Thank you so much Raymond. I'l make sure to check those and had read about
those tantalum caps going to short failure mode but didn't know where to
start testing. I am getting no voltage going into the regulator which is
why I'm focused on the CR1561 rectifier at the moment. I happen to have a
new NTE5318 rectifier on my bench that is rated to 200v and 4A, and will be
checking further for compatibility but think I can swap that in if the
other is faulty. If not I have a link to a parts cross reference to source
one from.
On Thu, Mar 31, 2016 at 10:49 AM, hewpatek@... [TekScopes] <
TekScopes@...> wrote:
I've confirmed a dead -8 volts at the regulator so my next steps are to
test and likely replace the rectifier
The absence of -8 V is caused more often than not by a short. You should
be able to check what's going into the regulator, thereby possibly avoiding
a lot of disassembly of the circuits upstream.
Usually, a dipped tantalum capacitor causes these shorts. Specifically,
I've seen C1569 being shorted. It's located on the A9 Interface Board, rear
side, near the middle and easy to reach and replace without removing the
board.
With the power off, measure the resistance across C1569. If shorted,
you'll measure anything up to about 30 Ohm.
You may temporarily replace it with any >= 20 uF cap with Working Voltage
(WV) spec. of at least 15 V.
An obvious difference between early and late >=B250000 versions is the
replacement of the vertical output amplifier, from an "integrated" version,
to a discrete version.
Raymond
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