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TECH: Pengo voltage weirdness

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Jason D. Bardis

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Mar 31, 1998, 3:00:00 AM3/31/98
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Howdy

I finally sat down to attack my Pengo.

Symptoms: would occasionally reset & start glitching, and the sound has
ALWAYS been incredibly scratchy & distorted.

Solution: Started playing with the pot on the power supply (a Peter
Chou--the pot regulates both the +5V & +12V together...Pengo doesn't
use -5V). I also noticed a considerable voltage drop between the PS
and the PCB, so I filled out the harness a little (they had used only 1
of the 6 +5V lines, 3 of the 4 GND, and 1 of the 2 +12V lines), which
seemed to help.

Anyway, as I cranked up the voltage, I noticed that, if I got the +5V
right on, the +12V would be way up to 14.1, and if I set the +12V to
be right on, the +5 would be under 4V. So, I popped in another power
supply that had closer voltages, and I never got the game to come up.
Went back to the original, and now, with the expanded harness, can get
"close" voltages: if I regulate +5 to be right on, +12 reads +13.2.

Anyway, as I cranked up the voltage, the sound would get better and
better until it was perfect. Unfortunately, the game wouldn't play
long at all at this voltage before it would go crazy. I could adjust
the PS pot high or low until the game popped back into non-crazy
mode, but it never liked to stay non-crazy for terribly long.

In any case, I now get nothing but a pattern of vertical blue/white
bars on powerup, and no sound. I'm wondering if I fried components
by tweaking the voltages too much: they saw a max of about 5.6V and
14.1V. Think that's enough to kill components? I tried reseating
all the socketed chips, which didn't do anything.

So, any daring soul have a Pengo board I could borrow to swap in to
my cabinet to test? Or anybody with a working Pengo setup want to
check my board? I'd like to know if I've killed the board or if my
cabinet is at fault. If it's a bum board, anybody got a spare Pengo
for trade?


Thanks
-Jason
--
Jason Bardis(jaso...@bolt.ucsb.edu www.engineering.ucsb.edu/~jasonbar)
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