DEC PDP-11/84 H7200 repair advice

[Lyle Bickley]

On Sunday 05 August 2007 05:39, Mr Ian Primus wrote:
> Well, I tried today to bring up my 11/84 - initial
> tests are showing me that there is something wrong
> with the power supply, an H7200. While the fans run,
> there doesn't appear to be any +5v. There is a faint
> ticking sound heard from the supply, and when I drop
> the power, there is a soft squeaking.
>
> So, before I take the this thing apart, are there any
> suggestions where I can look, common failures, etc?

Whenever I'm testing a new mini system, I typically document the system (incl. 
board locations, etc.), pull all the boards, check out all the PS capacitors 
(ESR if you have a tester - VOM/DVM otherwise) - then power it up. Lack of 
power can be caused by something as simple as a fuse or as nasty as shorted 
traces on a backplane or a bad diode, transistor, regulator, etc.

Once you've found the problem and fixed it, check all the supply voltages for 
ripple (either a scope or AC DVM are O.K.). Once the PS voltages and ripple 
are acceptable, reinsert the minimum of boards to test the system (typically 
CPU&Memory).

Again test all voltages. Then re-inert the remaining boards. If the PS problem 
"reappears", pull the latest set of boards, retest voltages and re-insert the 
boards one-by-one until you discover the board causing the problem.

Regards,
Lyle
-- 
Lyle Bickley
Bickley Consulting West Inc.
Mountain View, CA
http://bickleywest.com

"Black holes are where God is dividing by zero"