Datamuseum.dk needs 64Kx1 static RAM chips - Page 1
Forum section: electronics / general

author: bsdphk
author_rank: Regular Contributor
timestamp: August 25, 2023, 02:41:39 pm
content: The worlds last Rational 1000 computers live in Datamuseum.dk (https://datamuseum.dk/wiki/Rational/R1000s400)The I/O processor board ("IOC") has 72 static ramchips, 64Kx1 with separate data-in and data-out, but we are seeing a 30% failure rate on these chips.Since the chips also go bad when the computer is turned off, we suspect this is due to a design or manufacturing problems 30-40 years back.So if anybody happen to find some tubes of:CY7C187-35PCMB81C71A-35PHM6287P-35We in Datamuseum would really love to get an offer we can afford, because we have no money :-(Thanks in advance,Poul-Henning

author: up8051
author_rank: Frequent Contributor
timestamp: August 25, 2023, 04:08:40 pm
content: How many chips would you like to buy?All set 72pcs?

author: globoy
author_rank: Frequent Contributor
timestamp: August 25, 2023, 05:04:15 pm
content: Sorry I can't help you but the link you provided was interesting! Thank you for sharing that.That's a serious TTL computer. Are there any programmable logic arrays (PAL, PLA) in there or is it pretty much straight F-series TTL? Loved the huge PSU wires carrying the 5kW@5V supply.Also any pictures of what the GUI looked like?Good luck with your restorations.

author: bsdphk
author_rank: Regular Contributor
timestamp: August 25, 2023, 08:19:15 pm
content: Quote from: up8051 on August 25, 2023, 04:08:40 pmThat's a good question.In practice the answer is probably "as many as we can afford", since our goal is to keep these computers working for many more decades, but at least enough to keep one computer working for now.So to give you the full situation:The problem with these chips were known already back when these computers were production, producing the software for things like the Space Shuttle, ISS, GPS and who knows what else in the 1990ies.We miraculously have been given two of these computers, half of the only four known survivors, the rest have been shredded due to the classified nature of the stuff they were used for.We have a total of three IOC boards, one in each machine and a spare.All three boards are populated with 72 Fujitsu chips each, two banks of 32 bits + byte parity.On the two oldest boards, where chips have failed by the dozens already we have:MB81C71A-25P9109 M07 AD / 9109 M06 AD / 9109 M10 ADOne of these board have a "bank" of 9 "9019 C51 AD", which looks a lot like a previous repair.The newer board have the same Fujitsu chips, but date codes "9206 M64 AD". On that board we have replaced four chips already, and a fifth just died on us now.We have managed to scrounge some Cyrix chips from eBay, we are running out now.Our best hope is that the problem is isolated to the Fujitsu chips, and that replacing those with another brand will solve the problem for good, but we do not have enough experience with the replacements to know for sure yet.The precise observed problem is explained here:https://datamuseum.dk/wiki/Rational/R1000s400/Logbook/2019#2019-05-23So ideally we would like to get hold of around 200 non-Fujitsu chips, so we have enough for a total replacement, but I doubt there are that many just lying around in places we can find them, so we will take what we can find.Poul-Henning

author: bsdphk
author_rank: Regular Contributor
timestamp: August 25, 2023, 08:29:07 pm
content: Quote from: globoy on August 25, 2023, 05:04:15 pmIt is not only a very serious TTL computer, it is built by very serious people: It feels a lot like opening the hood of an old Bentley.For instance, they effectively invented JTAG: Each board has an i8052 "diagnostic processor" which do a boundary scan and drive all circuits on the board at speed using a diagnostic Finite State Machine.And in addition to the 20MHz x-tal, there is also a 21 MHz one, so the diagnostic tests can be run 5% faster than spec, just like the PSU can be told to deliver 5% high or 5% low voltage for the same purpose.The previous models used '74S' chips, but this last model used '74F'.Only two of the boards ("MEM32" and "RESHA") use PALs, they were designed for this last model.The rest of the CPU is the same as the previous model 100, 200 and 300, and they use 32x8 and 512x8 bipolar PROM's for some of the stuff a PAL would be used for later.The "GUI" was character based not graphical, you can see an example of it on our wiki page.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 25, 2023, 10:43:55 pm
content: What's the memory bus width? 32 bit? Does it use 2 banks of 32 x 1bit chips, +4 bit ECC?Do you want to keep it 100% original? There're mods using modern sram, might be interesting:https://www.amibay.com/threads/saruman-128-c128-sram-for-dram-replacement-board.118279/Old school srams failed a lot, but there're modern 36-bit srams with much higher densities, also much faster, like CY7C1354C-166AXI, providing 9Mbit, which is the double as the entire chips your're replacing.Should't be hard to make a board for it, and perhabs you could even enable this extra ram in the system?It's these 72 chips?

