Refurbing an issue one zeddy
Re: Refurbing an issue one zeddy
Why not cut away the plastic? It isn't needed once the top row is soldered
That might even give a nicer look.
That might even give a nicer look.
In theory, there is no difference between theory and practice. But, in practice, there is.
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Re: Refurbing an issue one zeddy
Do you mean the excess plastic or all of it?
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Re: Refurbing an issue one zeddy
I mean all the plastic on the pins, not the regulator of course
In theory, there is no difference between theory and practice. But, in practice, there is.
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Re: Refurbing an issue one zeddy
I have soldered it and I think this rates as 'good enough'!
I may try and scrape off the remains of the solder pads at the top of the board.
Lardo
I may try and scrape off the remains of the solder pads at the top of the board.
Lardo
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
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Re: Refurbing an issue one zeddy
I bought a heated desolder pump for about £10 and it is the best £10 I have spent in a long time! It is sooo much easier than the manual approach! Thanks Paul!Paul wrote: ↑Thu Jun 15, 2017 6:20 pm What I use is
this from ebay.
My main problem with manual pumps was always that during the time from taking away the soldering iron and placing the pump the solder was (going) hard again.
With this heated manual pump this doesn't happen anymore.
Works good and is MUCH cheaper.
Kind regards
Paul
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
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Re: Refurbing an issue one zeddy
Hi Mark
A few questions about your 16k mod as I am approaching a point where I will give it a go!
In the section about signals you note the position of M1 but there is no wire to this?
The link L2 is joined with uninsulated wire - is the lack of insulation significant? Or is it just easier to work with on such short stretch of wire?
Many thanks - trying to make sure I understand!
Lardo
A few questions about your 16k mod as I am approaching a point where I will give it a go!
The mod to allow for the 32k RAM option - given that I am unlikely to do this at this stage do I need to cut the +5V line? I assume this is the left most track cut of the middle part of the image?1024MAK wrote: ↑Sat Apr 29, 2017 12:41 pm The modern SRAM chips need a 28 pin socket. I showed how I did an issue 1 board here
Note that my mod is designed to allow a further modification to 32k bytes. Hence the cutting of the +5V track, then fitting a wire link across it.
Dave Curran of Tynemouth Software shows how he does an upgrade on an issue 1 board here.
So take your pick. They all do the same. Expand a ZX81 to have 16k bytes of internal RAM.
In the section about signals you note the position of M1 but there is no wire to this?
The link L2 is joined with uninsulated wire - is the lack of insulation significant? Or is it just easier to work with on such short stretch of wire?
Many thanks - trying to make sure I understand!
Lardo
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
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Re: Refurbing an issue one zeddy
Hi Lardo
Ask away...
The idea behind cutting the existing tracks on both sides of pin 2 is to fully isolate it from the +5V supply. Then having cut the +5V supply track in two places, the bits either side of pin 2 (but not including the bit left connected to pin 2) need linking back up with some wire.
If you never want any more than 16k of RAM, you don't need to cut either of the two track cuts for pin 2. The reason for doing the track cuts all at once, is simple. It's a lot more difficult to cleanly cut tracks after a socket has been fitted!
Having gone to the effort of isolating pin 2 from the +5V supply, a short wire is soldered to connect it up to a fixed logic level (either +5V or 0V, it does not matter, +5V just happens to be easier) until (if) a future modification is carried out.
Note that a SRAM does not care in which order it's address lines are connected up. As long as all of them have valid logic levels. The CPU also does not care. It may appear crazy, but all that matters is that each and every memory location is individually addressed.
Happy to help. If anything above still does not make sense, or you have any other questions, keep asking
Mark
Ask away...
On the new 32k byte SRAM chip, pin 2 is one of the address pins (actually A12 according to the datasheets).Lardo Boffin wrote: ↑Thu Jun 29, 2017 10:09 pmThe mod to allow for the 32k RAM option - given that I am unlikely to do this at this stage do I need to cut the +5V line? I assume this is the left most track cut of the middle part of the image?
The idea behind cutting the existing tracks on both sides of pin 2 is to fully isolate it from the +5V supply. Then having cut the +5V supply track in two places, the bits either side of pin 2 (but not including the bit left connected to pin 2) need linking back up with some wire.
If you never want any more than 16k of RAM, you don't need to cut either of the two track cuts for pin 2. The reason for doing the track cuts all at once, is simple. It's a lot more difficult to cleanly cut tracks after a socket has been fitted!
Having gone to the effort of isolating pin 2 from the +5V supply, a short wire is soldered to connect it up to a fixed logic level (either +5V or 0V, it does not matter, +5V just happens to be easier) until (if) a future modification is carried out.
Note that a SRAM does not care in which order it's address lines are connected up. As long as all of them have valid logic levels. The CPU also does not care. It may appear crazy, but all that matters is that each and every memory location is individually addressed.
Correct. I marked all the signals that were needed for the 16k RAM and what may be needed for a future modification for 32k bytes of RAM. M1 is one of the signals needed if RAM is to be used to store data in high RAM in the ZX81 memory map.Lardo Boffin wrote: ↑Thu Jun 29, 2017 10:09 pmIn the section about signals you note the position of M1 but there is no wire to this?
For such a short bit of wire, insulation is not needed. And indeed, it becomes a pain trying to keep such a short bit of insulation on such a short wire.Lardo Boffin wrote: ↑Thu Jun 29, 2017 10:09 pmThe link L2 is joined with uninsulated wire - is the lack of insulation significant? Or is it just easier to work with on such short stretch of wire?
Happy to help. If anything above still does not make sense, or you have any other questions, keep asking
Mark
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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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Re: Refurbing an issue one zeddy
There is a forthcoming 16K SRAM module without the need to cut tracks on the board. I'll post some info in a new thread shortly.
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Re: Refurbing an issue one zeddy
Thanks for the clarification Mark.
Depending on how easy the cut is on the right I may do the two cuts on the left. As you say once the socket is in place it will not be easy to do the cuts!
Are there instructions anywhere on how to do the 32k mod?
Depending on how easy the cut is on the right I may do the two cuts on the left. As you say once the socket is in place it will not be easy to do the cuts!
Are there instructions anywhere on how to do the 32k mod?
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
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Re: Refurbing an issue one zeddy
There are schematics for 32k RAM. But not highly detailed instructions like you have been looking at for the 16k RAM modification.
In fact, there are a number of ways of mapping the 32k RAM into the Zeddy memory map. The easiest is to put the "extra" 16k at the top of memory (48K to 64K). This area cannot be used for executing machine code, but can be used for storing data.
More info and diagram here.
Wilf Rigter describes various RAM upgrades on his web site. Read this one first
Mark
In fact, there are a number of ways of mapping the 32k RAM into the Zeddy memory map. The easiest is to put the "extra" 16k at the top of memory (48K to 64K). This area cannot be used for executing machine code, but can be used for storing data.
More info and diagram here.
Wilf Rigter describes various RAM upgrades on his web site. Read this one first
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.