Hi! I have saved a very early 486 mb (cam 33/50-p8) from battery leakage… now the motherboard work, but only with 256k simm, any another simm is totally ignored. Why? If is a hardware issue, what’s the difference from a 256k and 1mb simm? Electrically is not the same?
Are those 30 pin SIMMs? If so, remember that for a 486 you must install SIMMs in groups of 4 of the same size. For example 4 256k SIMMs (1MB), 4 1MB SIMMs (4MB) and so on.
A single 30 pin SIMM is not going to work.
TheMobRules wrote on 2022-03-31, 23:24:Are those 30 pin SIMMs? If so, remember that for a 486 you must install SIMMs in groups of 4 of the same size. For example 4 256k SIMMs (1MB), 4 1MB SIMMs (4MB) and so on.
A single 30 pin SIMM is not going to work.
Yes, you'll need to try four at a time. 30 pin SIMMs are "8 bit wide" and 386 and 486 have a 32 bit memory bus.
72 pin simms are 32 bit in one piece.
But, if it takes 4 of 256k it should take 4 of 1 MB.
Maybe not at the same time and some modules simply don't work on some motherboards. So in case you have several sets of 4 x 1 MB, try more of them.
In case you don't, the 1 MB are really everywhere and dirt cheap. Most are 70 ns and 60 ns are rare and prolly wont make much difference.
I like jumpers.
Also they need to be Parity SIMMS, 9 chip or 3 chip type and 60 to 70nS rated as per the docs for the board-and all 4 match, best to use 9 chip if you have them.
Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun
Could be A20 line problems, either physical, scraped trace, shorted tantalum... or logical, messed up chipset, KBC or switching gate.... or soft error, BIOS corruption etc.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
Yes, is implied, I use 4 simm at time 😉
@bitwrangler can be a20? Is near keyboard controller? But… with 8 simm of 256k each I have 1.6mb, gate A20 work?
Picture of the patient
marmotta wrote on 2022-04-01, 03:21:Yes, is implied, I use 4 simm at time 😉
Well, I did assume as much, but by starting such a thread, you have to account for the ravine-sized knowledge gaps between users here.
With some kids, it's a bit like with irony, sarcasm and Poe's law. No way to tell "goes without saying" from "I actually don't know the first thing."
It's not like I can deny such a gap between me and the cracks around here, as well... 😒
I like jumpers.
Cuttoon wrote on 2022-04-01, 10:16:Well, I did assume as much, but by starting such a thread, you have to account for the ravine-sized knowledge gaps between users […]
marmotta wrote on 2022-04-01, 03:21:Yes, is implied, I use 4 simm at time 😉
Well, I did assume as much, but by starting such a thread, you have to account for the ravine-sized knowledge gaps between users here.
With some kids, it's a bit like with irony, sarcasm and Poe's law. No way to tell "goes without saying" from "I actually don't know the first thing."
It's not like I can deny such a gap between me and the cracks around here, as well... 😒
Sorry, but my poor English not help ☺️
marmotta wrote on 2022-04-01, 03:21:Yes, is implied, I use 4 simm at time 😉
@bitwrangler can be a20? Is near keyboard controller? But… with 8 simm of 256k each I have 1.6mb, gate A20 work?
Right, so it's not the logical KBC or soft A20 problems but maybe physical at/near the SIMM sockets, stopping the sockets registering over a 1MB bank, or is the next address line up A21, stopping the system going higher to 4MB or higher.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
BitWrangler wrote on 2022-04-01, 14:18:marmotta wrote on 2022-04-01, 03:21:Yes, is implied, I use 4 simm at time 😉
@bitwrangler can be a20? Is near keyboard controller? But… with 8 simm of 256k each I have 1.6mb, gate A20 work?
Right, so it's not the logical KBC or soft A20 problems but maybe physical at/near the SIMM sockets, stopping the sockets registering over a 1MB bank, or is the next address line up A21, stopping the system going higher to 4MB or higher.
