Intersil HM1-6508-9 memory ic  - Page 1
Forum section: electronics / projects

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 02, 2012, 02:49:45 pm
content: Hi All,I did write this message once but it does not seem to have made it through to the board. Not sure why. It did have pic attachments, etc. Maybe it is still being validated. But that was a few days ago now.Anyway, I was asked to try and fix a memory board for an old CNC machine. They say they are getting parity errors reported when trying to enter a program to run. Some programs work and some do not.The memory board consists of a bunch of HM1-6508-9 ICs. They bought new ones and replaced the lot and it did not work. I even wrote a small program to test each IC. It simply wrote a 0 and 1 to each memory location of the IC and checked the write was successful. All the ICs I tested passed. I was wondering if the memory was maybe a bit slow. There does seem to be two speed variations. The fast running at 180ns whilst the slower one runs at 250ns. But I cant get hold of either part really. I think the ones they found and bought could be either. I do not know.I wondered if anyone has ever had any experience of these or might be able to suggest a replacement part that I could get that would work. I think these ICs are old now and out of production.They did say they would give me some money to try and back engineer the whole board but I think that could be a real pain and take a lot of work.Anyone have any suggestions?ThanksTrev

author: Unknown
author_rank: Unknown
timestamp: December 02, 2012, 06:46:34 pm
content: Hi, perhaps you could put the scope on the chip enable pin and check the duration of the negative pulse to work out the memory speed? according to the datasheet the HM-6508B-9 can go down to 180nS but the HM-6508-9 has a minimum of 250nS.Someone on Ebay selling the 250nS stuff; I can't seem to find any 180nS chips though.http://www.ebay.co.uk/itm/1x-HM1-6508-9-1K-X-1-STANDARD-SRAM-250-ns-CDIP16-/110893408866?pt=LH_DefaultDomain_0&hash=item19d1c32262

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 02, 2012, 09:43:47 pm
content: Hi, thanks for the response.The only thing I have at present is that it might be the speed difference. I do not know what the marking on the chips would be to indicate the difference in speed.Maybe I need to speed test the memory and stress them to their limits.Trev

author: free_electron
author_rank: Super Contributor
timestamp: December 03, 2012, 04:26:49 am
content: Who says its bad memory ? It could be a bad parity generator ...

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 03, 2012, 11:46:37 am
content: Good point. They moved some of the memory ICs around the the machine acted differently. Sometimes a small program can be loaded. Then they move memory around and it cant. This made them think it was one of the memory ICs.

author: amyk
author_rank: Super Contributor
timestamp: December 03, 2012, 01:30:09 pm
content: The 6508 uses a standard JEDEC pinout so any 1Kx1 SRAM of the right speed should work, but since 1Kbit SRAMs are very rare now you may have better luck replacing several of them with a single byte-wide SRAM of larger capacity (and much faster) that was produced for motherboard caches etc.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 03, 2012, 03:25:51 pm
content: Well this is where I was hoping someone might be able to suggest a replacement part.Failing that maybe I could make a board that plugged in to several of the sockets and wired to a new memory IC. But I would not know where to start looking at present. I would also have to start tracing out the actual board which is a bit of work.It would be a much better option if I could find a replacement part I think.ThanksTrev

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 03, 2012, 11:13:04 pm
content: I'd replace each chip with a plug-in board containing something like this:http://www.cypress.com/?docID=25678Wastes boatloads of memory, but it's cheap as chips. What's possible also depends on the mechanical situation.

author: amyk
author_rank: Super Contributor
timestamp: December 04, 2012, 08:54:26 am
content: Quote from: jeroen74 on December 03, 2012, 11:13:04 pmOr replace 64 of them with one of those... how much memory did the original board have? I'm guessing it's rows of 9 for 8 data + 1 parity. You can replace 8 parity chips with 1 x8 chip, using each bit of the data bus for one parity bit.If the memory board is a separate part that plugs into the system, you can figure out the address/data/control lines and from there it should be relatively easy to substitute the whole thing with one modern SRAM and maybe some glue logic.

