Oh okay... I thought F.I. was some type of electrical tech acronym or jargon that I wasn't pickup up on.

I certainly don't disagree that there may be something on the display board that may be pulling down the power supply. Looking for a hot chip is a good idea.

To go back to my original post, my reasoning for singling out the power supply as the source of the display problem was based on my observation that if I replace the power supply in my problematic Matrix 6 with the power supply from my full working (no issue) Matrix 6, the display problem is remedied. I have no problems at power-on, even with cycling the power switch on and off.

My other course of action could be to just buy another power supply from Syntaur (assuming the one they'd sell is good) and get on with it but I prefer to amuse myself somewhat trying to repair what I've got than spend money on replacement PCBs. I'm an engineer by education just not an electrical and I enjoy playing with these things. I've patched up a number of Korg and Roland keyboards. Most of the time I get a hold of these old vintage synths and the repair is often something simple. My other Matrix 6 wasn't working when I got it either. It was a simple fix in that CEM3396 chip wasn't fully seated and the #1 IC pin was broken off. I just soldered a new lead on it, reinstalled it and it's worked beautifully ever since. (I won't mention how much I paid for it.)

I've also go two OB-Xa's I'm playing with. One was fully working I picked up all original from the original owner. It's been fully functional however something has gone awry with the autotune. Pressing autotune, it cycles through all the voice boards okay and then flashes on 5, 6, 7 and 8. When it quits flashing voice boards 1 through 4 no longer have any output. I understand this is part of the ROM logic such that voice boards are shut off it they cannot be tuned. How to fix it What's faulty Haven't figured that one out yet... Anybody

My other OB-Xa was a basket case when I picked it up that wouldn't power on until I realized the crystal was bad. Removing the upper and lower control boards I kept hearing something rattle and figured out it was the crystal. Put a new one in now the OB-Xa lights up like a christmas tree and has output on all the voice boards. It's doing quirky things though like inability to switch to 'MANUAL' and I can also turn off (and back on) the 'UPPER' and 'LOWER' LEDs when the keyboard is not in 'SPLIT' or 'DOUBLE' which is not in agreement with what I'm reading in the owners manual. The bottom line is, now that this OB-Xa powers on as it should, I'm trying to decide whether or not it's operating correctly. So far my assertions are that it is not. It's been parked in the corner for a while as I play with some other toys like this problematic Matrix 6...

--- In oberheim@yahoogroups.com , Martin Ator <cyllall@...> wrote:
>
> I thought I was being modern with F.I, which in my head means for instance. Oh well that was a fail.
>
> A brown out is when a processor doesn't get enough power I think. Usually when you switch something on like a Matrix you get a certain amount of clock cycles holding the main processor at reset, so it doesn't switch on until the power supply is stabilised, so you don't get a brown out. Some Roland TR-909's had a problem like this back in the day.
>
>
> If you are having problems after a warm up period then it sounds like you have a 'chip' problem. Something connected with the display circuits then, if everything else works even though the display is garbled.Maybe you can feel a chip that's a lot hotter than the others but this doesn't always give an indication.
>
>
>
>
>
> ________________________________
> From: wesleyknick <wesknick@...>
> To: oberheim@yahoogroups.com
> Sent: Sunday, 5 August 2012, 16:09
> Subject: [oberheim] Re: Oberheim Matrix 6, Dead
>
>
>  
> I haven't as of yet tested the diodes either. I'm thinking it may be more trouble than just figuring out what to replace them with, getting the new diodes and putting them in...
>
> --- In oberheim@yahoogroups.com , Martin Ator <cyllall@> wrote:
> >
> > Have you tested the diodes You could upload some pictures, just in case what you think are diodes, may not be diodes. Depending on what diodes they are, modern 4148, 1n4001, 1n4004 can do the job of most oldies.The last 2 are most likely in a PS.
> >
> > What about capacitors   Electrolytics can smell a bit cat pissy if they have problems.Are you able to measure the correct voltages now
> >
> >
> > There may be a faulty decoupling ceramic capacitor near to a logic chip,or an intermittent logic chip involved in the display control. I'm guessing you may be having a 'brown out' on power up if it's the power supply.
> > Power regulators don't usually have problems unless something somewhere else has made them work too hard.
> >
> >
> > Sometimes it's easier to measure power at the components themselves.If a schematic says 15 volts F.I, then you can expect to find a little bit more or less on testing. But I would suspect a problem if I found 13.5v instead F.I.
> >
> >
> > If you switch your Matrix on and the display is OK, does it go funny after a while
> > If you let it warm up and then do a power cycle, does the display then go funny (try to answer these last two)
> >
> >
> >
> > ________________________________
> > From: wesleyknick <wesknick@>
> > To: oberheim@yahoogroups.com
> > Sent: Sunday, 5 August 2012, 3:54
> > Subject: [oberheim] Re: Oberheim Matrix 6, Dead
> >
> >
> >  
> > Assuming you were to replace the diodes on the power supply, is there a suitable substitute I'm having some trouble identifying the 2 different diode types visually. 6 of the diodes on the power supply are marked with what appears to be a 'T85' followed in smaller font by a '5D' or '5C'. The two separate spherical diode types are marked with what appears to be a 'T3B5H'. A Google search of any combination of the markings brings up very little in the way of any reference to diodes. None of the manuals uploaded on various websites have any additional information and the only place the diodes are depicted is the block diagram. Anybody have a parts list out there they can upload Most of the Korg and Roland service manuals have a parts list...
> >
> > --- In oberheim@yahoogroups.com , jim finch <jahg88@> wrote:
> > >
> > > You didn't mention how you were reading the powersupply voltages-but I didn't read the whole thread.If you use a O-scope you can see what is actually there,not just the D.C component. Most likely there is garbage riding on the +5V rail making the digital components see it as logic level shifts.
> > >
> >
>