Spectrum 48k Boot pattern

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
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Erm
Posts: 37
Joined: Thu Jun 20, 2019 7:07 pm

Re: Spectrum 48k Boot pattern

Post by Erm » Sat Aug 24, 2019 1:02 pm

I really feel I've learnt something here, about the various voltages on the Spectrum board and where they come from etc.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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Erm
Posts: 37
Joined: Thu Jun 20, 2019 7:07 pm

Re: Spectrum 48k Boot pattern

Post by Erm » Sat Aug 24, 2019 8:08 pm

I got my super-duper de-soldering solution and was able to remove the 8 lower RAM chips. Lifted 3 traces but was able to sort those in a neat fashion. Now it all looks good.

What sort of screen should I be getting with no lower RAM installed? With empty sockets it's exactly the same as before with the patterns and the almost always red border (rarely the border can sometimes be green and sometimes black).

When I insert random RAM chips in random places it affects the patterns and border colours a bit.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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Erm
Posts: 37
Joined: Thu Jun 20, 2019 7:07 pm

Re: Spectrum 48k Boot pattern

Post by Erm » Mon Aug 26, 2019 9:19 pm

I got new 4116 chips, inserted them all and the screen was still the same. So I tried 8 old but known good chips from the 'spare' Issue 2 (which is now also sorted, see below) and the patterns were very different.

So, because it was already socketed, I tried swapping the 6C001E ULA for the 5C112E that was in the Issue 2, and boom, 1982 Copyright message, all seems well now!!

On another positive note, with the non working Issue 2 I was able to diagnose TR4 as faulty. Replaced it and bam, everything now fine with that one, too!

So I now have 2 working Speccies, one with 16k and never upgraded, and a later one with 48k.

On the 16K Issue 2 the screen and the colours particularly are not great, even after having a play with those 2 variable resistors. Text seems to pulsate and isn't very sharp (or entirely black) either. Is that most likely to be the electrolytic caps?

Am very pleased though.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

Lardo Boffin
Posts: 1015
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum 48k Boot pattern

Post by Lardo Boffin » Mon Aug 26, 2019 9:23 pm

Those two adjustor pots are a nightmare. I have an issue two and even when I get them right once I switch off and back on again they drift a little.
Personally I always change the electrolytic caps in these.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

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Erm
Posts: 37
Joined: Thu Jun 20, 2019 7:07 pm

Re: Spectrum 48k Boot pattern

Post by Erm » Mon Aug 26, 2019 9:51 pm

I'll certainly do that. During fault finding I did change a couple here and there, but only had radial and not only does it look awful, it's also a bit risky with them potentially touching things they shouldn't!
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

Lardo Boffin
Posts: 1015
Joined: Sat Nov 26, 2016 2:42 am

Re: Spectrum 48k Boot pattern

Post by Lardo Boffin » Tue Aug 27, 2019 12:12 am

You can buy complete cap kits fairly cheaply (for example https://www.retroleum.co.uk/zx-spectrum-capacitors). Obviously you can get it cheaper over all if you bulk buy but if you are only doing a couple of Spectrums you may not want hundreds of caps lying around.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Various Spectrum 48ks plus a DIVMMC future and SPECTRA

User avatar
Erm
Posts: 37
Joined: Thu Jun 20, 2019 7:07 pm

Re: Spectrum 48k Boot pattern

Post by Erm » Tue Aug 27, 2019 12:12 pm

Yes, I wish I'd thought about that when I made the last fairly large order.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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