Vintage Synth Repair

Well like I say it's way cheaper than that guy sells them for...they
come on ebay a lot...I used to fix a lot of old arcade machines like
space invaders etc from the same era's and it is invaluable when you
have big banks of ram..Pull the processor out, plug in the relevant
pod then simply enter the ram address ranges and it runs some tests
like read and write compare etc amongst others..it spots things a
scope simply can't. It can also scan and generate a memory map from a
known good board. You can simply run the BUS,RAM,ROM and I/O test
routines or get more deep with it and program scripts for specific
boards/jobs..etc It is quirky but definitely is very capable. Just
another tool in the box really..

There's some more info here if you're interested:
http://tech.quarterarcade.com/tech/Fluke/9010A/



> > I actually have a thing called a Fluke
> > 9010 microprocessor trouble shooter..see:
> > http://artfromny.com/fluke%209010.htm it's great tool for helping
with this
> > sort of problem..takes like 2 seconds to test the data bus..ram etc..
> >
> > Ignore the prices this guy charges, you can get hold
> > of these systems for very little money now..
> 
> Looks nifty,  but it'd have to be *way* cheaper than what he's
talking about 
> there for me to even think about it.  :-)
> 
> And then there's the time spent hooking it up and such.  Sometimes a
scope is 
> not all that much slower...
> 
> > --- "Roy J. Tellason" <rtellason@...> wrote:
> > > On Saturday 19 April 2008 16:00, eggwheatis wrote:
> > > > If it were me and I know nothing about this synth
> > >
> > > by the way...I'd
> > >
> > > > start by looking at the PSU with a scope....
> > >
> > > Yup,  I looked through the diagrams pointed at, and
> > > the behavior described can
> > > only be a matter of the last couple of them in
> > > there...
> > >
> > > First thing I'd do is to check the power supplies.
> > > The +5 needs to be within
> > > a quarter volt of +5 or things won't quite work
> > > right.  A scope may show
> > > *some* hash on the power supply pins,  depending on
> > > how good the actual
> > > design is,  and some of that may be normal.  Not if
> > > there's a lot though.
> > >
> > > > then assuming this is perfect I'd be looking
> > >
> > > around the CPU to see what
> > >
> > > > activity I have going on again with a scope or
> > >
> > > logic probe referring back to
> > >
> > > > the schematics, reset lines..clock, ports etc etc.
> > >
> > > I'd then check the
> > >
> > > > circuit around the rom and ram etc..chip selects
> > >
> > > etc etc write enable
> > >
> > > > blah blah..theres so much it could be..you only
> > >
> > > need one dead node in
> > >
> > > > the logic circuit and the whole thing won't work.
> > >
> > > Yup. A scope is *much* better for this sort of thing
> > > than a logic probe.  I'd
> > > start out by scoping the data bus pins,  DO-D7 on
> > > the Z80.  Look for valid
> > > logic levels and transitions between them,  but not
> > > much time spent in the
> > > middle (though I have seen designs like the c64
> > > where stuff regularly did
> > > spend short bits of time in the middle.
> > > Nanoseconds...
> > >
> > > If there's a bad chip on the bus somewhere and it's
> > > messing things up to give
> > > the symptoms described this will be one way to find
> > > it.
> > >
> > > Next is scope the address bus pins.  Depending on
> > > where the software is taking
> > > things there may or may not be activity on all of
> > > them.  A logic probe with
> > > the ability to "catch" very short pulses might be
> > > handy here as well.
> > >
> > > Here's a trick you can try with that Z80.
> > > Temporarily solder a bit of wire
> > > across all of the data bus pins and to a ground
> > > point somewhere.  This is a
> > > whole lot easier if there's a bus buffer in the
> > > system,  but the diagram
> > > doesn't show one.  What this does is it feeds the
> > > chip NOP instructions,  and
> > > it just keeps on cycling through _all_ of the
> > > addresses and keeps
> > > on "fetching" them.   You should then see a square
> > > wave on each address bus
> > > pin,  with each time you go to the next higher bit
> > > the frequency is going to
> > > be half of what it was.  If you don't see this
> > > somewhere then there's a
> > > problem,  as something ks making one of those lines
> > > get "stuck".
> > >
> > > I don't know these instruments and don't know what's
> > > likely to be socketed or
> > > not.  From what I can see you should be able to
> > > remove the 68B50 and maybe
> > > the 8253 as well,  as the former is just for MIDI
> > > and I'm not sure what
> > > they're doing with the latter.  You should also be
> > > able to remove one or both
> > > RAM chips and see if there's any change in behavior
> > > -- if there is then you
> > > have a problem pinpointed.
> > >
> > > If you don't find anything in particular this way,
> > > start looking at the
> > > outputs of the decoders,  the memory address decoder
> > > especially -- a "stuck"
> > > output on any of the decoding circuitry can cause
> > > some bus contention,  check
> > > the outputs of the 74LS138s and also the outputs of
> > > the gates that connect to
> > > those outputs,  and figure out what they _should_
> > > be.  Like that ROM select
> > > line shouldn't be low _all_ the time unless the CPU
> > > never gets there.
> > > The "feed it NOPs" trick above will help you get
> > > there.
> > >
> > > > I'd say the rom is ok if you still have a problem
> > >
> > > with the test rom..
> > >
> > > Maybe.  Or maybe there's a fault which has done
> > > something to one of the bus
> > > lines and has ended up trashing them both.  One
> > > hopes not.  :-)
> > >
> > > > I don't see any benefit in bypassing the digital
> > >
> > > side even if it were
> > >
> > > > possible..what with the garbage on the screen
> > >
> > > there is quite clearly a
> > >
> > > > logic problem.
> > >
> > > Yes,  and in an instrument like this I don't see how
> > > it's possible,  or at
> > > least not practical.
> > >
> > > --
> > > Member of the toughest, meanest, deadliest, most
> > > unrelenting -- and
> > > ablest -- form of life in this section of space,  a
> > > critter that can
> > > be killed but can't be tamed.  --Robert A. Heinlein,
> > > "The Puppet Masters"
> > > -
> > > Information is more dangerous than cannon to a
> > > society ruled by lies. --James
> > > M Dakin
> >
> >       __________________________________________________________
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> >
> > ------------------------------------
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> >
> >
> >
> -- 
> Member of the toughest, meanest, deadliest, most unrelenting -- and
> ablest -- form of life in this section of space,  a critter that can
> be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet
Masters"
> -
> Information is more dangerous than cannon to a society ruled by
lies. --James 
> M Dakin
>