Search found 2414 matches

by 1024MAK
Fri Aug 23, 2019 5:12 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

I've put the full details of the DC/DC converter modification on my blog here ;)

Mark
by 1024MAK
Fri Aug 23, 2019 4:17 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

-4.3V is correct for that version of the DC/DC converter circuitry. If you want to get it closer to -5V, you have to perform the recommended Sinclair upgrade. I’ll post full details later. But here is a list of parts required: DC-DC CONVERTER MODIFICATION The following new materials are required: Di...
by 1024MAK
Fri Aug 23, 2019 1:50 pm
Forum: Software
Topic: HELP WANTED: ZX81 "lost" files
Replies: 1
Views: 92

HELP WANTED: ZX81 "lost" files

Over on the forum at Spectrum Computing a member is asking for some help with improving the archive of ZX81 software. Here is a copy of that post: Among the data imported from Martijn's WoS years ago, there were thousands of "lost" game files. These are files stored in the archive but not associated...
by 1024MAK
Fri Aug 23, 2019 11:06 am
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

Thanks so much for your time and expertise here, it's not the first time you've helped me with words of wisdom. I think I've done this right: On the input side of the regulator it measures 11.3v. The 12v leg on the RAMs are about 12.3v. Voltage measured on the anode side of D11 is -1.6v. Voltage me...
by 1024MAK
Wed Aug 21, 2019 11:31 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

Thanks for the photo. Your issue 3B board does not have the updated/later DC/DC converter circuitry. So it is possible that the unregulated +9V may be feeding through the coil to the +12V rail. If the voltage on the +9V input is slightly higher than the voltage on the +12V rail, then that is likely ...
by 1024MAK
Wed Aug 21, 2019 5:55 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

On the 4116 chips the +5v and +12v was fine, but the -5v showed a small (0.4+) voltage on all of them. My original Sinclair transformer puts out 14v (without load) so I'll also try a modern one that is actually 9v. Is it therefore likely that the TR4 and TR5 are dead? I just have a multimeter. If t...
by 1024MAK
Wed Aug 21, 2019 12:07 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

First, please test the supply voltages to the 4116 (or equivalent) DRAM chips, IC6 to IC13). Report your results here please. See this post for a pin-out. Although most of the circuitry runs off just the +5V rail, the 4116 DRAM actually runs off the +12V rail. But the 4116 also needs a -5V supply, p...
by 1024MAK
Tue Aug 20, 2019 6:47 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

Okay, I’ve watched the video. I would say that it looks like there is definitely a problem with the RAM.

Mark
by 1024MAK
Tue Aug 20, 2019 3:41 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

I’m mobile in a poor signal area, so can’t watch you video at the moment. With the exception of the ULA, and the 7805 voltage regulator, if any of chips are too hold to touch, then they should be treated as suspect. If TR4 or TR5 have been damaged due to an overload on the +12V or -5V lines, then th...
by 1024MAK
Tue Aug 20, 2019 3:26 pm
Forum: ZX Spectrum Lounge
Topic: Spectrum 48k Boot pattern
Replies: 21
Views: 331

Re: Spectrum 48k Boot pattern

If the -5V supply is not present, the ‘lower’ 4116 DRAM chips have a tendency to self destruct. So the first order of business is to sort out the DC/DC converter, TR4 & TR5.

Also the over voltage on the +5V line may have damaged some of the other chips.

More later...

Mark