Xpantastic!

Hi all,
Thank you very much for all the feedback and the hints of what to do.
After a day´s break from the Matrix-12, I once again got into it with  
renewed energy.
I *might* have found the error, but I am not sure. To recapture:

Today a took both voice cards and swapped positions of the "board ID"  
tag (strap). Earlier there was always voice 7 - 12 who failed, and  
after the swap, voice 1-6 failed.
So there is no doubt now: There is an error on the voice card.

I swapped the straps back to the original positions, and inserted the  
cards and tried a few other options:
- I tried new 4051 ICs at UX06 and UX07 on one of the voices. No change.
- I tried new TL084 at UX08 at one of the voices. No change.
- U108 (LM311) have been swapped. No change.
- I have swapped all critical ICs U812 to U815 with the working voice  
card. No change.
- I have swapped the processor U907 and the timer IC U921 with the  
working voice card. No change.
Voice card two (the upper card) fails on all 6 voices as regard to  
VCOs, VCFs and VCAs. It comes close, but not perfect (off by as much  
as 0,5 - 3 notes).

On the other hand, this is what is working:
- There is sound from all 12 voices (if I override the automatic  
tuning and turn all voices manually on)
- All 12 voices responds to keyboard, levers and such
- All 12 voices change sound according to the stored programs, and  
changes done on the front panel
- All voices pass tuning of PW (Pulse Width) and RES (filter resonance)

So I started backtracking to other ICs, and I might have found the  
error:
U811, the 3140 DAC chip. If I swap this between the voice card with  
tuning error and the working voice card, the tuning error follow the  
chip. Kind of strange, since all other activities also goes through  
that chip, and all other activities work as they should. Moving ICs  
before and after U811 changes nothing, but moving the 3140 DAC makes  
the tuning error move as well.

So I am tempted to borrow a 3140 chip from the other Matrix-12 to see  
if I can have this Matrix-12 completely working. If so, then I have to  
start sourcing a replacement - which seems to be quite difficult.
Any hints appreciated.


Thanks for the feedback on the heat of the ICs. They get somewhat hot,  
but I can touch them without getting burned, so it is probably OK. The  
power supply regulators also get somewhat hot, but the hearsinks seems  
to be able to handle it.



Terje Winther
terje.winther@wintherstormer.no
http://www.wintherstormer.no/