I just rebuilt a Gottlieb System 1 power supply. All the voltages are good with the exception of the 60v and 42v lines. Both the 60 and 42v pins on the power supply give off 17.7vdc. The POT adjustment has no effect.

The transformer lugs read 74-75 VAC.

On the power supply, using the negative lead on C6 as ground for the DMM, I tested the voltage on the diodes at the bottom of the board (CR6, CR7), and they read 41.5vac. From the schematic, they appear to be on a 90.4v line.

So, did I loose that much voltage from the get-go? Or am I testing the voltage incorrectly, and the problem actually exists further down in the circuit?

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All the diodes on the lower third of the board are fresh replacements (cr3, cr4, cr6-cr9, cr21, cr1, and cr2), as well as all the electrolytic pots, the large TO-3 regulator on the back, the POTs, and the header pins. Everything else is original. The regulators do not short to the backplate. The ground mod wire has been done on (on the back, so it's hidden).

a test fit for the ground wire mod

Ok, I replaced C7. The 60vdc pin is unchanged. The 42vdc pin is showing zero vdc.

The diodes and zener diodes test good.

The voltages on the banded side of the diodes are now:
CR7: 97.1vac / 0vdc
CR6: 32.9vac / 41.7vdc
CR8 32.9vac / 41.7vdc
CR9: 97.1vac / 0vdc

Those seem to be in the ballpark. I'll have to test the transistors and resistors a bit later.

I couldn't seem to find where C9 and C10 were on the schematic. The only caps I can see in the HV section are C6, C7, and C8. I'm not sure how C9 & C10 fit into the circuit.

On this board:
C7 was .1uf 50v
C9 and c10 are 1uf 50v.

It looks like the transistors are giving wacky readings with a diode test on each leg.

Q2 gives 734 & 1915
Q3 gives 1936 & 773
Q4 gives 76 & 704.

It seems odd that all of them would be bad

On the other hand, just as a sanity check, LIC1 reads 625 & 738, which seems ok.

A number of resistors seem to don't match the values on the two parts lists I'm looking at. I'll have to go though and read the bands on those next.

The parts values I'm looking at are from the Sinbad manual and from the 1982 parts catalog--the resistor values are different between the two.

Originally, this power supply had a "G" in the serial number, so I would guess that I should be looking at the newer parts values found in the parts catalog.

[edit]: Ok, what I think I'm going to do this weekend is replace Q2, Q3, Q4, and all the HV 1/2W resistors R10-R18. Since it looks like I'll have to replace a few of the resistors anyway, I might as well go ahead and put fresh new ones in for the rest while I'm at it.

Ok, I replaced Q2, Q3, and Q4.

Also R21, R10, R11, R12, R14, R15, R17, and R18.

I couldn't replace R13 since I didn't have any 33 ohm 1/2w restore on hand, but that one was giving the correct reading.

The end results weren't much different. The 60v pin is giving 13.3vdc. The 42v pin is giving zero vdc.

I guess C9 and C10 are up for replacement next.

Yes, the screws on the two transistors have insulators. There are also mica insulators between the backplate and transistors.

The tape is still in place under both transistors.

I found a schematic for a newer revision of the power supply, and it has C9 & C10 noted. They were absent on the schematic in the manual for Sinbad. So, now that I have a matching schematic, I can see how C9 and C10 tie into the circuit and could potentially be a problem area.

I'll probably do the replacement tomorrow.

The ones installed are 1uF 50v. The board is marked with a + sign for one of the leads on each one, which matches the + sign on the cap.

[Edit]: Boy, I sure am glad I did the mod for adding the wires through the board to the regulator on the back. I've already taken the board off the backplate 3 or 4 tines now.

I replaced the C9 and C10 caps, but no luck.

The 60v pin starts put around 17vdc and slowly drops down to 13vdc.

The 42 pin still reads zero vdc.

The caps I used were 1uF 40v ceramic, but had no polarity markings.

https://www.greatplainselectronics.com/proddetail.asp?prod=CCM-1.0uF-50V

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banded CR6 to banded CR8 = 73.5vac
banded CR7 to banded CR9 (neg lead on CR7) = it read about 40vac the first time I tested. However, when tried a second time to verify the exact voltage, it then read zero.

CR6-CR9 appear to all test good with the diode DMM test.

Thanks, that makes sense. However, at the moment, it doesn't appear to be shorted. I may have been mistaken in the OP about the 60v and 42v lines reading the same the first time around. Too many numbers floating around in my head, maybe.

Without a load attached, you can still test for a ballpark voltage within a couple volts of the expected voltage. I've done it on other games and have seen videos of other people do it. It's not going to be off by 50v like I'm seeing here.

I replaced CR6, CR7, CR8, and CR9 again. No change.

banded CR6 & CR8 = 73vac
banded CR7 & CR9 = 0vac

With a continuity test:
The banded sides of CR7 and CR9 are connected.
Pin 7 connects to unbanded side of CR9.
Pin 6 connects to unbanded side of CR7.

I replaced CR10, but there was no change.

CR7/CR9 still reads zero.

The 60v and 42v pins both read zero.

I'm not understanding what the issue is here.

cr7-cr9_voltage_test.jpg

cr6-cr8_voltage_test.jpg

I've always had trouble with understanding how to properly probe AC power.

Because the HV area has a separate ground, I was using the negative side of C6 to probe for VDC on the 60vdc/42dvc pins, since I saw that indicated somewhere. Should I also use the negative lead of C6 as ground if I want to probe the banded sides of CR7 and CR9?

As a sanity check, I tested a different power supply that had not been rebuilt, and it was giving all the proper voltages (only the A2J1 connector with input power was connected to the power supply).

It's not necessary in this case. You can still test for output voltages on a System 1 power supply. Besides, this is the method I prefer to use so as to avoid causing damage on other boards if voltages are shorting or incorrect. That way, I can fix smaller problems before they become bigger ones.

In any case, I pulled another system 1 power supply out of my parts stash, tested it, and got reasonably good voltages out of it. Then I tore it down and rebuilt it. And success--all the output voltages were as expected.

I'm still not sure why the earlier board I rebuilt is still having problems, though.

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Make sure you get all the solder with a vacuum pump, clip the leads (for the axial caps), then wiggle the caps loose.

[Edit]: also, I wrote up a guide on pinwiki for rebuilding the power supply, which might help a bit:

http://pinwiki.com/wiki/index.php?title=Gottlieb_System_1#Recommended_Power_Supply_Updates_.26_Repairs

I think I may have found where the problem was on the power supply where the HV section wasn't working.

I was clearing my worktable of projects, and I happened to notice that the C8 cap was bulging. I compared it to a working power supply that I rebuilt and noticed that C8 was backwards--the polarity was reversed.

In my defense, C8 , C9, and C10 are all packed in so closely together that it's hard to tell which component the + marking is actually for.

I haven't actually replaced C8 yet, but it sure seems like this may be the source of the original problem.

No, it's still on my workbench after all this time. I put it aside since the other rebuilt one was working, and never circled back around to this one.

I get it--most of the time I prefer to repair rather than replace as well.

I've done a few other power supply rebuilds that worked fine, but for some reason, this particular one didn't seem to want to work.

They're called shoulder washers--that should help you find them.