Replacing RAM chip with equivalent chip - Page 1
Forum section: electronics / repair

author: tyguy2
author_rank: Unknown
timestamp: March 05, 2016, 02:48:51 am
content: So I've recently got an old computer from a friend, and it looks pretty cool. I've gotten it to boot a couple of times, but RAM usage is pined at 100%, rendering the machine basically useless. I need to add more RAM to the machine, but the chips on the board aren't available on Digikey, Mouser, etc. Attached are some pics of the modules, and the name on the modules are Toshiba Tc514400AP-70, and the datasheet is below:http://www.downloads.reactivemicro.com/Public/Electronics/DRAM/Toshiba%20TC514400AP%201mb%20x%204bit%20DRAM.pdfDoes anyone know of an equivalent chip I could use? Thanks for the help.

author: Brumby
author_rank: Unknown
timestamp: March 05, 2016, 03:54:17 am
content: Before you get into chip chasing - do you know if the board has enough addressing lines to be able to access more memory?

author: tyguy2
author_rank: Unknown
timestamp: March 05, 2016, 03:56:56 am
content: It has 3 empty banks for RAM, and I'm fairly sure it can do it.

author: Brumby
author_rank: Unknown
timestamp: March 05, 2016, 04:01:33 am
content: LOL.OK ... That wasn't particularly obvious from the first photo.

author: Brumby
author_rank: Unknown
timestamp: March 05, 2016, 04:14:59 am
content: My quick check found some 70nS chips on eBay - but they were the ASJ suffix (not AP) which means they are in a different package. If you get stuck, you could always mount them on an adapter board.But I'm not well versed on chip sourcing - so I hope others here may have better suggestions.

author: Ian.M
author_rank: Super Contributor
timestamp: March 05, 2016, 04:15:21 am
content: You'll have to get them used or N.O.S. from a specialist supplier or possibly EBAY, as no one is making small DIP DRAMs any more. Any make of 514400 DRAM, 70ns or faster should do.

author: tyguy2
author_rank: Unknown
timestamp: March 05, 2016, 04:27:03 am
content: Would a chip with the suffix 80 do?

author: Brumby
author_rank: Unknown
timestamp: March 05, 2016, 04:31:22 am
content: Have an access timing of 80nS ... that is, it would be a bit slower.If your computer's timing is running at this or slower (bigger number), then all would be OK - but if it is running at the 70nS mark, you are likely to get problems.

author: Rasz
author_rank: Super Contributor
timestamp: March 05, 2016, 05:02:29 pm
content: if would help to specify full MODEL of the computer/motherboard

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 05, 2016, 05:33:08 pm
content: ... and the operating system installed. A small Linux distro might improve the performance, maybe...

author: tyguy2
author_rank: Unknown
timestamp: March 05, 2016, 07:32:27 pm
content: The problem is that this computer has no markings on it. Damn small linux is too big for the HDD on the system, and the processor is an i386. I wish I could give more info, but that's all I have.

author: tyguy2
author_rank: Unknown
timestamp: March 05, 2016, 07:35:31 pm
content: The system has Windows 3.1 installed. There is a 50 mhz Crystal on the board, but the jumper config has selections between 16 mhz and 40 mhz

author: MyHeadHz
author_rank: Regular Contributor
timestamp: March 05, 2016, 08:57:21 pm
content: Well, some google-fu may be in order.I imagine there are very few people looking for that particular part (25 years after the fact), and and fewer still posting individual spare parts online for it.You are talking late 80's, probably 87 or 88 im guessing. Search for date codes and get an idea of when it was sold. There were few manufacturers and models of PC's back then. The processor is an i386, so Apple is out. That is a start. Then just narrow it down from there with specs. Do you have/know the power supply? that could narrow it by region. Add up the RAM, and max RAM, HDD size, etc. That should give you a short list of computer models sold at the time. A quick check on the specs of those will probably lead to exactly one candidate. Then, you should have a much easier time searching for that model computer that you can salvage parts from.

