[sdiy] strange symptoms

[gilwein at walla.co.il]

it's strange that the short between the transistor legs is read only when the power is on.

When I turn it off, not short is being read between those spots.

Exactly the same occurs between to other spots that are near each other.


<mboracci at nfpcomputer.com>
RE: [sdiy] strange symptoms

Have you looked for cold ( cracked ) solder joints? They can be very hard to find, however now that the board is clean it will be easier. Breathe on the board closely to create a fog on the solder joints. Hairline cracks will show up as a thin ring around the pin which is protruding through the board. You might be surprised to find many of these which is a common failure on most wave soldered boards. 

Thermal flexing over time can open these cracks and make problems occur years after the board was made. 




-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of gilwein at walla.co.il
Sent: Tuesday, October 14, 2003 9:01 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] strange symptoms



Hi.

I have that problematic Kawai SX210 which had it's battery leaking,
probably causing it to behave strangely like playing notes automatically
and playing a few notes when you hit only one key.

I clean all the defective are and replaced a few parts,
replaced the battery and resoldered a few wires.
also cleaned up the whole pcb.

Than it actually stopped playing automatically, 
and a few notes when you hit one key,
BUT, now it misses some notes sometimes,
and sometimes when you hit a chord
the sound comes out in pulses. Also it will play some notes
with a slightly different sound than the preset used.


I replaced a few capacitors and just when starting it up 
the dial wheel has stopped to respond and I now cannot edit
any of the parameters !!!

I noticed that there's a short between two transistor legs
that comes on and off  (the transistor is not leaking and is OK).

I mean sometimes the short is there but sometimes it is not .....

how can this be caused and is this normal ?

I also noticed that the EPROM chip and another (very) large
chip made by Intel, are getting warm after a few minutes of operation (but not too warm...)
is that normal ?

moreover, is there any chance that the EPROM programming 
has gone defected ?

Thanks,

I really want it to get fixed !







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