Restoration Project #30 - HP µLAB 5036A

This one is a restoration I'm doing for a friend, Karpour. He's also into collecting old school nerdy stuff and occasionally asks me to fix some of it. I was quite honored when he asked to prepare one of his more obscure devices: a late 1970s microprocessor training kit from HP. The board was complete, with the exception of the speaker, but completely missing the original suitcase and power supply. There is very little documentation out and about, the "service manual" lists all the components, but has no circuit diagram. This leads me to believe that the original training manuals had that already in them. HP also made use of a weird "diagnostic tool" (which they call "signature analyzer") that seems to count pulses of logic signals and could be used to detect anomalies on chip inputs or outputs. But the numbers that are listed in the service manual are totally useless unless you have the matching tool.

At any rate, I had to do some reverse engineering of the circuitry in order to find out what was wrong with the device. And, oh boy, was there something wrong... Two logic chips and both SRAM chips were broken. It took quite a bit of tracing to find all the faults. Not to mention, that the board was designed to educate... and that includes "fault simulation" on the board via some unlabelled jumpers. It was much easier, once I found out that these jumpers were supposed to introduce faults; my reverse engineering was hampered quite a bit because I could NOT make sense of some of the options they selected...

But overall, I managed to get the board running again and could finish the request to make it into a functional display piece that can be hung to a wall as well as used - even on the wall if you so choose.
UPDATE: The textbook that went with this device seems to be "Practical Microprocessors Hardware, Software, and Troubleshooting by Michael Slater & Barry Bronson" based on a comment below and confirmed by a bit of internet research. It also led to some more sites dealing with the device that didn't show up when looking for the part number alone.
NOTE: soldering and de-soldering was a nightmare: the PCB is 2.5mm thick (1/10") and to get the solder up to temperature for a nice connection or de-solder job is almost baking the chips, especially with the VCC/GND rails, which are extra beefy and thus extra thermal sinks...
Another note: @adriansdigitalbasement2 recently had a video about a "free run" CPU tester for 68000 CPUs; while I only ever saw it on this board here myself, his video makes me think this might have been a common diagnostic tool back in the day... would be interesting if any other devices had something like that to do a "quick check" of the processor?
0:00 Intro / First Diagnostics

2:20 Address Bus Problem / Recapping
3:40 Customs Delay / Buffer Replacement
5:07 Second Diagnostics / ROM Dump / 74LS138
6:05 Third Diagnostics / Data Bus / IO Chip
6:45 RAM Maybe? / SRAM Test Botch
8:19 DIP and Jumper Description /
9:05 SRAM Update / Keyboard Matrix Problem
10:05 Board Cleaning / Speaker
10:58 Case Construction / Backer Board Frame
12:03 Barrel Jack Plate / Power Supply Cutout / Acrylic Cutout
13:03 OpenSCAD Spacers / Base Plate Treatment / Spacer Painting
14:06 Final Assembly / Power Supply / Blue LED Subtraction
15:14 Board Mounting / Magnets!
16:10 Acrylic Mount Schematic / Overview
17:30 Credits / Outtake
Music:
My Train's A Comin'
Unicorn Heads
(YouTube Audio Library)

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