Re: Williams System 11a Power Supply Issue

I'm unsure about your AC input voltage- IIRC, this game takes input to the
5vdc regulator circuitry from the 18/19vac winding in the transformer
secondary- ie: the two gray wires. I'd remove the 12-pin input connector
from the PS board and check these with meter on AC to make sure that voltage
is in spec.

If so, continue upstream- checking components along the way- there's not
much in this circuit so not too complicated.

One common cause of failure is one diode in the rectifier shorting and
blowing only 1 of the fuses that protect it (7 amp slow-blow). So check for
this. Remove both fuses and check physically with meter to be sure they're
good. Check rectifier while fuses are out of circuit (or input connector is
removed). This sounds like a classic blown fuse or open/shorted rectifier
problem, so I'd double or triple-check things in this area.

Beyond that, the filter capacitor is usually a must for replacement if it is
old/original. Look for bulging on one end of the cap which can indicate old
age/overdue for replacement. You could also have a bad 2N6057 regulator
transistor or IC1 regulator chip (LM723).

Don't forget to check solder joints on the back side of the connector pins
on the board- both input and output connectors. Cracked joints are
commonplace in these old games and you can't expect any reliability if these
haven't been inspected and overhauled.

Be sure to leave the output connectors off (both 6 and 15 pin connectors at
top of board) while doing your testing and repairing, to make sure nothing
else in the game interferes with the PS board or so the PS board doesn't
damage anything else if high voltages are present on low voltage lines

I'd focus on getting the 5vdc working first then move on if anything else is
still out of spec, but most likely you are seeing multiple symptoms of just
one single problem.

Hope that helps!

Ray J.
--
Action Pinball & Amusement, LLC
Salt Lake City, Utah USA
Web: www.actionpinball.com

We're serious about pinball. Anything else is just for fun!



<bleech1234@xxxxxxxxx> wrote in message
news:1135824330.586995.152430@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> I have a Fire! table that was working perfectly until it was turned
> off. When I turned it back on a few minutes later, all the GI lights
> came on but nothing else happened. I had a similar issue a few years
> ago which was caused by a low 5V output and ended up replacing most of
> the related components on the power supply board, which fixed the
> problem.
>
> Now, however, I'm having a different issue. The +12V test point is
> showing around 1.5V and the -12V test point is showing almost -40V
> (relative to the back of the backbox). The +5V test point is showing
> about 0.6V. I measured the voltages coming from the transformer on the
> wires that plug into 3J1. All the DC voltages are correct. The AC
> voltages (pins 10 and 11) show 10VAC relative to pin 12, which seems
> low but is most likely due to the 200V minimum range on the cheap
> multimeter I had to buy (since my good one is on the other side of the
> country :) ). When the plug is connected, pins 10 and 11 still show
> 20VAC relative to each other, but show 0V relative to pin 12. The
> diodes in the bridge rectifier test okay on the board.
>
> My guess is there's some sort of ground problem, but I'm not sure where
> to look. Can anyone suggest what would cause these symptoms, or give
> me some ideas on what else to test? Thanks in advance.
>
> -Brian
>


.

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