RCA 32V434T chassis ATC010A

[PlainBill]

Re: RCA 32V434T chassis ATC010A

Pulled the Horizontal output transistor Q405 out of circuit.

D3402
701II

DMM diode test:
B(+) C(-) .472
B(-) C(+) .OL
C(+) E(-) .OL
C(-) E(+) .493
B(+) E(-) .044
B(-) E(+) .044

Is the HOT good or bad?

It appears to have a base-emitter short; if so, it's bad. What is the base-emitter resistance?

PlainBill

[kc8adu]

Re: RCA 32V434T chassis ATC010A

in circut b-e will be low due to drive transformer.modern hots also have b-e resistor internal.99.999% of bad hots are e-c short.
btw lots of bad flybacks in these sets.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

It appears to have a base-emitter short; if so, it's bad. What is the base-emitter resistance?

PlainBill

Still removed from circuit.

DMM Diode test

B(+) E(-) .041
B(-) E(+) .041

DMM 200 Ohms test

B(+) E(-) 43.8 (ring tone)
B(-) E(+) 43.8 (ring tone)

[Village Electronics]

Re: RCA 32V434T chassis ATC010A

[QUOTE=PlainBill;197410]It appears to have a base-emitter short; if so, it's bad. What is the base-emitter resistance?

PlainBill[/QUOTE

H.O.Transistors come in two flavors. This flavor has a low resistance e-b. The only important resistance check is C-E.

More important, when the H.O.Transistor is removed is the B+ voltage. Does it return to normal? If it does the problem is downstream from the flyback transformer.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

Still removed from circuit.

DMM Diode test

C(+) E(-) .OL
C(-) E(+) .497

DMM 200-200K Ohms test

C(+) E(-) OL.
C(-) E(+) OL

DMM 20,000K Ohms test

C(+) E(-) OL
C(-) E(+) 655 and slowly ticks down by 1

DMM 20M Ohms test

C(+) E(-) 7.35
C(-) E(+) 1.71

[cmj21973]

Re: RCA 32V434T chassis ATC010A

This repair is on hold untill after Thanksgiving.

Workbench had to cleared, so family could eat at kitchen table.

Happy Thanksgiving!

[cmj21973]

Re: RCA 32V434T chassis ATC010A

Back to repair :

I soldered Q405 back in (I'm still not sure if it's good) and reassembled to test the run power suppy.

Set didn't turn on, lost 5V standby. Removed IC804 for testing.

LED test fine but, the phototransistor is shorted.

Would this one be a good replacement?
http://search.digikey.com/us/en/prod...17-5-ND/457901

[PlainBill]

Re: RCA 32V434T chassis ATC010A

Back to repair :

I soldered Q405 back in (I'm still not sure if it's good) and reassembled to test the run power suppy.

Set didn't turn on, lost 5V standby. Removed IC804 for testing.

LED test fine but, the phototransistor is shorted.

Would this one be a good replacement?
http://search.digikey.com/us/en/prod...17-5-ND/457901

I can't judge the dimensions, but electrically it looks like a match.

PlainBill

[randtek]

Re: RCA 32V434T chassis ATC010A

Did you pull the Horizontal output COMPLETELY out of the board? If so, and you are measuring .044 B-E in both directions, that transistor is bad. If you only unsoldered the collector, then you are probably measuring the horizontal drive transformer in paralell with the emitter-base junction.

[Village Electronics]

Re: RCA 32V434T chassis ATC010A

Did you pull the Horizontal output COMPLETELY out of the board? If so, and you are measuring .044 B-E in both directions, that transistor is bad. If you only unsoldered the collector, then you are probably measuring the horizontal drive transformer in paralell with the emitter-base junction.

This chassis uses a horiz. out xtr with an internal damper diode. They all read
low resistance B-E and E-B.

[randtek]

Re: RCA 32V434T chassis ATC010A

This chassis uses a horiz. out xtr with an internal damper diode. They all read
low resistance B-E and E-B.

Ah, my mistake. I thought the values gioven were resistance values, which should be in the 35-50 ohm range for E-B. I see now that the poster was giving Diode check voltage drop readings, which would appear to be normal for this transistor. My bad.
I gotta stop posting before I have had my coffee!

[cmj21973]

Re: RCA 32V434T chassis ATC010A

Replaced IC804

Applied power: no click from relay K802, no 5V STB

Following the guide on page 22 of RCA ATC010 Training Manual.pdf

1) IC860 pin(8) DC voltage 160.7
2) IC860 pin(1) DC voltage 9.54
4) IC860 pin(4) DC voltage 0.66

Since I've already replaced IC804, guess I have a problem with the feedback circuit off the 5V STB supply.

Since I don't have 5V STB on the Control Board (front panel buttons), I pulled T860 for testing.

Blue Ring tester: DMM Ohm's set to 200
pins 1&2 two steady red lights 00.8
pins 3&5 three steady green lights 2.9
pins 6&10 no lights at all 00.6

[cmj21973]

Re: RCA 32V434T chassis ATC010A

Well, tried to order mfg. p#274219 (T860) only to be informed that it's no longer available.

Guess I'm going to learn how to rewind a transfomer.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

The "E" ferrite cores broke.

I'm guessing that if I super glue them back together, that they will still be useless to use.

End of tv set repair, if I can't order them with reasonable shipping price.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

Latest trash/recycle find might yield EI ferrite core to rebuild T860.

Length, width, and height are a match. Will know about the center post after a 2 day acetone soak.

Meanwhile, I need to clean the magnet wires, 4 coils, so I get measurements.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

Okay, I've finished rebuilding T860.

Before: After:
Blue Ring tester: DMM Ohm's set to 200
pins 1&2 two steady red lights; 00.8 pins 1&2 three steady green lights; 00.7
pins 3&5 three steady green lights; 2.9 pins 3&5 three steady green lights; 2.5
pins 6&10 no lights at all; 00.6 pins 6&10 one red steadylight; 00.6

Next step is to test it out of circuit, to measure the secondary voltage ouputs.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

I soldered the rebuilt T860 back in placed. Was only getting about 76VDC on pins 5&3 (primary coil).

Found the negative solder pad for C861 had popped loose. Made a new pad, to bridge the solder traces, and solder it in place.

5V STBY power restored.

[cmj21973]

Re: RCA 32V434T chassis ATC010A

With the 5V standby opperational, I followed the "Run Power Supply Troubleshoot".

1)With C-E of Q861 shorted, applied AC power and measured IC801 pin4 = 32.8VDC steady.

2) Unsoldered pin 1 of IC801 and measured DC voltage on pad = VDC > 120VDC

3) Resoldered pin1 of IC801 and checked secondary power supplies. I used the voltage test points listed on page 11 of service manual.

TP 1) 130V @ D882 = 133.5
TP 2) 130V @ L801 = 133.5
TP 3) 33V @ R826 = 33.9
TP 4) 12V @ D820 = 14.0
TP 5) 12V @ L807 = 10.0
TP 6) 9V @ pin3/IC091 =10.0
TP 7) 5V @ pinOUT/IC090 = 5
TP 8a) 5V @ L851 = 5.1
TP 8b) 5V @ pin3/P001A = 5.1
TP 9) 1.8V @ pinC/Q201 = 1.8
TP 10) 1.8V @ pinc/Q203 = 0
TP 11) 3.3V @ pinE/Q080 = 3.5
TP 12) 208V @ R505 = 133
TP 13) 14V @ D404 = 0.4
TP 14) -14V @ D405 = -0.3
TP 15) 12V @ R1301 = 8.7
TP 16) 230V @ R505 = 133