 11 and got fairly bright Green, Blue, Red. If the short gets' left on a pin for more than a second or so the set shuts off again. I assume that is normal in this test.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

The TV will now come on using Pwr button and will show a full screen of snow for about 1 second then shuts down. If I press a menu button after powering on the menu appers but blinks and image gets vertically squashed then TV shuts off.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Very good headway! Maybe will take a photo of the screen, but I not clear get all.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Something else just went wrong, the screen is all white with retrace lines now even with screen control all the way down, turning it up it gets brighter and will shut off if turned up past a point.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Reported connector connected?

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

It's connected ok. The white screen started after I nudged the blue elecrolytic next to the flyback transformer when the set was on. I've pulled the cap and it checks ok. I'm looking for bad solder joints, etc. in that area but see nothing out of the ordinary yet.

[Agent24]

Re: RCA (Thomson) F20TF10 in a coma

It's connected ok. The white screen started after I nudged the blue elecrolytic next to the flyback transformer when the set was on. I've pulled the cap and it checks ok. I'm looking for bad solder joints, etc. in that area but see nothing out of the ordinary yet.

Might pay to just resolder everything in that area just in case, sometimes they're not easy to see.

I also noticed in a previous photo that capacitor is right up against a ribbon cable, perhaps it was not the capacitor being bumped but rather the capacitor bumping the wire?

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

That's a good call Agent24, in fact that cable had a bad contact at the CRT board on the same connector (BU004) that I repaired lifted pads/traces for, but it seems to have been the connector itself not quite seated and that problem is gone now. Now I'm kind of back to square one with HV but nothing on the screen, except the power button still works. I am going to touch up the soldering as you suggest.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Well folks, my repair of BU004 on the CRT board has failed. The stress from the stiff cable was too much for it plus I think the contact pins inside the plastic connector shell got mispositioned due to heat from soldering. I guess I could try eliminating the connector, strip back the cable and hardwire it to the board but I'm concerned that would suffer the same fate and tear the traces again unless I glued it down or provide some sort of strain relief for it.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

May be necessary to replace or extend the cable to the BU004. Use for this the softer and more flexible wire.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

That's a good idea. Thanks. I'll see what I've got that's suitable.