Star Tech Journal

STAR*TECH Journal
Beefing-Up Older Power Supplies
By James Beck
Greater Southern Distributing Conpany
Atlanta, Georgia
I would like to begin this month with
thanks to all of those readers who called
with ideas and conments. The majority of
those who contacted me wanted more
information on "beefing-up" some of the
older p:,wer supplies for conversion
purp:>ses.
Specifically the supplies found in the
Willians games (DEFENDER, STAR:;A.TE, etc.),
Bally card-rack system ( WOR, ROBBY RCIIO) , and the early Stern
games.
Before we begin, let me mention that while
the IOOdifications will work adequately for
most uses, some of the nore p:,wer-hungry
board sets may still require the use of a
switching regulator.
Since the Willians IOOdification has been
the nost reliable to date, I'll start with
it. On the tD-8359 supply (the one with
the series pass transistors mounted on the
board), remove R2. Replace it with a SK
ohm p:,t. This will be your +5 volt adjust.
'!bat's it!
On the #D-8784 supply (this one has the
transistors mounted on a separate heat
sink), remove R25. Replace it with a SK
ohm p:,t. Once again, that is your +5 volt
adjust. Pretty easy huh?
The Bally/Midway supplies are alnost as
easy, but don't supply the current that
the Willians supplies do. This rood is only
for the supply used in their "Conmercial
card Rack System".
First replace the two 5 volt rectifiers
with MR751 rectifiers or equivalent.
(These are located next to the 20K uf, @16
volt filter capacitor.) Finally, junper
pins 2 and 3 of the SG3532 regulator
together. Not too difficult, but keep an
eye out for burnt connectors. The
increased current flow through them will
really cause them to heat up.
September 1986 (8)
Now, here comes the Stem supplies. I do
not recormnend trying to get nore current
out of the t34C-849-S supply. That's the
one with the series-pass transistor
mounted on the p:,wer supply board itself.
If you IIRJSt, however, you can try putting
a 3 ohm, 25 watt resistor across the
emitter and collector of Ql, this should
allow you to increase the output by about
1.5 anps.
The #34C-978-S supply is the best of the
two. It has the series-pass transistor
nounted on a separate heat sink. First
remove R8 and replace it with a 22-25 ohm,
2 Watt resistor. Remove the connector J3
(male and female p:,rtions), and solder the
leads directly to the board. Add a 10 ohm,
10 watt resistor across the emitter and
collector of the series-pass transistor.
This completes the job.
Well, that should keep you busy for
awhile. Have fun and I'll see you next
month.
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