ZX80 3K Ram Pack memory

Discussions about Sinclair ZX80 and ZX81 Hardware
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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Thu May 03, 2018 6:30 pm

I too can't see any connection to 23B.

If your RAM chips are in sockets, try removing all of them. Then plug it in to your TS1000 and see what happens. The 74LS138 should decode the address and only enable the RAM in the TS1000 between 16384 and 17407 (giving a total of 1K).

If that does not work, and the 74LS138 is also in a socket, remove it from the board (so now the board will have no chips fitted at all). Then try again. With the 74LS138 missing, the /RAMCS line will not be overridden, so the TS1000 should start up with it's internal 2K of RAM.

Mark

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gammaray
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Re: ZX80 3K Ram Pack memory

Post by gammaray » Thu May 03, 2018 10:42 pm

If I am properly following thread, on next revision ... is jumper for TZX81000 or ZX80 needed?
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM

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mhudson52
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Re: ZX80 3K Ram Pack memory

Post by mhudson52 » Fri May 04, 2018 12:55 am

Mark, thanks for the suggestions. None of the chips are socketed, but having received a new batch of 2114's in today was planning on doing a little soldering this evening.

Instead, I will follow your plan and see what happens, taking it one step at a time. Will first install the capacitors and the edge connector and see how the TS1000 responds. Next will install the 74LS138 and see what happens. If at this stage all appears normal, will then install the 2114's and re-check. This procedure should mimic your method.

Let me know if you see any problem with doing it in this manner.

Regards,

Mike
TS 1000 bought in 1982 and brought back to life by Sir Ian

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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Fri May 04, 2018 1:07 am

gammaray wrote:
Thu May 03, 2018 10:42 pm
If I am properly following thread, on next revision ... is jumper for TZX81000 or ZX80 needed?
No. No need for a jumper.
Read the attachment in this post.

To sum up, on the Sinclair 1-3K RAM pack, edge-connector pin 23B is connected to 0V/GND. On the ZX80 (at least on mine) edge-connector pin 23B just goes to a track that ends in a rectangular pad (without any through hole), so connecting to 0V/GND has no effect. But on the ZX81 and TS1000, pin 23B is the /ROMCS signal. Messing with this will prevent the machine from running. So the solution is just to cut the track on the 1-3K RAM pack that goes to edge-connector pin 23B. The RAM pack should then work on a ZX80, a ZX81 or a TS1000 :D

Mark

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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Fri May 04, 2018 1:09 am

mhudson52 wrote:
Fri May 04, 2018 12:55 am
Mark, thanks for the suggestions. None of the chips are socketed, but having received a new batch of 2114's in today was planning on doing a little soldering this evening.

Instead, I will follow your plan and see what happens, taking it one step at a time. Will first install the capacitors and the edge connector and see how the TS1000 responds. Next will install the 74LS138 and see what happens. If at this stage all appears normal, will then install the 2114's and re-check. This procedure should mimic your method.

Let me know if you see any problem with doing it in this manner.

Regards,

Mike
Mike, it sounds like a plan. See how you get on.

Mark

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mhudson52
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Re: ZX80 3K Ram Pack memory

Post by mhudson52 » Sun May 20, 2018 4:17 pm

A little update on the RAM Pack seems to be in order here. Since the last episode all of the chips are now socketed and installed on the board as modified by Mr. Robson. The changes to the board consist of correcting the two crossed tracks that had required a little cutting and two jumpers installed, as well as improving the placement of a couple of other tracks for better clearance for the rivet holes.

Built one board containing only the sockets, edge connector header, and the two capacitors. Hooked it up to my TS1000 and fired it up with no problems and memory test showed 2K memory as expected. Installed the 74LS138 and retested, again no issues and 2K memory reported. Installed the 2114 AM chips and retested, again no issues and 4K memory reported.

Previously the RAM pack would either crash my TS or report a nonsensical memory test result, so I am very pleased that it now works just fine and dandy with Charlie's Issue 3 design. He must have sprinkled some of his magic dust on the new board, because the only meaningful changes made were those listed above.

To say I am pleased is a vast understatement. :D
100_5564.jpg
TS 1000 bought in 1982 and brought back to life by Sir Ian

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