Search found 122 matches

by mcarlson_sb
Wed Sep 09, 2020 5:56 am
Forum: WANTED
Topic: Wanted : a ZX81 I/O board extension
Replies: 6
Views: 5430

Re: Wanted : a ZX81 I/O board extension

Great proposal to share the Gerber file I haven't yet ordered and built the v2 extension board. And I found an error with the v1 boards I've been using (flipped A and B side pins) These work fine as dev boards for prototyping. But, I need to fix it before I can use them to plug a card in. Once I've...
by mcarlson_sb
Mon Sep 07, 2020 11:14 pm
Forum: WANTED
Topic: Wanted : a ZX81 I/O board extension
Replies: 6
Views: 5430

Re: Wanted : a ZX81 I/O board extension

Are you looking for old only (like the Maplin kits) or will new be okay also? Do you have specific interface needs? Are you looking for pre-made or is kit okay? I designed some quick extensions and can share the Gerber files if you want to order new PCBs. But you'd have to put then together yourself.
by mcarlson_sb
Sun Sep 06, 2020 7:04 am
Forum: Hardware
Topic: This weekends projects
Replies: 53
Views: 23077

Re: This weekends projects

I finished assembly of the LM386 version
Works great. It's nice to have the reset switch for the SP0256-AL2.
And I can see the volume control being useful in some situations.

The Gerber files for both can be found here
https://github.com/mcarlson-sb/talk-again
20200905_210005.jpg
by mcarlson_sb
Sat Sep 05, 2020 4:11 am
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

Okay. It turns out the keyboard membrane may just be bad. I removed the keyboard and used a jumper wire to "type" by connect between the two headers. Once I did this I got the inverted K and was even able to write a little program (PRINT 1 <ENTER>) So, I know the headers are good, the Z80 is good, t...
by mcarlson_sb
Sat Sep 05, 2020 1:31 am
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

Sometimes I also get a black square then this
20200904_162602.jpg
So, I really am guessing memory.
Typing at this point seems to do nothing.
by mcarlson_sb
Sat Sep 05, 2020 1:10 am
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

I think I've got some memory issues - but I've got signal!
20200904_160856.jpg
by mcarlson_sb
Sat Sep 05, 2020 1:01 am
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

:D :D :D

This is the signal going into the RF modulator
NewFile2.jpg
Which (to my untrained eye) looks a bit like a video signal.
by mcarlson_sb
Sat Sep 05, 2020 12:33 am
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

It looks like I got super lucky 4116 chips show +4.88v, - 5.17, 11.88 I'm getting a good 4mhz oscillation at the ULA TR 1 - base shows a signal TR 2 - base did not show a signal TR 2 - collector shows a signal TR 2 - emitter shows a signal I live in NTSC land. My TFT display auto detected a PAL sign...
by mcarlson_sb
Fri Sep 04, 2020 11:39 pm
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

The quickest way to kill a ZX Spectrum, is to apply a DC voltage to the power input with the incorrect polarity, or apply a AC voltage. The correct polarity for the 2.1mm/5.5mm mini power connector is: inside is negative and the outside is positive. :shock: :shock: :shock: Pretty sure I got that ba...
by mcarlson_sb
Fri Sep 04, 2020 4:57 pm
Forum: ZX Spectrum Lounge
Topic: It happened..
Replies: 12
Views: 6826

Re: It happened..

Issue 4S means it was made by Samsung I believe. It also means the keyboard membrane may even still be working! Some further info here http://blog.tynemouthsoftware.co.uk/2018/06/zx-spectrum-mystery-repair.html?m=1 Has it been recapped? Its unusual to be able to see all of the polarity and rating m...