not me, but there probably varies degrees of dead and causes of dead, and not dead but broken. I heard some rumor based on junk science that gold lead ram inserted in tin slots will disintegrate the slot pins, in 20 years of collecting I've never seen it 1st hand, and everytime I asked nobody else had.

That's odd. Never seen it (other than plastic clips breaking off) despite more than enough boards.

I'd say one of two things is up:
- where you live there are environmental conditions that the boards don't like (maybe hot & very humid?)
- misdiagnosis, the slots aren't really dead, just not accepting what you test them with.

Double check regarding the latter:
- are you testing with FP 72p SIMMs, not EDO? EDO support in 486 boards is uncommon.
- some boards habe trouble with double sided SIMMs. Best test is single-sided 4MB SIMMs with 8/9 chips.
- regarding 9 chips: some boards require parity SIMMs. Ruled that out?

pico1180 wrote on 2023-01-04, 05:42:

Hi there, […]
Show full quote

Hi there,

I was wondering if we could have a discussion about memory channels dead or dyeing on their 486 motherboard and maybe what the cause could be.

At first I thought I may be just unlucky. But I've had so many boards now with dead 72 pin mem slots I thought it would be worth mentioning. I had a 486 board with three (3) out of four (4) 72 pin slots dead. I currently have two 486 boards with two (2) out of the four (4) slots dead. and I just picked up a 4th board that has all four (4) 72 pin slots dead but none of the 30 pin slots.

I've been seeing this so much with my 486 motherboards I thought it would be worth a discussion. Has anyone else experienced this and does anyone know what the most prevalent cause of this may be?

Hello,

There is a lot of knowledge floating around in this forum.
So I would suggest, that you open 2 separate threads for both of your 2 boards where you have currently problems!
1) one board where only 2 slots works ...... I know that the famous Asus VLI SV2GX4 only accepts double sided SIMMs in 2 slots (from there 4). Maybe you have a similar problem?
2) board with 4 times 72 pin + 30pin slots: That is really rare. What board is that?

CoffeeOne wrote on 2023-01-04, 11:04:

1) one board where only 2 slots works ...... I know that the famous Asus VLI SV2GX4 only accepts double sided SIMMs in 2 slots (from there 4). Maybe you have a similar problem?

Indeed, there are boards that support only 2 banks, supporting a single single-sided module, a single double sided module, or two identical single-sided modules. They have a "primary" and a "secondary" slot for each of the two banks. The first side of the secondary slot is wired in parallel to the second side of the primary slot. The bank fails to work if the primary slot is unpopulated (even if a module is installed in the secondary slot), if the secondary slot contains a module that is different from the module in the primary slot, or the secondary slot is populated while a double-sided module is installed in the primary slot.

A slightly improved version of that is 2 banks that can be distributed over four ranks. This has most of the constraints explained in the previous paragraph, but it also allows two double-sided modules in the two slots that make up a bank. The UMC 8881 north bridge works according to this model: Each of the two banks may be populated with a single module in the primary slot, or two identical modules in the primary and the secondary slot for a bank. In either case, single-sided or double-sided modules may be used.

The SiS496/497 on the other hand is more flexible. It supports 7 sides in typical configurations (the chipset is short on pins - there are configurations allowing 8 sides but you lose one PCI master capable slot or support for 64MB/128MB SIMMs in that configuration, IIRC). Most SiS496/497 boards with 4 SIMM slots accept single sided SIMMs only in one of the slots.

I've seen actual dead RAM slots on at least 2 PC Chips M919 boards - they have a 1.2mm thick PCB so are susceptible to flexing. The UM8881F QFP that sits by the fake cache chips and the memory slots that seems to be the memory controller, some of the pins on the QFP weren't making good contact anymore. That's solved on one board by reflowing the UM8881F chip. It hasn't fixed the other fully but there's some scratched traces around the RAM slots on that board too.

Something else as well that I've observed is that some 486 boards are picky about which slots are used, again the M919. With the original BIOS on that board, it would not boot or function if there was no RAM in I think the 1st slot, just a "--" on the POST code reader. But with the later BIOS it'll happily run with memory in any of the slots.
If you're testing one slot at a time, it might be worth populating them all at once to see which ones work - you might've tried that already but it's worth mentioning.

also mkarcher, thank you for the low level explanation of the chipset's capabilities. I've mostly been sticking to single sided SIMMs to avoid having to deal with different ranks but that explains why some slots could use the fully amount of double sided SIMMs while some wouldn't.
And I didn't know about the 'identical single sided SIMM' limitation with some configurations.

I've got a couple of systems with dead or failing slots.

One, a Deskpro 6000 with a 440FX-based Slot 1 board. Two of the eight 72pin SIMM slots just won't recognize any memory modules that have been shoved into them. However, since the machine requires memory to be installed in pairs, it's possible that only one of the slots is actually bad.

The second is a PowerMac G4 MDD. One of the four 184-pin DDR slots is bad. It still recognizes memory, but the system becomes very unstable when memory is installed in the bad slot.