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 04, 2012, 11:43:57 am
content: Who cares about wasted memory? I think the one-little-board-per-vintage-memory-chip is the simplest, cheapest and fastest wayThe chip I linked to is available from Farnell for a couple of Euro's.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:11:48 pm
content: It may be a waste in technology terms but in real life if the fella can get his machine working again then it means a lot. If he has to replace the machine it will cost him maybe £40K. So a few ICs being wasted really means nothing to him.I have attached a pic of the board. Space isn't great really. I reckon if I could get the pinout of the board it probably would not be too much trouble to reproduce it with a couple of ICs but I can not find any information on it.Trev

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 04, 2012, 12:16:31 pm
content: Hmm, are the batteries ok?

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:25:00 pm
content: The batteries have been replaced. Apparantly they had a problem before that was fixed by replacing the batteries.

author: ecat
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:33:27 pm
content: The RAM chip second column from the left, second row down is the wrong way around!

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:38:46 pm
content: There are quite a few ICs there. I thought it were only 9 :/ In this case one large PCB that connects to several sockets to get all address lines and then one modern chip is better.But first try flipping that chip the right way aroundwho knows it survived.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:45:22 pm
content: Great spot on the memory IC but they have been messing around with the board swapping memory around. It wasn't working before and I am pretty sure them putting that chip in wrong is not the real problem. It is just them not helping matters by making that mistake.I think if they are banked in 8 + 1 then I can work something there. I only need the address lines from one ic of each bank and then the 8 + 1 data lines. So I could maybe make a board that sits in the sockets and has a couple of memory ICs doing the job.I think the memory currently is 4K in total.

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:50:05 pm
content: With a bit of luck the sockets are on a nice 0.1" grid and then you can even use prototyping board.You don't need multiple memory ICs; one is enough. Just ground unused address lines.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:55:07 pm
content: There are 36 ICs so I need 36bits of data. 4 x ( 8 + 1 )

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:59:31 pm
content: Are you sure about that? I cannot imagine it's a 32 bit processor. More likely it's just 4 banks of 1Kx9 where each bank occupies 1K in the memory map. That should be easy to find out, see if all data lines across the banks are interconnected or not.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 01:01:27 pm
content: Okay, that does make more sense. A lot more sense. Thanks for the help. Everyone has been great. I shall update if I get anywhere but it sounds hopeful.

author: amyk
author_rank: Super Contributor
timestamp: December 04, 2012, 01:57:14 pm
content: Looks like a 4K x 9 array.One CY7C185 (you'll waste half but they don't make 4K x 8 SRAMs) and one CY7C147 for the parity should be all you need. The board doesn't look too hard to RE since it's old low-density tech.(These parts were used as cache on old motherboards and what I was referring to earlier. If you find some scrap 386-486 motherboards you could check them for cache chips too.)

author: Unknown
author_rank: Unknown
timestamp: December 04, 2012, 02:41:06 pm
content: The 180nS HM1-6508B-9 stuff is on Ebay at £17.99 each! Although I wouldn't put all my money on the problem being down to the RAM.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 02:54:19 pm
content: Yes, just found it. I do not think the original parts were HM1-6508B-9 but are HM1-6508-9. So maybe it isn't down to the speed either. Hmm. Tricky.

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2012, 04:18:53 pm
content: Looks like a S100 bus. Have you looked for old s100 systems on Ebay to grab the memory cards out of them. Yes, that chip does look like it is in backwards.......I think I had some of those ram chips that I pulled out of old boards........ I do have a small box of 8255 PIA's

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 04, 2012, 05:25:21 pm
content: Wow, S100 bus. Now I am learning something new. That is cool. Least I have the pinout for this thing now. Thanks SeanB.What is a 8255 PIA?Trev

author: SeanB
author_rank: Super Contributor
timestamp: December 04, 2012, 06:06:28 pm
content: Look at the 8080 datasheet and the recommended layout and test circuit........en.wikipedia.org/wiki/Intel_8255

