Date   : Fri, 28 Jun 1996 03:08:53
From   : pnt103@...
Subject: Hardware problems

I hope the ASCII art is understandable -- here are the pinouts for the
connectors on the BBC power supply and a 5.25" disc drive:

         ______ ______
        |      U      |         BBC PSU (female) connector, 
     0V |  1       2  | 0V      viewed from outside PSU.
        |             |
        ]             [         Matching cable connector is
    +5V |  3       4  | +12V    AMP pin housing     1-250234
        |             |         male crimp pins AMP 350664-1
        ]             [
     nc |  5       6  | -5V     Farnell part nos 148-081 (min qty 10)
        |             |                      and 149-087 (pkt of 10)
         \___________/


      ______________I_____      AMP Commercial Mate-N-Lok
     |                    |     Cable connector housing 1-480424-0
     |  1    2    3    4  |     female crimp contacts 163304-2 (18-20 AWG)
      \__________________/                         or 163306-2 (14-18 AWG)

       +5V  0V   0V  +12V       Farnell part nos 148-085 (min qty 5)
                                             and 149-090 (pkt of 10 pins)
                                              or 299-571 (pkt of 100)

And for the sake of completeness, here's the info for 3.5" drives:


     ___I_____________          AMP Economy Interconnect
    |                 |     (NB1 this is 2.5mm pitch, not 0.1")
    |  1   2   3   4  |     (NB2 Only rated for a few tens of insert/replace
cycles)
   /  ______   ______  \    Cable connector housing 171822-4
   |_|      |_|      |_|    crimp contacts          170204-1 (26-30 AWG)
                                        or          170205-1 (20-26 AWG)
                            Farnell part nos 150-665 (min qty 5)
                                         and 150-666 (pkt of 10 x 170204-1)

The BBC PSU connector is the same as on Apple][ computers and some
others (except that on other machines the "missing" pin is normally
used for -12V).

Often it is sufficient to connect just one of the 0V (ground) wires, as
the two connections are internally connected on the PSU and most drives. 
Be careful if you daisy-chain connectors, though :-)

You mentioned that three wires on the disk cable have been cut.  Assuming
the striped edge is pin 1 (the standard), then it's a couple of ground wires
(pins 1 and 3) and pin 2 which have been cut.  I can't think of any reason
to do this for a Beeb drive, where pin 2 is usually not used (it's the Trk43
signal on a few old drives), but it's the speed-select signal on HD PC-style
drives.

As to your Cylon Attack problem, I can't help with the disk, but since
the heatsink was loose (common problem), it might be worth re-seating
all the socketed chips, just to make sure all is well.  Those tinned
sockets develop oxidation over the years, and *gently* prising the chips
loose with a small screwdriver, then pushing them firmly back into
place, will fix a lot of similar problems.  Do this with the power off,
of course.

Pete