Thanks for the tips, tomlee - like yourself I was suspecting something additional than the RAM to be at fault. Having tested the first chip, I wasn't confident that replacing another would result in a great deal of success.
However, I have some good news, having replaced a second chip - it's working! Once the board was in, it fired up straight away off the boot floppy stuck in the drive, to System 1.1g. It booted so fast by the time the CRT had warmed up it was almost at the desktop!
Picture 1: alive, perhaps after 20 years of no use
Picture 2: Circled RAM chips replaced with those from donor 512K motherboard
My very rough guide to removing RAM chips off 128K/512K motherboard:
- Using a solder sucker and iron (@ 350 deg C), remove as much solder as you can from the underside pads of the RAM chip. By the time you are done most pads should have a hole going through to the other side of the board.
- Gently, slightly bend the legs back to the centre of the hole (they are usually angled slightly diagonally, making it harder to pull the chip out if you don't do this)
- Holding the RAM chip firmly with some clamping pliers, heat the pads on the underside of the board using a mini butane torch (mine is a cheap DealExtreme torch/soldering iron, it was set to +++ full). Run the torch slowly up and down the pads, pulling the chip firmly as you do - it's tricky, but if hot enough it should slide out slowly and cleanly. It's daunting, but the hotter the flame better, I found - even if it did cause some slight cosmetic damage to the board itself.
- Once RAM chip is removed, clean up pads/holes again with solder sucker
- Replacement RAM chip should slide straight in, solder in.
JB
However, I have some good news, having replaced a second chip - it's working! Once the board was in, it fired up straight away off the boot floppy stuck in the drive, to System 1.1g. It booted so fast by the time the CRT had warmed up it was almost at the desktop!
Picture 1: alive, perhaps after 20 years of no use
Picture 2: Circled RAM chips replaced with those from donor 512K motherboard
My very rough guide to removing RAM chips off 128K/512K motherboard:
- Using a solder sucker and iron (@ 350 deg C), remove as much solder as you can from the underside pads of the RAM chip. By the time you are done most pads should have a hole going through to the other side of the board.
- Gently, slightly bend the legs back to the centre of the hole (they are usually angled slightly diagonally, making it harder to pull the chip out if you don't do this)
- Holding the RAM chip firmly with some clamping pliers, heat the pads on the underside of the board using a mini butane torch (mine is a cheap DealExtreme torch/soldering iron, it was set to +++ full). Run the torch slowly up and down the pads, pulling the chip firmly as you do - it's tricky, but if hot enough it should slide out slowly and cleanly. It's daunting, but the hotter the flame better, I found - even if it did cause some slight cosmetic damage to the board itself.
- Once RAM chip is removed, clean up pads/holes again with solder sucker
- Replacement RAM chip should slide straight in, solder in.
JB