Tech: Atari Big Blue

[Rich Marquette]

Hello,

I have a Dig Dug Cocktail game that seems to keep burning up the Big
Blue filter cap in it. It takes about 4 months for it to happen
playing a couple times a week. Every time, I don't find anything else
bad and after I replace it, the voltages are good and the game works
fine. I am replacing it with a fresh (not surplus) cap from reputable
suppliers. Anyone have any ideas why or what would cause this?

Thanks
Rich

[todd...@yahoo.com]

Bad Rectification. Check your bridge rectifier/diodes. If they're
just diodes and have never been replaced then you should go ahead and
do it anyway. Diodes are a lot cheaper than that big cap.

[[80s.fan]]

I am curious as to how to test for the current quality of this Big
Blue cap? What modes do I use to analyze wave form across both
terminals on the oscilloscope? What should I see? Thanks.

[John Robertson]

Simplest way to see if a bridge rectifier diode has opened is to simply
bridge a good diode across each junction and monitor the DC voltage
across the capacitor. If it rises then the bridge has an open diode! I
use a 6A-100PIV diode for this sort of thing, but a 3A-50PIV diode will
work fine as an
indicator - it will get warm if there is much of a load though.

Oh, polarity - well have the band of the diode always facing the "+" of
the bridge. So banded side of test diode to "+" non-band to AC1 (check
DC) then AC2 terminals - DC voltage still OK? Then band to AC1 and
non-band to "-" check DC voltage. OK? Then band to AC2 and non-band to
"-" voltage still OK? problem is elsewhere!

John :-#)#

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