Have I killed my ZX Spectrum?

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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flaviosr
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Have I killed my ZX Spectrum?

Post by flaviosr » Sun Aug 12, 2018 5:56 pm

Ok, do not insult me!!! I have already done the job by myself (many times)...

The story...
0. today I tested the new (old) ZX printer and... and I made the big big big mess... :(
1. first of all I connected the printer to the Spectrum... turned on! :( from now on I am going to hate USB...
2. I noticed the stupid thing and I immediately turned off the Spectrum, connecting the printer with the Spectrum off... but the computer turned on in a bad way...
3. I looked more carefully AND I noticed there wasn't the small plastic part to push the connector rightly aligned to the port (obviously this issue was making damage even at point 1);
4. I put a small plastic part and the Spectrum turned on the right way BUT... it is not working!

I made two tries (both with bad results):
° if I type J (LOAD) it's ok... when I type the two " on the screen strange chars appears and when I press ENTER the Spectrum resets (or simply hangs with strange chars all around the screen);
° If I try to write a basic line it's ok, but when I press ENTER the Spectrum resets (always).

Insults apart... do you think it's serious? :(

Please forgive me...

One more note: the ZX printer is safe and working.
One last note: motherboard ISSUE 3.

Thank you
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Ast A. Moore
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Re: Have I killed my ZX Spectrum?

Post by Ast A. Moore » Sun Aug 12, 2018 7:43 pm

The good news is that the Z80 and the ULA are likely okay. The not-so-good—but not particularly bad—news is that you’ve probably fried a RAM chip or two (or more).

I’d check all the power rails (although the +5V rail is likely to be working properly) before looking into replacing the RAM ICs. (It’s probably the lower RAM that you’ve killed.)

Don’t beat yourself up too hard. I’d say you dodged a bullet.
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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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1024MAK
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Re: Have I killed my ZX Spectrum?

Post by 1024MAK » Mon Aug 13, 2018 11:50 am

Yeah, the first thing is: don't leave it powered for more than 20 to 30 seconds, until you know that the -5V supply is okay, so...
Using a multimeter, either test the -5V on the edge connector, or on the 4116 (or equivalent) DRAM chips.

I recently wrote a bit about testing the voltages here.

If the -5V is missing / or wrong, or the +12V is missing or low, renew TR4 and TR5 transistors.

If all the supply voltages are okay, it's likely that one or more of the 4116 (or equivalent) DRAM chips, and maybe one or more of the 32K bit DRAM chips has been damaged.

There are loads of threads about fixing faulty ZX Spectrums over in the hardware section of World of Spectrum forums ;)

Mark
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flaviosr
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Re: Have I killed my ZX Spectrum?

Post by flaviosr » Tue Aug 14, 2018 11:24 am

Later this afternoon (now a bit of relax after lunch and drinking a coffee...) I am going to make the voltages checks... I am also waiting from Amazon two new low bookcases for my laboratory so I will be heavily busy today.
Anyway I looked over internet about my issue and I have read that 4116 chips are very very very (very!) delicate and they could have been the sacrificial lamb of my carelessness.
Assuming they are to be changed I see 3 possibilities:
1. simple replace them;
2. replace them using sockets;
3. substitute them with one of this: https://www.sellmyretro.com/offer/detai ... dule.-2741 (it could even be cheaper...)

Questions:
° is it possible to use sockets in a Spectrum 48k first type (not QL look) still being able to mount it again (I know I can make tests but if somebody have already tried it is more sure...)?
° how about the "new" solution? Have somebody tried it?

Thank you
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Ast A. Moore
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Re: Have I killed my ZX Spectrum?

Post by Ast A. Moore » Tue Aug 14, 2018 1:37 pm

flaviosr wrote:
Tue Aug 14, 2018 11:24 am
Questions:
° is it possible to use sockets in a Spectrum 48k first type
Sure, why wouldn’t it be? Plenty of space.
flaviosr wrote:
Tue Aug 14, 2018 11:24 am
° how about the "new" solution? Have somebody tried it?
It’s not that new. The guy has been selling them for years. By the way, he has a YouTube channel with tons of excellent, highly detailed videos covering all sorts of Spectrum repairs.
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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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1024MAK
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Re: Have I killed my ZX Spectrum?

Post by 1024MAK » Tue Aug 14, 2018 7:13 pm

Will a RAM chip fit in a standard socket and will the keyboard and case fit okay? - Yes!
Will the replacement board fit and will it work? - Yes!

I would not describe 4116 DRAM chips as delicate, but they sure don't like abuse. The manufacturers datasheet makes it clear that the -5V supply is essential. The trouble is, it's far to easy to kill the transistors that provide this supply, or to short out lots of the address, control and data lines when an expansion is fitted, or removed with the power on. Or when the locating pin is missing or ineffective. These problems are very likely to have accounted for a very large number of dead ZX Spectrums. I know, it happened to me (back in 1983/4) when the locating pin went missing from a Sinclair Interface 2. They guy when handing over the now repaired ZX Spectrum gave my dad and me a lecture about it...

The 4116 DRAM chips are also an old design, but mass production of such highly integrated memory back then was still problematic. Couple that with the old capacitors (which were never intended to last this long) in the DC/DC converter (that TR4 and TR5 are part of) that provides the -5V supply, and it's not really surprising that failures occur.

Mark
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flaviosr
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Re: Have I killed my ZX Spectrum?

Post by flaviosr » Fri Aug 31, 2018 10:38 pm

The Spectrum is alive and kicking!
I changed all 4116 putting them on sockets. I also found that TR4 was dead. And a new membrane also helped.
Thank you to all for the help.
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1024MAK
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Re: Have I killed my ZX Spectrum?

Post by 1024MAK » Sun Sep 02, 2018 5:56 pm

Well done :D

Have fun with your repaired Speccy 8-)

Mark
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