One more possible cause of issue with some memory slots could be related to some signal traces being cut on the bottom of pcb. It's quite common for boards being taken from dumpster or scrapyard, where usually they are mixed with other electronic boards and it's easy to get the scratches on their surface.

I'm not sure what was your source for these boards, however if you don't know the previous life of these boards then try to check the pcb traces on bottom side for some scratches.

Its time to invest in proper ESD mat and grounding wrist strap

There is a lot of brilliant information in this thread.

First off,
I feel dumb. With the information I learned in this thread, I went back and scrutinized my configurations against the manuals. Sure enough, the boards are extremely specific as to what can go in what slot. That is what I get for doing sloppy computer work. I am pretty convinced I may be the problem here.

Second:
The board that has the 4x 72 pins and 4x 30 pins is a U-Board KS TG919

Third :
Per suggestion by @CoffeeOne let me break down each motherboard and it's specific problem:
Gigabyte GA-486VS REV 7 (REV 8 BIOS): Only accepted a 4Mx36 (16MB) module in Bank 0. Closer scrutiny reveals you cant just toss a 4Mx36 in any slot and expect it to work. You have to progress through the banks. PROBLEM SOLVED

Free Computer Tech 486F38X: Only accepted 4x36 (16MB chips) in Banks 0 and 1. Same thing as the GA-486VA, you have to progress through the banks. PROBLEM SOLVED

VLI-486SV2GX4: Only accepted 4x36 in Banks 0 and 1. Per CoffeeOne I realized only Banks 0 and 2 will accept doubled sided RAM. PROBLEM SOLVED

U-Board KS TG919 Ver 1: This one is a little harder. No 72 pin configuration that I can come up with allows this board to post. I only have two (2) 4MB so if it requires all for 72 pin slots to be populated I can not do that at this minute. And of course I cant find a manual to reference and Retro Web treats this board as a ghost.

I learned a lot from all you feed back. Including that I am an idiot 😁

rasz_pl wrote on 2023-01-05, 00:58:

Its time to invest in proper ESD mat and grounding wrist strap

I do use an ESD. For no other reason then better stability and to protect solder points. I do not, however, believe in wrist straps.

pico1180 wrote on 2023-01-05, 02:03:

I do not, however, believe in wrist straps.

It doesnt really matter what you believe in, its physics.

I don't believe in them either, or let me say. If I was in an environment, and conditions of that environment, be it weather, building materials of the place I'm in I believe in them environment. Than I believe in it. But I don't live in dry climate and i dont have carpet, or walk around on rubber mats... In 30+ years I have never ESDed anything, because I don't have static and I don't get static and I know many other people share the same experience.

pico1180 wrote on 2023-01-05, 02:02:

[...]

The board that has the 4x 72 pins and 4x 30 pins is a U-Board KS TG919

Are you sure about that? All the pics I see show 3x 72p and 4x 30p:

Is this your board?

U-Board KS TG919 Ver 1: This one is a little harder. No 72 pin configuration that I can come up with allows this board to post. I only have two (2) 4MB so if it requires all for 72 pin slots to be populated I can not do that at this minute. And of course I cant find a manual to reference and Retro Web treats this board as a ghost.

Highly unlikely it requires multiple slots to be poulated, the 486 memory bus is 32 bits wide, so 72p modules go one by one.

The manual is on UltimateRetro. The last page indicates supported memory configs, but clearly contains errors (single 1MB SIMM in bank 1 would give 2MB total...?), but reading this, for 72p-only SIMM configs, you should try identical SIMMs in slots 2 and 3.

Just a double-check: does the board work with 30p SIMMs? Otherwise it could be something totally unrelated to memory causing it not to boot...

rasz_pl wrote on 2023-01-05, 02:09:

pico1180 wrote on 2023-01-05, 02:03:

I do not, however, believe in wrist straps.

It doesnt really matter what you believe in, its physics.

nah. disproved long ago.

dionb wrote on 2023-01-05, 02:43:

Are you sure about that? All the pics I see show 3x 72p and 4x 30p: https://www.elhvb.com/webhq/models/486vlb3/kstg919v2p.jpg […]
Show full quote

pico1180 wrote on 2023-01-05, 02:02:

[...]

The board that has the 4x 72 pins and 4x 30 pins is a U-Board KS TG919

Are you sure about that? All the pics I see show 3x 72p and 4x 30p:

Is this your board?

U-Board KS TG919 Ver 1: This one is a little harder. No 72 pin configuration that I can come up with allows this board to post. I only have two (2) 4MB so if it requires all for 72 pin slots to be populated I can not do that at this minute. And of course I cant find a manual to reference and Retro Web treats this board as a ghost.

Highly unlikely it requires multiple slots to be poulated, the 486 memory bus is 32 bits wide, so 72p modules go one by one.

