Sharp PC-1261 with faulty RAM

[robve]

A PC-1261 with a faulty RAM chip.

The fault appears to affect only one bit in RAM that always stays 0. This bit is associated with variable B. So assigning 77777 to variable B gives 77773 instead. I don't believe there is a way on this machine to remap RAM to work around this (some Sharp PC models have address pointers to POKE to change the location of variables and BASIC programs).

The PC-1261 has a separate PCB for RAM. I could swap that out if I can find a spare PC-1261 RAM PCB somewhere. Or I could try replacing the RAM chip, which is surface mounted.

The RAM chip is marked:
4K1
SC613256
G77

I have no idea if these RAM chips (or PC-1261 RAM PCB boards) are still obtainable. Any suggestions?

- Rob

[Didier Lachieze]

(09-25-2023 05:14 PM)robve Wrote:  The RAM chip is marked:
4K1
SC613256
G77

This is not the RAM chip, this is the ROM. The RAM is composed of 5 chips integrated in the Chip On Substrate (COS) black package on the top of the board:



The schematic is visible here.

Reference: http://www.silicium.org/forum/viewtopic....46&t=48635

[robve]

(09-25-2023 06:08 PM)Didier Lachieze Wrote:  This is not the RAM chip, this is the ROM. The RAM is composed of 5 chips integrated in the Chip On Substrate (COS) black package on the top of the board: ...

Thanks for the info! It won't be possible to replace the RAM then.

(09-25-2023 06:08 PM)Didier Lachieze Wrote:  Reference: http://www.silicium.org/forum/viewtopic....46&t=48635

Strange why Sharp also put the ROM on a separate removable PCB. So the ROMs of the PC-1260 and PC-1261 may also be different? Not only the RAM? The PC-1260 and 1261 are supposedly identical except for RAM size. Other Sharp and Casio systems check for RAM size (making some of them upgradable), but perhaps the PC-1260/1 do not.

- Rob