Re: Gottlieb System 1 power supply/transformer question

The AC voltage isn't out of range, it can vary a lot at those pins.

I misspoke (typed) a bit before, the A2P3 ground only applies to the 60 & 42 volt reading, you need to use the A2P2 ground for the 4 & 8 volt measurements.

Assuming A2P3 not connected & A2P3 pin 5 used for ground on your meter...

Cathode (strip) end of CR7 or CR9 or + side of C6 should be about 90 volts DC. If it is, and you're getting the readings you mentioned on DC setting of your meter for 60 & 42 volts, there's a problem with the regulator circuitry.
If you don't have 90 VDC, as above, but do have approx 70VAC on A2P1 6 & 7, you have CR6 thru 9 or C6 problems. (or possibly (unlikely) several bad downstream component)

How are you with soldering & semiconductors?

terrencel@xxxxxxxxxxxxxx wrote:
On Jan 20, 9:50 am, Bob Russo <pinballDontSpam...@xxxxxxxxxxx> wrote:
The 69 volts transformer tap has no ground reference. Measure the
voltage between pins 6 & 7. You may be OK.

Also, when the supply isn't connected to all the downstream boards, the
A2P2 and A2P3 grounds are isolated. Be sure to use the A2P3 ground when
measuring A2P3 pins. You may OK here also.

terren...@xxxxxxxxxxxxxx wrote:
Hello Fellow Pinballers,
I'm restoring my first machine right now. It is a Gottlieb Dragon SS.
I've been diligently following the System 1 repair guide at to whoever did that, it is great).
Of course the board had acid damage - I have already ordered a Ni-
Wumpf replacement.
So here's the situation. I actually removed all of the electronics
from the box so I could clean and repair the lower cabinet. I have now
reinstalled everything that belongs in the lower cabinet and have also
reinstalled the power pcb.
I re-pinned the entire wiring harness, as recommended (not fun) and I
replaced the C1 capacitor on the power board with a new 10,000 mfd 16
volt. Up to this point, everything I have done fits with what the
repair guide expects.
I just now got to the point of attaching the power board to the bottom
panel AC power system and I'm getting weird readings.
The bridge rectifiers tested out correctly according to the guide.
Here are the readings I got with my multimeter at the pins on the
power board:
A2-P1/J1 (bottom most power supply connector).
A2-P1 pin (11.5 volts AC) = 12.3 VAC
A2-P1 pin (11.5 volts AC) = 12.3 VAC
A2-P1 pin 4 (14 volts AC) = 14.8 VAC
A2-P1 pin 5 (14 volts AC) = 14.8 VAC
A2-P1 pin 6 (69 volts AC) = 38.9 VAC
A2-P1 pin 7 (69 volts AC) = 31.5 VAC
A2-P2/J2 (top most power supply connector).
A2-P2 pins 1,2 (+5 volts DC) = 5.1 VDC (trim pot works fine)
A2-P2 pin 6 (-12 volts DC) = -11.77 VDC
A2-P3/J3 (right edge of power supply board).
A2-P3 pin 1 (60 volts DC) = 13 VDC
A2-P3 pin 3 (42 volts DC) = 0 VDC
A2-P3 pin 7 (+4 volts DC) = 80 VDC
A2-P3 pin 8 (+8 volts DC) = 81 VDC
I'll ask the easy question first:
Is -11.77 VDC too far out of spec to safely operate an orignal system
1 board ? The guide says -11.9 VDC minimum. What about for the Ni-
Wumpf replacement board? I don't think it uses the -12V supply, but
haven't dug into the literature yet. If I need to get it within spec,
how would I do this?
Here's the hard question:
Is my little transformer fried? The 69 VAC drives the 60 VDC, 42VDC,
4VDC, and 8VDC signals, so I'm assuming the low input voltage is the
first problem to solve. Is there any component in the signal path
between the transformer and the power board input that could have
failed? I get the same VAC reading between ground and the 69 V fuse.
Are these transformers still easy to find? I've seen lots of posts of
people looking for one. Can a replacement transformer be purchased at
an electrical supply store?
Thanks for your input,
Terry- Hide quoted text -
- Show quoted text -

Hi Jim and Bob,

Thanks so much for your response. I think the transformer is OK - the
reading from pin 6 to pin 7 is 73.4 VAC. That isn't too far out of
spec, right?

FYI, I did run a ground from the negative lead of C1 to the chasis, as
the guide suggested.

I double checked my readings on the pins at A2-P3/J3. I did mess up on
the measurements, but they're still not right. Here's the update

A2-P3/J3 (right edge of power supply board).

A2-P3 pin 1 (60 volts DC) = 13 VDC (trim pot has no effect on
A2-P3 pin 3 (42 volts DC) = 0 VDC
A2-P3 pin 7 (+4 volts DC) = .17 VDC
A2-P3 pin 8 (+8 volts DC) = .17 VDC

On another note, would you buy a broken Williams Tri Zone that has a
cracked glass and "needs circuit board work" for $250?

Thanks again,