Repairing self-inflicting damage to my 45 year old Commodore 2040 disk drive

In the world of vintage computing, sometimes we’re our own worst enemy. After accidentally damaging my DOS 1 Commodore 2040 disk drive, I take you through the diagnosis and repair of its IEEE-488 circuitry.

Repairing self-inflicting damage to my 45 year old Commodore 2040 disk drive - floppies rock ep17

In this episode, I track down why my DOS 1 Commodore 2040 disk drive has stopped talking to me. The culprit? A failed MC3446N bus transceiver that handles the vital IEEE-488 communication protocol.

Follow along as I use an multimeter, oscilloscope, and service manual schematics to track down this communications fault. You’ll see practical debugging techniques for tracking down digital bus problems in vintage hardware.

Timestamps

00:00 Intro
01:11 Symptoms
03:16 Schematic
05:35 Initial diagnosis
10:25 Testing with oscilloscope
18:40 Replaced bus transceiver
23:40 It verks!
25:25 Wrap-up

Problems:

While the disk drive appeared to boot OK, the device I used to connect to the disk drive was hanging when I attempted to talk to it.
I tracked down the problem to a failed MC3446N bus transceiver, UB2.
I replaced the MC3446N with one pillaged from another of my IEEE-488 drives. This resolved the problem.
I suspect I either shorted out some IEEE-488 pins or introduced some static to the bus to cause the bus transceiver to fail.

You can find the other videos about my 2040 here: https://www.youtube.com/playlist?list=PLXs34HaWLi10C6ZdFEMkyiR1x8duq9cft