[sdiy] Trident MKII - suddenly went out of scale !

[Gil W.]

Hi all,

I thought I might be able to get some help from the
analog experts here ;)

I own a Korg Trident MKII which have bad tuning on one
of the VCOs. I was trying to debug it, using a freeze
spray over various compnents on the Siganl Generator
board. Too shame, as at some point suddenly all
keyboard scaling went bad, playing much larger steps
between each note and the one following it (i,e C4 to
C5 plays like C4 to G5). That is very furstrating as
it is so rare and so much good sounding ! I thought
you might be able to help me fixing the problem.

My thought so far was that the uA276 antilog amp. has
gone defected, because as far as I understand this is
the component which is responsible for the scaling.
Does this makes sense ?

The uA276 does get its required _+15v and -15v, and
not short can be seen between the embedded transistors
in it (it B,C and E don't short). BUT I did notice
that it doesn't heat up anymore ! If I'm not wrong, I
recall it being quite hot when I touched it.

Could it be that it has gone bad as result of the
momentary freezing ? (That is all I did before the
problem showed itself).
Is there also a chance that the thermal sensor (TH1)
controlling it has gone bad and that this is what
causing the problem ??

I'd be so much thankful for any help, as I don't
really know where to start and I don't want to order a
uA276 before verifying that it is indeed defected. Any
way to check whether it is defective or not ?

Secondly, I wonder whether the antilog calibration
procedure for Trident MK-I and MK-II is identical...
Unfortunately my first reaction was trying to readjust
VR3,4,5 (Antilog parameters) which of course didn't
help (as the problem was not related to adjustemnt). I
do not have the calibration procedure for MK-II.

Thanks very much !!

__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com