Sinclair ZX80 / ZX81 / Z88 Forums

What is strange is that the interference (for want of a better word) occurs exactly three times in the 52us of the visible part of the width of the picture (the visible part of a PAL tv line is normally 52us). If you do the calculations, that makes it a 57.7kHz signal. But what is unusual is that i...

I'll certainly try that. When the board is out it's easy to get a finger under it while it's on.

Multimeter and PC Oscilloscope. Noticed with the QL-VGA that the waving corruption is even worse when you change the screen colour to something other than white. Black was ok, unless that's changed since the re-cap.

If you enter the 128K or 48K editor, does this make any difference to the symptoms? Also if possible can you use your RGB to SCART lead, at least until the fault/problem is found. On that subject, have you tried it on another display? Mark 48k mode makes no difference. Reverted to the RGB Scart lea...

Thanks both. In that case I may as well bundle it with my other centronics items.

I changed C45, C47, C32 and C3 - no difference. C41 seemed to be way out (25µF instead of 100) so thought that may be an issue - changed it and C23, no change. So I swapped out all the electrolytics and it's still got the same fault. There did used to be an occasional jumpiness of the pic, particula...

On offer here for £30 plus whatever postage costs, is a ZX81 RS232 interface. Manufacturer unknown (it's most probably a German made product - Weidner is on the PCB). It uses a National Semiconductor INS8255N chip to do the business. I cannot test it, but if it doesn't work I'll gladly take it back....

Hello. For sale here is a Memotek I/F Centronics Type Parallel Printer Interface plus what looks to be a home/kit made Centronics Interface of some kind. The Memotek device: is in excellent condition, gorgeous satin black metal with hardly a mark on it. The PCB inside also looks great. I don't have...

XavSnap wrote: ↑Tue Sep 22, 2020 7:06 pm Thanks to all contributors.

Pretty sure it was just me!

If anyone finds this thread, the Memotek I/F Centronics device and the other related add-on are still for sale.

Just about to email you the new version...

Let me know how that is.