Sinclair ZX80 / ZX81 / Z88 Forums

I would try with 70% alcohol, but this is not the only wheel to degrease - don't forget the other one on the motor shaft.

I have Watford SPDOS Disk Interface which requires system disk. Unfortunately, I do not have it :( . I have created 27C64 -> 27C16 interface and fried KDOS on 27C64 hoping that support logic is the same, but it does not work. If I could get the Kempston schematic I would be able to compare them and ...

Hi, thanks for info ! I have tried that but in vain. So I think the article is rather related to Kempston Disk Interface than to Watford because KDI has 8k ROM which contains all required SW. If you compare those two (there is a video clip https://www.youtube.com/watch?v=-2v_zSRfens on Youtube where...

Hi, I have an interesting peace of hardware - Watford SPDOS. It does not show any life signs unless a drive is connected but then it requires a boot disk to be inserted :( I have not been able to find it - does anybody have this device and the related boot disk ? Eventually, there is one more possib...

I investigated a little bit... Well, some of 4164 chips indeed have 256x256 type of matrix thus need 8-bit refresh. However, as you said, TMS4164 is organized as 128x256 in two banks where A7 (at RAS) controls which bank is used (0/1, lower/higher). OKI3764 works in a bit different way - it is organ...

Hi, so I have replaced 74LS14 and 74LS00 IC's but with no success. :( Then I checked are there any shorts between pins and are there proper connections between address and data lines and edge connector. Everything OK. I have no dedicated test gear for DRAMs, only a few 48k Spectrums and Sinclair's t...

Hi, I have one of this in mint condition, boxed, with manual, no scratches - real beauty :mrgreen: Of course, something must be wrong - it does not work, produces blank screen when attached to ZX 81. I tried it on three of them so it really does not work. 20211125_222341.jpg So, I have replaced both...

I have tried this as well but in vain.
Anyways, after I had replaced both 74157's, it has started to work.

The most weird thing in this case is defective chips behavior - they are usually either completely functional or completely malfunctional.

Hi, let me describe my experience with this beauty. In this case, there was no boot issue but random characters had started to pop-up at random places on the screen after several seconds. Usually it ended with a blank screen or black stripes. But, before crash, I was able to execute a few lines or c...