KINGCHEF wrote:As the disc i/face is now not working with 2 of the QLs and only with Minerva I thought I would look at that first.
This says the board is border line on the signals and might be loading the QL outputs or not giving enough on the QL inputs so putting it on a straight through backplane would make things worse. Perhaps the mod was done because the board always had the problem and might be pointing to the problem area.
KINGCHEF wrote:It may be that the board was sold with 256/512 options or that a previous owner had added memory later.
Would the board work one of the outputs so you know it works if it had no memory chips that would reduce its power consumption.
KINGCHEF wrote:On the subject of modifying the backplane or the expansion board there is a paradox.
Not really for the above reason. Keep the backplane straight through and simple.
KINGCHEF wrote:Checking the backplane connections were done from pin to socket using a dummy connector to get to the socket pins.
We assume end to end you checked for shorts by going around the three adjacent pins on every pin.
KINGCHEF wrote:I'm more interested in the +12v and -12v readings which are much lower than that. How/where is it regulated and what is it used to power?
Watch out for the AC output on the power supply I didn't realise one was AC that gives a low reading on DC measurements on the meter.
KINGCHEF wrote:Does it actually power anything in the peripheral board?
Check the medic circuit. Some old ram used funny voltages.