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IBM External Diskette Adapter

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Shadow Lord

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Hi,

I was wondering if anyone had any info on the IBM External Diskette Adapter? Mostly part number(s) or an actual one they are not using and wish to sell. Just to be clear this is not the same as the IBM FDC w/ an external port found on the 5150/5155. That one has an edge connector on the end for the internal floppy cable. Thanks.
 
Chuck,

I've only seen this adapter referenced in the GTO for the XT286. I have to go through the OA and see if there is any mention of it there but so far the XT286 GTO is the only one. According to the illustration the card has two set of pin connectors on the top. You connect the signal cable from the original Fixed Diskette and Disk Drive Adapter (FDDDA) to the External adapter (EDA) and then there is a cable (presumably included with the EDA - although I believe it is just a short length signal ribbon cable) from the EDA back to the FDDDA. This allows the use of an external 1.44MB drive with the XT286. The illustration in the GTO do not show an edge connector on the EDA. I'll try and scan the page and post it in a few minutes.
 
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I vaguely remember that thing--didn't it function basically as a "switch" and require a driver? AFAIK, the DC37 pinout should be the same as the 5150 adapter.

@Mike, the IDC connector is a very high quality unit. I've done a number of these and never had a failure yet. Let the analists fret.
 
Chuck(G) said:
I vaguely remember that thing--didn't it function basically as a "switch" and require a driver? AFAIK, the DC37 pinout should be the same as the 5150 adapter.
Click to expand...

Yes it does require a driver. I didn't think the 5150 external FDC connector had built in power (i.e. I thought the drive had to have a separate PSU). Also, wouldn't the 5150 FDC have a conflict with the FDDDA? So you couldn't have the FDDDA and the 5150 FDC in the same system.

EDIT: Chuck(G) - would you have a part number for it by any chance? No part number is specified in the GTO. Thanks.
 
I'll have to look to see if I can find a part number.

I think that I recall that power was distributed via the first few pins on the DC-37, but I'll have to check. Of course, the 5150 FDC did rely on the external box having its own power supply. There were also third-party external drive adapters for the 5170 and its ilk very similar to this one. Altogether, not a very elegant solution as 5150 software that relied on direct hardware access to get to the second set of drives flopped utterly. By the time that the 3.5" drive came along, slimline (half-height) 5.25" drives were also available. I think most XT (XT286) users just crammed a 3.5" and a 5.25" in the same box.
 
Thanks Chuck. I appreciate it. The drives I have, which I believe are the external drives mentioned in the manual, actually have 26pin connectors and have no separate PSU. I know I can cram a 3.5" drive in the 5162 but mine has both a HD and a DD 5 1/4" which makes it a great in between system. Having an external 1.44MB drive would make it perfect for basically transferring files from one IBM floppy format to another.
 
IIRC, that card was simply a way of getting the Diskette Drive adapter's signal interface to the rear of the box so that one could attach the External 3.5 inch 720KB Diskette Drive. The PC and PC XT did not need it because the interface was present on the back of the Diskette Drive Adapter.

In addition one needed splitter cable for the supplying power. I had one of these on my PC XT at work because at the time I was country technical support for the IBM PC Convertible. (IBM's first box with 3.5 inch diskettes.)

1.44MB 3.5 inch diskettes did not arrive until the PS/2 in 1987 and (again IIRC) the IBM solution for diskette interchange was not 1.5 drives for previous boxes but rather 5.25 inch drives for PS/2s
 
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Beerhunter said:
IIRC, that card was simply a way of getting the Diskette Drive adapter's signal interface to the rear of the box so that one could attach the External 3.5 inch 720KB Diskette Drive. The PC and PC XT did not need it because the interface was present on the back of the Diskette Drive Adapter.

In addition one needed splitter cable for the supplying power. I had one of these on my PC XT at work because at the time I was country technical support for the IBM PC Convertible. (IBM's first box with 3.5 inch diskettes.)

1.44MB 3.5 inch diskettes did not arrive until the PS/2 in 1987 and (again IIRC) the IBM solution for diskette interchange was not 1.5 drives for previous boxes but rather 5.25 inch drives for PS/2s
Click to expand...

That meshes pretty well with whats in the XT286 GTO. Now if I could find one as I do have the external drive....
 
I've dug through my IBM service manuals and can't find a single reference to that particular adapter except where you originally noted it. No part #'s and no pics. Since IBM put it in the manual it did exist. At least for a little bit.

