Time Machine - Data East power supply board help

[WannaTheater]

Symptoms:  No display power.  Game boots up and plays fine.
Power Board: 520-5000-00
After disconnecting the display (power and signal connectors), I measured across R11 and R10.  R10 provided -100Vdc.  R11 provided .7VDC,  So something appears to be wrong with the +100VDC circuit.
I removed both transistors (TR1, and TR3).  They tested OK on the bench.  I lifted legs and tested diodes and resistors in the +100VDC circuit, and they tested OK.  Frustrated, I ended up replacing R11, D5, D6, D9, TR1, and TR3.I reflowed all solder in the circuit.  When components were out of the board, I rang out continuity between pads... then rang them out with components back in the board (leg to leg).  I did not think the issue could be with the filter cap (C13).  Because I didn't have any replacements, I swapped C12 with C13.  The problem did not move to the -100VDC circuit, but it also did not fix the +100VDC circuit.

Measuring across D5 and D7 provides 120VDC.
Measuring across C10 (same as D6 cathode to ground) provides 120VDC (VAC bounces around)

One thing I did notice when replacing TR3 which was different than in the -100VDC circuit:  In the -100VDC circuit, TR4 has a plastic (I think) spacer between the backside and the heatsink.  TR3 did not have this spacer.  I am thinking this is not important?

Any ideas/advice, before I waste another 4 hours on this thing?

Thanks!

[FUNWIZ]

Can I get some pictures of the positive output area, components and traces?  Thanks.

[WannaTheater]

Sure-  Not the greatest pictures, but please let me know if this works:
https://photos.app.goo.gl/SvdVtcgdXpu7DHnE7

I am using the schematic in the manual from the IPDB site: https://www.ipdb.org/machine.cgi?id=2565 (Inside the document - English Manual (with paginated schematics; board diagrams are in color)


The big capacitor C4 is a bit puffy on the end, but that does no seem to be in the same circuit.

Nothing looks off on the top of the board, or the bottom.

[FUNWIZ]

Did you try swapping around R8 and R9?  Then there is R12 and R13. One of those resistors has to be out of tolerance or opened up.

[WannaTheater]

I measured R12 with one leg lifted, and it was OK.
I did nothing with R8 and R9... will check

[WannaTheater]

FUNWIZ!!!  R8 is indeed open.  So much for my theory of "resistors never go bad, unless they are visibly cracked in half."

Thank you!

[WannaTheater]

Follow up question-
The replacement resistor I purchased from Mouser is physically much smaller:
https://photos.app.goo.gl/sNoircpYY5KFqrTY7

This is the product I purchased from Mouser:
https://www.mouser.com/ProductDetail/Vishay-BC-Components/PR01000103902JA100?qs=ClR5yMXwuUe8EVhwXaMv5A%3D%3D
Metal Film Resistors Through Hole PR01 5% A1 39K

The purchased replacement is still 39K at 1W, just physically much smaller.... Can I still use it?

[HammysHangout ( Hammy )]

that will be fine. as long as its 1w.

[WannaTheater]

Thanks Hamster.

Replaced and tested board in the game.  Sad to say, there is still no +100Vdc

Since the game is a mile from my house, swapping and testing is becoming a PITA!

Any other suggestions/places to look?

[FUNWIZ]

I would love to have a picture of a 1950 resistor, so we can compare the differences over the years in wattage and size. That said, you need to take a meter reading of everything, placing the black lead on ground, and test each component on all sides of the hundred volts, positive and negative sides, just for comparison sake.  ✍️ write it all down.  TR1 sends a control voltage to the base to turn TR3 on, and something is not correct in that area. Usually it’s D9 Zener diode. You’ve said you’ve checked all that, but let’s get a measurement of all the voltages, and see if there’s low or missing voltages at the base of the two transistors that control the flow of voltage to the displays. Are the displays disconnected while you are testing this area? You could have a shorted display and pulling down the voltage also.

[HammysHangout ( Hammy )]

i would suspect if the r8 was open, the zenor diode failed short, (or now open ) .

[WannaTheater]

All testing is being done with displays signal and power harnesses disconnected.  Will be able to do some more testing (write down voltages) next weekend.  Will also check the Zener diodes.

[WannaTheater]

Hammy was right- D6 was bad.  Replaced, and now I have both +100VDC and -100VDC.  Displays are working properly.

Thanks all!