Intermittent fault on Korg SDD 3300

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.

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

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..

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..

Thanks for your suggestions, I feel like there was some substance use going on when this unit was designed and servicing it makes me feel the same way so at least there is symmetry..