Customer Complaint Possible Failure Possible Action
No Power, No Lights, No Life Blown DASP 8 ASIC. If this IC is extremely hot, to the
touch, then it is faulty.
Bad +5V rectifier diode (D22) The cathode should read roughly
10V (with some ripple). It has
been noticed that 1N4001 seem
to have problems, and since then
have started using 1N4003
diodes exclusively.
Unit lights up, but there is no LCD
Display. Unit locks up.
Bad Reset circuit. Check reset (U32 pin 9), both
during power up, and down.
Troubleshoot if necessary.
Bad 80C31. Replace, and re-test.
Bad 24MHz Crystal (Z1). Some crystals are shock
sensitive. Tapping on the crystal
can sometimes reveal this.
Bad LCD. Replace and re-test.
Bad LCD cable. Replace and re-test.
No Memory.
Bad reset circuit. Check reset (U32 pin 9), both
during power up, and down.
Troubleshoot if necessary.
Distorted audio. Bad power supply rail. Check PS rails, and troubleshoot
if necessary.
Faulty DASP-8 ASIC. Replace and retest.
Faulty trace, particularly between
the DASP 8 ASIC, and the
DAC, or analog switch (U19).
Troubleshoot, and replace if
necessary.
Faulty op-amp. Troubleshoot, and replace if
necessary.
Faulty analog switch (U19). Troubleshoot, and replace if
necessary.
Faulty power supply bypass
capacitor, particularly the cap
at the analog switch (U9).
Troubleshoot, and replace if
necessary.
No MIDI in. Faulty Opto-isolator (U28). Replace and retest.
Faulty 8031 (U32). Replace and retest.
No MIDI out. Faulty 8031 (U32). Replace and retest.
Faulty transistor (Q2, Q3). Replace and retest.
A few final notes: The DAC output is an extremely important test point. Familiarity with the
appearance of this signal on a scope, will greatly facilitate troubleshooting audio problems. Exercise
caution when examining the output of comparator (U21). Accidentally shorting pins 7, and 8 together
will instantly result in a dead ASIC. Other than there, and in the power supply, you really can't do any
harm with a scope probe, so explore.
Be on the watch for user error. (I.E., if a user complains that it won't load from a DataDisk,
check to be sure that SYSEX ENABLE is turned on.)
Remember to install ALL of the latest revisions, before returning the unit. This can help
prevent many unhappy returns.
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