RiscPC CMOS Issues

Hi all,

I’m not entirely sure I’m posting this in the right place, but having been away from the RISC OS scene for quite some years I am rather out of touch with the preferred discussion areas. I was hoping someone might be able to point me in the right direction on this one.

Having read some information about leaking CMOS batteries I decided to dig out my old RiscPC and replace the offending item. Luckily the battery had just begun to go furry; no fluid leakage or damage to the board, or so it seemed (to my eye it looks pristine). I removed the battery and fitted a 1.2V AAA on flying leads, measured the voltage on the board and all looked good.

However, turning off the RiscPC will sometimes (not every time) result in a red screen when the machine is powered back up, with the CMOS settings all gone. Sometimes it needs as little as 20 seconds of power off for this to occur, while occasionally 20 minutes can pass and the machine starts normally. Resetting (both by the button and CTRL-BREAK) works perfectly – I get a green screen and the reboot commences with correct CMOS values.

I have seen talk of measuring voltages on the motherboard, but other than the pinout of the PCF8583T CMOS chip I’ve not found much to go on. If somebody could point me in the right direction I would really appreciate it; other than this issue the RiscPC is running perfectly. If only for the nostalgia I’d like to have the system behaving properly again.

All the best,

Hi Andy,

It’s probably worth asking about this on The Icon Bar forums, since that seems to be the go-to place for Arc/RiscPC tech support at the moment.

I have heard stories that the CMOS chip in the RiscPC gets a bit temperamental if the battery dies or is removed, so that could be the problem you’re seeing. If that’s the case then I think CJE or APDL have a service where they’ll fit a new one for you.

It might also be worth checking out the RiscPC technical drawings over on Chris’s Acorns (bottom of the page), since they might give some more clues as to what voltages to look for.

Good luck!

Ah, the Icon Bar! Good to hear they’re still going – thank you for the pointer!

I’ll have a word on their forum and see if anyone has ideas. Thank for the link to the tech drawings too; that’ll give me some light bedtime reading. ;)

All the best,