Hi,
I recently acquired a Solid State Music SB-1 from which all the chips had
been removed. I've reinstalled all of the chips (I located an SSM2000) and
I've been trying to figure out why this board crashes my computers. The
conclusion that I've come to is rather astounding. The board specifies two
74ls85 4 bit binary comparator chips to perform address decoding. The
designers of this board seem to have had incorrect pinouts for it. Every
source that I can find specifies:
B3 1 16 VCC
A<B (in) 2 15 A3
A=B (in) 3 14 B2
A>B (in) 4 13 A2
A>B (out) 5 12 A1
A=B (out) 6 11 B1
A<B (out) 7 10 A0
GND 8 9 B0
The 7485s that I was able to get have this pinout. BUT! The SB-1 is
designed as:
B2 1 16 VCC
A2 2 15 A3
A=B (out) 3 14 B3
A>B (in) 4 13 A>B (out)
A<B (in) 5 12 A<B (out)
A=B (in) 6 11 B0
A1 7 10 A0
GND 8 9 B1
I Ohm'd out the board to verify this and it matches the schematic here:
https://wiki.theretrowagon.com/wiki/Solid_State_Music_SB1
What the heck??? Did the pinout of the 7485 just arbitrarily change at some
point? Was this some competition between manufacturers? Is there any way
to get the "right" 7485?
Thanks,
Bill
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