5 Sep
2000
5 Sep
'00
3:57 p.m.
ard(a)p850ug1.demon.co.uk (Tony Duell) wrote:
Hi Tony
I received a pdf from one of the others on the list. The pdf shows
that the 861 is not exactly like the 7420, in that the unused pins
of the 7420 are for gate expansion on the 861. The circuit that uses the
part, I think is failing, doesn't use these pins. The biggest potential
problem I see is that the original designer used two outputs tied
together. This means that the other output has to pull it down
as well. I tried a 74LS20 and it didn't work but I think it is
just that the 74LS20's have a strong pull-up. I'll try to locate
a 7420 and give it a try. I've also found a part supplier that
stocks old DTL and even RTL parts. I haven't contacted them
yet but if the 7420 doesn't work I'll give them a try. They
have these in the Motorola part numbers. For others looking for old
parts, they are:
http://lansdale.com/~lansdale/index.html
I'm sure these will be expensive but then what the heck.
Thanks for the reply
Dwight
Hi
I need some pinouts for some old TTL? or DTL? parts
These are in my computer and I think one of them is
causing a failure. These are all TI parts:
SN15846
SN15849
SN15861
SN15863
THose are DTL chips. The generic number is the last 3 digits, 846, 849,
861, 863.
The 846 is a quad 2-input NAND gate, pinout as the 7400. I've found this
one in some old service manuals, so I am pretty sure of the pinout.
I also have a somewhat untrustworthy 'equivalents list' which confirms
that the 846 is similar to the 740. It says that the 849 is also a quad
2-input NAND with the same pinout, that an 861 is dual 4-input NAND,
pinout as the 7420, and that the 863 is a triple 3-input NAND gate,
pinout as the 7410.
I would treat that latter data with some suspicion, but it may be a start.
-tony