I’ve had an HP 9123 Dual DS DD 3.5″ Drive Unit sitting on a shelf for a couple of years. This drive unit was intended to operate with the HP 150 II rather than the HP 150, but i thought it might work ok with my older machine anyway.
Unlike the 9121 it does not include a power supply; it was intended to draw power from the host computer. Although it uses HP-IB to communicate with the computer, it uses a different protocol: SS80 instead of amigo. I was pretty sure that i had used SS80 on an emulated drive, so i figured that would not be a problem. I wasn’t sure what the computer would make of the double-sided disk drives.
In these situations, there is only one thing to do: suck it and see.
I started by ungumming the drives. The lubricant used on these old Sony drives seems to set like glue with enough time. IPA cleans it out pretty well. I re-lubed with some light oil.
The service manual indicated that the power requirements. This unit was the thirstier option.
I had a 5A 12V power brick, so i figured i could use a buck converter to make the required 5V. I found a suitably low cost converter, which turned out to be tiny. After buzzing out the supply lines, i made up a little adapter box, checked the voltages, and plugged it all in.
The unit fired up, spun the drives, exercised the head carriage and extinguished the self-test light as it should.
I set up the address to 04 and configured the HP 150 to use drives at that address. Initial accesses did not go well – lots of errors and a disturbing amount of noise.
I thought that i had cleaned the heads, but closer inspection with a dental mirror and bright light showed a couple of stubborn spots on the top heads. These were dragging on the disk surface, generating noise, and gouging the disks. IPA is the usual goto for head cleaning, but i find that sometimes some water/detergent on a cotton bud is more effective. Once the heads were spotless, things went a lot better.
I found that i could read and write disks that had been formatted as single-sided in the 9121 drive unit. I could not format disks on the 9133 – the HP 150 format program failed. I tried with MS-DOS 2.1 and MS-DOS 3.2.