Issue 6A weird picture

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driverpt
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Joined: Wed Aug 28, 2019 11:02 pm

Issue 6A weird picture

Post by driverpt » Thu Aug 29, 2019 1:29 am

Hey guys,

I have a ZX Spectrum recapped, composite modded, TR4, TR5 and Diodes replaced and I'm getting this picture with no Lower RAM installed.

Anyone ever had this kind of issue?

Thanks
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IMG_20190622_162427.jpg

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Issue 6A weird picture

Post by 1024MAK » Thu Aug 29, 2019 6:52 am

Hello and welcome to our forum.

It is hard to tell from your photo, is there a border around the central coloured area?

This video shows what should happen for a normally working machine.

With no lower RAM, the CPU should still be able to execute the start of the ROM code after power up or reset, and one of the first things it does is to set the border to white.

At a guess, I would say that the ULA could well be faulty.

But first, do you have a multimeter, if yes, what voltages do you get on the +5V, the +12V, the -5V (all on either the edge-connector or the pins of the 4116 (or equivalent) ‘lower’ DRAM chips (see the link to pin-outs in my sig below). And what voltage do you have on the (nominal) +9V input?

Also which issue board is it?

Mark

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Paul
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Re: Issue 6A weird picture

Post by Paul » Thu Aug 29, 2019 9:01 am

Good morning Mark, I guess it's an issue 6A (from the subject)
In theory, there is no difference between theory and practice. But, in practice, there is.

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Issue 6A weird picture

Post by 1024MAK » Thu Aug 29, 2019 10:57 am

Gahhh!!! Can’t see the wood for the trees :lol: Thanks Paul :D

So being an issue 6A, at least it has the latest version of the DC/DC converter circuitry.

Mark

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