Hi,
Thanks for the feedback.
Good idea to compare with the Xpander service manual, as it is all
there. I have been though all the procedures now.
> You probably already checked these things but just to be sure:
> Do the 2.2uF caps that were replaced have a 50VDC rating? If not
> they will not
> pass the audio signal correctly.
>
Yes, 2.2uF caps with 50VDC rating.
> I would start at the DAC circuit ( page 19 xpander service) There
> is a trimmer
>
Checked all the voltages according to the service manual, and they are
all well within the specs. Some of them almost perfect, but then I
have done service on the power supply (lots of new parts in the power
supply). The DAC offset was quite good, but now it is perfect. I did
the reset again, and those automated test, and they all came out good.
Still the same error.
> If not :
> There is also a procedure for checking the board reference voltage
> ( page 34) If
> this voltage is off spec it could cause errors.
>
There is no trimmer to adjust this, but it is 3.98 and 3.99 on the
boards, well within the 4V spec.
> Try swaping DAC's between the "known good board" and your failed
> one. Or any
> other parts in the DAC circuit.
>
I have systematically swapped one chip at a time, rebooting and
checking to see if it made any change. DAC, opamps, logic chips ...
still the same.
> There is a circuit on page 31 (Lower right hand corner in Xpander
> service)
> Which is used in the auto tuning routine. It is built around an
> LM311 voltage
> comparator
>
Tried swapping it, but still the same.
I suspect there is something wrong in the processor board, now,
because I found another error as well:
- The top 8 keys do not work.
I originally wrote that off as dirty keys, and planned to do that as
part of the final cleaning of the synth. But when I did clean the
keyboard today, the error is still there. I checked the keyboard
contact board, the lines between keyboard and processor board (the
parallell cable) and all seems to work properly.
Terje Winther
terje.winther@...
http://www.wintherstormer.no/
Message
Re: [xpantastic] only one board active
2012-07-09 by Do It Yourself Synth
Try to reseat the U921 chip. This timer (8253) is used to test the frequency of VCO and VCF self oscillation. It may be dead too. The best is to test with an oscilloscope on pin 7 while doing an autocheck. You may see a short signal when the CPU test each of the 6 voices.
Kris
Le 9 juil. 2012 à 15:54, Terje Winther a écrit :