There are a few US based Ebay sellers of the 74L85. Tom
On Tue, Sep 20, 2022 at 10:50 AM ben via cctalk <cctalk@classiccmp.org> wrote: > On 2022-09-19 8:07 p.m., William Sudbrink via cctalk wrote: > > 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? > > > They are both right. > 7485,74LS85,74S85 top pin out. > 74L85 the bottom pin out. SB-1 > TTL data book 1985. > > > > Thanks, > > Bill > > > > > I suspect they used the L for low input loading > for the address bus. The 74C85 (fairchild ) would be the sane > substitute for the 74L85. > Ben. > >
