Re: Re: PC3K8 Going Out Of Tune

Thanks for all of that.  I will probably have to take it in for service and I can print this email out to help him out.  Someone else said they sprayed the contacts and it seems to have done the trick....not sure what to do....yet.

For this weekend’s show, I might have to disable pitch band altogether, unfortunately. Thanks so much. 

Dave

From: [email protected] [KurzList] 
Sent: Tuesday, October 09, 2018 8:53 AM
To: [email protected] 
Subject: [KL] Re: PC3K8 Going Out Of Tune

  

It has taken a a very long time to track the source of this PC3K8 issue, including replacements for most PCBs and the wheel housing to no effect.  The issues were pitchbend activates, dropping the pitch (never upwards), intermittent sustain pedal, so notes would release without letting the pedal go, SW1 and SW2 would not work, although the LEDs would light.  The unit was returned to the distributor for fixes maybe 4 times, to no effect.
I very nearly binned it.

If you have intermittent pitch bend problems, you need to use the diagnostics mode (press and hold 456 for a moment) to see what you can see.  


If the pitch bend sits at approximately 128 when you let it centre itself, the wheel is working fine.  If it centres 126-130, there is a small screwdriver adjustment which can be made through the bottom of the casing, to get it to 128. Wear and tear can cause this precision to fade, so if it settles at on a few different numbers this can indicate wear and the wheel housing unit can be replaced.


Now, if you notice the pitchbend dropping huge and apparently random amounts, but always lower than 128, then what is likely to be happening is the voltage on the scanner is dropping from 5V to a lower value, so the DAC  which reads the potentioneter is reading a lower voltage.  Mine would drop to 100, or 80, even 0 on occasions, then work perfectly for a session, before striking again. 


The root of the bad scan, lies in the way the looms are connected to the main board internally.  The IO, Fader and wheel housing PCBs are connected to the main board by a single armoured loom, which has a ferrite bead around it at the mainboard end.  This loom was the problem in my PC3K8.  The sheer weight of the ferrite, had stressed the tiny wires to the connector to the point of intermittent connection.  I have heard from other techs this loom does not work whether loose or tag tied - the bead can cause impact damage on the mainboard or strain on the cable.    

The solution was to fabriacate a new cable using PC ribbon cable, Molex crimps, and use a series of ribbon ferrites spaced along the cable and away from the mainboard connection.  In the end, we fitted some small posts to the case and tag tied the ferrite beads to those to preventm movement in transit, and left the molex connectors generous room to move unhindered and unstressed.

So far so good.

My Twitter feed has some photos, and the trail of woes - from July 7 through to Sep 2.
State upon opening - https://twitter.com/All97Notes/status/1015673290889875457

My new fabricated loom - https://twitter.com/All97Notes/status/1033007694242881538
Keybed reported wrong - https://twitter.com/All97Notes/status/1030485036548730880

I hope this helps you.  It was extremely hard to find as a fault.
  https://twitter.com/All97Notes/status/1033007694242881538