Alesis MidiVerb 3 Service Manual page 12

Customer Complaint
No Power, No Lights, No Life
Unit lights up, but there is no LCD
Display. Unit locks up.
No Memory.
Distorted audio.
No MIDI in.
No MIDI out.
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.
All Trademarks are property of their respective companies.
Possible Failure
Blown DASP 8 ASIC.
Bad +5V rectifier diode (D22)
Bad Reset circuit.
Bad 80C31.
Bad 24MHz Crystal (Z1).
Bad LCD.
Bad LCD cable.
Bad reset circuit.
Bad power supply rail.
Faulty DASP-8 ASIC.
Faulty trace, particularly between
the DASP 8 ASIC, and the
DAC, or analog switch (U19).
Faulty op-amp.
Faulty analog switch (U19).
Faulty power supply bypass
capacitor, particularly the cap
at the analog switch (U9).
Faulty Opto-isolator (U28).
Faulty 8031 (U32).
Faulty 8031 (U32).
Faulty transistor (Q2, Q3).
Possible Action
If this IC is extremely hot, to the
touch, then it is faulty.
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.
Check reset (U32 pin 9), both
during power up, and down.
Troubleshoot if necessary.
Replace, and re-test.
Some crystals are shock
sensitive. Tapping on the crystal
can sometimes reveal this.
Replace and re-test.
Replace and re-test.
Check reset (U32 pin 9), both
during power up, and down.
Troubleshoot if necessary.
Check PS rails, and troubleshoot
if necessary.
Replace and retest.
Troubleshoot, and replace if
necessary.
Troubleshoot, and replace if
necessary.
Troubleshoot, and replace if
necessary.
Troubleshoot, and replace if
necessary.
Replace and retest.
Replace and retest.
Replace and retest.
Replace and retest.