Bad voice troubleshooting, part 1

[ddvdave]

Hi Forum,

My EIII arrived with voice #5 (counting from 1) disabled in the Output Disable menu. The symptoms of this noisy voice are a little bit perplexing:

• The voice has "digital noise" that seems to change when adjusting sliders/knobs etc.
• The voice noise issue does not move with the output cards. It always stays on voice #5 (0x04)
• The noise/buzzing is only apparent when the filter cutoff frequency is below 10Khz or so
• The noise appears to be coming before the CEM3387 since I can lower the volume of the noise and pan the noise.
• The noise is more apparent when sampling silence and playing back.

Any ideas where to start looking? I scrutinized the schematics for a while, looking for anything that is unique to voice 0x04, but other than digital signals (address/data bus leading to the various control voltages), I found nothing.

Could be the analog jack board I suppose, but then the level of noise shouldn't attenuate with VCA volume or pan.

Suggestions appreciated, as always!

Best,
Dave

[12bit]

Hey Dave.

I would start by reseating all IC's on the boards in the EIII. If this does not help I would try to exchange one IC at a time from e.g. voice 1 to voice 5 until voice 1 doesn't work. This way you should be able to figure out which IC is the problem.

Best;

Kenneth
theEMUs.com

[ddvdave]

Thanks for the suggestions!

The problem I'm finding here is that the noise doesn't appear to be tied to the output board, since it's always affecting voice #5 (upper output board).

If I were to move all the ICs from the lower board (9-16) to the upper board (1-8), it would be essentially the same as moving the whole board, right (and I have already swapped the boards).

The other difficulty is that my output boards don't have all the ICs socketed. All the CEM3387s are socketed on both boards, but on one board I have 3 DACs socketed and 5 soldered and the other has 4 DACs socketed and 4 soldered.

I did swap all the SSM2300 S/H chips from one board to the other just as a test, but that didn't change anything.

I also tried swapping the F-Chip and CEM3387 from voice #5 (0x04) to voice #1 and vice-versa, but this also didn't affect anything.

I don't like the idea of desoldering one of the DACs, besides it just doesn't feel like a problem with the Output Card, since it doesn't move with the cards. Maybe it's time to take it to a tech? 

-Dave