Vintage Synth Repair

Hi, took your advice and recapped the PSU.

5vm measures as 4.27v and therefore pin 37/reset on the gets 4.27 ,all other voltages are spot on.

Funny enough as I put my meter on pin 4 and 5 on the 74c00 it will freeze until I remove the probes.
I am in the process of tracing the reset for the cpu and replacing the 74c00.

question , I could only get a 74 HC 00 , is that a suitable replacement ?

Thanks a lot Dennis!
Arnar.



----- Upprunaleg skilaboð -----
Frá: "Dennis Matana" <connect2techno@...>
Til: vintagesynthrepair@yahoogroups.com
Sent: Sunnudagur, 2. Febrúar, 2014 15:52:54
Efni: Re: [vintagesynthrepair] Re: Matrix 1000 Freeze.







Hi, 


I would recommend to recap the power supply. The psu gives out -12, +12, +5, -5 and 5Vm (for memory coming from the battery) and 5VL. Make sure that you upgrade with higher voltages caps then the ones that are in there...Oberheim used 16v ones which is pretty close to the 12v lines they are on.
btw 5Vm is also connected to a 74C00 Nand gate (ic14) which is controlling the CS line of the 43256 eprom. I have seen these go bust...


Looking at the schematics the cpu does get a reset on pin 37. The signal coming in is called VPV but i cant seem to find that anywhere else on the schems...maybe trace down that track.


good luck in fixing it and keep us up to date, br Dennis



2014-02-02 plat@... < plat@... > :








Thanks a lot, this gives me something to look for .

cheers
Arnar

----- Upprunaleg skilaboð -----
Frá: "Lorne Hammond" < lhammond@... >
Til: vintagesynthrepair@yahoogroups.com
Sent: Laugardagur, 1. Febrúar, 2014 15:59:16
Efni: RE: [vintagesynthrepair] Re: Matrix 1000 Freeze.

A bad cpu is rarely the issue. In the tr-909 the blame is often the cpu but the real cause is usually the caps/traces/switching transistors on the reset circuit, located back on the power board.

Some cpus have a circuit that protects them from switching on until they have a stable +5 v from the power supply, to prevent memory scrambles of what your saving.

You might want to check to see if the matrix cpu has a reset pin and trace that trace back to the power supply. A transistor may be slow to fail, or a ground cap is a bit flaky and as they heat up something lifts internally or external to the component. On the 909 traces are delicate and its easy to melt one that is hidden by the big capacitors that it cuts across underneath, continuity trace catches if that is teh issue. So teh circuit does what its supposed to when part of it fails

when the reset drops below 5V and it immediately switches the cpu off, which leaves the display hanging or blank in mid-operation?

Just musing aloud not speaking from any matrix experience.

Lorne in Canada

rom: vintagesynthrepair@yahoogroups.com [mailto: vintagesynthrepair@yahoogroups.com ] On Behalf Of tim p
Sent: January-30-14 1:59 PM
To: vintagesynthrepair@yahoogroups.com
Subject: RE: [vintagesynthrepair] Re: Matrix 1000 Freeze.

Please define what you mean by "cpu has been changed"...

From: plat@simnet.is
Sent: 30/01/2014 21:42
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Matrix 1000 Freeze.

Hi everyone.

I have a Matrix 1000 that I am trying to bring back to life.

The issue is as follows:

I can turn it on just fine but it will freeze after a few minutes , this happens even though I just leave it alone.
Sometimes it will also randomly change presets but that does not happen often.

I have reseated all socketed chips,checked that battery, done the initialization but it keeps freezing.
CPU has been changed (I have two more CPU´s) * Software is 1.11

Any thoughts ?

Thanks
Arnar