Can anyone point me at drawings for this unit please? I've found a partial one that someone has drawn up, but it only covers the input and output conversion sections.
Thanks for reading
Hi, Thanks for the response. I've managed to work out a bit from the chipset data.
The unit produces loud digital-type white-ish noise via it's ADAT output. No trace of it is evident in the audio input stages, but I did find that the -ve rail to the input TL074's was at +0.9v. Sure enough a 7915 was faulty.
However, replacing that has not cleared up the noise issue, and the reg is getting pretty hot when the front panel PCB is connected. I have that board out now (no mean feat), but have not pinned down why that is happening yet. I have found the loading gets progressivley worse as I reconnect the input con's back to the main PCB, so I may be going round in a circle a bit there.
To come at it from another angle, I lifted the 4 clock signals to the 1201 ADC's, hoping to eliminate a good portion of the input ciruit. With now only the 1401 multplexer/optical driver going, I still get some noise, which gets instantly as bad as before when any one clock signal is reapplied.
So, I'm suspecting an issue with that device, as well as possibly something else too, I note that the 1401 doesn't use any -15v rail. I'm trying to remember the clock freq I measured now (32MHz?), I do remember it appeared stable on my counter anyway.
Edit: I've just noticed that the crystal is 11.2896MHz, so I will look into that again.
I'm letting the problem mull a bit this morning while I get on with other stuff, I'll return to that bench later.
Last edited by Brian Swatton; 11-12-2011 at 10:56 AM. Reason: More info
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