FWIW, my IBM 4865 came with an adapter plug that inserts into the 4865 power supply receptacle and converts it to a standard power supply plug.
View attachment 11529
View attachment 11530
 
That is the standard 720 3.5" Diskette drive setup. The power cable "splits" the existing diskette drive power cable. The small power plug clips in the back of the case where the External Drive plugs into it.
 
Ah, you have the magic power adapter .... I can probably reverse engineer the pinout on it, but if you were to use a multimeter and post the results that would be helpful.

A few years ago I was looking at two 3.5" 4869s, one with the square four pin power plug and one without. I was confused for a while until I found out that there were a few variations of drives:

  • Drives for use on the PC or XT; no internal kit required because they have an external floppy port on them. Those drives also have their own power supply. (Presumably these are 360K 5.25" drives or 720K 3.5" drives only.)
  • Drives for newer machines without the external floppy connector; these required the internal adapter to route the 'B' drive outside of the machine. These drives could be any density.
  • Drives that could be driven entirely from the host power supply and did not have their own power supply; these drives have the four pin Molex connector you have above. These definitely need the internal kit.

I'm speculating that your adapter is actually nonstandard. The internal kit to route the B drive outside would have the power plug on it, which fits nicely through an ISA bracket. I'm betting that somebody purchased that or hacked it up, and that it is not and IBM part.


Mike
 
mbbrutman said:
Ah, you have the magic power adapter .... I can probably reverse engineer the pinout on it, but if you were to use a multimeter and post the results that would be helpful.
Click to expand...

I'll pin it out, probably later today after football.
 
mbbrutman said:
I was confused for a while until I found out that there were a few variations of drives:

  • Drives for use on the PC or XT; no internal kit required because they have an external floppy port on them. Those drives also have their own power supply. (Presumably these are 360K 5.25" drives or 720K 3.5" drives only.)
  • Drives for newer machines without the external floppy connector; these required the internal adapter to route the 'B' drive outside of the machine. These drives could be any density.
  • Drives that could be driven entirely from the host power supply and did not have their own power supply; these drives have the four pin Molex connector you have above. These definitely need the internal kit.
Mike
Click to expand...

Thanks for that info Mike. I apparently have the type two drives as mine have no power connectors. They also have a smaller D-Sub Connector:

  • EXTFDD1.jpg
  • EXTFDD2.jpg
  • EXTFDD3.JPG
 
mbbrutman said:
Ah, you have the magic power adapter .... I can probably reverse engineer the pinout on it, but if you were to use a multimeter and post the results that would be helpful.
Click to expand...

Mike, I just plugged it in to a power supply and read voltage. The picture is of the adapter side of the plug. Wire colors are black (GND) yellow (12v) and red (5v)
Note the male retaining pin on top (clip on drive plug secures to it) and odd shaped plug on lower right of first pic. I don't think this is IBM either as there are no markings on the adapter anywhere. Is this enough info?

Voltages marked on pic.
View attachment 11535

And a side view showing the top retaining pin and wire colors.
View attachment 11536

And one more pic showing alignment of plugs.
View attachment 11537
 
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mbbrutman said:
1. Drives for use on the PC or XT; no internal kit required because they have an external floppy port on them. Those drives also have their own power supply. (Presumably these are 360K 5.25" drives or 720K 3.5" drives only.)
2. Drives for newer machines without the external floppy connector; these required the internal adapter to route the 'B' drive outside of the machine. These drives could be any density.
3. Drives that could be driven entirely from the host power supply and did not have their own power supply; these drives have the four pin Molex connector you have above. These definitely need the internal kit.

4. I'm speculating that your adapter is actually nonstandard. The internal kit to route the B drive outside would have the power plug on it, which fits nicely through an ISA bracket. I'm betting that somebody purchased that or hacked it up, and that it is not and IBM part.
Click to expand...
Here's from what I remember from back then and what we have in the Museum at Hursley park.
1. They were powered from the splitter cable, the 4-pin end of which clipped into a hole in the back of the case. The 3.5" drive only came in 720KB form but there was no 5.25 External dive. (We have one of those drives and power cable in the Museum.)
2. The PC AT and XT286, had a combined Hard File and Diskette Drive Adapter with no external diskette port and so required the adapter card AND the splitter cable.
3. Both 1. and 2. required the splitter cable. I do not remember any exterrnal drive from IBM that was powered in any other way other than with either the splitter cable or (later) its own mains power supply e.g. The PS/2 External 5.25" External Drives.
4. I disagree, see 1., 2. & 3.
 
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