RCA (Thomson) F20TF10 in a coma

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I elected to try repairing the connector and connections on CRT board. I epoxied the connector shell to the board and it is solid. Connections from the main board through the cable and the pins on the CRT board connector are good. I soldered thin wires to replace borken traces on the CRT board and continuity checks are all good.

Before I reconnect everything and test again I want to ask if it is ok to leave the Gem Star 4 board disconnected? I've never used that function and I won't.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Hi SteveNielsen, welcome back! I do not know what it Gem Star, but perhaps control processor needs information about the board and its serviceability.

[Agent24]

Re: RCA (Thomson) F20TF10 in a coma

No idea but this: http://www.justanswer.com/tv-repair/...el-remote.html suggests it's OK, at least for that model.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Thanks for the link Agent. I'll try it unplugged. It uses those plastic film ribbon cables that like to come out of connectors and/or break.

Hi Kas. Gem Star (or Gemstar) is a TV Guide service that tells you all about what's on TV channels sort of thing. I don't think it's available where I live and even if it was I'd never use it.

Well, anyway, I got the junk all plugged back in and same story, no HV to the CRT, no low voltage turning on. It made no difference having the Gemstar unit plugged in or not. All the previously measured voltages are the same as last time:

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

Oh yeah, I also touched up all the solder joints in the area of the flyback.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Check the voltage at DP57 (+14VE) and again "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

Check the voltage at DP57 (+14VE) and again "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"

DP57 = 12.5v but is not the same as +14VE, +14VE is 0v.

edit: I may be measuring the wrong point for +14VE, I tested the point directly above the printing, however the point to the right has 12.5v and does trace back to DP57.

These are the best pics I can get. In trying to trace out the paths I get lost under the printing in the n/p x 1 area.
edit: that was tracing the emitter of TP390 though.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

DP63 cathode must be 14V, while the inlet and IP330 is 12V and the output level 9B. So this very little 12.5V. It is necessary to check the CP64 and Zener DP57

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

CP64 is a 3300uF 16v and tests 3026uF, 2.8 ohms ESR.

DP57 tests ok. It reads as diode, Uf 807m, 32pF.
(I don't know what "Uf" is supposed to mean on this tester for a diode, forward voltage? In transistor testing with this tester Uf indicates base-emitter threshold voltage. I assume that it is indicating that the forward voltage is 807mv.)

I also checked C62 (470uF 25v) which reads 450uF, 3 ohms ESR.

edit: both caps are 85c
edit: corrected typo in line 1 to read 2.8 ohms, not .28 ohms.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

DP57 painted as zener.UF807m can not find in the series UF800 not http://pdf1.alldatasheet.com/datashe...TE/UF806F.html. And as the voltage DP63 cathode?

[Agent24]

Re: RCA (Thomson) F20TF10 in a coma

DP57 painted as zener.UF807m can not find in the series UF800 not http://pdf1.alldatasheet.com/datashe...TE/UF806F.html. And as the voltage DP63 cathode?

UF807M is not the model, he says his tester shows 'Uf 807m" which is probably the forward voltage.

CP64 is a 3300uF 16v and tests 3026uF, 2.8 ohms ESR.

I also checked C62 (470uF 25v) which reads 450uF, 3 ohms ESR.

edit: both caps are 85c
edit: corrected typo in line 1 to read 2.8 ohms, not .28 ohms.

In a switching PSU around 3 Ohms ESR would be terrible. Here where they use general purpose capacitors it may be more acceptable, but a 3300uF should test lower.

Check this ESR table (http://www.jestineyong.com/esr-meter-table/):

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Thanks Agent24 for the correction, and I look very tired search diode UF807m

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I'm sorry about that Kas. Thanks very much for the effort.

Thanks Agent, I figured 3 ohms was pretty high for it too. The 470uF ESR is pretty high too. I have a lot of gp caps in my collection, I'll look for replacements.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

False alarm, my cheap ESR meter wasn't working right, needed new battery. The caps are ok after all.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

I did for the ESR meter external power supply used for this charging adapter from a cell phone. Just tired of changing batteries.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I might do something like that. It wasn't just the battery either, I was using cheap alligator clip test leads that weren't making good contact. They haven't given me much trouble like that before but I suppose it mattered more when the battery got low.

[Agent24]

Re: RCA (Thomson) F20TF10 in a coma

It makes me think though, maybe you should check all the capacitors in the power supply.

I had a fault in my own TV last week where two capacitors went open-circuit on the -23v rail resulting in a huge amount of ripple on that rail. In turn, that caused the RGB amplifiers to fail to operate correctly and the picture to vanish.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I've already checked the PSU caps but am thinking of checking all the caps.

I found the source of the hissing sound though, it is the transformer in the lower center of the board near the power supply. I used a modified stethoscope to find it.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

If the source of the noise LP02, it may be damaged by the ferrite core inductor

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Here is a small example of how customer to look for the noise in the power supply and also thought that the noise transformer and even delayed his wire. A faulty filter capacitor 47uF turned 400V - he was just broken one pin. While the receiver was working, was only affected by noise from the power supply.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

It is LP03 that hisses, the one with the yellow around the frame and copper strap. It's marked
VDE (in triangle) 2114390 FEC 0105c
SRV3906-010

Searching on any of those numbers has no results.