1986 Fisher television

[Alex KL-1]

Some testing to try...
1 - measure the photocoupler diode voltage (pin 1 to pin 2, IC001). If is less than 1V, the primary switching is soft, no longer providing sufficient power, and secondary comparator A003 no catch it and not makes the diode to conduct. Suspects: the A002 module or capacitors near it, including the C011 and all small ones (since some couple pulses and high ESR on then upsets the regulator).
2 - if measures 1V or a little higher in the photocoupler (indicating conduction of internal diode), the A001 module was in error in it's internal reference. For testing this, a dangerous proposal: sub this module for a series string of 110V zeners (or a 110V zener) only for testing, removing the A001 module (and changes the photocoupler connections for proper conducting, I can draw it if you wants to test it), to check if restores near 110V regulation. Is not recommended to run continously the zener string due to temperature voltage drift.

[zchrisz1986]

Originally Posted by Alex KL-1

Some testing to try...
1 - measure the photocoupler diode voltage (pin 1 to pin 2, IC001). If is less than 1V, the primary switching is soft, no longer providing sufficient power, and secondary comparator A003 no catch it and not makes the diode to conduct. Suspects: the A002 module or capacitors near it, including the C011 and all small ones (since some couple pulses and high ESR on then upsets the regulator).
2 - if measures 1V or a little higher in the photocoupler (indicating conduction of internal diode), the A001 module was in error in it's internal reference. For testing this, a dangerous proposal: sub this module for a series string of 110V zeners (or a 110V zener) only for testing, removing the A001 module (and changes the photocoupler connections for proper conducting, I can draw it if you wants to test it), to check if restores near 110V regulation. Is not recommended to run continously the zener string due to temperature voltage drift.

i'm pretty sure the A003 module is not working correctly. i'm trying to source the part but having no luck.

optocoupler pin 1/pin 2 measures 0.963volts

[Alex KL-1]

If is impossible to locate the A003, a replacement to consider will be something analogous to my explanation, but using low drift devices: 3x series 33V tuner voltage regulator (like TAA550 or equivalent), plus 2x 5V6 zener, all in series with the optocoupler anode, and optocoupler cathode wired to ground. This will results in a sufficient low drift substitute.
I made some voltage regulator based on these 33V tuner devices with very good results. One just for a TV, with failed regulator, for saving it from dumpster.

[zchrisz1986]

thanks Alex, it's not looking good on finding a replacement. although i can put things together. i'm not a design from the ground up circuit inventor.

it seems over in india they have these power modules that will solve what i'm trying to do. none in the usa

[zchrisz1986]

i took out the IC. it has a resistor, zener diode, and an npn transistor on it. are the flat black blocks just trace connectors? the schematic shows a wiggle line.

see pic.

[zchrisz1986]

Just to update.

with the help of Alex i determined it is the error detect module. i substituted some zener diodes and resistor and the picture is perfect at 111 volts on the B+

[Alex KL-1]

Excellent! One more TV working!

For completness, below I include the drawing of the low temp drift option I mentioned; needs to use it ONLY if common zener string changes +B voltage too much when chassis is hot.