1040STF RAM disturbance

[ijor]

My old "faithful" 1040STF that worked flawlessly for years, not anymore. I didn't use that computer for a couple of year or so. Now, the computer resets before completing the boot process. Depending on the floppy inserted, I can sometimes barely see the desktop before it resets.

Diag cart flashes, nothing is displayed on the monitor, and outputs the following at the serial port:

Code: Select all

I2 RAM disturbance   0000000000000000 0000100000000000 000712
I2 RAM disturbance   0000000000000000 0000100000000000 000712
...
repeats for ever

Is it the RAM really? Changing power supply for a new working one doesn't help. Would have been an easy fix :(.

[rubber_jonnie]

Not sure what 'RAM disturbance' constitutes, but it looks like you have a bad bit, 5th from the left IIRC.

[frank.lukas]

See the picture ...

D9-10-11-error.jpg

target values / actual values

[czietz]

The last column is the address. If the diag cart reproducibly always give the same address (0x712), then yes, it very much points towards (at least) one faulty bit in one of the RAM chips. Frank has already posted the "decoding guide" for the bits. Find out which DRAM chip is connected to D11 in the lower 512k bank (the one driven by RAS0, CAS0) and replace it. I have to say "find out" because chip numbers vary wildly from board revision to board revision.

[ijor]

Thanks a lot guys.