Search found 11 matches

by citizenfish
Mon Jun 21, 2021 10:01 pm
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 9
Views: 1017

Re: ZX81 Troubleshooting

Resurrecting this

Pin 6 -looks OK

Image

Pin 16 - pulsing ?

Image

Pin 17 -maybe dodgy?

Image
by citizenfish
Fri Jun 11, 2021 9:50 pm
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 9
Views: 1017

Re: ZX81 Troubleshooting

I’m away on holiday right now.

But I need to redo my tests with my new Hantek scope and report back. The cheap handheld I was using may not be giving decent results.

None of the chips are socketed which is a pain
by citizenfish
Wed May 12, 2021 4:56 pm
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 9
Views: 1017

Re: ZX81 Troubleshooting

Voltage reg outputting 4.9V So far all of the Z80 test pass with the scope showing exactly what you described There is activity on A14/15 and A0-13 D2 and D6 are not very active only tiny blips on the scope. The other data lines show activity. The SRAM is labelled MOSTEK MK4118N-4 8037 I tried with ...
by citizenfish
Wed May 12, 2021 9:17 am
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 9
Views: 1017

Re: ZX81 Troubleshooting

Thanks Mark do we know each other? That’s exactly what I needed to get me started and you are right I had my chips mixed up .. just like my cooking. I’ll tinker further and answer your questions in due course. I’m teaching myself electronics as part of this journey including learning how to use a sc...
by citizenfish
Tue May 11, 2021 2:52 pm
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 9
Views: 1017

Re: ZX81 Troubleshooting

One thing is that all chips are heating up apart from IC2 which I think is the ROM?
by citizenfish
Tue May 11, 2021 2:49 pm
Forum: Hardware
Topic: ZX81 Troubleshooting
Replies: 9
Views: 1017

ZX81 Troubleshooting

I've got a ZX81 Issue one board with composite mod that is just giving a white screen without a cursor. I've got access to a scope and multimeter where should I start looking? This board appears to be untampered with, the Rom version is 8111. If it doesn't exist already I'd like to use this as the s...
by citizenfish
Fri Apr 16, 2021 11:07 am
Forum: Hardware
Topic: Didatik M
Replies: 0
Views: 585

Didatik M

As part of my new found addiction to Sinclair retros and copies I've bought a Didatik M spectrum clone I'm looking to hook it up to a monitor and notice it has the monitor ports on the back. I'm hoping these are RGB. Does anyone know where I can find any schematics or technical info on this machine....
by citizenfish
Mon Apr 12, 2021 9:52 am
Forum: Hardware
Topic: ZX81: What's going on with this processor mod?
Replies: 9
Views: 837

Re: ZX81: What's going on with this processor mod?

1024MAK wrote: Sun Apr 11, 2021 9:13 pm Getting or making a logic probe is worthwhile.

Do you have a digital multimeter?

It’s worth checking any socketed chips are firmly pressed into their sockets.

Mark
I do.

There were a few dry joints which I've soldered and am going to work through it component by component.
by citizenfish
Sun Apr 11, 2021 8:39 pm
Forum: Hardware
Topic: ZX81: What's going on with this processor mod?
Replies: 9
Views: 837

Re: ZX81: What's going on with this processor mod?

I’m not selling! This is part of my own personal collection. Now how do I get it working, might be time to invest in an oscilloscope.
by citizenfish
Sun Apr 11, 2021 8:01 pm
Forum: Hardware
Topic: ZX81: What's going on with this processor mod?
Replies: 9
Views: 837

Re: ZX81: What's going on with this processor mod?

Thanks does that make it more collectible?