Vintage Synth Repair

All Fixed!! Thanks for your input duncan..I got the
schematics from Roland..checked the PSU..all ok..After
what you said I went through the CV/gate checks
again..through the front I got no sound apart from the
filter oscillating..So i plugged in my arp quadra and
fed it some CV and gate..still nothing..basically I
was using brand new mini mono jack to big mono jack
converters on the CV/gate leads and these were
faulty..this threw me off the scent big time!

Once I figured that out off it went, working OK
inputting CV/gate. So obviously VCO synth section is
all ok.

Played some guitar through it to check the pitch to
voltage section and CV/gate outputs..CV signal is
stuck fully open on 15 volts but gate is fine..so now
I know why I get no pitch this way..

So worked my way back through the chain of IC's from
the CV output and eventually find (IC15)the LF353N op
amp in the PV section is shorted..popped a new one in
and away she goes..fully working again.

And doesn't this thing sound bloody great? Huge! well
worth getting in my opinion!

Thanks, Phil.




--- duncan <ferrograph@...> wrote:

> >>The triggering side seems to be ok as you can make
> the self ocillating
> > filter sound by playing a guitar into it or
> hooking up cv/gate. It has
> > no relation to the pitch but then I dont expect
> the filter oscillation
> > to react to pitch like the proper VCO's would.<<
> 
> it should. the filter should track perfectly if the
> generated CV is
> doing anything. first thing to check is that the CV
> coming back out of
> the box is 1v/oct like it otter be.
> check all the power supply rails inside- you don't
> need to have the
> schemos to discern a problem in this area, since
> this vintage of kit
> will certainly have a rather basic linear psu,
> probably running
> symmetrical + & - 15V or something in that
> neighbourhood, & possibly a
> 5V rail or two for any digital stuff in there.
> 
> hth-
> duncan.
> 
> 



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