4000 screen problems

Sad to report the screen reverted back to twitchy flickering, or solid blue. I'm running out of ideas for what is up with it, but it's bumming me out because I just want to use the machine!

Sorted the CD Drive. Bought a PLEXTOR PX-800A and works a treat. Pretty quiet, black facade, works as expected.

I bought a new flat ribbon cable to try that. But despite checking the service manual and being super precise with what I was ordering I got the wrong item.

What's needed is a RIBBON CABLE CORD FFC P1.25 L480 14P

I bought this: https://www.ebay.co.uk/itm/185449597692 ... 3251813271

Perhaps the 'pitch' is wrong. I'm wondering is this is the width.

If anyone has a thought then please let me know. Regret trying these screen upgrades. The OEM one I had was fine, but wanted to avoid the whine, and improve the legibility.

Unfortunately the pitch (distance from line center to line center) is wrong indeed.
You ordered 1mm, but need 1.25 mm, as expressed in the specs...

Yes indeed. My error.

I've board a new display PCB from mpcstuff which includes the contrast pot. Think I've damaged the circuits now anyway with my sub-par soldering. So fingers crossed this new board and pot will finally solve this and get me back working with the machine instead of nursing it!

It was probably the wrong line pitch of the flat ribbon that shorted some lines and killed the tiny LM358 opamp on the display driving circuit, though there‘s some possibility for a soldering fault, too.
(iirc there‘s a line from the pot to the LM358)
In my case it was manual fiddling with the (worn out) ribbon on the main circuit socket that made the display go dim and never wake up again. Replacing the opamp cured it.
Anyway... best of luck with the replacement

I didn't actually install that ribbon cable as it clearly wasn't the right size. So that's not the route of this new 'low-res' issue.

Installed the replacement display PCB (inc contrast pot) from MPC Stuff (pricey) and that's solved the intermittent / highly sensitive display issues. But the issue with the 'low res' screen is new and now another thing to solve!

Any insights ?

I only looks like „low res“. In fact some pixels are set at the wrong time, so kind of slipping on the current line when it‘s drawn.
Make sure that the main (long) display ribbon is placed correctly.
It doesn‘t have a tight horizontal limit at the edges, or the tip of the ribbon may not be deep enough in the connector.
(there are 2 clock lines on that ribbon and since you didn‘t have the effect previously it‘s either the ribbon misplaced or something on the display driving circuit (on the back of the LCD) is wrong. Which is rather unlikely.
Inspect the ribbon’s connection end (at the main cuircuit board side) with a good magnifier/light. The lines are made from conductive ink and are not very robust.

best if luck, Tom