Vintage Computing: TEAC FD-55FV

Recently I finished installing two new (never used!) floppy drives on my Tandy Color Computer System, these were meant as an upgrade to the original disk drive unit: a full height 5 1/4" double density single sided unit. One of those weekend projects.

I had been looking to do this for a while now, and as time went on it was getting more difficult to find the suitable half height DSDD 40 track capable drives at a decent price - the prices on Ebay for pulled units are most of the time unfair but that's the usual price to pay for oddities of the computing world in modern days.

One good moment I saw a posting for a set of three Teac FD-55FV brand new units, the price couldn't be beat: $10.00 for all three (plus shipping). The reason for this stems from the fact that these drives are 80 track 720K 5 1/4" units, not many vintage 8 bit computers are capable of using them - for certain the disk controller in my CoCo could not.

The units can be retrofitted for 40 track operation - finding the information was not easy, ended up reading some pages stored on a German server, all in all it was enough to know what to do. This post provides for some visual cues on what to look for if any reader ever encounters him or herself under such situation.

What we need to locate is resistor R19 on the main board of the drive:

The resistor needs to have one of its ends lifted from the board. Some may prefer to nip either end but that would render a retrofit back to original condition more troublesome - a little effort now can save some headaches later if it's decided to jump back to 80 tracks operation.

It will be easier to desolder one end of R19 if we remove the board, remove the two white edge connectors clearly seen in the picture above. There are three screws holding the it to the frame, but first we need to disconnect three small blocks from underneath the board:

R19 is located between an IC and a cap, some FD-55FV boards might be populated a little different depending on the production run - on some I have seen a transistor mounted right in front of R19, the particular board revision I had was completely open:

Carefully desolder one end and lift it. An enterprising hobbyist will see that attaching a small switch between the lifted end and the board connection point will permit an on-the-fly switchover 40/80 tracks, a suitable mounting will have to be provided for the switch though. In my case I don't see going to 80 tracks ever so I just left the resistor as shown:

Once this was done I installed the board back on the drive frame, set in all the pulled connectors and verified the Drive Select jumper settings. When Radio Shack released the first CoCo drive systems they decided to do the drive select by pulling teeth out of the 34 pin connectors, I replaced the stock ribbon cable with a normal straight thru drive cable (no cable twist as with the IBM PC type) and do the DS with the jumpers provided on the drive interface board.

Both drives were promptly installed in the full height case and a quick test revealed I had a perfectly working dual drives unit. Needless to say I am a happy camper.

Please remember that the drive model discussed here is the Teac FD-55FV-13-U (FD-55FV for short). As noted above, some board revisions will look different - I don't think I need to go with great detail to put a disclaimer here on what to expect if anyone out there embarks on a similar project. Get as much information as possible before heating up the soldering iron.

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