Blank screen issue...

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
rps
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Re: Blank screen issue...

Post by rps » Tue Jun 19, 2018 1:39 pm

Here is the cpu closer. In real life it all looks original to me.

If you want a better photo, I can try get one for you?

Thanks

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rps
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Re: Blank screen issue...

Post by rps » Tue Jun 19, 2018 1:49 pm

Sent the wrong photo!!!

Image

Image

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

Post by Ast A. Moore » Tue Jun 19, 2018 2:27 pm

Yes, looks legit.

I should have asked this sooner, but are all the voltages within range? (They likely are, but still.)
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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 19, 2018 2:58 pm

Erm, I have no idea about that, sorry can’t answer that question.

My friend if bringing my volt meter back tonight so will that help with anything?

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

Post by Ast A. Moore » Tue Jun 19, 2018 3:05 pm

rps wrote:
Tue Jun 19, 2018 2:58 pm
My friend if bringing my volt meter back tonight so will that help with anything?
Oh, absolutely. ;)
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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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Joined: Tue Jun 12, 2018 7:39 pm

Re: Blank screen issue...

Post by rps » Tue Jun 19, 2018 7:06 pm

Hi,
Is there something in particular that I can check, such as chip and what pins?

I am guessing that is a huge question?
thabks
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Ast A. Moore
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Re: Blank screen issue...

Post by Ast A. Moore » Tue Jun 19, 2018 7:28 pm

rps wrote:
Tue Jun 19, 2018 7:06 pm
Hi,
Is there something in particular that I can check, such as chip and what pins?
I’d start with the lower RAM ICs (IC6–13). These take three different voltages: +5V, –5V, and +12V. The ground is on pin 16, pin 1 is –5V, pin 9 is +5V, and pin 8 is +12V. Just be careful not to short anything.

Then check the voltages on the upper RAM (IC15–IC22). These just use the +5V rail. Pin 16 is ground, pin 8 is +5V.

IC25 and 26 have the same power pin arrangement.

Next, check the gates IC23 and IC24: pin 7 is ground, pin 14 is +5V.

This is just to make sure each IC is getting power.

Post your results here.
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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 19, 2018 8:50 pm

On the lower ram they come in about half what they should be...
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Ast A. Moore
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Re: Blank screen issue...

Post by Ast A. Moore » Tue Jun 19, 2018 8:59 pm

rps wrote:
Tue Jun 19, 2018 8:50 pm
On the lower ram they come in about half what they should be...
:shock: Really? Are you sure? Even the +5V rail? How about the rest of the ICs I mentioned, then? Surely, the +5V rail must be close to spec; otherwise the machine wouldn’t function at all.
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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.

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

Post by Ast A. Moore » Tue Jun 19, 2018 9:30 pm

Test the voltage on the emitter of TR5 to ground (any ground). The emitter should be pin 1 (leftmost pin, looking from the flat side).
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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.

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