Sinclair ZX80 / ZX81 / Z88 Forums

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

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.

There is one bit in lower ram broken.
This needs replacement. It's usually soldered in without socket.
I wonder why it still works
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

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?

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

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 9:26 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

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.

Hi Paul!

In effect, it gives 0...

Paul wrote: ↑Tue Jul 04, 2017 1:01 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.

That explains why your spectrum still runs.
So RAM is ok, the ULA might be damaged

Yes, and the only option I have is to "cannibalize" another Spectrum, isn't?

Paul wrote: ↑Tue Jul 04, 2017 1:30 pm That explains why your spectrum still runs.
So RAM is ok, the ULA might be damaged