Search found 2010 matches

by 1024MAK
Sat Jul 21, 2018 2:27 pm
Forum: Hardware
Topic: Yet another repair
Replies: 18
Views: 358

Re: Yet another repair

IMG_7517.PNG
by 1024MAK
Thu Jul 12, 2018 9:16 pm
Forum: Hardware
Topic: ZX81 Repair (No video for starters!)
Replies: 7
Views: 314

Re: ZX81 Repair (No video for starters!)

It's the ULA. I noticed that IOREQ wasn't pulsing, swapped out to Andys ULA and hey presto pulsing. Looked at the video signal in more detail and there was indeed modulation (very noisy signal), held a composite cable against the modulator case and signal and whoosh a "K" on the TV. Bummer that you...
by 1024MAK
Thu Jul 12, 2018 9:14 pm
Forum: Hardware
Topic: ZX81 Repair (No video for starters!)
Replies: 7
Views: 314

Re: ZX81 Repair (No video for starters!)

Doesn’t the ULA produce the modulation independant of the CPU? (I.e it halts the CPU and does a read of the ram). No, it's more complicated than that. HALT is used for synchronisation. Read the information available here ;) For a more in depth explanation of the video system, read this ;) Mark
by 1024MAK
Thu Jul 12, 2018 8:54 pm
Forum: Welcome Area
Topic: Hello
Replies: 4
Views: 273

Re: Hello

Yep, here, on StarDot, on World of Spectrum forums, Spectrum Computing forums, QL Forum, Atari-Forum, Memorum and a some others that I visit less often.

Mark
by 1024MAK
Wed Jul 11, 2018 11:43 pm
Forum: Hardware
Topic: ZX81 Repair (No video for starters!)
Replies: 7
Views: 314

Re: ZX81 Repair (No video for starters!)

The video generation is done by the Z80 CPU and the ULA working together. If the CPU is not running, for whatever reason, the ULA will not and cannot produce a valid video signal. So we start with testing the Z80 pins with either a logic probe, a logic analyser or a oscilloscope. What are /RESET, /M...
by 1024MAK
Wed Jul 11, 2018 11:36 pm
Forum: Welcome Area
Topic: Hello
Replies: 4
Views: 273

Re: Hello

Hello Ade

Welcome to our forum :D

Mark
by 1024MAK
Wed Jul 11, 2018 11:33 pm
Forum: Hardware
Topic: ZX spectrum 48k repair
Replies: 28
Views: 1091

Re: ZX spectrum 48k repair

Well done :D

Mark
by 1024MAK
Tue Jul 10, 2018 10:50 pm
Forum: Hardware
Topic: Half dead 8300
Replies: 3
Views: 218

Re: Half dead 8300

Have you tested the supply voltage to the ULA? And is the 5V supply okay as well?

I'm mobile at the moment, but will have a look at the picture later. Meanwhile, incorrect characters on screen can be due to address or dataline faults (including memory chips).

Mark
by 1024MAK
Thu Jul 05, 2018 7:33 pm
Forum: Hardware
Topic: ZX81 rebuild
Replies: 124
Views: 7667

Re: ZX81 rebuild

Image
by 1024MAK
Wed Jul 04, 2018 5:25 pm
Forum: Welcome Area
Topic: Wandering across
Replies: 5
Views: 274

Re: Wandering across

Hello Alan Welcome to our forum :D Have fun :D If you do want help, please do ask. Simon would no doubt love extra Zeddy software to add to his site ;) World of Spectrum also hosts Zeddy software New site (under construction), existing site . Spectrum Computing also supports ZX81 software. Mark