16K RAM pack
16K RAM pack
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.
Anyone know if many ULA's survive RAM pack treatment?
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.
Anyone know if many ULA's survive RAM pack treatment?
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: 16K RAM pack
Good luck
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
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
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: 16K RAM pack
Thanks Mark, much appreciated.
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
I thought that this may be a factor, I wonder if there are RAM pack ULA tests.
Re: 16K RAM pack
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.
I'll rewire the PCB next.
Re: 16K RAM pack
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.
Perhaps it was incorrectly replaced and caused the problem.
Perhaps it was incorrectly replaced and caused the problem.
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: 16K RAM pack
If a 1N4148 was fitted in place of a zener, that would definitely cause problems!
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: 16K RAM pack
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?
Would anyone happen to know of such a diagram or list, I wonder?
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: 16K RAM pack
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
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
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
Standby alert
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: 16K RAM pack
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.