Vintage Synth Repair

Fixed it last night.....the reason for the hi hat pitch going up and
down from selecting pattern play or write was caused by the +5 supply
to the 14584 rising up and down and having no regulation. It was at +8
sinking to +7...basically the 6.8v zenerdiode that regulates the +5
was inoperative due to a hairline split in the track near a component.

The open hi-hat not decaying...well..I checked the circuit through and
I just could not find the problem..The transistor seem fine, the caps
seem fine, diodes..I checked the continuity of the circuit for broken
tracks..just couldn't find anything wrong.

So anyway the manual states C45 should be 1uf 50v so I changed it to
4.7uf 50v and I now have a very nice decaying open hi-hat...

I changed about ten of the tactile switches to make it perfect.

A little bizzare but what can I say..It works!

Another nice unit advertised as 'FULLY WORKING' on ebay.

Phil.


--- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> wrote:
>
> Hi guys..bought a supposedly fully working 606 of off
> eBay to find it has problems...
> 
> 1. It wouldn't work with an AC adaptor, batteries
> only. Anyway I fixed that, was some shorted caps and a
> bad regulator. It had some battery damage too around
> that area.
> 
> Next job..the Hi-hats and cymbal sounded really weird,
> kind of flutey and going up and down very slowly in
> pitch. Scoped it and found a bad 4558...fixed? Well
> sort of, the cymbal sounds fine, the hi-hat sounds ok
> except that the open hi-hat sounds identical to the
> closed hi-hat i.e. not open with a long decay. 
> 
> All the transistors in the hi-hat circuit check out
> fine. I've changed the 2904 op amp, the oscillator IC
> is fine (4584). The trigger is fine from the CPU...
> The tempo clock signal is ok as well to the Hi-hats. I
> thought maybe the closed hi hat trigger was triggering
> the open too or something. 
> 
> So I moved to caps. I've changed every single
> Electrolytic marked in the hi-hats section. No change.
> I notice one thing. If I change the value of cap C45 I
> can make the open hi-hat decay longer but I'm moving
> it well away from the stated 1uf it's supposed to be.
> 
> One other thing; when you start a pattern off the
> first hi hat beat is raised in pitch also when you
> switch between write mode or play mode, the pitch of
> all the cymbals, hi-hats change. You get a higher
> pitch in play mode.
> 
> So to recap I basically have an open hi-hat that
> sounds identical to the closed hi-hat. And some weird
> pitch change stuff going on.
> 
> Im looking at it again tonight so if anyone has any
> ideas, shoot.
> 
> Thanks, Phil.
> 
> 
> 
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