16k Sinclair issue 1 pack
16k Sinclair issue 1 pack
I have an issue 1 Sinclair 16k RAM pack. I can find a few pictures, but only external ... https://www.zx81stuff.org.uk/zx81/hardware/Sinclair16K
Is there a need for internal pictures?
Also, high res graphics is sort of working, but sort of not working... so I'm not sure what set of instructions to follow, to enable high res graphics... or whether to leave this pack as is and give high res a miss.
Is there a need for internal pictures?
Also, high res graphics is sort of working, but sort of not working... so I'm not sure what set of instructions to follow, to enable high res graphics... or whether to leave this pack as is and give high res a miss.
All that I've learned - https://msknight.com/bbc/index.html#zx81
- 1024MAK
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Re: 16k Sinclair issue 1 pack
Sinclair (and most other brands/makes) 16K RAM packs that use DRAM chips normally need a modification for full Hi-Res graphics to work correctly.
I thought we had some photos of an issue 1 RAM pack, but either I was mistaken, or I just can't find them... (we do have photos of issue 2 and issue 3 though).
Mark
I thought we had some photos of an issue 1 RAM pack, but either I was mistaken, or I just can't find them... (we do have photos of issue 2 and issue 3 though).
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
Re: 16k Sinclair issue 1 pack
OK - I'll take some. Where'd you want 'em?
Which mod instructions should I be looking at?
Which mod instructions should I be looking at?
All that I've learned - https://msknight.com/bbc/index.html#zx81
- 1024MAK
- Posts: 5165
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: 16k Sinclair issue 1 pack
Photos in this topic please. Also send copies to me via email (see my PM)
Hi-res mod for a 16K RAM pack, see this topic
Mark
Hi-res mod for a 16K RAM pack, see this topic
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
Re: 16k Sinclair issue 1 pack
OK - so this is my meagre diode collection. I have some 1N4148 and I presume I'm going to need a slightly higher resistor than the 4.7K specified?
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: 16k Sinclair issue 1 pack
So I'm doing the following...
1) Identify RD on pin 16 top side, cutting the line and inserting a diode in its place.
2) Identify RFSH on pin 23 top side. Cut the line.
3) Take 5v and feed it in to the chip where RFSH went - can normally be done between pins on the same chip, using it's own 5v pin.
4) Take 5v and feed it through a resistor, then through a diode, and out where RFSH originally came in, on the edge connector.
Do I have that right please?
1) Identify RD on pin 16 top side, cutting the line and inserting a diode in its place.
2) Identify RFSH on pin 23 top side. Cut the line.
3) Take 5v and feed it in to the chip where RFSH went - can normally be done between pins on the same chip, using it's own 5v pin.
4) Take 5v and feed it through a resistor, then through a diode, and out where RFSH originally came in, on the edge connector.
Do I have that right please?
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: 16k Sinclair issue 1 pack
OK - so, RAM pack still works, but high res doesn't. What did I do wrong?
*) Diode on RD which has the track cut underneath.
*) RFSH is cut and destination pin is wired to +5 of the same chip.
*) +5V through 4.7K resistor and another diode to RFSH
System works, but high res is not happening. JBRacing results in a completely black area and also 1K 3D Maze results in blocked maze walls. This is the same behaviour as the pack did before I modded it.
*) Diode on RD which has the track cut underneath.
*) RFSH is cut and destination pin is wired to +5 of the same chip.
*) +5V through 4.7K resistor and another diode to RFSH
System works, but high res is not happening. JBRacing results in a completely black area and also 1K 3D Maze results in blocked maze walls. This is the same behaviour as the pack did before I modded it.
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: 16k Sinclair issue 1 pack
Does the 5v, after the resistor, also have to be connected north of the diode to RD? Is that what I'm missing?
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: 16k Sinclair issue 1 pack
I tried the 5v to the side of the RD as well as the RFSH... it didn't like that at all.
Do I have to raise the value of the resistor because of the diodes I'm using?
Do I have to raise the value of the resistor because of the diodes I'm using?
All that I've learned - https://msknight.com/bbc/index.html#zx81
Re: 16k Sinclair issue 1 pack
Well, if no one has any ideas to help on this, then I reckon I've got a few more days before I'm going to have to abandon this and the vintage RAM, so I can clear my workbench and move on. I don't really know where to go forward from here as I'm just guessing now.
All that I've learned - https://msknight.com/bbc/index.html#zx81