OP
Quoted from adalogue:
VAC inputs to power board in head are high, CR1 and CR2 look fried and don't check out electrically. Not dead short but not proper diode drop either.
14 VAC - 24VAC measured
11.5 VAC - 29VAC measured
69 VAC - 72VAC measured
My theory is that CR1/2 fried and damaged xfmr secondaries and needs replacement. Anyone disagree? Anyone know a source for the smaller transformer??
Odd thing to me is that power outputs are good, except 4VDC is a bit low (3.5 or so). Game does not boot but has corrosion issues also.

The two voltage should be doubled (i guess you switched the two). I had the same question couple days ago and found a topic that explained it.

#6 6 years ago

adalogue

Pinheads Pinball

12y 36,650 423

Quoted from G-P-E:
How are you measuring this voltage?
To each other or with meter to ground? If ground - "which" ground are you using?

The VAC measurements are between incoming and return, not ground. I didn't see a center tap shown in the schematic. Maybe it's misleading and it's 11.5 and 14 VAC on each side of a center tap used as ground.

#7 6 years ago

adalogue

Pinheads Pinball

12y 36,650 423

Quoted from Mrhankey91:
The two voltage should be doubled (i guess you switched the two). I had the same question couple days ago and found a topic that explained it.

Why would the VAC off then xfmr be double what is shown in the manual? Entirely possible I transposed the numbers and measured double. If that is correct, it would mean there is some center tap used for ground, I don't remember seeing that in the schematic.

#8 6 years ago

RGM

Mrhankey91

Inactive member

Bakel

7y 17,300 29 6

OP
Quoted from adalogue:
Why would the VAC off then xfmr be double what is shown in the manual? Entirely possible I transposed the numbers and measured double. If that is correct, it would mean there is some center tap used for ground, I don't remember seeing that in the schematic.

For more info: https://pinside.com/pinball/forum/topic/gottlieb-system-1-power-problems#post-2086737 Its not running throught the two bridge rectifiers, but has some diodes on the power supply that block one of the ac incoming, leaving you with half the voltage.

1 week later

#9 6 years ago

GPE

G-P-E

GPE

Omaha, NE

13y 76,800 2,778 4

OP
Quoted from adalogue:
Why would the VAC off then xfmr be double what is shown in the manual? Entirely possible I transposed the numbers and measured double. If that is correct, it would mean there is some center tap used for ground, I don't remember seeing that in the schematic.

The System 1 rectifier is called a "center tap, full wave bridge rectifier". Uses half the diodes but requires an extra wire back to the transformer. The center tap is ground (return) and exits the power supply's P1, Pin 3.

The voltage measurements they give are measured between the transformer output to the transformer center tap. If you measured directly across the transformer outputs - you would get 2x the listed voltage.

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