DS345 Successfully repaired

[SoundTech-LG]

Picked up this SRS DS345 for a reasonable price with the following self test error on boot up...




The manual has a listing of self test errors, with helpful but vague areas to check.
It would be better to include "check surrounding circuitry as well."



After much troubleshooting I found the output of the DAC was a bizarre looking signal. Two and a half times the expected frequency and DC offset on both diff. outputs.



Checking all the digital inputs from the ECL translator chips (MC10124) I found that pin 14 (MSB) on the DAC had no input. That led back to U504D. Changing  U504D solved the issue. Now passes all tests.
Hope this can help someone spend less time troubleshooting.

[bostonman]

I assume this wouldn't be applicable to the problem you and I have discussed in the other thread?


https://www.eevblog.com/forum/repair/standford-research-ds345-error/msg4436569/#msg4436569

[SoundTech-LG]

No, unfortunately not!
Still trying to track that issue down!

[SoundTech-LG]

I assume this wouldn't be applicable to the problem you and I have discussed in the other thread?


https://www.eevblog.com/forum/repair/standford-research-ds345-error/msg4436569/#msg4436569

So, I was working not on the original DS345 with the drifting offset you mention evidenced at U600 on the lower board. I did, however use it (the drift unit) to swap two major IC's, the ASIC DDS345 (U300), and also it's DAC, the TRW TDC1110, (U500).
The problem I fixed (bad MC10124) in this other DS345 is working good... but it MAY have new problems!!! BECAUSE... the drift in the original DS345 seems to have stopped solid. I can adjust the offset trimpot now and it seems to hold the DC setting solid. Will know more come morning after a soak overnight. There is, of course possibilities there were bad connections to the IC's as another possible cause. The unit I just repaired now has the possible bad IC (one of the two). I do know that the TRW TDC 1110 DAC is no longer made. You cannot get it on ebay either. TRW Electronics is defunct. The later DS345 units do not use it. They have a daughter board soldered on top of that area of the top board with a new DAC and circuitry. I will now of course be checking the "repaired" unit to see if the drift problems transferred to it. That would rule out bad connections. Stay tuned!

[SoundTech-LG]

So as the saying goes...  all the best laid plans of mice and men...
We had a power outage last night, and this was not under UPS backup, although the generator and ATS did kick in. I need to restart the setup.

[SoundTech-LG]

Unfortunately, I inadvertently pulled my monitor wire off from the output of U600 
Sorry...  total false alarm, it still has the drift