S-100 Bus Voltages

From: Edwin P. Groot <epgroot_at_ucdavis.edu>
Date: Sat Jun 2 18:22:58 2001

     Anybody know the voltage tolerances for S-100 bus computers, or where
such info. can be found? I am preparing to run a 1981 vintage, 19-slot
S-100 system.
     After pulling all but one of the cards out I powered up the system.
Fans run fine, but the motherboard voltage supplies are rather high. For
+8V I measure 10.7V; for +16V I get -19.3V; and for -16V I get -19.3V. Is
this some careless engineering, bad components, or is the board really NOT
supposed to receive the nominal voltage?
     Many of the S-100 boards are discoloured brown-green on the solder
side opposite these large transistor-like things with heat sinks. Is that
something to worry about?
     I also measured the DC voltages of the pins of one of the slots. This
is what I got (assuming that pins 1|51 is at the power supply end):

volts pin# volts | volts pin# volts | volts pin# volts | volts pin# volts
----- ----- ----- | ----- ----- ----- | ----- ----- ----- | ----- ----- -----
 10.7 1 51 10.7 | ? 13 63 ? | ? 26 76 ? | 1.4 38 88 1.4
   ? 2 52 -19.5 | 5 14 64 ? | ? 27 77 ? | 1.3 39 89 1.3
  5 3 53 0 | ? 15 65 ? | ? 28 78 1.3 | 1.3 40 90 1.3
  5 4 54 5 | ? 16 66 ? | 1.6 29 79 1.3 | 0.1 41 91 0.1
  5 5 55 5 | ? 17 67 5 | 1.3 30 80 1.3 | 0.1 42 92 0.1
  5 6 56 5 | 5 18 68 ? | 1.3 31 81 1.3 | 0.1 43 93 0.1
  5 7 57 5 | 5 19 69 ? | ? 32 82 1.3 | 1.3 44 94 0.1
  5 8 58 ? | 0 20 70 0 | ? 33 83 1.3 | 1.3 45 95 0.1
  5 9 59 ? | ? 21 71 ? | ? 34 84 0 | 1.3 46 96 1.3
  5 10 60 5 | 5 22 72 5 | 1.4 35 85 0 | AC? 47 97 AC?
  5 11 61 ? | 5 23 73 5 | 1.4 36 86 0 | ? 48 48 5
  5 12 62 ? | 1.3 24 74 5 | ? 37 87 0 | 1.3 49 99 5
                  | ? 25 75 ? | | 0 50 100 0

Does that look safe enough to put the boards back and see how this system
runs?
     A fair amount of current runs through these slots. I nearly welded my
probe to the slot when I accidently shorted two pins!

     Any help, encouragement is much appreciated!

     Edwin
Received on Sat Jun 02 2001 - 18:22:58 BST

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