Spectrum+ 48k repair

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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1024MAK
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Re: Spectrum+ 48k repair

Post by 1024MAK »

Slauri wrote: Sat Feb 15, 2020 4:24 pm
Slauri wrote: Fri Feb 14, 2020 6:15 pm Hi everyone, i got 2,98 volts on the pin 1 of the lower ram. The other voltages were good.
Yestreday i measured the -5v rail the voltage was much lower.
Strange :shock:
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1024MAK
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Re: Spectrum+ 48k repair

Post by 1024MAK »

@Slauri
Can you please post a photo of your Spectrum board as it is now.

Mark
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Re: Spectrum+ 48k repair

Post by Slauri »

Image
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Slauri
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Re: Spectrum+ 48k repair

Post by Slauri »

Everything I have replaced:
1)electrolytic capacitors
2)the entire lower ram
3)zilog z80 cpu
Slauri
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Re: Spectrum+ 48k repair

Post by Slauri »

I don't know what to do.
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1024MAK
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Re: Spectrum+ 48k repair

Post by 1024MAK »

Can you please take a close up photo, under good light, of the underside area of the board where the 4116 DRAM chips are.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
Looking forward to summer later in the year.
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Re: Spectrum+ 48k repair

Post by Slauri »

Image
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Ast A. Moore
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Re: Spectrum+ 48k repair

Post by Ast A. Moore »

I’ve enhanced your picture and marked a few areas that I suspect might be solder bridges/shorts:

Image

Perhaps Mark will be able to see more. I’d remove the lower-RAM board and inspect the traces on the logic board underneath it.
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Re: Spectrum+ 48k repair

Post by Slauri »

I've cleaned the board multiple times with alcohol. Those bridges weren't there before. Maybe they have come from my workdesk? I have not cleaned it for a while. Some of those may look like bridges but they are just reflections of the soldering mask that has melted away due to my bad soldering skills.
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