12 Apr
2008
12 Apr
'08
4:55 a.m.
Hi folks,
I have a H7864 PSU for a pdp11 (Rev C1 or Rev-12)
which blew up last friday.
A friend and I found out that the only thing that had
gone wrong was that a 0.47uF X2 Cap had failed, so I
bought a replacement and I've soldered it on now. So,
maybe the PSU will work!
However, there's an internal lead called J11 with a
funny socket on the end:
It looks like this (if you view in fixed point)
[Side view] [Front view] [Plugs into ] [Which looks
like on
the outside of
the casing]
+------+ _____
| : : | / 230 \
_____ | : : | > <
__/\ | " " | | : : | \_____/
=======| / ------- +------+
\_/ \###/
The far end of the lead connects to a PCB where it
says "+Fan 1-"
Now I think that when I dismantled the PSU I unplugged
it from the bottom two prongs of a 6 pronged plug of
which the other side displays "230" through a glass
panel on the outside of the casing.
There are connections and a resistor across the other
4 prongs of that plug. I figure that the the 6-pronged
plug is for selecting the mains voltage, which in my
case is 230-250v as I'm in Europe, but what are the
bottom two prongs for - how could they power the fan?
I was pretty sure I needed to plug J11 in - and this
is the only place I could find and it's a tight fit!
However, when I dismantled the PSU for my microVax II
I found that J11 isn't plugged in at all!
So, I'm not sure what the correct connections are. My
choices are:
1. It doesn't matter if it's plugged in or not
(unlikely, since fan cooling is important).
2. It should be plugged in on the pdp11 AND the
microVax, so I should plug it in on the MicroVax II
too. It'll only go in one way, it'll collide with the
PCB with the 0.47uF X1 cap if I try it upside down.
3. It shouldn't be plugged in either of the machines
and so the microVax is correct and the pdp11 is wrong.
4. It should be plugged in the pdp11, but not the
microVax.
Note: the MicroVax has a later power supply, Rev E1
from 1983.
Sorry to be pedantic about all the connections, but
advice would be helpful!
-cheers from julz @P
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