From Newsgroup: rec.games.pinball
On 2021/10/02 3:22 p.m.,
sch...@gmail.com wrote:
On Friday, September 13, 2013 at 9:45:24 PM UTC-5, mrsodapop wrote:
HI All,
Sorry for the delay getting back to this, been away for a while.
Here is details. From what I understand some Ballys just run a little
high on the 12vdc circuit, this one runs at about 15.89. The Alltek MPU
is sensitive enough to detect this and consider it "over voltage". The
solution was to remove the lower left IC (U17?). I do not have the
schematics in front of me now, but I believe this is the over voltage
regulator. After removing this (U17), the system bypasses the over
voltage circuit.
Perhaps someone could explain why some - or this machine run high on
the 12vdc circuit. My AC voltage going into the diodes is 14.2 -14.3vac,
spec. is 14.2vac. Voltage coming out of (old/original) diodes was
15.96vdc(TP3 on rectifier pcb), I replaced the 4 diodes and TP3 is now
15.89vdc. So why is voltage high if I have factory spec. ac voltage
going in, with proper original and replacement diodes BOTH producing a
high DC voltage?
Thanks for interest
Aaron
--
mrsodapop
Wanted: Photo/sticker booth.
This USENET post sent from http://rgparchive.com
Its actually U13 and I had the same problem in a working pin after installing a new Rectifier board. The over 5 volt LED light came on and the Allteck MPU would not boot. Removed U13 and its boots perfectly
From Dave, the designer of the Alltek MPU:
"The over voltage chip looks at the +5vdc line, not the 12vdc line.
What people don't understand is the over voltage a lot of the times is
the AC on the DC line because the large blue cap on the SDB is bad. So
you get 5vdc plus as much as 10.5vac riding on the DC signal too. That
is why the chip shuts down the board for protection. With this said it doesn't mean a chip doesn't go bad. It's rare but it can happen too."
So do NOT remove the overvoltage protection circuit unless you want bad
things to happen to your board. This will obviously void the warranty too!
John :-#(#
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