Search found 802 matches

by Pr0f
Tue Apr 13, 2021 10:16 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

I think it is a fix for IORQGE - as that signal wasn't good from the ULA for some batches - but it's been some time since I've looked at the old boards
by Pr0f
Tue Apr 13, 2021 9:22 am
Forum: Hardware
Topic: 68K-MBC
Replies: 11
Views: 363

Re: 68K-MBC

I don't get the impression he was ever aiming to make a QL - just a minimal chip count 68K based computer - so goal achieved.
by Pr0f
Tue Apr 13, 2021 9:13 am
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

Testing the RAM chips is a good idea, but only tells you the RAM chips are working - if the issue lies on the board itself, then you won't see the fault with the RAM chip out of the spectrum.

Power supplies, glue logic, even just something stuck on the PCB could cause the issue.
by Pr0f
Mon Apr 12, 2021 9:37 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

If it's processing through the ROM then yes. What you really want is a plug in cartridge or similar that has it's own ROM in it - see if that gives a legible display. There is a good diagnostic ROM for the spectrum (well actually several), that will attempt to test cpu, memory, screen etc. This will...
by Pr0f
Mon Apr 12, 2021 9:14 pm
Forum: Hardware
Topic: 68K-MBC
Replies: 11
Views: 363

Re: 68K-MBC

I wonder why they went for a 68008 instead of a 68000 ? It was a screwup and mismanagement. Clive thought he could do QL with 64K RAM as a fot in the door and with substantially cheaper 68008. But when it came out, 68008 was _more_expensive than 68000. Also, 128K in QL used 16 DRAM chips. And as it...
by Pr0f
Mon Apr 12, 2021 9:11 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

That's very similar to the 'blackout screen' you get just before the prompt comes up. Suggests that it's having an issue somewhere, as you are not seeing a fully black screen.
by Pr0f
Mon Apr 12, 2021 3:41 pm
Forum: Hardware
Topic: 68K-MBC
Replies: 11
Views: 363

Re: 68K-MBC

Probably the ease of connecting an 8 bit bus rather than a 16bit one, and also the pic is emulating the boot rom forthe 68K part
by Pr0f
Fri Apr 09, 2021 8:07 am
Forum: Compatibles Corner
Topic: Q40/Q60 Roms
Replies: 26
Views: 2673

Re: Q40/Q60 Roms

I was looking at the Minipro - there is a Linux version of programming tool on GitHub - I think they may use a different method to define what chips it can program, as the Windows executable uses just a single DLL file with all that info in it. Still trying to get my head around what is actually in ...
by Pr0f
Thu Apr 08, 2021 1:57 pm
Forum: Compatibles Corner
Topic: Q40/Q60 Roms
Replies: 26
Views: 2673

Re: Q40/Q60 Roms

I think you can program those EPROMS, but you won't be able to erase them as they are probably the OTP type - if there is no Window on the package, then these are one time only programmable - so no erase - just program then verify. You may also have to turn off ID notification checkbox on the TL866 ...
by Pr0f
Thu Apr 08, 2021 1:48 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

The display pattern suggests the ULA is working well enough to provide video signals with correct sync, and the coloured squares show the attributes memory has some random data in it. Since this is the 48K model - the video is coming out of the lower 16K contended RAM. Are any of the major chips soc...