From: ehsjr@verizon.net   
      
   On 1/25/2025 12:29 PM, bitrex wrote:   
   > I have a Korg SDD 3300 triple digital delay rack unit that was a bit of   
   > a basket case when I got it. Someone had tried to "fix" it at some point   
   > and it had a number of issues including the wrong voltage regulator   
   > slapped in the negative rail, miswired output jacks, dead EL backlight,   
   > bad SRAM 2032...   
   >   
   > Fixed that up and I was able to get a copy of the service manual and use   
   > the three-finger-salute button combo to get its mind back after SRAM   
   > battery replacement as is common on units of this vintage, followed the   
   > adjustment procedure in the service manual and everything seems to work   
   > as it should now except one really irritating intermittent fault   
   > remains: the LCD will occasionally garble up at power-on or in use as so:   
   >   
   >    
   >   
   > It's annoyingly unpredictable and seems somewhat related to how it's   
   > mounted? I can power it up 25 times on the bench and it works fine   
   > making me think I solved the problem, then slide it back in the rack and   
   > it starts acting up again.   
      
   When the failure is position sensitive, look for a bad switch or cable   
   that causes a line to float between a logic 0 and 1.   
      
   War story: I had a bad ice maker in the freezer that failed only when it   
   was installed. Worked 100% on the bench and not possible to troubleshoot   
   when installed. Turned out to be a bad micro switch that failed (high   
   resistance instead of ~0 ohms when closed) only when I held the thing at   
   an angle.   
      
   Your problem looks like a tough one if it's a switch or cable. :-(   
      
   Ed   
      
      
   I've tried a number of things like adding   
   > bypass capacitance on the display board which is separated from the CPU   
   > by good distance, disconnecting the backlight thinking it might be   
   > interference from the inverter, moving the wiring around, also recapping   
   > the PSU which I was planning on doing anyway. Doesn't seem to help.   
   >   
   > Here is the upper digital board (the analog board is on the lower   
   > level), the lines to the LCD from the NEC Z80 variant are on the far right:   
   >   
   >    
   >   
   > Thinking about just trying a new display with LED backlight at this   
   > point but I've read that this unit can be finicky in accepting   
   > aftermarket LCDs.   
   >   
   >   
   >   
   >   
   >   
   >   
      
   --- SoupGate-DOS v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)