Xpantastic!

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/