35 year old Casio AZ-1 Midi Controller (Keytar design)

[Skyhook1985]

I bought my AZ-1 +/- 35 years ago.  Everything still works except for one thing; soon after I start playing, it starts to sustain on it's own.  This issue started about 10 years ago, so the AZ-1 has been safely kept in a Bass Guitar case.  I am in a musical group where it would be cool to bring this out on stage again.

I have tried many sound sources, midi cables, batteries and power cords.  I have taken it apart and cleaned all the plastic switch covers to make sure it wasn't something mechanical.  I am pretty confident this is an electronic circuit component problem or a S/W and/or F/W issue.  But I am leaning more towards a component that is heating up, malfunctioning, and then causing the sustain circuit to fail.

I hope I can repair it.  It's a fun instrument to keep in my magical bag of tricks on the stage.  Thank you in advance.

 

Edited March 15, 2022 by Skyhook1985
I miss counted the number of years

[Chas]

The AZ-1 is a midi controller, so everything on it is basically a switch or a digital encoder. I'm not totally familiar with the layout, but it most likely has a sustain button. If this button sticks, then it would be sending the midi sustain message to whatever sound module it is triggering.

 

For help in identifying the issue, connect it to a midi program/ app that can show what midi data is being sent. Once you know what midi is coming from the AZ-1 then you will know where to zero in on the problem.

 

Because of the age of the AZ-1, it likely predates FW and/ or SW upgrades. My suspicion is a sticking sustain switch (if it has one).

 

Btw, the AZ-1 was released circa the late 80s, so would be around 35 years old! 

 

 

[Chas]

At the end of the grab handle are two push button switches - portamento and sustain. I am almost certain that the sustain switch is your culprit.  You could try squirting in some contact cleaner to see if that would help.  Otherwise you may need to take the AZ-1 apart and check the sustain switch with a multimeter. 

 

[Skyhook1985]

Yes, I apparently counted all my toes twice, it is 35 years old not 45.  I bought it in 1987(ish). I think I also had that jacket and tie. 

Also yes, it does have a sustain switch, I will open it again and physically test the switch with a meter to confirm how or if it is operating.  For some reason I remember ruling out the switch the last time I had it open.  It actually plays for 5 to 10 minutes or so before it starts acting up.  That is one of the reasons I was thinking a component on the circuit board warming up beyond tolerance and then crapping out or possibly a capacitor.  Though I have the original manual I do not have a schematic.   I have had it record into a sequencer program and when it acted up it does record and hold a sustain code.  The only way to stop it is to turn the AZ-1 off.  When you turn it back on it takes less time for it to act up then the previous time unless you had it off for a while.  That again led me to believe heat and/or capacitor as a catalyst.  I truly appreciate your feedback and I'm going to open her up and operate on her this week and see what happens.  If in the mean time you can think of anything else, please let me know.

[CYBERYOGI =CO=Windler]

Is there battery leak acid spilled on the PCB? This can make the PCB material itself conductive and cause all kinds of trouble. Also water trapped under rubber contacts (e.g. when rained on) can make such problems.

 

If battery acid (with alkaline batteries it is a strong lye instead of acid), everything needs to be taken apart and cleaned with water and dishwashing detergent to prevent corrosion damage. Residues than can be removed with isopropanol. Be careful with printed carbon traces on PCBs (trace bridges and key/button contacts), those tend to corrode away by acid but also might get damaged by isopropanol when scrubbing too strong.