Zx Spectrum 48k vertical black lines on boot problem

AmintaSpectrum
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Zx Spectrum 48k vertical black lines on boot problem

Post by AmintaSpectrum » Mon Jul 03, 2017 11:32 pm

Hi all!

I've just bought a Zx Spectrum 48k one eBay: all it was working goof but I made a mistake: I've extracted the Kempston interface before plugging out the power. I don't know if this is the cause, but now when I power up the machine I get these vertical black lines and I have severe graphical issues in games too...

Any hint?

Many thanks in advance,

Davide


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Lardo Boffin
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Re: Zx Spectrum 48k vertical black lines on boot problem

Post by Lardo Boffin » Tue Jul 04, 2017 12:13 am

Easily done but unplugging something when it is switched on can cause damage.

If no one in this site can suggest a course of action then Mutant Caterpillar Games is a good place to get it repaired.
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Paul
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Re: Zx Spectrum 48k vertical black lines on boot problem

Post by Paul » Tue Jul 04, 2017 5:36 am

There is one bit in lower ram broken.
This needs replacement. It's usually soldered in without socket.
I wonder why it still works :shock:
There are diagnostic cartridges around and the affordable dandanatore mini addon offers such function as well.
But that is only to know which ram is faulty.

Can you solder?
If not - Mutant caterpillar is a good possibility.

Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

AmintaSpectrum
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Re: Zx Spectrum 48k vertical black lines on boot problem

Post by AmintaSpectrum » Tue Jul 04, 2017 8:03 am

Hi Paul!

Me too I believed the Ram was faulty, but I made the Ram test with

PRINT PEEK 23732 + PEEK 23733 * 256

and I got 65535, the correct value.

I can soldier and usually I do.

Maybe the ULA is the culript?

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Paul
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Re: Zx Spectrum 48k vertical black lines on boot problem

Post by Paul » Tue Jul 04, 2017 8:26 am

That ramtest only shows that 48k are installed. Not much use.
More interesting would be what a peek into video ram returns
Maybe the first byte of video ram?
On a white page this should be 0 I guess but I stand corrected.
Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

AmintaSpectrum
Posts: 9
Joined: Mon Jul 03, 2017 11:12 pm

Re: Zx Spectrum 48k vertical black lines on boot problem

Post by AmintaSpectrum » Tue Jul 04, 2017 11:28 am

Thanks Paul! I don't know how to peek the first byte of video ram, but according to http://www.worldofspectrum.org/Spectrum ... uide/#fram the Ram is faulty only if you got a number below the total of the Ram installed....

Or am I wrong?
Paul wrote:
Tue Jul 04, 2017 8:26 am
That ramtest only shows that 48k are installed. Not much use.
More interesting would be what a peek into video ram returns
Maybe the first byte of video ram?
On a white page this should be 0 I guess but I stand corrected.
Kind regards Paul

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Paul
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Location: Germanys west end

Re: Zx Spectrum 48k vertical black lines on boot problem

Post by Paul » Tue Jul 04, 2017 12:01 pm

The sinclair ram test is only to see wether 16K or 48 K are installed. It doesn't really look for faulty ram im afraid.
Screen memory in a Spectrum starts at 16384.
so with a blank Screen the Data should be zero.
10 CLS
20 Print PEEK(16384)

Should give 0.
In theory, there is no difference between theory and practice. But, in practice, there is.

AmintaSpectrum
Posts: 9
Joined: Mon Jul 03, 2017 11:12 pm

Re: Zx Spectrum 48k vertical black lines on boot problem

Post by AmintaSpectrum » Tue Jul 04, 2017 12:15 pm

Hi Paul!

In effect, it gives 0...

Image
Paul wrote:
Tue Jul 04, 2017 12:01 pm
The sinclair ram test is only to see wether 16K or 48 K are installed. It doesn't really look for faulty ram im afraid.
Screen memory in a Spectrum starts at 16384.
so with a blank Screen the Data should be zero.
10 CLS
20 Print PEEK(16384)

Should give 0.

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Paul
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Location: Germanys west end

Re: Zx Spectrum 48k vertical black lines on boot problem

Post by Paul » Tue Jul 04, 2017 12:30 pm

That explains why your spectrum still runs.
So RAM is ok, the ULA might be damaged :(
In theory, there is no difference between theory and practice. But, in practice, there is.

AmintaSpectrum
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Joined: Mon Jul 03, 2017 11:12 pm

Re: Zx Spectrum 48k vertical black lines on boot problem

Post by AmintaSpectrum » Tue Jul 04, 2017 12:34 pm

Yes, and the only option I have is to "cannibalize" another Spectrum, isn't?
Paul wrote:
Tue Jul 04, 2017 12:30 pm
That explains why your spectrum still runs.
So RAM is ok, the ULA might be damaged :(

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