On May 14, 2012, at 3:51 PM, Rob Jarratt wrote:
I have a H7140 that I am *still* trying to repair
after more than a year of
failure and despite the valiant attempts of one person on this list to help
me, and it is in much better condition than the one in the pictures.
However, I am hampered by my poor knowledge of PSUs (which is gradually
improving), my slowly developing desoldering skills, and my unwillingness to
spend a lot of money on oscilloscopes, bench PSUs, ESR testers and goodness
knows what else.
Well, I'll gladly tell you to spend some money on a decent scope. You will
come to wonder how you ever got along without one, even if it's a 2-channel
analog scope with relatively low bandwidth. They're so useful for so many
things; I promise you won't regret it (as long as you don't go bargain-
hunting and find one that you also have to fix).
My scope is a 100 MHz analog scope with 4 channels that I got on eBay for
about $200. Everything worked great in it except for a fan, which was easy
enough to replace. You should be able to find plenty of good ones in OK
condition for around that price, assuming the UK second-hand market is in
any way similar to ours.
If you only need 5v or 12v, AT power supplies (or jury-rigged ATX ones)
make reasonable ones. I'm willing to bet you have at least one of those
lying about. :-) My 11/23, for example, runs off an AT supply (though
its rather thin wires tend to get warm, so one of these days, I'll make
the upgrade to a decent enclosure). Most AT supplies also offer -5v and
-12v, should you need them.
- Dave
One advantage to using a switching supply to replace the old linears is
that failure in linears can put the supply B+ through the regulator
transistor and this may let the smoke out of ICs, whereas switching
supplies simply shut down when they fail. Shut down is much preferred to
roasted electronics!
John :-#)#
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Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)