It happened..

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
mcarlson_sb
Posts: 122
Joined: Wed Apr 08, 2020 4:48 am
Location: San Francisco

Re: It happened..

Post by mcarlson_sb »

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.
mcarlson_sb
Posts: 122
Joined: Wed Apr 08, 2020 4:48 am
Location: San Francisco

Re: It happened..

Post by mcarlson_sb »

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, the ULA is good, and the ROM is good.

One thing that worries me is that the leads in the keyboard membrane look scorched.
The tips that connect to the headers are black, and part of the wires look annealed
20200904_190744.jpg
20200904_190815.jpg
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: It happened..

Post by Lardo Boffin »

I have seen that effect in keyboard membranes a few times in otherwise fine computers.

From ZX81s:

01D4EF3E-BA9F-4A3C-B871-F91768505461.jpeg
281B5F0E-3C27-42B8-9736-9C2C7DAB9E79.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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