The manual is on UltimateRetro. The last page indicates supported memory configs, but clearly contains errors (single 1MB SIMM in bank 1 would give 2MB total...?), but reading this, for 72p-only SIMM configs, you should try identical SIMMs in slots 2 and 3.

Just a double-check: does the board work with 30p SIMMs? Otherwise it could be something totally unrelated to memory causing it not to boot...

that looks like version 2. I believe mine is version 1.. Pic uploaded for reference.

there is no issue with the 30 pin simms. I have 16MB in 4 30 pin simms and the board posts just fine with it. I did try two identical 8MB double sided ram in slots 2 and 3. no joy.

pico1180 wrote on 2023-01-05, 03:37:

rasz_pl wrote on 2023-01-05, 02:09:

pico1180 wrote on 2023-01-05, 02:03:

I do not, however, believe in wrist straps.

It doesnt really matter what you believe in, its physics.

nah. disproved long ago.

Prove it.

pico1180 wrote on 2023-01-05, 03:47:

dionb wrote on 2023-01-05, 02:43:

Are you sure about that? All the pics I see show 3x 72p and 4x 30p: https://www.elhvb.com/webhq/models/486vlb3/kstg919v2p.jpg […]
Show full quote

pico1180 wrote on 2023-01-05, 02:02:

[...]

The board that has the 4x 72 pins and 4x 30 pins is a U-Board KS TG919

Are you sure about that? All the pics I see show 3x 72p and 4x 30p:

Is this your board?

U-Board KS TG919 Ver 1: This one is a little harder. No 72 pin configuration that I can come up with allows this board to post. I only have two (2) 4MB so if it requires all for 72 pin slots to be populated I can not do that at this minute. And of course I cant find a manual to reference and Retro Web treats this board as a ghost.

Highly unlikely it requires multiple slots to be poulated, the 486 memory bus is 32 bits wide, so 72p modules go one by one.

The manual is on UltimateRetro. The last page indicates supported memory configs, but clearly contains errors (single 1MB SIMM in bank 1 would give 2MB total...?), but reading this, for 72p-only SIMM configs, you should try identical SIMMs in slots 2 and 3.

Just a double-check: does the board work with 30p SIMMs? Otherwise it could be something totally unrelated to memory causing it not to boot...

that looks like version 2. I believe mine is version 1.. Pic uploaded for reference.

there is no issue with the 30 pin simms. I have 16MB in 4 30 pin simms and the board posts just fine with it. I did try two identical 8MB double sided ram in slots 2 and 3. no joy.

Most likely you found that already by yourself .....
https://www.elhvb.com/webhq/models/486vlb3/kstg919.html

Only 4MB or 16MB 72 pin modules are allowed I think. And bank 0 is either the 4 30 pin SIMMs or the first 72 pin slot, you cannot use both obviously, there are only 4 memory banks (while the board has physically 5 banks)

CoffeeOne wrote on 2023-01-05, 09:41:

Most likely you found that already by yourself ..... https://www.elhvb.com/webhq/models/486vlb3/kstg919.html […]
Show full quote

pico1180 wrote on 2023-01-05, 03:47:

dionb wrote on 2023-01-05, 02:43:

Are you sure about that? All the pics I see show 3x 72p and 4x 30p: https://www.elhvb.com/webhq/models/486vlb3/kstg919v2p.jpg […]
Show full quote

Are you sure about that? All the pics I see show 3x 72p and 4x 30p:

Is this your board?

Highly unlikely it requires multiple slots to be poulated, the 486 memory bus is 32 bits wide, so 72p modules go one by one.

The manual is on UltimateRetro. The last page indicates supported memory configs, but clearly contains errors (single 1MB SIMM in bank 1 would give 2MB total...?), but reading this, for 72p-only SIMM configs, you should try identical SIMMs in slots 2 and 3.

Just a double-check: does the board work with 30p SIMMs? Otherwise it could be something totally unrelated to memory causing it not to boot...

that looks like version 2. I believe mine is version 1.. Pic uploaded for reference.

there is no issue with the 30 pin simms. I have 16MB in 4 30 pin simms and the board posts just fine with it. I did try two identical 8MB double sided ram in slots 2 and 3. no joy.

Most likely you found that already by yourself .....
https://www.elhvb.com/webhq/models/486vlb3/kstg919.html

Only 4MB or 16MB 72 pin modules are allowed I think. And bank 0 is either the 4 30 pin SIMMs or the first 72 pin slot, you cannot use both obviously, there are only 4 memory banks (while the board has physically 5 banks)

here is what i found for the mem configuration, but it seems a little vague to me. i'm guessing the 1-s indicates one single sided memory module? it indicates it will accept double sided, but doesn't give any double sided configurations?

my concern is the board wont post with any of my 4mb 72 pin modules that i have. tested good in other systems.

OK, so did you already try a single 4MB module 72pin in bank0 without any 30pin SIMMs?
Bank 0 is the one next the 30pin slots.

EDIT: I screwed up the quoting, so deleted everything 😁