16K RAM pack

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sP1d3r
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16K RAM pack

Post by sP1d3r »

I recently got an old Sinclair ZX 16K RAM pack with no case and 7 out of 8 ram chips and ULA etc.

I checked the ram chips, they all work and if the ULA also works there'll hopefully be 16K of ram.
The PCB tracks need a lot of work and it seems to have had a major power event causing the 1N4148 diode leg to overheat.

Desoldered 16K RAM pack component side
Desoldered 16K RAM pack component side
Anyone know if many ULA's survive RAM pack treatment?
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1024MAK
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Re: 16K RAM pack

Post by 1024MAK »

Good luck 🤞
sP1d3r wrote: Wed Mar 08, 2023 12:06 am Anyone know if many ULA's survive RAM pack treatment?
Typically, it’s either failure of the DC/DC converter, a failed DRAM chip (or more than one), or the ULA.

I suspect, but don’t have any evidence, that the ULA may get damaged if it’s inserted to a already powered up Zeddy. Or gets pulled off while the system is powered.

Having said that, some earlier ULAs do appear to die more often than later ULAs. So it could just be that.

Mark
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sP1d3r
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Re: 16K RAM pack

Post by sP1d3r »

1024MAK wrote: Wed Mar 08, 2023 12:38 am Good luck 🤞
Thanks Mark, much appreciated.
1024MAK wrote: Wed Mar 08, 2023 12:38 am Typically, it’s either failure of the DC/DC converter, a failed DRAM chip (or more than one), or the ULA.
The coil doesn't seem to have become hot, the enamel turns dark if it has.
The 74LS157 may be the problem but as the 4116 chips are 12V it's likely DC converter or RAM chip failure
1024MAK wrote: Wed Mar 08, 2023 12:38 am
I suspect, but don’t have any evidence, that the ULA may get damaged if it’s inserted to a already powered up Zeddy. Or gets pulled off while the system is powered.
I thought that this may be a factor, I wonder if there are RAM pack ULA tests.
RAM chips, demux and ULA
RAM chips, demux and ULA
sP1d3r
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Re: 16K RAM pack

Post by sP1d3r »

I checked the DC-DC converter components and the ZTX 750 transistor identifies as an 8.2 ohm resistor on my LCR meter, all other parts work that I've so far checked apart from the 5V1 Zener diode, which I'll check.

I'll rewire the PCB next.
sP1d3r
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Re: 16K RAM pack

Post by sP1d3r »

I've noticed that in Mark's post viewtopic.php?p=33555#p33555 that D4 is a 12V Zener diode but the one in my RAM pack was the one that over heated and it was a 1N4148 and it wasn't the same as the other 1N4148 diodes.
Strange 1N4148 diode, different to the others
Strange 1N4148 diode, different to the others
Perhaps it was incorrectly replaced and caused the problem.
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1024MAK
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Re: 16K RAM pack

Post by 1024MAK »

If a 1N4148 was fitted in place of a zener, that would definitely cause problems! :lol:

Mark
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sP1d3r
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Re: 16K RAM pack

Post by sP1d3r »

I've searched through quite a lot of 16K RAM pack threads and posts and although there's a circuit diagram for the DC-DC converter, there aren't any of the associated component identifiers, e.g. D1, D2, C1, R1 etc. for the Sinclair issue 3.

Would anyone happen to know of such a diagram or list, I wonder?
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1024MAK
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Re: 16K RAM pack

Post by 1024MAK »

I’ve never seen an official diagram of any apart from the first issue version.

I do have a non-working issue 3, so if you want photos, or any other help with identifying parts, that’s fine. But not till later on.

Mark
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
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sP1d3r
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Re: 16K RAM pack

Post by sP1d3r »

1024MAK wrote: Sat Mar 11, 2023 1:27 pm
I do have a non-working issue 3, so if you want photos, or any other help with identifying parts, that’s fine. But not till later on.
I'm afraid I desoldered all the parts believing that I could easily find out which ones go where, so any help you could give me would be much appreciated, thanks Mark.

Please post when you have enough time.
Moggy
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Re: 16K RAM pack

Post by Moggy »

Is this of any use?

Click on it to enlarge.
Attachments
SQ Syntax Quarterly 2-2_0036.jpg
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