Floppy Drive Cleaning

IMG_2937My NorthStar Horizon came with two Tandon TM100 floppy drives. As I mentioned previously, these were jumpered for drives 3 and 4. I don’t have any other drives to plug in to this system, so I need to re-jumper these for drives 1 and 2.

Even though the service manual is easily downloadable from the net, I don’t have an alignment floppy disk, so I needed to be careful disassembling and cleaning those drives. I took great care not to take apart any assembly that would alter the alignment of the heads or the track 0 sensor. This limited me to basically removing the circuit board to gain access to the mechanism below.

IMG_2821The floppy drives were in remarkably good condition. The belts are snug, with no signs of slipping. The circuit board was in good shape. I removed the strange ID4 add-on wire (mentioned in an earlier post) and returned the jumpers to ID1 and 2. I had no terminator resistor pack, which needs to be installed in the last physical drive in the chain, so I had to manufacture one. The service manual mentioned a value of 150Ω so I grabbed some 1/4W resistors, cut them to length, and inserted them into the terminator socket. The on-board electrolytic capacitors were checked for tolerance and ESR, and all passed. I couldn’t locate any tantalum capacitors (good).

IMG_2945The drive rails were in good condition, but needed a clean and some lubrication. The heads had a bit of oxide build-up, so had to be cleaned. I placed a lint-free wipe soaked in isopropyl alcohol in between the two heads, and closed the mechanism so the heads pushed up against the wipe. The bottom head is a nice solidly mounted head that I’m used to seeing in 5 1/4″ drives, however the top head was a very delicate unframed head held in place with a fragile-looking spring mechanism. Any lateral force (such as pulling the wipe sideways) would possibly bend this mounting mechanism, so I had to be careful. Several open-close motions cleaned the oxide buildup from the heads quite well.

IMG_2948After re-assembling the drives, I powered them up using a current-limited supply, to make sure there were no shorts. Everything looked good, so it was time to mount them back in the case. It took me a little while to determine NorthStar’s factory placement of drive 1 and 2, but after some digging, I was able to find out that drive 1 was the right-most drive (not what I would have guessed, but I’m trying to be authentic).

IMG_2955For such a spacious case, the floppy drives are quite a squeeze, and it was a careful dance to get the drives partially in place, then the power and data cables connected, then sliding the drives all the way in. I learned the hard way that this procedure had to be performed with both drives at the same time, after many attempts at doing the drives one at a time.

The machine is really starting to look like a real computer now. Once I get the floppy controller back in, I should be able to attempt a boot!

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