author: Rasz
author_rank: Super Contributor
timestamp: March 05, 2016, 09:09:54 pm
content: you are like a npc tasked with giving bad clues in a shitty murder mystery gametake a picture of:_whole_ board, not fragmentscomputer casepost messages, bios banner70 vs 80ns is 12 vs 14mhz, should be fine

author: tyguy2
author_rank: Unknown
timestamp: March 05, 2016, 09:48:31 pm
content: Listen man, I'm working off the same clues you are. It doesn't help that the file size limit is only 1000 kilobites. I'll try to get more pictures and information, but the computer literally has no markings on it. No logos, no information, etc, it was all rubbed off. I'll post more pictures tonight

author: sleemanj
author_rank: Super Contributor
timestamp: March 05, 2016, 10:17:08 pm
content: Quote from: tyguy2 on March 05, 2016, 09:48:31 pmPut your images on imgur.com problem solved.It must be a quite early 386, SIMM sticks became the dominant memory format during the 386 reign. Some had both socketed DRAM ic and SIMM from memory (or maybe the socketed was for cache...)Personally. I don't see much of interest to be playing with a generic old 386. Certainly not enough to put energy into finding memory for it.

author: helius
author_rank: Super Contributor
timestamp: March 05, 2016, 11:20:32 pm
content: DRAM packages were fairly standard between brands. You want 4Mbit, 1Mx4 fast page DRAMs. If you're up to designing an adapter, it's also possible to use higher density RAMs to replace each bank. 4Mbit chips became uneconomical to manufacture a couple decades ago.Timing may or may not be critical depending on the design of the board. 70ns is just one of the many, many timing specs on DRAM chips: the critical timing could be one of the others not marked anywhere but in the datasheet. But in general, each 70ns chip with the same organization will be a drop-in replacement for another.

author: Ian.M
author_rank: Super Contributor
timestamp: March 06, 2016, 01:10:21 am
content: The interesting thing is that its an i386SX, and the 16 bit bus SX variant was introduced three years later than the i386, by which time 30 pin SIMM sockets were starting to become fairly common. I've only ever seen 80286 era boards with just DIL sockets.Incidentally, I have a Kangaroo Portable 286 (luggable), that I upgraded with an i386SX board, that runs Windows for Workgroups 3.11 on its internal mono (Hercules) monitor. That's got 8MB RAM (4x 1M 30 pin SIMM on board + a fully populated Intel AboveBoard + daughterboard), a 380MB SCSI hard disk, and it still runs like an arthritic dog.The Intel AboveBoard is stuffed with 41256 256Kx1bit DIP DRAM chips, 72 of them on the board for 2MB and another 72 on the daughterboard. Acquiring and testing enough used RAM chips to fully populate it was quite a challenge even back in the '90s.

author: tyguy2
author_rank: Unknown
timestamp: March 09, 2016, 03:53:41 am
content: Sorry, I've been busy for the past few days. I think I'm just going to abandon trying to get new chips for this, it's just not cost effective. I'm probably just going to gut the system for parts. Thanks for the help, though.

author: Ian.M
author_rank: Super Contributor
timestamp: March 09, 2016, 04:06:34 am
content: Windows 3.1 is fairly useless by today's standards but will run reasonably satisfactorily in 1MB if the memory configuration is carefully optimised. However such a PC is far more useful as a DOS box for interfacing and running legacy hardware. You wont fond any parts worth keeping apart from mounting hardware, random wire to hack up, case parts, and if you are *REALLY* into hard-core embedded hardware development, ISA VGA cards and NICs with well documented chipsets.

author: tyguy2
author_rank: Unknown
timestamp: March 09, 2016, 04:44:46 am
content: I already have a legacy PC for DOS and whatnot, and I do have some uses for these components, so I guess I'll just move on from there.

author: Ian.M
author_rank: Super Contributor
timestamp: March 09, 2016, 04:48:10 am
content: It can be worth salvaging crystal oscillator modules, and if you are interested in legacy computers, any windowed EPROMs.

author: tyguy2
author_rank: Unknown
timestamp: March 09, 2016, 04:51:13 am
content: Yeah, defiantly interested in those.

author: Ian.M
author_rank: Super Contributor
timestamp: March 09, 2016, 05:01:01 am
content: If you are an EBAY seller it *may* be worth searching completed sales to see if there's any market for the individual boards.