Reviving my own thread here, because I have finally got back to my stack of dead RiscPCs.
So, where was I... this one had got to the point where it was actually booting OK, but with no sound. Then it stopped being able to boot, and was flashing a Virq error POST code.
Rather than tackle this problem, I noticed another odd thing, which is that the HDD light glows constantly, even though there is no HD currently fitted. Looking at the schematic, I can see that 5V is constantly present, and the LED is switched on (presumably) by the hard disc grounding pin 39 of its connector, which is joined to the negative pin of the LED. In the absence of a hard disc, I measured the resistance between 0V and the negative pin of the LED. This should be infinite, but seemed to vary constantly between kOhms and MOhms - never showing any signs of settling. I guess this is consistent with the "glowing" behaviour of the LED. Shorting pin 39 to ground caused the LED to light up brightly.
I decided that the issue might be caused by battery gunk that has collected under LK11/LK12 and is shorting out the pins, so I desoldered both headers and cleaned up underneath . It was certainly a little bit contaminated, but nothing major.
Having put the headers back on and reconnected everything, the "glowing LED" problem is unchanged, and furthermore the machine no longer displays the floppy drive POST code.![:(]( "Sad")
I am starting to think this board is probably unrecoverable, because of the way it seems to be deteriorating without obvious reason. I wonder if this current path that is affecting the LED might be caused by alkali which has got between the layers of the PCB perhaps, and which has other more serious consequences? This board was probably the worst-affected by the battery damage.
Or might the LED issue have a simpler explanation?
So, where was I... this one had got to the point where it was actually booting OK, but with no sound. Then it stopped being able to boot, and was flashing a Virq error POST code.
Rather than tackle this problem, I noticed another odd thing, which is that the HDD light glows constantly, even though there is no HD currently fitted. Looking at the schematic, I can see that 5V is constantly present, and the LED is switched on (presumably) by the hard disc grounding pin 39 of its connector, which is joined to the negative pin of the LED. In the absence of a hard disc, I measured the resistance between 0V and the negative pin of the LED. This should be infinite, but seemed to vary constantly between kOhms and MOhms - never showing any signs of settling. I guess this is consistent with the "glowing" behaviour of the LED. Shorting pin 39 to ground caused the LED to light up brightly.
I decided that the issue might be caused by battery gunk that has collected under LK11/LK12 and is shorting out the pins, so I desoldered both headers and cleaned up underneath . It was certainly a little bit contaminated, but nothing major.
Having put the headers back on and reconnected everything, the "glowing LED" problem is unchanged, and furthermore the machine no longer displays the floppy drive POST code.
I am starting to think this board is probably unrecoverable, because of the way it seems to be deteriorating without obvious reason. I wonder if this current path that is affecting the LED might be caused by alkali which has got between the layers of the PCB perhaps, and which has other more serious consequences? This board was probably the worst-affected by the battery damage.
Or might the LED issue have a simpler explanation?
Statistics: Posted by jms2 — Wed Mar 26, 2025 1:10 pm