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Powered Prototype Board: Laying-on of Hands Repair

One of my very first projects, after setting up my very first home shop in our very first home, was building an overly elaborate prototype board with five (!) linear power supplies:

Proto Board - overview

Proto Board – overview

The components come from the mid-70s and the shop happened around 1980, so it’s been ticking along for nigh onto four decades. Of late, the supply voltages became erratic and I eventually popped the top:

Proto Board - innards

Proto Board – innards

Yeah, linear pass transistor regulators driven from bulk cap storage, hand-hewn bridge rectifiers, and multi-tap transformers. Everything mounts on screws tapped into the 1/8 inch aluminum chassis, with power transistors on a huge finned heatsink attached to the rear panel. The thing weighs 11.6 pounds = 5.3 kg.

Not a trace of firmware to be found. Heck, surface-mount components hadn’t yet come into common use.

The circuitry lives on a crudely etched phenolic board:

Proto Board - etched circuit board

Proto Board – etched circuit board

There may be a schematic somewhere in my collection, but it hasn’t surfaced in a long time. I’m mildly surprised I didn’t tuck it inside the case, which may have been a life lesson yet to be learned.

Based on my recent experience with the Tek AM503, I wiggled the two metal-can regulators and the ceramic (!) regulator, gingerly plugged in the line cord, flipped the switch, and all the supply voltages once again work perfectly.

Whew!

 

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  1. #1 by madbodger on 2018-10-23 - 09:52

    Ah, that’s a thing of beauty! I built a similar beast, but with fewer power supplies and cosmetic touches (big open frame mess built into the carcass of a calculator). I also made a trivial one consisting of a solderless breadboard screwed to the top of a little power supply. I still use that one, even though some of the holes in the breadboard are melted from a TTL wiring mistake decades ago.

    • #2 by Ed on 2018-10-24 - 12:36

      melted from a TTL wiring mistake

      The contact fingers definitely lose their griptivity when the sun rises inside the plastic block …

  2. #3 by RCPete on 2018-10-23 - 10:31

    Allied Radio did a tape deck kit (Knight Kit) that used plug-in boards for the modules. Since that wasn’t risky enough, all the transistors were installed in sockets. I didn’t override that suggestion, for some reason.

    I didn’t keep the deck long enough for the inevitable to start happening. [grin]

    • #4 by Ed on 2018-10-24 - 12:41

      Know when to fold ’em!

      I just un-wedged the meter switch on an ancient HP power supply (more later) with no plug-in anything: all the wires and components were soldered directly to the main PCB. I had to dismantle the switch kinda-sorta inside the chassis and lube the (silver!) contacts in place. Worked out OK, but gives one an appreciation of why (well-made and gas-tight) IDC connections took over the electronics world.

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