Hi all,
I have now personally replaced the pads on over 200 microdrives, and I have made the following observations:
There are three main groups of microdrives. The most notable difference between them is the design of the spring clip on which the felt pad mounts.
The first design appears on mostly 1983-4 microdrives. The spring portion of the clip is 80% of the width of the pad area. These are quite strongly sprung. I call these the "fat pad" microdrives. These account for about 8% of the cartridges I see.
The second design has a much thinner spring section, about 20% the width of the pad area. The spring section mounts centrally on the pad area. These account for about 80$ of the cartridges I see.
The third design is very similar to the second, but the spring section is offset slightly - these clips go in one way around only, with the wider gap facing the top/front of the cartridge. These account for the remaining 12% of cartridges I see.
Cartridges fail in three main ways:
As a baseline, a normal cartridge in good condition requires 0.012 amps of current at 9.0 volts to run. The motor on a microdrive runs within a very narrow range of speeds anywhere from 7 to 13 volts.
1. The felt pad crumbles, falls apart and debris gets scattered in the cartridge. The tape no longer contacts the head well, becomes hard to read, and the debris may or may not make the drive harder to turn. Replacing the pad and running the drive for a while usually resolves the problem.
2. The felt pad detaches from the metal plate. The pad and sticky goo stick to the white roller that the capstan opposes to drive the tape. When the tape gets squeezed against the goo, it sticks the tape to the white roller. Tape loops around the white roller 2-3 times then the drive jams. Replacing the felt pad, gently easing the tape out and then feeding it back in is occasionally successful if the microdrive does not have black labels or on-body printing. If it does have black labels or on-body printing, it is always unsuccessful, and the tape will completely jam within 10-30 seconds. This failure mode seems to mostly happen with fat pad microdrives.
3. The tape stretches slightly over time, or was not installed correctly so there was too much slack tape feeding in before being spooled. These tapes jam. The failure sometimes looks like 2, but there is a lot more tape available so it winds 4-6 times around the white roller, or jams internally.
I have devised two methods of cartridge restoration.
A. Works best with failure mode 1 - "the felt pad crumble" on microdrive styles 2 and 3.
I carefully remove the pad spring clip, and soak it in acetone to dissolve the glue. I hold the clip on my finger and scrape off the residue with an x-acto knife. I clean the pad with a lint-free cotton swab. I let it dry, then apply the new pad. I let the pad bond to the metal for 20 minutes, then I re-insert the spring clip in the microdrive - a skilled task! The trick seems to be to re-bend the spring clip mounts to a 60 degree angle from the foam pad area. Once mounted, I place the cartridge in a bare Samsung microdrive unit connected to a bench PSU set to 9 volts. I watch the ammeter - >=1.2 amps is the ideal. Cartridges in the 1.2 <> 1.3 amp area follow one of two paths... Either the debris gets drawn through, comes out and sticks to the new felt pad - replace and repeat. Or, the load gradually increases until it hits about 1.4 < > 1.5A, at which time resistance overcomes the capstan's ability to drive the tape.
The microdrives that spin at <=1.2 amps get put in a "passed" pile, and the others get put in the "failed" pile. The fail rate for smooth spooling is about 15%. This is separate from actually recovering data from the tape.
B. Needed for the fat bad spring microdrives. It is not possible to remove the pad springs on these without really messing them up.
I lift the tape slightly, so it bows stably without popping back in. I slide an aluminium (non-magnetic) smooth flat tweezer under the spring from back to front, carefully. The other arm of the tweezer goes just under the tape loop, holding it clear. I use an x-acto knife to remove the worst of the pad, preventing the debris from falling into the cartridge. I then wet the area with acetone using a lint free cotton bud. I wait 20 seconds, then repeat, and carefully scrape off the glue. The glue on these pads is a harder, more resinous material than on the thin pads, so this takes one or two minutes. Once cleaned, I dry the area with a clean cotton bud. I wait for the acetone to fully evaporate, then carefully apply the new pad and press it down - particularly the leading edge. I remove the tweezer, then use a clean pencil rubber to turn the tape against the white roller to draw it back inside the case.
I have included instructions with the pads I have shipped that state to repair the pad in place in the cartridge: This is the safest method if you are just doing a few. However, if you are doing a LOT and have the time to get into the flow of things, removing the spring clips on all the non-fat pad spring cartridges is much more effective.
Nobody has stepped forward to offer this as a service within the EU. Therefore, I have decided to offer this as a service, directly. The cartridges will be turned around within three days. I will always separate those which test well from those which test badly.
This is a skilled and very time-consuming task, and I have become very proficient at it. I will do agreed pricing for any quantity.
I will continue to offer this service until someone in the EU (where postage costs are lower) offers to do it.
[EDIT: removed pricing - I think it's best to discuss this on a case by case basis.]