Track zero sensor of the ST-506 in a Profile

[pintoguy]

As I was low level formatting four of my ST-506 which I had messed up with a bad controller board, I encountered one issue with a recalcitrant drive. It would start LLF, but after three tracks, the actuator would go crazy and hit the crash stop. I also noticed that the actuator would not home to track zero upon startup, which it does on a healthy drive. I suspected that the track zero sensor (see photo) was messed up, and upon switching with one from a good drive, the actuator would indeed home to track zero and complete the LLF with no issue.

Has anyone encountered the same issue. With a DVM, I could detect that it's the unit connected to the black and brown wires (furthest away from the stepper motor) that's defective, and it's likely the IR emitter diode. Does anyone know if there is a replacement available ?

Thanks very much

PS: Apologies. The picture shows up as an attachment. For the life of me, I could never figure out how to insert a picture in this forum, when it's so easy to do in 68kmla

[pintoguy]

OK, so I can confirm that the IR emitting diode that's part of the track zero sensor was fried. I found a replacement (SPX4251) on Walmart.com that cost me $9 (including S/H), installed it, and voila, I've got a working ST-506 in my Profile again (caution, polarity is important). And in the process, I found out why my pic would not show in the body of the message (the BB does not recognize TIF file format). So in the photo below, you can see the sensor assembly with the IR sensor (black with red and orange wires), and the bad IR emitter (yellow, with black and brown wires). In those days, HDD drive design was so friendly to tinkering