Spectrum+ 48k repair

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
Slauri
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Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 11:54 am

My old spectrum+ 48k won't work. I have replaced the electrolytic capacitors, and it didn't fix it. Here's a video of what it does when i switch it on:



Help, please.
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Ast A. Moore
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Re: Spectrum+ 48k repair

Post by Ast A. Moore » Sun Sep 22, 2019 12:28 pm

Does the image change when you press the reset button? What happens if you press and hold it?
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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.

Slauri
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Re: Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 12:42 pm

Nothing happens
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Slauri
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Re: Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 1:01 pm

And the manufacturer of the power supply is unknown.
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Ast A. Moore
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Re: Spectrum+ 48k repair

Post by Ast A. Moore » Sun Sep 22, 2019 1:08 pm

First, check the voltages on the RAM, ROM, and the CPU.

It’s likely the CPU or (less likely) the ROM that is fried. If you have an oscilloscope, test the clock on the ULA (Pin 39) and the CPU (Pin 6). Check TR3 for the presence of the clock pulse.

The usual procedures (i.e. checking for broken traces, solder splashes, etc.) also apply, naturally. Was the machine working before recapping?
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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.

Slauri
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Re: Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 1:27 pm

I don't have an oscilloscope, and it didn't work before the recapping, but the video quality is much better after recap.
I have a multimeter.
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Ast A. Moore
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Re: Spectrum+ 48k repair

Post by Ast A. Moore » Sun Sep 22, 2019 1:42 pm

Slauri wrote:
Sun Sep 22, 2019 1:27 pm
I don't have an oscilloscope . . .
I have a multimeter.
Proceed to checking the voltages as I stated above. On the Z80, Pin 29 is ground and Pin 11 is Vcc. On the ROM, it’s pins 14 and 28, respectively.

The lower RAM chips (ICs 6–13) have three voltages: –5V on Pin 1, +5V on Pin 9, and +12V on Pin 8. Pin 16 is the ground.

Incidentally, what’s your logic board revision? Is it an Issue 4B?
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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.

Slauri
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Re: Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 1:43 pm

In my opinion, it looks like lower ram fault. But i'm still a beginner in these things.
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Slauri
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Re: Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 1:44 pm

Issue 2
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Slauri
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Re: Spectrum+ 48k repair

Post by Slauri » Sun Sep 22, 2019 1:45 pm

And btw i should get a new power supply for this thing
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