17 Jul
2015
17 Jul
'15
9:17 p.m.
Thank you for the detailed information. I need to
figure out how im going
to get it out of the rack and moved to a place where i can test it over the
next couple days where it will not be in the way. Ill find some way to do
a dummy load and do an extended test to be sure the supply is working
properly. All fingers crossed, god it better not have damaged any of the
boards, i do not know where i would get replacements.It took years for me
DEC PSUs of that vintage have a crowbar circuit which effectively short-circuits
the PSU (using an SCR) if the voltage rises too high to protect the rest of the
machine.
On the other hand if the +5V line did get too high it could have wiped out
just about every IC in the unit. Ouch!. I've only ever had this happen once, and
it was in a much lesser machine than a PDP11 (fortunately).
to get the machine, who knows how long it would take
to find a specific
board that is bad. I did buy an oscillicope and a logic analyzer well in
In general you should be thinking of repairing these machines on the component
rather than board level. You may well have difficulty in finding a particular board
(and how do you know that the replacement is good?) but finding one of the logic
ICs is very easy.
advance in preparation for getting this machine,
however short of pressing
the power button no clue how to use them or basic troubleshooting
procedures. Guess i just have to learn by doing....
That's how quite a few of us (including myself) learnt...
The basic procedure that I use goes like this :
1) What should the machine be doing? In other words, from the schematics I deduce that
there should be a clock signal on 'that wire' or data flowing there with enable
pulses on that
pin.
2) What is the machine doing (determined by examining said signals with a 'scope and
LA)
3) Why the difference? If they are the same then that part of the machine is mostly
working
properly. If not, then what could explain what I am seeing, How can I determine what the
cause is? Aha... What is _that_ signal doing? Check it....
-tony