Repairing a digital audio procesor. Symptom it makes an horrendous noise like swarm of hornets and bagpipes with chorus and reverb. There is a reset line that connects reset pin of the system micro to a reset pin of the DSP 144 pinner and reset pin of an associated memory. Long trace and ribbon around and between a couple of boards. Nothing found in the way of power-on reset IC to this line. But touching this line with a probe tip , resets the system to full operation. Just touching a finger to this line does not reset. Touching the metal of the probe when touching the trace does reset. No equipment available to check for any circa nanoseconds reset pulse, seems to be H always. A 15nf cap to ground and 15 inches or so of test lead , one end to ground does reset, with a 680pF cap there insted, no reset. main ICs are ATMEGA88, p1 DSPB56720ag, p111 S29AL032D70TF103 , p12, pinning assumed to be same as S29AL016, data found . Incidently no ferrite torroid or cylinder on the maker's SMPS wall wart. How to regularise / repair this situation?
- posted
10 years ago