[TUHS] PDP11/34 boot problems, here i am again :)

asbesto asbesto at freaknet.org
Tue Apr 15 10:00:37 AEST 2003


some months ago i asked for help booting a pdp11/34 here at
freaknet medialab :)

well, i think now we have a more complete knowledge of the REAL
problem !

the M7891 board (128K x 18 bit MOS MEMORY MODULE) have the D2 red 
led light turned ON when turning on the CPU !

this means PARITY ERROR on this board :(

checking the board we found 2 problems:

1) a 74LS175 chip named E15 on our schematic diagram, that seem
   phisically BROKEN on an edge (there is a fessure on the plastic
   DIP package). i can't change it now because i don't have a 
   soldering station here to do a nice job, but looking the chip i
   think it may work...

2) a 5 Kohm 4-resistor bridge named R22 on our diagram, that is phisically
   BROKEN. this bridge give +5V on signals named DATA OC L, CSR OC L, OC L
   and X ADD OC L. i changed it with a 4.7Kohm 4-resistor bridge, without
   any result. (maybe the 74ls175 is really broken :)

an other ipothesys may be: some electrolitic capacitor in short circuit.
we had this problem on a decwriter III ! :)

the real problem is: if we aren't able to repair the M7891 board, where
can we find a "new" one ???

can somebody help us ? it's a shame for us to have our pdp11/34 offline :((

any help is appreciated ! *:)

[asbesto : freaknet medialab : radio#cybernet : GPG key on  keyservers]
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[http://www.freaknet.org/asbesto :::::: http://kyuzz.org/radiocybernet]
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