If it is a more or less faint white noise, hiss, rather than some digital noise, then it means that the A/D converter is delivering some meaningful digital data stream to the engine. In which case you'd need to look for the problem before the A/D converter, i.e. in the analogue part, as anyhorizon pointed out.
My first guess would be to check the cable, which is a thin grey shielded 'wire' with white 3 pin connectors on both ends. It runs between the line control card - the one with the V-pots and buttons - of the 9 fader unit and the DCA board. The DCA board is the one right behind the input connector board on the back (and a shielding plate). Of course it is nearly impossible to reach the cable without taking the whole thing apart...
See picture below.
If you can unplug the cable on the line control board end, you might want to inject some faint signal (a couple of 100 mV) using the pins on the cable connector (pins 1 & 2 are carrying the differential signal according to the schematic) for a check. If the opamp preceeding the A/D converter and the A/D itself works correctly, then you'll need to look for the problem on the line controller board, all TB mic related electronics are located in the vicinity of the mic. Alternatively, you can check the relevant pins on the line controller card (e.g. hooking it to a headphone amp), microphone signal should be continuously output on these terminals (the TB switch works in the digital domain).
- Thin grey shielded cable carrying TB signal at the far bottom end (near the level display) of the case.
- 07042011377a.JPG (Array KiB) Viewed 1691 times
Edits: typos, improved readability
Posted: Sat Jul 02, 2011 4:50 pm