I recently got a working RAM pack with a zeddy and while recapping it spotted the following:-
How was it even working? So many dry joints.
I resoldered the joints and replaced the caps. All good.
Ran it for about 30 mins and now it is dead. I have very little luck with these. Maybe I should leave the original caps in? But I assume they are part of the power circuit and will kill it if they fail? Maybe these things are just a little fragile?
Sinclair 16k RAM pack - how was it even working?
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Sinclair 16k RAM pack - how was it even working?
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
- 1024MAK
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Re: Sinclair 16k RAM pack - how was it even working?
Is the -5V present on the 4116 DRAM chips? That voltage should always be tested as soon as possible after powering up. A missing -5V supply is known to kill 4116 DRAM chips, as it is the bias supply for the substrate.
Mark
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
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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.
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Re: Sinclair 16k RAM pack - how was it even working?
I will check thanks Mark.
If the caps are ok what would cause the voltage not to be there?
If the caps are ok what would cause the voltage not to be there?
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Sinclair 16k RAM pack - how was it even working?
The 16K RAM packs use an earlier version of the DC/DC transistor converter/inverter as used in the ZX Spectrum.
They draw power from the nominal +9V power pin on the edge connector and convert this to a semi-regulated +12V and a stablised -5V supply. 4116 (and equivalent) DRAM chips need a +12V supply for their internal circuitry, a +5V supply for the internal interface circuitry (for communicating with the CPU) and as I said, a -5V bias supply.
Causes of failure may be faulty capacitor(s), faulty transistor(s) or the coil having been damaged. If a DRAM chip failed and then went short circuit, this may then in turn kill the transistor(s), and then the loss of the -5V may cause more DRAM chips to fail...
I’ve not investigated or repaired the DC/DC transistor converter/inverter on the faulty Sinclair 16K RAM pack that I have, because the DC/DC transistor converter/inverter works. I think on mine, it is a failed ULA chip (it’s the later issue board).
Most people quickly give up trying to fix these and use a modern SRAM based solution instead. So if you do decide to continue, I wish you the best of luck. I will help where I can,
Mark
They draw power from the nominal +9V power pin on the edge connector and convert this to a semi-regulated +12V and a stablised -5V supply. 4116 (and equivalent) DRAM chips need a +12V supply for their internal circuitry, a +5V supply for the internal interface circuitry (for communicating with the CPU) and as I said, a -5V bias supply.
Causes of failure may be faulty capacitor(s), faulty transistor(s) or the coil having been damaged. If a DRAM chip failed and then went short circuit, this may then in turn kill the transistor(s), and then the loss of the -5V may cause more DRAM chips to fail...
I’ve not investigated or repaired the DC/DC transistor converter/inverter on the faulty Sinclair 16K RAM pack that I have, because the DC/DC transistor converter/inverter works. I think on mine, it is a failed ULA chip (it’s the later issue board).
Most people quickly give up trying to fix these and use a modern SRAM based solution instead. So if you do decide to continue, I wish you the best of luck. I will help where I can,
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: Sinclair 16k RAM pack - how was it even working?
So the TS1500 has its own DC/DC transistor converter/inverter section, too! The TS1500 has own 8 DRAMs "4116" chips.1024MAK wrote: ↑Sat Feb 23, 2019 1:48 pm The 16K RAM packs use an earlier version of the DC/DC transistor converter/inverter as used in the ZX Spectrum.
They draw power from the nominal +9V power pin on the edge connector and convert this to a semi-regulated +12V and a stablised -5V supply. 4116 (and equivalent) DRAM chips need a +12V supply for their internal circuitry, a +5V supply for the internal interface circuitry (for communicating with the CPU) and as I said, a -5V bias supply.
Causes of failure may be faulty capacitor(s), faulty transistor(s) or the coil having been damaged. If a DRAM chip failed and then went short circuit, this may then in turn kill the transistor(s), and then the loss of the -5V may cause more DRAM chips to fail...
DesSony
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Re: Sinclair 16k RAM pack - how was it even working?
Thanks Mark. I have a ZXpand so am ok for extra RAM it just would have been nice to have a working Sinclair RAM pack. Maybe next time...
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA