14 Mar
2013
14 Mar
'13
4:18 a.m.
On Wednesday (03/13/2013 at 05:03PM -0700), Brent Hilpert wrote:
Also, specific to the SWTPC 6800, you might want to closely inspect the
white Molex connector(s) at the power supply PCB. The pins in those
connectors were too whimpy for the amount of current typically carried
through them. They will heat up and degrade over time. On one of my
systems the PCB is even brown from the heating.
I mod'd this part of the machine, installing a heavier duty in-line Molex
connector off the board and then soldering wire directly into the holes
in the PCB where the (burnt) connector used to be.
In my case, this was the reason the +8 was too low on the backplane.
Chris
--
Chris Elmquist
Fuse replaced and all is happy. So, the lesson is: check your fuses
carefully.
Interesting fault mode, but I wouldn't express that as the fuse
"drawing a lot of current". That fuse should be the one in the +8V
line and it looks like what was happening is your cards were drawing
current just short of blowing the fuse. As the fuse filament heated
up it's resistance increased, so more of the +8 supply voltage was
dropping across the fuse, reducing the +8V output level. (Overall
current should actually be going down).
Yay, another SWTPC 6800 (I have one too).