Search found 641 matches

by bwinkel67
Tue Apr 13, 2021 10:15 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

Hi, I have repaired about 8 Spectrums during the last 20 years, not so many and I am far away from being an expert: Stephan One question, that transistor on the CPU, is it needed? I only see it with 48K issue 2 boards in online pics. Mine is only 16K (in fact, neither voltage jumper has ever been s...
by bwinkel67
Tue Apr 13, 2021 10:13 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

So I've read for issue 2 boards that you have a 10% tolerance with the -5/12/5 volts and I'm showing 4.69/11.73/4.85 which are within that. I've also read that specifically for issue 2 that -4 volts is sufficient. Every video I've seen on repairs of Spectrums has shown a slight drop at the 5 volts c...
by bwinkel67
Tue Apr 13, 2021 1:46 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

I double checked the RAM today...replaced the RAM with other working RAM and the same screen (nothing changed). I've looked closely at the PCB so it's not anything obvious. There are two 74LSxxx logic chips next to the ULA that will likely be my next focus. I'm assuming the ROM, ULA and Z80 are work...
by bwinkel67
Tue Apr 13, 2021 12:52 am
Forum: Hardware
Topic: 68K-MBC
Replies: 11
Views: 363

Re: 68K-MBC

So he basically confirmed this. They would have got good price with 68000 but everlasting Poker Genius chose 68008 to save literally few pounds. So David Karlin notes that the 68008 was close to 40% cheaper than the 68000 in mass quantities and he was there when those contracts with Motorola were m...
by bwinkel67
Mon Apr 12, 2021 10:55 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

Thank you...I will have to re-check the RAM. I popped each chip into (a single test socket of) the ZX81 RAM pack and booted the ZX81 to the K cursor but perhaps that doesn't thoroughly test the memory.
by bwinkel67
Mon Apr 12, 2021 10:31 pm
Forum: Hardware
Topic: 68K-MBC
Replies: 11
Views: 363

Re: 68K-MBC

So no way to verify this: https://retrocomputing.stackexchange.com/questions/15570/were-there-really-any-cost-savings-in-sinclair-ql-because-of-it-being-8-bit-desi But the top replier (posted July 12, 2020) claims to be David Karlin: Yes, there was a significant cost saving. For a start, Motorola ch...
by bwinkel67
Mon Apr 12, 2021 9:29 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

Pr0f wrote: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.


Does this suggest that the ROM is working? I did test the RAM so that is good. The ULA seems to be OK.
by bwinkel67
Mon Apr 12, 2021 8:24 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

Some progress. I replaced the Z80 and now I get this. So this seems to be part of the startup sequence where the ROM is checking how much RAM you have (not checking if the RAM is ok) but then doesn't continue to clear the screen and put up the "(c) 1982 Sinclair Research, Ltd" and cursor. ...
by bwinkel67
Fri Apr 09, 2021 7:32 am
Forum: General QL Chat
Topic: The little revenge of the microdrive?
Replies: 10
Views: 502

Re: The little revenge of the microdrive?

My favorite is when you are accessing a large file and the tape moves forward, stops, then moves forward again, stops, and so on with little pause between stops. Like when you copy a long program to console it does that. It partly reinforces that it's a good microdrive and it's so satisfying.
by bwinkel67
Thu Apr 08, 2021 8:10 pm
Forum: Hardware
Topic: Question about a non-working ZX Spectrum
Replies: 19
Views: 738

Re: Question about a non-working ZX Spectrum

Thank you for all the feedback. I'll try and answer all the questions: ⋅ When I reset the computer (I do have a switch on the power supply) it just gives a similar picture, changing random colored squares slightly ⋅ I've been told issue 2 boards are better with regulated supplies...