author: BrianHG
author_rank: Super Contributor
timestamp: August 25, 2023, 11:02:22 pm
content: Quote from: DavidAlfa on August 25, 2023, 10:43:55 pmbsdphk requires SRAM chips with a separate data in and data out pin unlike that SRAM replacement board.However, in some old computer designs using these SRAMs, they already just tie the Din and Dout together. A special replacement board needs to be made.If a replacement board is allowed to keep these computers working, a tiny FPGA board may be used to simulate the SRAM with a separate din/dout perfectly, where 1 FPGA may replace 8-9 ram chips at once. Only the Write Enable needs to be verified that it crosses 8 or 9 bits at a time.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 25, 2023, 11:11:03 pm
content: Found the schematics:https://datamuseum.dk/bits/30000961Indeed, it uses 4-bit parity.

author: BrianHG
author_rank: Super Contributor
timestamp: August 26, 2023, 02:33:33 am
content: (Only read if an alternate ram chips are acceptable.)If bsdphk's computer uses a 9 bit bus across all ram chips and his access cycle is slower than 30ns, then he can use this 1 ram chip on a carrier PCB with a 100mhz oscillator and a small GAL/PAL for high address bit decoder. Wired to 1 socket plus all the data pins of the 8 adjacent horizontal sockets with upper address bits wired through the GAL/PAL to the vertical ram socket's chip enable.https://www.nxp.com/docs/en/data-sheet/MCM67Q909.pdfQuest Components has stock.Again, if bsdphk can confirm is the data in and data out pins are shorted on his motherboard. If so, then any single static ram chip will work with a GAL/PAL for OE-> upper address decoding as any single 512kx9 chip will work, or use 8 individual 64kx9 chips.

author: bsdphk
author_rank: Regular Contributor
timestamp: August 26, 2023, 05:13:45 am
content: Quote from: BrianHG on August 26, 2023, 02:33:33 amUnfortunately they are used separately, because there are three "clients" to this memory all in all.The memory is organized as 2 (banks) x 64K x 4 (bytes) x (8 + 1)Byte reads and writes are possible, so using a single 36 wide chip is not an option.As a computer museum, we have to keep things original, but having three IOC boards does allow us to modernize one of them, if there are no other way to keep the hardware running.If you want to study the schematics, there is a KiCad version here:https://github.com/Datamuseum-DK/R1000.Emulator2/tree/main/Schematics/Hw/IocI entered the schematics in KiCad as the initial stage of writing a software emulation of the R1000. The only way to approach it was to start with a hardware emulation, because the instruction set (which are Ada Primitives!) is not documented.

author: bsdphk
author_rank: Regular Contributor
timestamp: August 26, 2023, 05:24:46 am
content: Quote from: DavidAlfa on August 25, 2023, 10:43:55 pmHmm, I didn't know that SRAM has reliability problems in general. Do you happen to know if anybody has researched the failure mechanisms ?Yes, we are talking about the SRAM is in the G and H columns.There is a full set of photos of one of the IOC boards here:https://datamuseum.dk/wiki/Bits:30002618This is probably the most gentle introduction to the computers architecture:https://datamuseum.dk/wiki/Bits:30000927Our full documentation archive is here:https://datamuseum.dk/wiki/Bits:Keyword/RATIONAL_1000

author: up8051
author_rank: Frequent Contributor
timestamp: August 26, 2023, 03:37:38 pm
content: In a local parts store are avaliable HM6787P-30.HM6787P-30 is Hi-BiCMOS verison of HM6287Phttps://pdf.ic37.com/pdf/download/?id=1845787_142976Price is about 2,50€/pcsBR JarekC

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 26, 2023, 03:48:40 pm
content: Quote from: bsdphk on August 26, 2023, 05:24:46 amI say so because I see srams failing all the time in vintage computers restoration videos (Adrian's Digital basements, LGR, The 8-bit guy, etc)...

author: djsb
author_rank: Super Contributor
timestamp: August 26, 2023, 03:48:58 pm
content: Maybe there is some company such as Rochester Electronics who could donate some surplus chips as a philanthropic gesture? I have no connection, but if I was in the chip remanufacturing business, I'd donate them for free.