On 9/19/22 19:07, William Sudbrink via cctalk wrote:
Have a look at the 74L85 (not LS). it's one of those oddities that some of the "L" 74 series logic have different pinouts than the standard/LS/S/H/F/.... One notable aspect is that it's possible to wire-OR the L series outputs--something that you don't want to do with the others. --Chuck > 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 > > > > > -- --Chuck Sent from my digital computer
