SWTPC 6800

My 2cents Some of this may have been mentioned. Your going to need an oscilloscope, and a scope probe with a good ground. Your 'scope probe should be less than 15 pF. Anymore and the probe will start to filter out any high frequency noise. Is the supplies output grounded ?, If so that point is where you put your ground clip. Since this will be 90% of what you will find, I won't go into non grounded DC sources. Check what the output of your DC supplies looks like. The actual voltage and the amount of ripple (60/120 or 50/100 Hz noise) and other noise and what the ground at the exit of the supply looks like. Yes the ground. If your happy with no ground noise you can use that point for your ground clip. Lets assume you have boards that plug in to a backplane. With all the boards installed what do the supplies and again the ground(s) look like ? Have an extender ? For each board, look at where the boards ground passes to the backplane, if that point looks good, then you can move your probes ground to that location. Now do the same thing, if just a 2 layer board look at the ground pins on various devices, starting with the 'big' chips, then bus drivers, etc. Basically the devices that swing a lot of current. Unique for memory boards. do the same for every device. Is the ground and power pin clean ? One reason to look at every device is there maybe a defective decoupling cap. Or sadly not enough of them. If the board is only 2 layers and there is not a cap for each and every memory chip the fun beings. To keep things short, if the supply lines do not looks clean, your going to be wasting a lot of time. What is clean, there is not short answer, think about < 50-100 mV on every chip, specially memory devices. Even the 'big boys' that should have know better designed and shipped a lot of hardware that totally sucked. On Fri, Aug 5, 2016 at 9:56 AM, Brad H <vintagecomputer at bettercomputing.net> wrote: