Advice for diagnosing PC88?

[Fixer69]

Hello,

 

I have an old pc88mx with a problem and wondered if any of you has seen this problem and knows what is the most common cause?

 

The issue is that the sound just cuts out in the middle of playing. Here are some details:

 

The keyboard was working normally, but I opened it up to fix one note that was too loud. I started by cleaning the contact board with 99% isopropyl alcohol. After reassembly, it seemed to work normally at first but then I noticed the sound would stop completely (actually it is still there, just incredibly faint, and also each note lasts about a second longer than normal) without warning. Pushing the panic button restores the sound, sometimes for just a note or two, sometimes for a few seconds or minutes. Some days it doesn't act up. Usually it is fine for the first 45 minutes at least. FYI I also replaced the battery.

 

It's hard to believe I didn't cause this by opening it up since it never did this before then, but I've checked all the connections and don't see any obvious candidates.

 

During the work I bent the pins a bit for one of the pressure strip ribbon cable connections on the wheel board, but was able to straighten them and connect the cable. After reassembly, the pressure strips and wheels seemed to be functioning normally, but I don't know if something there could have caused this.

 

I also noticed that I can hear midi output through my laptop even while the speaker output is misbehaving.

 

I also got an idea from a forum post to run Midiscope to look for errors, and when I do, the display is flashing as if the wheels (ch 1 cn 1 cv x, along with sometimes along with "pitch bend") are sending messages constantly. Not sure if this is normal or not. It persists even if the wheel unit is removed.

 

I tried running the diagnostics and I don't think they ran correctly. At first it bypassed the screen to choose between diagnostics and reset, but after a few tries that came back. Also in burn-in mode the led's don't light up, so I can't tell if it's passing or not.

 

Any help will be much appreciated!

[Delaware Dave]

"...During the work I bent the pins a bit for one of the pressure strip ribbon cable connections on the wheel board..."

 

Danger Will Robinson!!!!!

 

Try 'support@kurzweil.com' and seek their advice.

[Fixer69]

Thanks! Yes, I opened it without a manual (dumb but fun), and found the service manual later. I tried one support e-mail and it didn't go through, so I'll try this one.

[Fixer69]

In case anyone else has this problem I thought I would add that I've noticed the problem with mine never occurs unless the room gets to a certain temperature, say 72 degrees fahrenheit, or the unit has been on for many hours. This makes me think there's a component that is faulty and allows too much current through when it gets warm, triggering a protective cutoff circuit (which is reset when you push panic). But of course I'm not sure. I don't think I'm going to mess with it as long as it works almost all the time.

[Delaware Dave]

Did you ever reload the operating system. A fresh install often cleans up a lot of problems.