RCA (Thomson) F20TF10 in a coma

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Fuse MP 50 can be repaired using a wire from the glass fuse of the same rating. Gently crush him, and to get the wire soldered to the conclusions of the burnt MP 50(wire soldered directly to the terminals closer to the body) pre-checked load resistance after the fuse in the circuit, which would not be short-circuited. 7809 test separately from the TV. Applied to the input (pin 1 and 2) 12-volt power supply and check the voltage at the output (pin 3 and 2)

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Thanks for the tips. I did meter the 7809 using diode function as well as restance and there's no short. I'll test it on 12v and see if it still functons. I haven't been able to find a 500mA 66volt fuse of any type though.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Not necessarily put the fuse on the 66 volt, can be used on a larger voltage

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Thank you for the info. I was unsure about fuse voltage ratings but I have (re)educated myself about it.

I tested the 7809 regulator and thankfully it works within tolerance; output is 8.86v with 11.78v input. Now to find a suitable fuse I'll keep you updated.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Ok!

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Ok, I've got the 7809 back in (fastened with a nice screw into freshly drilled hole on the heatsink, to hell with that clip crap) and the fuse repaired and installed as directed. The fuse reads 1 ohm, same as before I took it out of the glass.

So now I've got the 9v supply as well as the HV from the flyback. Should I try grounding the RGB CRT pins now with the screen up a bit like you said before?

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Well, TV is turned on, the screen is dimly-lit, mirror set, is used to test one wire end is connected permanently to the ground, (praying) briefly regard to the second end of wire to RGB pins CRT are alternately

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

No go. The screen control has no effect now, no dimly-lit screen, grounding the pins does nothing.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

The CRT heater measures 5 ohms but the votage across it has dropped to 6vac. The flyback is still putting out 27Kvdc but perhaps something internal of the flyback unit has faulted?

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Repeat 1-how many volts on pin 5 BU004 crt board. 2- how many volts to pin 2,3,4,6 BU003 crt board.

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

BU004
5 = 188.8

BU003
2 = 1.2
3 = 1.2
4 = 1.2
6 = 8.7

Essecially unchanged from before.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Measure the VG2 to CRT board and as the value changes when rotating the screen on flyback

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

VG2 = 75 to 534vdc from full ccw to full cw.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

may be a bad solder pin 4 on flyback

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Retouched that and also 5. I also cleaned up my repair where the 7809 is and double checked for shorts prper voltage, all good.

Now there is no CRT heater AC at all, heater still reads 5 ohms.

BTW, once again the front panel power button has zero effect on anything. I try pressing it and measuring everything again and it makes no difference.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Where are you measuring the resistance of the filament-heater directly on the CRT socket, with the removed board CRT ?

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

I measured the heater resistance both connected and disconnected from the circuit board. It is the same. 5 ohms.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Сheck all connections and the rest of the fuses on the main board

[SteveNielsen]

Re: RCA (Thomson) F20TF10 in a coma

Already found another open MP 50 fuse near the 1st one, on the 7806 6v regulator pin 1 (input), which comes from the 7809 output BTW. Guess it's time to break open another .5A glass fuse.

I'll pull the 7806 and test it too. At least it has a screw to the heatsink

7806 is fine. 12v in, 6v out.

[kasfamily]

Re: RCA (Thomson) F20TF10 in a coma

Very well,expect to continue