Ok can be the right way! I have new details: my keyboard controller not have the pin 22 (a20 gate) connected, is managed by chipset? I found the difference from 256k and 1mb simm: the chips on 256k Simm are 16pin, on 1mb are 18 pin. One pin is for testing (I think is not useful), another is the address a9 (256k have address a0-a8, 1mb have address a0-a9). Can be useful?
The Varta poison is on some tracks, where I can reach I have tested and eventually bridged, but I not want to desolder all simm slots, if the bad track is under the sockets is a big problem...
Yes, they need one more address line to be recognized is what I'm saying so you need to check for breaks or corrosion in that from all the sockets.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
BitWrangler wrote on 2022-04-01, 15:48:Yes, they need one more address line to be recognized is what I'm saying so you need to check for breaks or corrosion in that from all the sockets.
But the sockets is very difficult to desolder… hot air can damage it. 😞 (the tracks under the pcb and the logical ic near simm seems to be ok)
Yes, you don't want to remove the sockets right away, but to test the connections right through from source to inputs of the CPU an/or chipset with a continuity tester, maybe they can have jumper wires to route them if they are damaged inside the board.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.
BitWrangler wrote on 2022-04-01, 16:07:Yes, you don't want to remove the sockets right away, but to test the connections right through from source to inputs of the CPU an/or chipset with a continuity tester, maybe they can have jumper wires to route them if they are damaged inside the board.
With schematics is easy, without no… the address lines are directly connected to chipset? Or pass from various logic ic? I try 😉
I traced the pin 18 of simm (address a9), go to one resistor and then go to a logic ic 74f244 (tested good). After the logic ic I not able to know where the signal go....
One suspect: the motherboard born for 50mhz 486dx, I have changed the oscillator and installed a dx33. Can be a problem? (the motherboard not have a clock jumper selection)
is the address line a9 connected to all the sockets and the 74f244 ? ie no breaks inbetween somewhere.
Right to repair is fundamental. You own it, you're allowed to fix it.
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weedeewee wrote on 2022-04-01, 23:04:is the address line a9 connected to all the sockets and the 74f244 ? ie no breaks inbetween somewhere.
No breaks
Only the first simm of each bank (0-1/1-1), the sockets 0-2/3/4 and 1-2/3/4 follow another way. I need to investigate 😉
Edit, investigated: the sockets 0-2/3/4 and 1–2/3/4 going to a resistor pack and then go to another pin of the same 74f244. No breaks
Assuming this is the board: https://www.ultimateretro.net/en/motherboards/974 based on the actual board picture.
Just to refresh: For DX33 the oscillator crystal should be a 66Mhz.
After you do that then the jumpers:
CPU Speed - OSC1 - P30 - P31 - P32 - P39 - P97
80486DX33MHz - 66MHz - Closed - Closed - Open - N/A - Closed
Can you take a picture of: the motherboard looking down on it AND the 1MB simms you are trying to use ?
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Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun
Horun wrote on 2022-04-01, 23:21:Assuming this is the board: https://www.ultimateretro.net/en/motherboards/974 based on the actual board picture. Just to refresh […]
Assuming this is the board: https://www.ultimateretro.net/en/motherboards/974 based on the actual board picture.
Just to refresh: For DX33 the oscillator crystal should be a 66Mhz.
After you do that then the jumpers:
CPU Speed - OSC1 - P30 - P31 - P32 - P39 - P97
80486DX33MHz - 66MHz - Closed - Closed - Open - N/A - Closed
Can you take a picture of: the motherboard looking down on it AND the 1MB simms you are trying to use ?
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The board is almost identical, but I not have this jumpers (empty spaces on pcb). And in this manual is strange (I think a error) the jumpers for dx33 and dx50 are the same, change only the clock… if the jumpers are the same, what divide the 66mhz clock to 33? And why use the 66mhz oscillator?