author: TerraHertz
author_rank: Super Contributor
timestamp: December 06, 2012, 09:23:31 am
content: Well it _was_ probably just one flaky chip. Now it's two.First, mark that reversed chip - it's very likely dead if they powered the board up like that.Second, those sockets look like the flat-spring kind, not machine pins. Very prone to having the contacts bent and making intermittent contact. Inspect every pin with a magnifying glass. Replace any sockets that look sus. Ditto with ICs - someone needs to extract every IC and inspect for bent legs. Then clean all pins by rubbing lightly with an ink eraser. The pins are tin or solder plated - notorious for developing oxide films that make intermittent contact over time.This is actually a dreaded syndrome I remember well - flaky memory boards that used cheap sockets for the RAMs.[Edit: also do the same for all the logic. Same type of sockets, same tinned IC legs. There's no guarantee the fault isn't an intermittent in those circuits, not the RAMs.]As for identifying the original bad chip...Do they have any programs that will fit in 1K?Take all the chips out but the 9 in one row (top or bottom, experiment to find out which works.)There may be jumpers or something to indicate how many K are installed. No documentation at all?Still getting parity errors? If so, swap to another 9 chips. Repeat till you have a set of 9 that always works.Then swap in other chips in one position, one at a time, till you find the bad one.About doing a hack with newer RAMs-Since the board obviously has battery backup of the data, there'll also be some circuitry that disables writes when supply rail droop is detected (if it's done badly), or on a power-fail warning signal from the PSU (if it's done right.)If you decide to use a newer SRAM to replace the lot, you'll need to ensure that it is a low power in standby type, with a write-enable that is compatible with the data protection scheme used on that board.That's going to be interesting with the 9-bit words. The cache RAMs people are suggesting don't tend to be designed with power-down data retention in mind.Or you could just use two 8bit 64KB or 128KB CMOS RAMs, and waste most of the the storage space. <gasp>

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 06, 2012, 04:11:34 pm
content: Wow, everyone is giving me so much great information about this board. Thanks.I will have another proper look at the board over the next few days. As I can now identify the edge connector pinout I may well be able to trace things a little easier.I may well try and change all the IC holders. I do not want to damage the board. Removing those holders will be a pain.

author: jeroen74
author_rank: Frequent Contributor
timestamp: December 06, 2012, 05:02:52 pm
content: To remove the holders, it best to crush the plastic, then remove each pin by heating it up, then pull it out when hot with tweezers. Or the brute force method, an hot air blower

author: TerraHertz
author_rank: Super Contributor
timestamp: December 07, 2012, 03:36:08 am
content: Wait, wait! I didn't suggest changing ALL the IC sockets. Only any ones that have obviously bent contacts. Which there may be none of.How tight do the IC's feel during insertion? If it takes a sensible amount of force to insert or remove them, the sockets are probably fine. There were a few makes of sockets that were really horrible, but these ones don't seem to be any of the really bad ones I know of.From my experience, trying to replace a large number of sockets on a board has a very significant risk of doing serious damage to the PCB. So best to avoid. Especially if the socket pins were bent over or trimmed on the solder side.Any you do replace - yes, if you can, remove the plastic case first, then lift out each pin with a soldering iron on the component side, then use a solder sucker on the rear side very carefully to clean the through holes out. Without the socket preventing airflow from the component side of the board, and the pins in the holes keeping some solder in there by surface tension, the solder-sucking can be done much quicker and with less heating, reducing risk of lifting pads and tracks off the fiberglass. But many socket types don't allow for easy removal of the plastic body, without putting a lot of force on the pins. Which can separate the copper from the fiberglass.With very old boards, it also helps to put a spot of fresh flux-cored solder on the solder-side pads before using the sucker. This removes the oxide layer, allows better heat flow and makes the solder flow easier during the suck.

author: amyk
author_rank: Super Contributor
timestamp: December 07, 2012, 07:36:02 am
content: I don't think it's S100. Not enough contacts. Probably a proprietary interface.TerraHertz: You're right about using cache RAM, didn't notice they have several mA of standby draw (rather high for CMOS) whereas the original's standby is in the uA range. In that case, something like a CY62256N would be more suitable.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 07, 2012, 03:36:54 pm
content: Hi.My problem I suppose is that I cant really test very easily at present. I would have to spend a day with the machine. Trying all these things. Maybe that is what I need to do before anything else.That is why I was thinking of replacing all the sockets. Because a few hours doing that is easier than guessing if is one of them. Replace the lot and see where we get. The confusing thing is that I tested all the memory. I wrote a small program that wrote a 1 then read back. Wrote a 0 then read back. It did this for all 1024 addresses.All the memory passed. But when they got the board and had a play they found that is did not work still. And then when they moved memory around it worked slightly differently. A small program would load. So it seemed like some of the memory was bad and was being moved around. But I tested it all?Maybe dirty IC holders are not helping? What else could cause such a scenario?

