Hi guys,
Last week I picked up a nice clean IBM 5150 with keyboard from the original owner. It's nice and clean and has a HDD,a full 256K of RAM on board, a Paradise CGA/mono card, an asynch serial card, and an IBM 256K RAM expansion card (the type with 4 16-pin memory modules) described here: http://www.minuszerodegrees.net/oa/OA - IBM 256KB Memory Expansion Option.pdf . It worked great for about two hours when it just shut down out of the blue. When I tried to turn it on, the fan whirred for 1-2 sec and then it shut down again. I pulled all the cards and pin pointed it as the RAM expansion card. After setting the DIP switches on the MOBO to only look for on-board RAM, the machine works as usual, so the board seems to be ok. I even tried the RAM card in a different ISA slot, but that didn't help.
I'd like to try to repair the 256K card, if possible and wanted to see if you could give me some ideas. All the tantalum caps look ok, and even after removing all four memory modules, the computer will still not power up with the card in. I've checked the 1st and 3rd legs of the LM317T voltage regulator and I'm only getting 0.6V on each for a second or so...so this is a problem. FYI, I didn't check the center leg b/c I'm accustomed to those being a ground...turns out the center pin is output, but the 0.6V readings on the other legs are a problem. With the card out, I checked the diode near the voltage reg at CR1 and I'm getting a 520 mV voltage drop using the diode test on my DMM. I'm not sure if this is a little low or if it's ok.
So now I'm out of ideas. I'd really appreciate any input you guys can give on how to test this further. It's an original IBM card and I'd love to get it working.
BTW, I attached an image of the card.
Thanks!
Last week I picked up a nice clean IBM 5150 with keyboard from the original owner. It's nice and clean and has a HDD,a full 256K of RAM on board, a Paradise CGA/mono card, an asynch serial card, and an IBM 256K RAM expansion card (the type with 4 16-pin memory modules) described here: http://www.minuszerodegrees.net/oa/OA - IBM 256KB Memory Expansion Option.pdf . It worked great for about two hours when it just shut down out of the blue. When I tried to turn it on, the fan whirred for 1-2 sec and then it shut down again. I pulled all the cards and pin pointed it as the RAM expansion card. After setting the DIP switches on the MOBO to only look for on-board RAM, the machine works as usual, so the board seems to be ok. I even tried the RAM card in a different ISA slot, but that didn't help.
I'd like to try to repair the 256K card, if possible and wanted to see if you could give me some ideas. All the tantalum caps look ok, and even after removing all four memory modules, the computer will still not power up with the card in. I've checked the 1st and 3rd legs of the LM317T voltage regulator and I'm only getting 0.6V on each for a second or so...so this is a problem. FYI, I didn't check the center leg b/c I'm accustomed to those being a ground...turns out the center pin is output, but the 0.6V readings on the other legs are a problem. With the card out, I checked the diode near the voltage reg at CR1 and I'm getting a 520 mV voltage drop using the diode test on my DMM. I'm not sure if this is a little low or if it's ok.
So now I'm out of ideas. I'd really appreciate any input you guys can give on how to test this further. It's an original IBM card and I'd love to get it working.
BTW, I attached an image of the card.
Thanks!