ZX81 memory troubles

[ArtemKuchin]

I have three zx81.
Two are working find, one has faulty memory.
I also have two 16k ram packs but both seems to fail also.
So, i want to make an internal memory upgrade at least for two of my zeddies.
I found this:
http://www.zx81.de/english/32k-rame.htm

Question 1: I don't understand how i should solder a 28pin socket into IC4 place. IC4 is 18pin dip chip.


Then i want to repair at least one ram pack. It uses 4116 chip which need tons of different voltage and tend to die easily. So,i'd rather use some dram chip that use only +5.

Question 2: Is there known tested mod for ram packs which uses such dram chips?

[PokeMon]

Question 1: I don't understand how i should solder a 28pin socket into IC4 place. IC4 is 18pin dip chip.

Well if take your glasses you will find that the small 18 pin chips are IC4a and IC4b (2 4-bit 1k memory chips). There is printed on my ISS3 board the outline of a wide space 28 pin IC around the 18 pin IC4a.

Look here, you can see it for an ISS1 board as well (handrouted).


You have to desolder the small 18 pin first (both !).
On the old boards there is IC4a / IC4b not printed.

[Paul]

Question 2: Is there known tested mod for ram packs which uses such dram chips?

Yes, there is.
Have a look here: http://bitcycle.org/retro/spectrum/SRAM_replacement/ It is about replacing the lower 16K of a spectrum, but MIGHT as well work for a 16K Zeddy RAMPACK.
But I don't think this is a reasonable way.
I can only advise you not to mod the original RAM PCB but to make a new PCB (e.g. wirewrap...) to fit into the case of your favourite RAMPACK or directly into the zeddy.

A good way for "homebrewing" would would be :
http://forum.tlienhard.com/phpBB3/viewt ... =479#p6226
This post gives a 56K internal or external RAMPACK and, if you like to, also a connection for a vdrive2 USB adapter from vinculum (to be found in the same thread on a different schematic that clearly states its for the vdrive).
This gives a far better RAM extension than is previous version that you had linked to.
RAM can be battery (or goldcap) buffered and the area from 8-12 and 12-16 can be optional writeprotected (e.g. to hold the USB driver)
This latest version can also be capable or running MC in the area from 32-48k (M1not MOD also required in addition) and is of course HRG ready.
It was built several times already, as well for memotech cases as for Sinclair 16k RAMpack cases and also internal.
The whole thing is to be seen as the low cost alternative to zxpand.
Usage of the USB would (at the moment) be PRINT USR 8888;"L3DM.P" as an example for loading the 3DM.P into the zeddy so its usable, but not as comfortable as the zxpand.
Of course there is no need at all to include the USB part.
This version of the RAMPack has been specially designed for low cost using standard TTL chips available everywhere so everyone can build it without the need for GAL/CPLD/FPGA "burning" or Eprom "burning".
If you are capable of using GALs this can easily fitted into a small one.
And about the comfort, holmatic (and some of our crew) is busy developing a patched ROM so LOAD "3DM" will be sufficient.
If you have translation issues or other questions, do not hesitate to contact me.
HTH
Paul

[ArtemKuchin]

Well if take your glasses you will find that the small 18 pin chips are IC4a and IC4b (2 4-bit 1k memory chips). There is printed on my ISS3 board the outline of a wide space 28 pin IC around the 18 pin IC4a.

Look here, you can see it for an ISS1 board as well (handrouted).

sheeezzzz.. i do have my glasses constantly on but i guess i need new ones
Thank you!

Now i see the place for 28pins. The holes are closed, I wonder if it is just solder or there are no actually holes there. I have issue 1.
The image does not seem to load. It is dyndns, so, maybe the host id down.

[Paul]

The holes are closed, I wonder if it is just solder or there are no actually holes there.

No need to fear, they are drilled and filled with solder. Getting them free of solder can be a pain.
It was easier for me to desolder the two 2114 and make a little pcb for my RAM extension and solder single wires to the PCB. For fitting a new socket much more work is required as the holes need to be free of solder...

[ArtemKuchin]

Question 2: Is there known tested mod for ram packs which uses such dram chips?

Yes, there is.
Have a look here: http://bitcycle.org/retro/spectrum/SRAM_replacement/ It is about replacing the lower 16K of a spectrum, but MIGHT as well work for a 16K Zeddy RAMPACK.
But I don't think this is a reasonable way.
I can only advise you not to mod the original RAM PCB but to make a new PCB (e.g. wirewrap...) to fit into the case of your favourite RAMPACK or directly into the zeddy.

I agree. I'd rather make a complete new board with sram and put it in a rampack. I saw this mod for speccy. I guiess i have to play with it and figure out for myself.

A good way for "homebrewing" would would be :
http://forum.tlienhard.com/phpBB3/viewt ... =479#p6226
This post gives a 56K internal or external RAMPACK and, if you like to, also a connection for a vdrive2 USB adapter from vinculum (to be found in the same thread on a different schematic that clearly states its for the vdrive).
Paul

Oh! that's fantastic! I will need spend my time reading google translation of it. I even have vinculum development/debug kit and Vin-II chips i bought for other projects, so,maybe could integrade the usb drive into ram pack

[ArtemKuchin]

No need to fear, they are drilled and filled with solder. Getting them free of solder can be a pain.

I have a desoldering iron with hand pump. I guess it should do the job easily.

[sirmorris]

I recommend getting 'solder wick' rather than the pump - it's generally easier to use, though in this case I suppose you could have the iron on one side of the board and the pump on the other which would work well.. To wick the solder away you add some flux to the joint, put the wick on top then apply heat - the solder is sucked into the copper braid and your hole is left nice and clean!

Some of the cheaper brands don't have any flux applied to them - you must do this yourself for best results. It's quite expensive though; ~1E / meter.

C

[ArtemKuchin]

no, not an iron and a pump, but a desoldering iron with built-in pump
like this one:
http://www.ebay.com/itm/220V-30W-Desold ... 3f1a992654

[sirmorris]

Even better!