A Mystery Block of Electronics

Back in the day, this surely represented an achievement in high-density electronics packaging:

Electronics Block - 1

Electronics Block – 1

A view from the other corner suggests the layout wasn’t quite right:

Electronics Block - 2

Electronics Block – 2

It has no identification, the transistors have house numbers, and the PCB looks like a prototype. As nearly as I can tell from the capacitor date codes, it dates back to the mid-1960s.

Two pairs of electrically isolated and thermally bonded transistors suggest an analog Class-AB driver + amplifier or a pair of digital flipflops, but there’s no way to tell.

Judging from the ugly solder and dislodged via rings, somebody had to apply extensive modifications after initial assembly; it trailedĀ half a dozen red wires soldered to vias and components.

One hopes it eventually worked…

  1. #1 by Daniel B Martin on 2015-10-16 - 09:02

    Where did this prize come from? It’s too late in the year for the Easter Bunny, too early for Santa. Have you lost any teeth recently?

    • #2 by Ed on 2015-10-16 - 20:35

      I haven’t a clue; it’s just one of those things that mysteriously appears from time to time around here.

      Had a root canal earlier in the year…

  2. #3 by eriklscott on 2015-10-16 - 10:40

    It doesn’t look like Western Electric (wrong caps), so that narrows it down. :-)

    Early solid state Op Amp? Time to trace out a schematic.

    • #4 by Ed on 2015-10-16 - 20:40

      “Tracing”… in this context, I think that word does not mean what you think it means.

      I’m not even sure what’s in the middle of that block: the parts are so well hidden by everything around them!

      • #5 by eriklscott on 2015-10-17 - 23:47

        What I meant was “follow the traces and make a schematic from that”, not “find a schematic and trace it”. :-) Let alone “inject a signal and trace it”. I see how that word could have a lot of meanings. Now, if you can’t see into the middle of the lump, that’s another problem entirely…

  3. #6 by Andrew on 2015-10-16 - 11:02

    Seem to recall the textbooks called this the “cordwood” construction method, maybe due to the shape and color of those resistors favoured by US manufacturers back in the day. Clearly no fun at all to debug.

    • #7 by Ed on 2015-10-16 - 20:36

      If they didn’t build it with those resistors slanted like that, I don’t see how they could insert them that way. Phew!

  4. #8 by steve on 2015-10-16 - 11:50

    +/- 10% resistors… Remember no band implies +/- 20%???

    • #9 by Ed on 2015-10-16 - 20:38

      Yeah, well, a good analog design doesn’t depend on the components. Right?

      At least the way the Perfect Masters did it. We mere mortals need a tad more dependability from the hardware.