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5 1/4" Floppy Drive Not Reading?

I took my multimeter and touched one probe to the molex connector where the red wire would attach, and the other probe to pin 12. The reading is 145-150 ohms.
 
Well, there you go--there's a still a terminator resistor pulling things up somewhere. Your job, should you wish to accept it, is to find the culprit.
 
I thought a resistor would lower the voltage, not make it higher. Can someone explain what's going on here? While I am fairly knowledgeable about computers, and have some basic electronics know-how, I know almost nothing about floppy drives.
 
It's less about computers than about electronics. The floppy drive uses what amounts to a 60's era technique for running multiple devices from a single cable (i.e. a bus). The idea is that (1) a "low" voltage signifies "true" or "active". (2) All drivers for signals on the bus are "open collector", that is, there's nothing in a gate's output connected to Vcc--a gate can only pull a line down toward 0V. (3) At one end of the bus, usually opposite from the driving gates, a resistor is used to pull the line toward +5V (inactive).

It's easy to see that when all lines are inactive, the bus isn't drawing power--there's nothing that's pulling a line low or "active", no matter how many devices you have on the bus. Any device can pull a line low with its driver gate--and that's when the device draws power through the terminating resistor.

When floppies first came out, it was with "normal" TTL, not low power. So a 150 ohm pullup was common and the usual gate to pull against that was a SN7438. If we assume that "active" is 0V, you can see that we'll need to drop 5V across 150 ohms, or 33 ma (166 mw), which is pretty hefty for most LSTTL drivers. So, when 3.5" drives came along, the pullup requirement was relaxed to about 2K, which reduces the amount of power needed tenfold--and so many floppy controllers were designed with this goal in mind, which means that the old 150 ohm pullup is too small to get a V[sub]il[/sub] in the area of 0.8V.

So what you want to do is to find those 150 ohm terminators on your drive and replace them with 1-2K.
 
That seems like way too much trouble to find and replace the said resistor. I am going to a repair shop tomorrow to browse anything they may have for sale, so what type of computers do you think will support a 5 1/4" floppy drive? I would assume Win98 and earlier machines, but is there anything else I should look out for?
 
That's not a really good question. There were some 5.25" HD drives that work fine with any PC capable of high -density operation. I run a 360K 5.25" (Teac FD-55BR) from a P4 server.

So it depends not only on the PC, but also the drive.
 
In trying to help you, I looked up your drive on Google, and found lots of people having problems with this drive similar to yours.

I'd just buy another 5.25" 1.2mb drive on eBay or from a local parts place before replacing the whole system. Especially if 3.5" drives work fine.
 
You can't really go wrong with Teac--they were used a lot of people and there's still plenty of documentation on them.. If you're looking for a 1.2M drive, it'll be the FD-55GF-xxxxx series. If you're looking for a 360K drive, it'll be the FD-55Bxxx series (e.g. 55BR, 55BV, etc.) Unless you want a problem, do not get the FD-55Fxxx--it's a 720K (96 tpi) drive and will not do high-density. Sort of a 3.5" DSDD drive in a 5.25" package.

And interesting hybrid is the Teac FD505--a 1.2M and a 3.5" 1.44M drive in the same half-height package.
 
CompuNurd said:
I probably should have mentioned this a while back, but I will be using it to write disks for my Osborne 1, IBM PCs, and any other CP/M or DOS systems I acquire.
Click to expand...
Since the Osborne and IBM PC both have Double Density floppy drives you'd be making a mistake to get a High Density drive to write disks for them. That's because some DD disks written on HD drives can not be successfully read on DD drives. You should seriously consider getting a DD (360K) drive to write disks for those machines.
 
CompuNurd said:
...I will be using it to write disks for my Osborne 1, IBM PCs, and any other CP/M or DOS systems I acquire.
Click to expand...
Be advised that Osborne-1s do not have a standard floppy disk drive nor controller board. Osbourne took two drive manufacturers drives and replaced their electronics interface board with a non-standard board. They also redefined the floppy disk controller board inside the Osborne to a unique design, that among other departures, includes putting 5Vdc and 12Vdc down the floppy ribbon cable. In short, don't hook up a standard floppy drive to an Osbourne-1 until you've read everything about their floppy interface and have appropriate modifications.
 
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JDallas said:
Be advised that Osborne-1s do not have a standard floppy disk drive nor controller board. Osbourne took two drive manufacturers drives and replaced their electronics interface board with a non-standard board. They also redefined the floppy disk controller board inside the Osborne to a unique design, that among other departures, includes putting 5Vdc and 12Vdc down the floppy ribbon cable. In short, don't hook up a standard floppy drive to an Osbourne-1 until you've read everything about their floppy interface and have appropriate modifications.
Click to expand...
??? I thought he was getting the floppy drive for his WIN98 machine so he could write disks for the Osborne, etc. ???
 
Right. I will not be replacing the drives in the Osborne. I just want software so the machine can do something more than be a paperweight in my office.

Can anyone provide the model number for a 360K drive by TEAC? I know Chuck(G) did but when I searched it nothing came up.
 
I only found 5 360K TEAC drives, so they seem scarce. They are all untested or in a higher price range than I would expect to pay for a floppy drive.
 
I'm used to going to my local PC repair shop and dropping $10 on 5 3.5" drives. Of course, I wouldn't mind paying $20 + shipping for one. I'd say I would be fine paying $50 for a TEAC, but that seems steep for a floppy drive.
 
Did you ever solve your 5-1/4" drive problem? I have a very similar condition with my Chinon FR-506. It's a 1.2 MB drive. It's recognized by BIOS as a B: drive, the heads wiggle and the LED comes on startup for a short while, which makes me think it's hooked up mostly correctly.

But when I try it under all OS's (DOS, Win98, WinXP), the light comes and the disc spins, but no head movement. Depending on the OS it tells me either "Drive Not Ready" or "Insert a Disc in Drive B:". So I gather neither OS can see it has a disc in the drive.

It's jumpered TERM on, DS1 on, D-R on and MS1 on.
I tried turning TERM off, no cigar.
Same with turning D-R off.

Motor does not seem to be controlled by the PC - it's on as soon as a disc is in and the lock shut, off if it is not. The LED seems to be controlled by PC alright.

I also have a 3-1/2 floppy in the chain recognized as Drive A: that works fine.

Any clever ideas?

Marc
 
Open the cover of the drive and make sure that the heads have not been ripped off or bent. If there is no damage, a careful cleaning could bring the drive back into service.
 
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