1986 Fisher television B+ Low

[drunkendwarf]

Hi guys, i have a 1986 Fisher PC420 television. Chassis #A7R-42000

it works but has no picture width and some barrel distortion. i narrowed it down to low B+ 89volts. service manual says it should be 111volts.

it uses these Sanyo hybrid IC chips for error detection and drive that are discontinued and i cannot find anywhere. i found one post regarding a Sanyo TV with same symptoms and the resolution was the error detect module.

Part # JU0161 and JU0148

i'm now looking at bypassing that error detect to the optocoupler circuit somehow with my own. i don't have the skills to design a circuit and don't know where to start.

at 89VDC the optocoupler diode measured from pin 1 and 2 is 0.963 volts


i'll attach pics of the IC's and schematics. any help is appreciated.

thanks

[R_J]

Re: 1986 Fisher television B+ Low

Have you tried replacing the electrolytics (C014 etc.) in that circuit first instead of going after those modules?

[drunkendwarf]

Re: 1986 Fisher television B+ Low

Have you tried replacing the electrolytics (C014 etc.) in that circuit first instead of going after those modules?

Yes, I apologize. I forgot to mention I replaced all the electrolytic caps.

[R_J]

Re: 1986 Fisher television B+ Low

Do you have the voltages from the Error Drive Unit? What are the voltages compared to the schematic, that might give a clue to where the problem is.

[drunkendwarf]

Re: 1986 Fisher television B+ Low

on the error drive i got the following on what i measured.

Error Drive Measured. Schematic
Pin13 0.650v 0.70v
Pin12 18.22v 23v
Pin8 19.80v 19v
Pin6 1.286v 1.6v
Pin4 -1.401v -1.7v
Pin3 1.294v 2.1v
Pin2 0.612v 0.3v

on the Error Detect.

Measured Schematic

Pin10 88.9v 111v
Pin9 88.9v 111v
Pin 7 7.17v 6.0v
Pin 1 33.3v 40v

on the switching IC Q002

159v measured schematic says 150v


i've also removed the main resistor that drives the flyback transformer and the B+ went to 107volts. i was told the regulator still isn't working as it should have been around 130volts

Thanks

[R_J]

Re: 1986 Fisher television B+ Low

Try replacing the optocoupler, the voltages are close so something is off value but not totally bad. The switching power supply is working so hopefully it is not a fault of one of the modules. Can you post the complete schematic?
With the main resistor removed that supplies the flyback does not totally disconnect the power supply output as it looks like it also connected to R477 and that circuit?

[drunkendwarf]

Re: 1986 Fisher television B+ Low

i did replace the optocoupler with a tlp621 that i had on hand with no change.

attached the power supply schematic.

[drunkendwarf]

Re: 1986 Fisher television B+ Low

it is the JU0161 Error detect module. i substituted some zener's and resistors and the B+ came up to 111volts and the picture is perfect.

now if i can only find one of the replacement modules.

[R_J]

Re: 1986 Fisher television B+ Low

Just a couple ideas:
Can you isolate the faulty component on the module, using heat or cold spray?

Maybe you can use something like a SE110N error amp ic to drive the optocoupler, Sony chassis ba4d uses a SE135N-LF12 to drive the opto to regulate it's 135v

[drunkendwarf]

Re: 1986 Fisher television B+ Low

i tested the SOT23 Transistor and zener diode and seem okay. the problem is the thin film resistors on it. the manual doesn't specify the resistance.

i have a tv shop looking for one.

thanks