Hybrid Circuits

B

Boris Gjenero

Guest
I'm curious about those hybrid circuits I find in the form of some
sort of coated SIPs on some boards. Here's a picture of some from a
Xerox copier controller board:
http://enosys.ath.cx/HybridCircuits.jpg
The board is at the bottom. It used to contain lots of DTL and a few
TTL logic ICs, some optocouplers, and a few discrete components. (I
got the ICs off by heating the board from below with a paint stripper
and then as soon as the solder melts prying stuff off.) The date
codes were generally from '74 (kind of funny, non-TTL logic with 74xx
on it)

I'm just curious what sorts of applications stuff like this is used
for and why they were used instead of the more familiar IC packages.
I've also seen hybrid circuits in disk drives from the 80s.

For the record, what appears to be part numbers on these are:
133P126C
133P127
133P128C
133P129
There's also an unidentified 14 pin DIP labelled 133P124.

--
Boris
 
In article <0d2j00h1q37agi3ekefsusaolcro23fv1s@4ax.com>,
enosys_at_yahoo_dot_com@no.spam.ca mentioned...
I'm curious about those hybrid circuits I find in the form of some
sort of coated SIPs on some boards. Here's a picture of some from a
Xerox copier controller board:
http://enosys.ath.cx/HybridCircuits.jpg
The board is at the bottom. It used to contain lots of DTL and a few
TTL logic ICs, some optocouplers, and a few discrete components. (I
got the ICs off by heating the board from below with a paint stripper
and then as soon as the solder melts prying stuff off.) The date
codes were generally from '74 (kind of funny, non-TTL logic with 74xx
on it)

I'm just curious what sorts of applications stuff like this is used
for and why they were used instead of the more familiar IC packages.
I've also seen hybrid circuits in disk drives from the 80s.

For the record, what appears to be part numbers on these are:
133P126C
133P127
133P128C
133P129
There's also an unidentified 14 pin DIP labelled 133P124.
Click to expand...
Xerox field techs weren't the brightest stars in the galaxy so the
boards had to be easily T/Sed and repairable. Often the stuff like
these were made to interface the sensors and relay closures to the
logic. I'd guess they would be mainly pi RC networks and such. They
probably don't have any active parts on them.

A neighbor worked for Dyna-Lease, one of the Xerox competitors. He
gave me a lot of old Xerox boards and stuff. I think I had some stuff
from the original 914 copiers which were mostly relay logic.

--
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They look like RC networks, to me. The square lumps are probably ceramic chip
capacitors. One of them looks like it may have something else on it, as the
lumps are less regular. The other possibility is a chip resistor of a value
that would be inconvenient to screen print.

Tom
 
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