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 07, 2012, 03:46:40 pm
content: Quote from: trevwhite on December 07, 2012, 03:36:54 pmIf I read this correctly you tested the board in another machine?QuoteIf you tested the board ok in another machine, it could be that there is an error somewhere else in the address or data lines.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 07, 2012, 03:56:08 pm
content: Hi. No I did not test the board in another machine. I took each IC out and hooked it up to a dev board. I then wrote a small program that addresses the IC and did write/reads to each location. Testing that I could write a 1 and a 0 to each.When the fella took the board away he tested it in the original machine. It did not work. They moved some memory around and it worked a little. They could load a small program in but nothing good enough to make it useful.So it might just be dirty/unreliable ic holders and dirty ic pins?

author: TerraHertz
author_rank: Super Contributor
timestamp: December 08, 2012, 09:26:44 am
content: Quote from: trevwhite on December 07, 2012, 03:56:08 pmPossibly. That type of fault can produce very confusing results during swapping, since every time you pull the board out you're slightly moving the intermittent contacts.On an old machine such a fault can be anywhere, starting with the solder joints of the edge connector to the backplane, the contacts on the edge connector socket, dirt on the edge connector itself, a through-hole plating gone intermittent, IC socket contact springs gone weak, legs of the ICs having grown oxide layers, etc.Even an actual faulty IC - which can be temperature dependent or just plain intermittent.Oh, and of course in a machine shop there's the chance of iron filings/swarf getting to the board, which can make horrible vibration-sensitive intermittents. Some IC pins and sometimes the socket pins may be iron cored - which means they are magnetic, which means magnetized iron filings may like sticking to them.Take a closeup photo of the board, then take ALL the ICs out (and those jumper headers.) Inspect every socket pin and every solder joint under magnification. With the solder joints you're looking for hairline cracks, especially around the leads of through-hole components, that suggest dry joins. ANY joint that looks suspect, resolder - it does no harm.Visually check the edge connector socket in the rack with a flashlight. No bent pins, no corrosion, no foreign material stuck down there?Lightly clean the gold edge connector pads with an ink rubber. (Not too much, don't want to wear the gold off!)It's also possible to clean the edge connector socket pins, for example with a bit of cardboard soaked in alcohol, held in tweezers or a surgical clamp. But be extremely careful not to snag on the pins and distort them. You have to look at the contact shape, and decide how to do it. Bear in mind that if you wreck one pin on the backplane, you've definitely killed the machine.Check every IC pin is straight. Any that are bent, straighten with fine flat-nosed pliers. Then lightly polish the flat faces of the IC leads with the ink rubber. Blow the PCB off with compressed air, both sides. Any dirt, scrub it with isopropyl alcohol and a stiff toothbrush. Dry with compressed air, put all the ICs back per the photo.Did it make any difference?If still flaky, then you have a candidate for attempting electronic diagnosis.

author: amyk
author_rank: Super Contributor
timestamp: December 08, 2012, 10:37:35 am
content: Quote from: trevwhite on December 07, 2012, 03:56:08 pmFigure out the pinout of, and test the whole board at once via the edge connector. If any bits fail their address can lead to the clue as to where on the board the problem is.

author: trevwhite
author_rank: Frequent Contributor
timestamp: December 19, 2012, 11:25:02 am
content: Hi All.Update on the board. I think I have fixed it now. Thanks everyone. I went back and checked the board again. There were bad connections, bent pins, broken tracks. I replaced the memory ic that was the wrong way round. I found tracks broken from the battery backup. The battery is connected directly to the memory for its power down mode.I cleaned up all the ic holders. I think they will need replacing at some point but for now some switch cleaner did seem to do the trick.Thanks for all the help. There is a bloke in a factory who is so happy to have his machine back working.Trev