Vintage Synth Repair

Hi Duncan,

Thanks so much for your detailed response!

I did read every word, and I see what you're talking about.  
Ultimately, I'm concluding this is a bit beyond both my abilities and 
the time I want to invest in the unit.  

It does have the compact psu... and I've unplugged/cleaned/replugged 
a number of cables, and whereas there does seem to be a slight 
differenece in performance, there is little improvement.

Everything on the board seems soldered in place so there's no simple 
way to remove/clean/reinstall (which did wonders for my Kurz px1000)

I kind of suspect (based on your post) that the 26v could be where 
the problem is...but then ultimately I don't think it's worth me 
going any further with it.  :(  

After giving it a go, I think it's time to let it loose on ebay.  
Either somebody will want it, or it's time for the electronic 
recycling center.  Hate to do that, but I never use it anyway.

Thanks so much for your detailed responses!  It did help, even if 
I've ultimately given up.

Cheers,

Fred

--- In vintagesynthrepair@yahoogroups.com, "ferrograph632" 
<ferrograph@...> wrote:
>
> >>I'm experienced enough to check the voltages, and come away with 3
> brands, 4.37, 11.87 and 26.  Does that sound ok?  Is the 26 for
> professional operation?<<
> 
> I wouldn't expect a 26V rail anywhere in a hybrid digital/analogue
> circuit, but then they aren't all the same.  please bear in mind 
that
> I'm writing this with no knowledge of this particular box or it's
> schemos :-) I have a similar korg box here though, the sdd3300.
> 
> there may be a higher voltage for the display backlight but this 
would
> probably be quite a bit higher (80V or so) & probably there'd be an
> inverter to generate this close to the display itself.
> again, I can't be certain on any of this, but it would be typical. 
for
> all I know, the backlight could be a bunch of LEDs like in my old
> cheetah sampler, or a fluorescent job with an inverter like in my 
emu
> samplers.
>  
> so the 26V- you might be measuring across the whole of a +12 to -12,
> of course.... no obvious negative voltages? 
> & the 5 & 12 seem to be low, especially the 5. this might prevent 
the
> CPU operating properly.
> 
> if you can read any of the chip numbers, especially things like 
audio
> op-amps (5532, 4558, that sort of thing) then check their pin-outs 
on
> a datasheet, you may discover more. 
> the digital chips are where the problem probably is though, since 
the
> box has scrambled brains, so you'd need to identify any of the logic
> ICs & check those locally (i.e. instead of at the power supply); it
> could be a cracked track on the back of the board, or a single bad
> chip dragging a whole rail down. again, you might see familiar chip
> numbers, 74xx or 474xx or even 4000-series stuff, 12 or 14 pins on
> them, used as latches, gates & buffers. there are bound to be some 
of
> these around the control panel.
> 
> thinking about that- you might want to dismantle the control panel &
> check for contaminant ingress causing a shorted button- devices like
> this can behave in a peculiar way sometimes if a button is "held 
down"
> while they boot.
> 
> do you know what sort of power supply it is? is it a linear psu, 
with
> a big mains transformer, bridges, big electrolytic caps & series
> regulators? or a compact switched-mode device? the latter are easily
> identified since they are so much smaller, & usually the host device
> will work on any voltage from about 80 to 300, 50 or 60 Hz.
> switched-mode psu's generally fail completely too.
> if it's a linear power supply, it would usually have obvious output
> regulators, either 78xx/79xx three-pin devices on heat sinks, or 
power
> transistors performing the same function.
> 
> if you can find these devices & measure something "traditional" 
(12s &
> 5s, I mean) then the problem is probably with the CPU or the
> associated ram. I had a juno 106 once that wouldn't start up because
> the CPU ram was damaged; the memory battery was fine on that 
occasion,
> but I had to replace the combined CPU & memory (with a revised 
design
> comprising two separate devices that came separately by boat from
> japan!)  
> 
> >>What do you think...beyond me?<<
> 
> I couldn't possibly say! :-) the aforementioned 106 was written off 
by
> a professional synth service company & would be scrap but for my
> persistence. do you know any decent techs near you? I don't know 
what
> roland are like where you are, but they weren't much help to me; 
when
> I wanted to fix the 106, I ordered a CPU & of course, the CPU turned
> up 60 days later with no internal memory... 70 days after that I got
> the thing working well enough to deal with it's many other issues.
> 
> oh well- hope this helps.
> 
> duncan.
>