Risc PC600 white screen

[gshaw0]

One of my Risc PCs was afflicted by the dreaded battery leak while it was in storage (didn't know about it back then ) and was failing to boot.

It flashed the floppy drive to which I remember someone telling me was a video fault and sometimes had a red screen.

Had some free time this week so stripped it down and cleaned the area of board where leakage was (a single 181 SMD resistor next to the battery area). Used white vinegar to remove the green stuff then cleaned with 99% IPA.

Checked the resistor, was showing 180-ish ohms so put the machine back together. Slight improvement, now I don't get the floppy drive blink code and a plain white / greyish colour screen.

Any ideas where to go next with it? (Risc PC in the picture isn't the one in question in case you're wondering why there's no LEDs lit )

[Kazzie]

You'll need to use a multimeter to check for continuity between that resistor and the other components that it's connected to. To do this, you'll want to get a copy of the circuit diagrams for the RiscPC; the Chris' Acorns website has a copy, among others. Note that, depending on the revision of board you have, there may be some minor differences in circuit and layout. (If you tell us the Issue number at the northern edge of the board next to the network connector, we can work out what issue of board you have.)

The flashing floppy drive LED can tell you what RISC OS' power on self-test thinks is wrong with the machine. Make a not of the long/short pattern of flashes, and they can be decoded using a nifty tool on this site.

[gshaw0]

Dug this machine out today and went through the blink codes giving me the output below with a red a red screen that then goes black / no signal

I've tried holding Del / R but doesn't change the blink code.
The Num and Caps lock lights still respond on the keyboard after the speaker clicks off at the end of the floppy light sequence.

Board details
0297,000/S1 ISS.1
MAIN PCB 0197,000 ISS.

Fault code:
0000C199

VIDC Sirq (Sound Interrupt) timing failed
VIDC Virq (Video Interrupt) timing failed
CMOS RAM checksum error
VRAM detected
ARM 3 fitted/ARM ID read and not ARM2
Long memory test performed
Self-test due to power-on

Been reading a few threads and it'll be likely that troublesome battery area (no surprises there)

I did clean this board up a while back, kinda surprised how OK it looks from the top now though imagine the underside or underneath some chips might be a different story.

I'm well out of my depth with multilayer PCBs, does anyone do repair services on these later boards?

[philpem]

VIDC Sirq (Sound Interrupt) timing failed
VIDC Virq (Video Interrupt) timing failed

These both point to issues with the VIDC -> CPU bus interface, which usually means RP16.

CMOS RAM checksum error

Not surprising if the board's had no battery connected.
This won't clear up until the Virq/Sirq issue is sorted and you do a delete-power-on reset.

VRAM detected

This is never a bad sign on a board with battery damage - though it may be worth testing without the VRAM to see if it's affecting VIDC.

ARM 3 fitted/ARM ID read and not ARM2
Long memory test performed
Self-test due to power-on

Spoiler: you have a RISC PC
These are all normal status updates from the early boot process, and not faults.

Been reading a few threads and it'll be likely that troublesome battery area (no surprises there)

I did clean this board up a while back, kinda surprised how OK it looks from the top now though imagine the underside or underneath some chips might be a different story.

I'm well out of my depth with multilayer PCBs, does anyone do repair services on these later boards?

There are a couple of people here who might chime in - can you post some photos of the area around the battery and RP16 so we can get an idea how bad the damage is?

[gshaw0]

This is never a bad sign on a board with battery damage - though it may be worth testing without the VRAM to see if it's affecting VIDC.

The not so good news being I already removed it as part of trying to strip back additional components as from memory the VRAM did have some gunk around the socket.

Will get some pics when I get it back out in a few days, thanks for the details so far

[omx5o]

Not sure it will help, but when I cleaned some corrosion off the last three lanes of the VRAM with a fibre pen, I noticed vertical white lines all across the screen. I applied a small amount of pressure at that end of the VRAM and it fixed it. Been fine since. Perhaps the interface to the board needs some attention, cleaning etc? Or try applying a little bit of pressure and see if anything changes on screen.