7 Jul
2012
7 Jul
'12
7:35 p.m.
Some good news after thinking about this overnight.
I took a small 25VAC plugpack out of the junk box to make comparative
testing of the two 7441 supplies easier.
When I tested the known working 7441 it worked fine with the plugpack.
When I tested the "faulty" 7441 it also worked fine.
Reconnecting the faulty 7441 to the main transformer and bringing the
voltage up with the variac and it didn't work.
The problem is the rate of voltage increase. If I bring up the variac
output slowly (say 0-240v over 5 seconds) then the 7441 will hang with the
output under 1 volt. If I increase the voltage quickly (within 1-2
seconds) then it powers up fine and shows a good 5v on the output.
The one known difference between the two 7441's is the faulty one has the
original input cap which tested out OK. I could replace this if anyone
thinks it is important.
Otherwise I think it is time to put the regulators back in the chassis and
try powering up the back plane.
On Jul 8, 2012 7:30 AM, "Andrew Quinn" <jaquinn2001 at gmail.com> wrote:
I am continuing to make progress with the power supply
modules for the PDP
11/04.
The previous week involved testing and replacing a few of the electrolytic
caps... a few pictures and some comment (although no great technical
insights) at http://www.quicktrip.co.nz/jaqblog.
Today I got a chance to test the modules. One of the H7441 +5V supplies
works fine (http://www.quicktrip.co.nz/jaqblog/images/BLOG_PDP11_5V_2.jpg)
... the output is a little high at 5.5v but that could be my meter
calibration. I haven't played with the adjustment pot yet until I can
confirm that my meter is reading correctly.
The other +5V supply doesn't run (
http://www.quicktrip.co.nz/jaqblog/images/BLOG_PDP11_5V_1.jpg)... goes up
to just over 1v as the AC comes up and then settles back to 0.5v.
The DC voltage after the rectifier and across the main input capacitor
looks OK on the meter.
I have the PDP11/34 technical drawings with the schematic for the H7441 so
will work though it but to get a head start, are there any common failure
modes for these supplies that I should check first?
The H745 -15V (
http://www.quicktrip.co.nz/jaqblog/images/BLOG_PDP11_-15V.jpg) supply
works fine although the Power OK bulb on the back has failed. I will
replace it with an LED + resistor like the H7441.
And assuming I sort out the last H7441 are then any recommendations on
powering up the backplane?
It has the following boards installed plus grant continuity cards as
appropriate:
M7257 RK05
M7256 RK05
M7255 RK05
M7254 RK05
M7258 Printer
M7856 RS232/SLU
M7860 General Device Interface
M7856 RS232/SLU
M7847 Memory
M7847 Memory
M7859 Console Interface
M7263 Processor
M9301 Unibus Terminator
M7850 Parity Board
M9202 Unibus Connector
I assume it is good practice to draw a map of all the board locations,
then remove them all, power up the backplane and check the power... but
what is the next step.
My guess is that a minimum set of boards would be the following:
M7847 Memory
M7847 Memory
M7859 Console Interface
M7263 Processor
M9301 Unibus Terminator
M7850 Parity Board
Any suggestions?
Regards
Andrew
