OBERHEIM SYNTH

Hey everybody!

A while back my Matrix started playing up one day at a friends house and kept on turning off randomly.

One day I took it home and from what I can remember, the sounds were completely off and the display was jumbled, then shortly after it stopped turning on.

I performed a diy fixes myself and replaced the caps and rails, assuming it could have been a PS problem.

Replaced some buttons, bought and replaced some CEM chips, replaced the battery, hell I even replaced most caps with 'audiophile' grade nichicon caps for fun.

Currently, I've got my Matrix 6 with a tech right now and he thinks there might be something wrong with the display- hence why the matrix isn't booting at all.

The power supply was tested and found nothing wrong.

It's been over a few months and I havn't brought it up since, he suggested it could be a tricky job trying to identify the root cause.

Can anyone help with this?

Would love to see this baby home safe soon.

Pretty sure the CPU does not read anything back from the display, so
if the display is not working, it should not prevent the synth from working.

Does the synth do anything at all?   

The display uses a higher voltage than the rest of the circuits.   If that's not present,
then the display would not work, but everything else should.   Also, there is a fuse
on the front panel board for the display voltage.  You might want to check that.

Are you saying that you replaced CEM chips as preventive maintenance?
If so, can I have the ones you removed?  :-)

Bob


--------------------------------------------
On Fri, 2/19/16, fknchino@... [oberheim] <oberheim@yahoogroups.com> wrote:

 Subject: [oberheim] Oberheim Matrix 6 Display Issues?
 To: oberheim@yahoogroups.com
 Date: Friday, February 19, 2016, 11:36 AM
 
 
 
 
 
 
 
 
 
 
         
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Hey everybody!
 A while back my Matrix started playing up one day at
 a friends house and kept on turning off randomly.
 One day I took it home and from what I can remember,
 the sounds were completely off and the display was jumbled,
 then shortly after it stopped turning on. 
 
 I performed a diy fixes myself and replaced the caps
 and rails, assuming it could have been a PS problem.
 
 Replaced some buttons, bought and
 replaced some CEM chips, replaced the battery, hell I even
 replaced most caps with 'audiophile' grade nichicon
 caps for fun.
 
 Currently, I've got my Matrix
 6 with a tech right now and he thinks there might be
 something wrong with the display- hence why the matrix
 isn't booting at all.
 The power supply was tested and found
 nothing wrong.
 It's been over a few months and I havn't
 brought it up since, he suggested it could be a tricky job
 trying to identify the root cause.
 Can anyone help with this?
 Would love to see this baby home safe soon.

As your tech should know, after checking the power supplies,
you would check the oscillator to the CPU, and also the reset signal 
to the CPU.   If those are OK, then try reading the EPROM that holds
the code, to make sure it's still intact.   (At some point you may also 
want to upgrade to the one that's on my site, tauntek.com, but only
after you get it fixed)   If everything is OK so far, then scope the 
address and data lines coming from the processor and look for strange
voltage levels, which would indicate a signal that is shorted to vcc or gnd.
But test the synth first to see if maybe it's working and just the display 
is bad.   That would be a different situation.

The service manual for the Matrix 6 is available, so your tech should
get that if he doesn't have it.  It's a free download.   It least then he will 
have the schematics.

Bob


--------------------------------------------
On Tue, 2/23/16, fknchino@... [oberheim] <oberheim@yahoogroups.com> wrote:

 Subject: [oberheim] Re: Oberheim Matrix 6 Display Issues?
 To: oberheim@yahoogroups.com
 Date: Tuesday, February 23, 2016, 1:59 AM
 
 
 #yiv2231702039 #yiv2231702039 --

Another thought:

I believe the service manual for the Matrix 6 has some errors with regards
to the display.
If I recall correctly the service manual specifies 2x9VAC as coming from
the transformer (at least on the block diagram) but in reality it's 2x42VAC.

What I also found a problem occasionally is the multi pin connectors
between the boards. Contact problems with those can result in strange
things including garbled characters.

Of course "Reset and initialize" should probably be performed first. At
least in one case this was already enough to bring a Matrix 6 back to life
that otherwise  behaved very erratically.