Suspect faulty DAC

[Samnunn92]

Hi all and thanks for reading. I have a Hammond-Suzuki XB2 keyboard that I'm trying to fix and I was wondering if anyone would have any ideas about it (I know it's not a stompbox but still!) Basically when I got it no sound was produced at all, although the keyboard appeared to work fine (and still functioned perfectly over MIDI etc.) After having a peek inside I noticed there was a loose screw on the drawbar section inside the case so I screwed it back in and voila - sound, but very very distorted. Theres a lot of noise, it doesn't reliably produce the note and with effects on like vibrato/Leslie the signal becomes even more distorted and only the octave C1-C2 actually is audible (lower and higher octaves just hiss).

Without doing any testing yet I am thinking that its the DAC that's died. Would these sorts of symptoms point to that or am I completely in the wrong area? Studying the DAC assy board there seems to be quite a lot of heat damage - theres a lot of old flux everywhere and the surface of the PCB has gone quite bubbly, which further fuels my suspicions.

Any help/ideas would be great! I'm planning on ringing Hammond-Suzuki tomorrow although I'm pretty sure as the keyboard has been discontinued and support dropped they won't have much to say.

Thanks very much

[Seljer]

You could probably use an audio probe (a capacitor and alligator clip on the end of an audio cable) to find the output of the DAC and check if the audio is already bad there or in the circuitry following it (which I'm guessing is a bundle opamps or something)

[pjwhite]

The fact that putting in the loose screw made a change makes me think there might be some cracks in the circuit board traces.  Does the unit show signs of having been being dropped at some point?  In my experience, Hammond Suzuki circuit boards used very thin copper and extreme flexing could cause traces to break.  Once the board returns to flat, the breaks can still be there, but very difficult to see.
Is it a single sided board?  Is the board made from phenolic (brown material) instead of fiberglass?  Either of these might make broken traces a likely suspect.