Vintage Synth Repair

Cheers Duncan,

The synth is mine - well I was given it last summer. It was on 100volts with a power adaptor/transformer, which was burned out!

So the first thing I did was install a 240v transformer. It played great for a week or so, then I started having problems.

There are some caps near the filter (cut-off) slider that needed changing. Apparently a common fault. Then I was losing all the 'F's... but intermittently. I suspected those large (and obsolete) divider chips... but then noticed that this TOS chip was running VERY hot. I tried heat-sinking it. In the end it just stopped working totally. I reckon this TOS chip was on it's way out from the start!

I located a (supposedly) drop in replacement in the form of this KS-196 retro, (but it was stated on the packaging that it was meant for Organs - which use this same chip!)

It all sprang back to life - but with this out of tune/drifting/noisey oscillator issue. I have it sorted now...it's just an extra cap and a small run of wire. But it is solid. Was playing it all day yesterday.

I don't think I'll have any more problems with that retro, even humitidty wise. It's too defined a reaction when I strapped the wire to the cap casing. And bringing the "touching/pushing the IC" thing to the front panel would have been do-able, but the whole synth was unplayable so there wouldn't have been any point. No, I am happy and it's sounding great- just add lots of reverb and some echo...;c)


Cheers again,
TOM



--- In vintagesynthrepair@yahoogroups.com, "duncan" <ferrograph@...> wrote:
>
> thanks for sticking with it, tom, & for returning to tell us what happened. is the korg yours or is this for a client? I think, in the fullness of time, I'd've been inclined to swap out that one chip. this sounds like an output impedance thing, as someone else suggested.
> if the other end of the wire is not attached explicitly to something, then you may find you have drifting pitch again with changes in humidity.... just a thought.
> 
> me, I'd've brought it out onto an insulated metal plate on the panel somewhere & make it a performance controller.... :-)
> 
> duncan.
>