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You know, I didn't really think about it, but the problem might be the
replacement transformer! Check your +5 volts on the game board and
see if it is too high or too low. Voltmeter OK, but scope is even
better. None of this applies if you have only ONE humbar.
<p>Possibility one, too low. In this case either the capacitor is
bad OR the transformer voltage is too low, causing the regulator to drop
out of regulation.
<p>Possibility two, too high. In this case, since this is an early
Atari board, the voltage peaks (if high enough) can cause the regulator
to quit regulating. What happens is these old boards run most of
their current through a large resistor connected across the regulator with
the regulator picking up the last little bit of current. Otherwise
the regulator will overheat and shut down. Now, IF the transformer
voltage were too high, the regulator current would drop to zero and ALL
the current would go through the resistor. This would happen during
voltage peaks and cause the +5 volts to increase (but only during the peaks).
<p>What got me thinking about all this is that the problem didn't start
until the transformer got changed. If you do have a high voltage
condition and you are lucky enough to have a higher voltage primary transformer
setting available (example, you currently are using the 110 volt tap and
switch to using the 120 volt tap) you can fix it that way.
<br>
<p>Rodger Boots wrote:
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<p>Paul Sommers wrote:
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<ul><font face="Arial"><font color="#0000FF">The 8000uf at 80v won't fit
on the board (the one that is their is surface mount) so I'll get a couple
of big ones in series - that should do it.</font></font> <font face="Arial">BUT,
before we get too carried away with this, I have a question. Is there
ONE hum bar or TWO? Very simple rule here:</font>
<p><font face="Arial"> ONE hum bar = bad rectifier (or
fuseholder in series with rectifier)</font>
<br><font face="Arial"> TWO hum bars = filter capacitor
problem.</font></ul>
<font face="Arial"><font color="#0000FF">That's a good tip to remember.
No hum bars. It's a continuous wave.</font></font>
<p><font face="Arial"><font color="#0000FF">Imagine a grayscale light to
dark - then put another on with the light side butted to the dark edge.
There is no break - it just keeps coming. It's a vertical monitor - so
it is going across the screen(or down/up if it was horiziontal). I guess
if two hum bars mean a filter cap problem - 8 could mean a bad filet cap
problem.</font></font></blockquote>
<p><br>OK, you're saying you have TWO dark waves? Or two greyscales?
Whatever, if there are two of anything the capacitor (8,000 uF) is bad.</blockquote>
<p>--
<br>Windows:
<p>32 bit graphical interface for a
<br>16 bit patch for an
<br>8 bit operating system written for a
<br>4 bit processor by a
<br>2 bit company that can't stand
<br>1 bit of competition.
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Received on Mon Sep 25 11:15:59 2000
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