Substituting for the DEC 384 and DEC 6380 IC's

[DaveH]

I was recently asked to expand about a passing reference I made to a small PCB I use to substitute for the above IC's.

The 6380 is a quad 2 input NOR and the 384 a quad 2 input OR , both are fairly extensively used on Omnibus boards, especially the 6380 as a bus receiver, both are Signetics chips with apparently no pin compatible 74 series equivalents
.
They both seem to have a fairly high failure rate , for me anyway.

Now functionally a 7402 will replace a 6380 and a 7432 the 384, you "just" need to adapt the pin out ( even the VCC and Gnd are on the wrong pins ) , Pic2.

I did one or two by bodging in a header (Pic 1) but this wasn't a very elegant solution and when it became apparent that I would be doing quite a bit of this I had a small adapter board made up. ( Pic3)

Now here we had a bit of luck, looking at the pin out for the 7402 and the 7432 I realized that I could use the one PCB for both IC's, simply inserting one " upside down " and adjusting the vcc and gnd's, so one PCB will do both devices. (Pic4)
I use an 74 LS if the fanout is 3 or less and a "full" TTL if not. Some cards need a few . Pic5

Sorry about the picture quality, my little cheap camera don’t do macro
Dave

 

[m_thompson]

Both the Signetics SP380 and SP384 are still available in eBay and from brokers, but they are getting expensive. Since these parts are NOS they may still have a failure rate like the ones on your boards.

 

[pbirkel@gmail.com]

Thanks for sharing more details. You don't have a clearance problem between the piggyback PCB and the next DEC Module? How tight is it?

I was recently asked to expand about a passing reference I made to a small PCB I use to substitute for the above IC's.

The 6380 is a quad 2 input NOR and the 384 a quad 2 input OR, both are fairly extensively used on Omnibus boards, especially the 6380 as a bus receiver, both are Signetics chips with apparently no pin compatible 74 series equivalents. They both seem to have a fairly high failure rate, for me anyway.

Now functionally a 7402 will replace a 6380 and a 7432 the 384, you "just" need to adapt the pin out (even the VCC and Gnd are on the wrong pins). I had a small adapter board made up.

Now here we had a bit of luck, looking at the pin out for the 7402 and the 7432 I realized that I could use the one PCB for both IC's, simply inserting one "upside down" and adjusting the vcc and gnd's, so one PCB will do both devices.

I use an 74 LS if the fanout is 3 or less and a "full" TTL if not.

 

[DaveH]

Thanks for sharing more details. You don't have a clearance problem between the piggyback PCB and the next DEC Module? How tight is it?

In general its fine, on some boards, I seem to recall that the sense inhibit is one, you need to space the adapter a little further of to clear adjacent components, normally caps, then you have to be a little careful as it does touch.
Dave

 

[Crawford]

In general its fine, on some boards, I seem to recall that the sense inhibit is one, you need to space the adapter a little further of to clear adjacent components, normally caps, then you have to be a little careful as it does touch.
Dave

Dave,
If you really ran into space issues, a surface mount chip could allow the adapter board to be the same outline as the original IC. Probably not worth it for Omnibus boards where the IC spacing is very generous.

Thanks for sharing your design. Is there a substitution list for obsolete DEC IC's or do we need to start one?

- Crawford

 

[m_thompson]

Vincent has a substitution list, but it needs to be updated. Many of the original parts are still available from brokers, but just a little expensive.

 

[pbirkel@gmail.com]

Thanks. But I was thinking more about the overhead-clearance (to the module in the next slot -- the one with all of those pointy solder-tails sticking out :->) rather than clearance laterally to other same-module components, which is also an issue of course. What was just a chip-height (probably shorter than any nearby decoupling capacitors) is now a socket+PCB+chip-height.

In general its fine, on some boards, I seem to recall that the sense inhibit is one, you need to space the adapter a little further of to clear adjacent components, normally caps, then you have to be a little careful as it does touch.
Dave