From: user@example.net   
      
   On 1/25/2025 2:58 PM, Dave Platt wrote:   
   > In article <67951f89$1$3620713$882e4bbb@reader.netnews.com>,   
   > bitrex   wrote:   
   >   
   >> 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. 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:   
   >   
   > I'd be looking for things which could cause an intermittent connection   
   > on that cable and its connectors... maybe a bad or dirty pin or   
   > socket, maybe a hairline crack where one of the pins is soldered to   
   > the PCB.  A bad bus-driver on the main PCB (either a separate chip, or   
   > dedicated pins on the microprocessor) might have a similar effect.   
   >   
   > If the characters being shown were characteristically off by one bit,   
   > it'd point to one of the data lines.  As it is, they seem to be   
   > rather unpredictably garbled, which suggests to me that one of the   
   > clock or handshaking lines might be bad.  Glitchy rising or falling   
   > edges on the "latch your data" signal might result in data being   
   > latched at the wrong time, while the data bus was in transition,   
   > and this could lead to all sorts of nonsense being displayed.   
   >   
   > Might be worth pulling the cables, fluxing and re-flowing the   
   > connecting pins on the PCB, cleaning everything thoroughly.   
   >   
   > If you have a DSO or logic analyzer which has a "look for glitch and   
   > runt pulses" acquisition feature, scoping the data and handshaking   
   > lines at the LCD while actively driving the display, and tapping on   
   > cables and the PCBs, might prove instructive.   
   >   
   >   
      
   Thanks for getting back, I'll follow up on those suggestions thank you!   
   No logic analyzer available at home unfortunately but I have one I can   
   probably use for a time if nothing else works..   
      
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