Blank screen issue...

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rps
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Blank screen issue...

Post by rps » Tue Jun 12, 2018 7:50 pm

Hello,
I recently acquired a zX Spectrum + (plus) as a friend had a spare. I was told there was an issue with it however looking online, the only thing I could find was a suggestion that it could be an issue with the upper ram.

Powers on with black paper and grey surround. There is no text, cursor or spectrum text, nothing at all.

Just wondering if anyone knows what the fault may be before I start buying new chips etc and de soldering a board!

Thanks in advance!
Rps
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Ast A. Moore
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Re: Blank screen issue...

Post by Ast A. Moore » Tue Jun 12, 2018 8:28 pm

White border is (usually) a good sign. Ideally, I’d try to reset the CPU (rather than simply power-cycle the whole computer), and see if anything happened on the screen. Can you do that?

Oh, wait, it’s a Plus, you say, so it has a dedicated reset button. Press it briefly while looking at the screen. Describe what you see.
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

rps
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Re: Blank screen issue...

Post by rps » Tue Jun 12, 2018 9:09 pm

Thanks for the reply, do all the plus versions gave that? I thought it was just the plus 2 or plus 3? If so, where is that located as I definately see no buttons!

It is the one on this page... http://blog.tynemouthsoftware.co.uk/201 ... d.html?m=1
just to make sure we are talking about the same on.

Thanks
Rps
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Ast A. Moore
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Re: Blank screen issue...

Post by Ast A. Moore » Tue Jun 12, 2018 9:59 pm

By “Spectrum+” I mean the original 48K Spectrum in the hardshell case (as depicted in the link you posted). There were two distinct “versions” of the Plus: an upgrade (Sinclair sold the cases, and the owners of the original rubber-key Speccies could take the logic board out of the old case and put it in the new one), and factory-made Spectrums that came in this new case. The latter came with the reset button fitted on the left side of the case:
Image
Image
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

rps
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Re: Blank screen issue...

Post by rps » Wed Jun 13, 2018 6:50 am

Ah that! I completely forgot that was there when I originally looked over the unit. :roll:

I pressed the button and you can hear a change in the static noise briefly, then you get a split second where there are red vertical lines on the black paper.

Thank you
Amy
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Ast A. Moore
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Re: Blank screen issue...

Post by Ast A. Moore » Wed Jun 13, 2018 7:29 am

That’s also a good sign. Means that the RAM test runs, at least partially. The CPU and the ULA are likely okay. The issue might be with one or more of the RAM ICs. Whether it’s the lower or upper RAM depends on how long it takes for the RAM test sequence to complete. That’s more of a feel thing (although you can use an emulator to get the feel for it).

After the ROM completes the RAM test, it proceeds to set up some system variables and then clears the screen and prints the Sinclair Research copyright message. Since it fails to do so on your machine, it’s probably the lower RAM that’s faulty.
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

rps
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Re: Blank screen issue...

Post by rps » Wed Jun 13, 2018 8:19 am

Oh ok. The place I looked at suggested upper ram. So can I show you the link that shows where it says that? Just curious to know what you think of what they have written there?

Here is the link and I am looking at the 6th one down...
http://hardware.speccy.org/reparar-i.html

If it is the lower ram as you say, is there a way to test it or is it a case of just replacing it?

Thabks
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Ast A. Moore
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Re: Blank screen issue...

Post by Ast A. Moore » Wed Jun 13, 2018 12:11 pm

rps wrote:
Wed Jun 13, 2018 8:19 am
Oh ok. The place I looked at suggested upper ram. So can I show you the link that shows where it says that? Just curious to know what you think of what they have written there?
Perhaps it makes more sense, since the video is working fine. Upper RAM ICs are cheaper and easier to source, anyway.

Finding the faulty one (ones) is kind of tedious, and requires a digital oscilloscope. What you could do instead, is cut the +5V legs of each upper RAM IC and bend the stubs away to make sure they don’t make contact with the other halves. If the problem is indeed in one of the upper RAM ICs, the Speccy should boot up normally and work as a 16K machine.

Then it’ll be easier to replace the whole lot.
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.


rps
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Re: Blank screen issue...

Post by rps » Thu Jun 14, 2018 10:52 am

Hi guys, thanks for all the info and all the links. Think I will have to wait til the weekend to loook over everything.
Then I’ll be back on here and let you know how it goes!
FINGERS CROSSED :)

Thanks
Rps
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