From: Daniel ForróSent: Monday, April 08, 2013 11:47 PMSubject: Re: [vintagesynthrepair] Yamaha CS40m problemRecently I tried to switch on my two CS40m synths which I have used
for the last time about 7 years ago. Main fuse on both machines was
blown after one second.
So I have recapped both PSU, and tried to switch on again. On one
machine big two resistors connected in series to output rails +15 and
-15 V became so hot that their textile envelope (yes, they were
covered by some textile pipe) started to smoke. (On the other machine
not so bad, but again main fuse and another one in the secondary
circuit was blown.) I have immediately switch off, put both PSU out of
the instrument, switched on without a load, and both PSU are OK,
everything works. So I could set all four voltages to their spec
levels (+15, -15, +5, -10).
Am I right to suppose there's a short circuit on some board? I wonder
how it could happen when the instrument was not at all used for years.
In one instrument there was small leakage of RAM battery (as they use
standard 2 AA size batteries in battery compartment, no damage was
caused by this). Otherwise everything looks well.
Has somebody any advice how I should continue and where to find the
source of this problem? Could it be some shorted tantalum capacitor? I
can't use PSU and switch on the instrument. I plan to recap, clean and
check all boards, clean connectors... usual stuff. Then try again to
switch on... If it will work without blowing the fuses or burning
components, then I can check voltages and signals. I have Service
manual.
Thanks in advance for any hint.
Daniel Forro
Message
Re: [vintagesynthrepair] Yamaha CS40m problem
2013-04-09 by 65 Lotus
On the DM board, check the capacitors on the
±15 volt power rails (connector C60. See if they're tantalums and
shorted.
There's two by the connector, but two others
elsewhere on the board, so track them down. I'd replace with electrolytics
in this case, simple power rails.
Also, there's a couple on the 5 volt rail too
(connector C12), might as well replace those while you're in there.
Scott in Ohio
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