1986 Fisher television

[zchrisz1986]

Originally Posted by zeno

First there are 2 grounds. One is the primary ( hot ) of the SMPS & the
other the chassis ground. gotta use the right one or voltages
will be wrong.
If the 2 lines ARE from the set its 120 cycle hum & most likely a cap
on the primary side.

Zeno

thanks Zeno

i got rid of those two hum lines. the service manual tells me exactly which two test points to check. which i get ~88 volts manual says 111v.

i tried the heat gun trick near the octocoupler and the b+ goes down as well as the voltage to the octocoupler. manual says 40v in but i'm getting 32v.

i wonder if it's one of those error modules which i cannot seem to find.

[jbattles]

your smps is running its has a oscillator like a horizontal sectioned the problem is after bow hot air on the capacitors. just fallow along the traces on the board and check the voltages.

[zeno]

I dont know your level so dont take this wrong !

Primary side ( hot) ground for your meter is the negative end of C011. Use it
for measurements on the RIGHT side of the SMPS transformer.

The chassis ( cold) ground is the tuner & IF shields, CRT dag etc.
The left side of transformer windings are the only cold grounds.

The isolator is to feed back the cold B+ to the hot side for a reference voltage
to control the PS output.

In the olden days we saw quite a few of these. If the transistor was OK we
would change the 2 modules & isolator. This fixed almost every one.

If you have a variac you can try turning it up & down a bit & see what happens.

Enuf fer now
Zeno
LFOD !

[zchrisz1986]

thanks, i had another isolator i swapped out no change.

i don't know a lot about televisions but know my way around electronic components.

i disconnected the main resistor to pin one on the flyback and the b+ went to 107 which is still less than the manual states.

do you have any clue what those modules are called? i did a search and cannot find any info.

thanks.

have a great weekend!

[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.

[Alex KL-1]

Originally Posted by 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.

Ops... a error: where reads "TAA320" is TAA550 or equivalent (33V tuner reg. IC).