16 Sep
2006
16 Sep
'06
7:43 p.m.
The recent discussion of Julian's PDP-11/34 inspired me to look at an
abandoned one that I adopted some while ago. The particular computer in
question is a /34A-DE.
After looking at the prints and checking a few voltages, I find I have
no +5. Reviewing the recent thread and looking closer at the prints, it
seems that I am missing two H7441s. (It does have a H754 and H745, with
the 54-10864-YA [Rev. L] distribution board.) Is that correct? It
needs (one or) two H744 or H7441 (in my case) in order to operate?
Thanks,
John
16 Sep
16 Sep
9:57 p.m.
After looking at the prints and checking a few
voltages, I find I have
no +5. Reviewing the recent thread and looking closer at the prints, it
seems that I am missing two H7441s. (It does have a H754 and H745, with
the 54-10864-YA [Rev. L] distribution board.) Is that correct? It
needs (one or) two H744 or H7441 (in my case) in order to operate?
Yes, I believe so. The only 5V source is from those regulator blocks, and
of course most of the logic runs off a 5V supply. AFAIK there are 3 types
of regulator you can use, the H744 (rated at 25A), the H7440 (also 25A,
but a revised design) and the H7441 (32A). Apart from the rating,
they're compatible, so if 25A is unough you could use any of them. They
also don't both need to be the same type.
I can't remmeber how the 5V line is 'split' Certainly the complete CPU
backplane runs off one regulator, the leftmost 2 'system unit' postions
run off the other. It's the middle 'system unit that I can't remmber, I
think it's off the regulator that runs the leftmost 2 positions too. In
other words one block runs the CPU backplane, the other all the expansion
backplanes. But I would have to check the prints to be sure.
-tony
17 Sep
17 Sep
6:14 p.m.
dundas at caltech.edu wrote:
The recent discussion of Julian's PDP-11/34
inspired me to look at an
abandoned one that I adopted some while ago. The particular computer in
question is a /34A-DE.
After looking at the prints and checking a few voltages, I find I have
no +5. Reviewing the recent thread and looking closer at the prints, it
seems that I am missing two H7441s. (It does have a H754 and H745, with
the 54-10864-YA [Rev. L] distribution board.) Is that correct? It
needs (one or) two H744 or H7441 (in my case) in order to operate?
Depending upon how many backplanes you have in your box and how much
stuff in each backplane, you need anywhere from one H744 (25A at 5V) to
two H7441 (32A at 5V each, 64A total).
The first H744(1) will power the 9slot CPU backplane. If you have a true
11/34A with FPP and/or cache module the H7441 is required. A minimal
11/34A (no FPP or cache) can use just an H744.
The second H744(1) slot powers the expansion backplanes. If they are not
present, you don't need it at all. If they are fully loaded, then the H7441
is your choice.
The -YA version of the power distr board is designed to handle the
additional load of the H7441s. It will work with either H744 or H7441.
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ak6dn＠mindspring.com -
ard＠p850ug1.demon.co.uk -
dundas＠caltech.edu