REPAIRS TO THE MSD SD-1 (SINGLE) AND SD-2 (DUAL) DISK DRIVE Latest updates and corrections: 9-12-2023 I NO LONGER SERVICE THESE DRIVES. I found someone who does: Wes Wiese repair of CMD HD & RL, MSD drives Note: I recently learned that the Tandy (Radio Shack) TRS-80 floppy drive uses the same drive mechanism as the MSD drives and I now have the service manual: "Tandy TRS-80 Service Manual.pdf" thanks to Jeff Birt . This article describes what needs to be done to all MSD SD-1 and SD-2 disk drives to keep them working. It has to do with the mechanical drives PC boards, the ones mounted on the top and bottom of the mechanisms. Before I describe those problems, let me first mention a few recurrent faults I've encountered on that side-mounted MSD controller board: 1. The IC sockets for the DOS ROMs seem to be of poor quality. Reseating the chips (remove, scrape the IC pins, reinstall) in those sockets was necessary to restore normal operation in a few drives I worked on. In one case, electrical contacts in those sockets were so loose, the IC's fell out of them in transit. For any repeat problems with sockets, it's best to just replace them both. 2. The connections from the power transformer to the main PC board sometimes go intermittent. If your drive fails, especially if it's intermittent, extract the transformer plug and socket, and solder the wires directly to the board for a permanent fix. 3. The metal shield cup under the head often falls loose and blocks the head from moving forward. Read the last segment for that repair. DRIVE MECHANISM PROBLEMS (TEC FB-501) First of all, the mechanisms used in the MSD series are unique. Most 360K "generic" replacement drives such as old IBM types do not work. I found a few Panasonic mechanisms that did work with a few modifications in an SD-1, but none that ever worked in an SD-2. That makes it necessary to repair the original TEC mechanisms. NOTE: This is from someone who did find suitable replacement mechanisms: "I was able to swap out the old TEC drives with a pair of Matsushita JA-551 DSDD drives that were pulls out of old XT computers that I had acquired over the years. Aside from setting the drive select setting & termination resistor, no other changes were needed. I did a lot of research and reading before arriving at this conclusion. The orientation of the 34 pin floppy changed as this connector on drive is higher within enclosure with the JA-551 drives. So there is not as much slack as before in the ribbon cable. I had cable installed backwards during initial testing and this delayed resolution / repair." As old as they are, whether they have been used or not, this series of MSD disk drives have or will have -all- developed a unique fault. There are two PC boards on the drive mechanisms. The top one is the disk controller board and the one on the bottom is the spindle motor drive board. Between them, these boards have over a dozen small electrolytic capacitors that must -all- be replaced. When these old caps leak their electrolyte, that corrosive substance eats away at the copper board traces as well as nearby components. The damage is sometimes hard to see but corrosion in the area around the caps is noticeable if you look carefully. Symptoms may range from sudden inability to read or write to complete failure of the mechanism which is indicated by 7 blinks of the LED's on power up. Even if the drive is working perfectly now, those mechanisms are all affected and must be reworked before damage to the board makes repairs more difficult or impossible later. To effect a complete repair, all of the electrolytic capacitors must be removed, the board cleaned of all electrolyte residue and corrosion, and all the caps replaced. In many instances, the residue has gone under components such as IC's, so those chips and other board components must be removed and board repairs done underneath them before they are re-installed or replaced. The electrolyte tends to creep along copper board traces, so some damage can appear inches away from the bad capacitors! The replacement caps will likely be taller than the original unless special "low profile" caps are used. The taller caps can be used if they are installed folded down so they don't stick out too far when the mechanism is re-installed in the drive. For the spindle motor board, the caps must be oriented so they don't touch or block anything during board installation back in the mechanism. Note what might be in the way as the board is re-installed before you decide on the orientation of those caps. Much of the damage to board traces (the printed copper foil circuitry) is hidden underneath the factory paint over the traces. This paint must be carefully scraped off to expose the copper. Anywhere the paint is darkened has probably suffered damage and the entire area must be carefully cleaned and examined under strong light so that all breaks in the foil are located and repaired. After scraping, I use an old typewriter eraser (remember typewriters?) to "polish" the copper so it shines which makes breaks easier to see and makes soldering easier. I use Isopropyl Alcohol or Acetone (which seems to work better) to clean up the cap residue. I use needles on the ends of my ohm meter leads to poke into the copper traces at each end to make sure there are no open circuits along their paths. Some open circuits are hard to see but the meter will find them. Although conductive paint (used for car rear window defogger repairs) should work to fix the open traces, I prefer to use solid copper wire for this type of repair because some connections go through the board from top to bottom and conductive paint will not work if that connection is broken. If wire is used, it must necessarily be very thin. I use one strand out of a piece of stranded hookup wire. For example, when an IC is removed to repair the damage underneath and I see that the copper trace at the hole is eaten away, I poke the wire through the hole and solder it to good copper on both sides of the board to effect a permanent repair. I then seal the board with clear nail polish over all the affected areas. That prevents any future damage to the exposed copper. When the polish dries, I reinstall all components and sockets for the IC's. It's important to solder quickly to secure the IC (socket) pins and avoid unsoldering the repair wires. Note that some areas of the board will be corroded and soldering is impossible. I am including some before-and-after photos of these repairs. Included are pictorial diagrams of the boards showing the location of the capacitors and their polarity. Note that there are three different versions of the spindle motor PC board. These have different cap numbers and board locations. In one version, three of the caps are special non-polarized types. It's important they be replaced with the same type (also called bi-polar) electrolytics. As of this writing, I have repaired about a dozen MSD drives. In almost every case, the drive didn't work after the first rework. I had to go back repeatedly to repair open traces that I missed the first time around. One fault produced an error that showed up as no BAM update when a disk was changed. Another drive would read but not write. Some foil breaks are impossible to find because the opens are under components so the trace can't be followed by hand. Extracting components subjects the board to further possible damage which must be repaired. For traces that can't be visualized and repaired, board jumper wires might have to be used. Much like a cancer, it's a frustrating problem that may take many tries to cure completely. If you do manage to clean all the residue and fix the boards, it's still possible you'll have problems later since the corrosion will continue unless all is found and removed. This is the most disgusting work I've ever done. It's far from a normal repair since the faults are not "logical" as a component failure would be. Age, shaky hands and reduced eyesight make it too difficult for me to continue. I should add one more thing I've discovered. There is a metal shield just under the head and it often loosens and falls free, blocking the assembly from moving forward. Rather than taking the drive all apart, pull the shield forward and put some contact cement inside, then press it back into place under the head. Before it sets up, make sure the head will go all the way forward to the stop. If not, slide the head back, push the shield up from underneath and try it again. It should stay in place by itself but it might be a good idea to let it dry with the drive upside down and the head assembly moved all the way forward. There should be no restriction... no scraping of the shield when the head assembly is moved. Ray Carlsen