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make an external 5.25" FDD out of an internal one (is it possible?)

G

giobbi

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Hi,
I got an old "laptop" (ah ah ah, about 6 kg), 8088 based. It has an external floppy drive. The manual shows the pinout, and it seems to match the 5.25" drive connector pinout... So I was wondering if it's possible to use a spare 5.25" , 1.2 Mb internal drive and a case to build an external drive.

Attached there are the external FDD port pinout from the manual and a fdd connector pinout I found on the web.

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oh, btw... Happy Xmas!!!
 

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What model of laptop? Some of the parallel port style floppy connectors expected a special chip that returned a code and thus only worked with the matching external enclosure. Do you know of anybody with the correct enclosure who can take pictures of the internals?

It looks possible to do and, if the diagrams are correct, the external floppy drive uses the laptop controller chip which should simplify matters. Does the laptop have support for HD drives? Many 8088 systems only had the more limited DD controllers.

I don't like the design having the power connecting pins adjacent to data pins with grounds off to the other side. Makes it far too easy to accidentally short a pin and fry everything. Be very, very cautious in creating the 25-pin to floppy and power cable splitter. Get someone else to double check your work before turning it on. You do not want to lose both laptop and drive. Use the best 25-pin cable you can get; a lot of power will be passed through in order to power a floppy drive.
 
krebizfan said:
What model of laptop? Some of the parallel port style floppy connectors expected a special chip that returned a code and thus only worked with the matching external enclosure. Do you know of anybody with the correct enclosure who can take pictures of the internals?
Click to expand...

It's Bondwell Pro 8 Turbo (1988). I'm not sure what you mean with "internals". Are you talking about the internals of an external drive? However the manual doesn't talk about a specific external FDD brand/model (I'm don't even know if Bondwell made an external FDD) so I suppose it should fit a standard model for the era.

krebizfan said:
It looks possible to do and, if the diagrams are correct, the external floppy drive uses the laptop controller chip which should simplify matters. Does the laptop have support for HD drives? Many 8088 systems only had the more limited DD controllers.
Click to expand...

Yes the same model came in two flavors, 1 HDD-1 FDD or 2 FDDs (3.5").
Ok these days I'm busy but I will try to do that soon and I will report the result here.

Btw I also own a 1987 Zenith SupersPort 8088 Laptop with an external floppy connector. I'm looking for some info about it, to check in the external FDD has the same pinout.

krebizfan said:
I don't like the design having the power connecting pins adjacent to data pins with grounds off to the other side. Makes it far too easy to accidentally short a pin and fry everything. Be very, very cautious in creating the 25-pin to floppy and power cable splitter. Get someone else to double check your work before turning it on. You do not want to lose both laptop and drive. Use the best 25-pin cable you can get; a lot of power will be passed through in order to power a floppy drive.
Click to expand...

I agree, quite dangerous; but I believe I can make the connection without to fry the laptop, LOL... but you're right, a lot of care and a double or triple check are required...


--- EDIT: The Zenith Supersport FDD drive has a different pinout, with no DC power at all. I suppose the Zenith external FDD came with its own power source...
 
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There were even several ISA floppy controllers with a DC37 on the bracket with jumpers to set up power pins accordingly (e.g. Micro Solutions, Sysgen). They varied a bit between floppy models--some had the +5 and +12 interchanged or the ground on strange pins. But sure, you can usually do it. 1.2M 5.25" drives can present a problem for powered connectors made for 360K drives, as pin 2 is the density select pin. The better boards even had fuses in the power lines.
 
Have anybody here a right pinout for 5.25", 1.2Mb FDD drive connector? Im' not sure about the one I found and posted.... and it seems to be incomplete, too..
 
Chuck(G) said:
1.2M 5.25" drives can present a problem for powered connectors made for 360K drives, as pin 2 is the density select pin. The better boards even had fuses in the power lines.
Click to expand...

I suppose the PC controller can't support 1.2 Mb drives, only 360 Kb... should the drive work in 360 kB configuration without any change, or should I change something on FDD side?
 
Stone said:
It's very incomplete...

http://pinouts.ru/Storage/InternalDisk_pinout.shtml

You're also gonna need a 360K drive -- a 1.2MB just isn't gonna cut it.
Click to expand...

thank you.

btw I found this info: "Previously, for the conventional 1 MB and 2 MB AT mode drives, a single Density Select input was used by floppy drives to select between high density and low density drives. A high on this input enabled high density"

Can't I use a 1.2 Mb FDD simply connecting FDD pin 2 to gnd? I haven't a 360 kB drive :-(
 
There's a bit more to it. A 1.2M drive is nominally 96 tpi, while a regular 360K drive is 48 tpi. If you have a 1.2M-aware BIOS, then it knows to make two steps for every single-step a 360K drive might make. In addition, the 1.2M drive spins at 360 RPM, while the 360K drive spins at 300., so a different bit clock (300 KHz) is needed instead of the standard 360K bit clock (250KHz). A 1.2M-aware controller can not only double-step, but also has three bit-clock rates: 250KHz, 300Khz and 500KHz. (Of course, there are "buts" and "ifs"--I'm describing the general case--for example, there was an outfit back in the 80s; I think it was Welltec, or some such thing, that made a 1.2M-capable floppy drive by switching the high-density rotational speed to 150 RPM. It was a 96 tpi drive, so you also needed the double-stepping as part of an installable driver. Piece of garbage, it was--I doubt that you could locate one today).
 
--- SOLVED --- (I wish to modify the title of this thread, but I don't know how, and if it's possible)

...................

After few solders and some test I got a working 5.25" external FDD out of an internal unit. I'm leaving here some info for future reference, just in case somebody will need it.

The PC I used for testing is the "laptop" Bondwell PRO 8 Turbo, a portable PC 8088 based made in 1988. It has the 2 internal FDDs configuration, and no HDD.
The FDD I used is a Chinon FZ-502, a 5.25" drive that should be a 360 kB unit, made in 1989.

Even if the PC supplies the power for the drive, I decided to use an external power source (I made a power supply out of and old ATX psu).

Drive config:
I had to leave the TERM jumper open (it was closed when I tested it as drive A: inside a PC using a twisted cable).
The drive is set as DS1

I used a 34 pin male connector from a broken Motherboard and an old LPT printer cable. I cut out the centronics connector and I soldered the wires to the 34 pin FDD connector.
This way, I can plug there a normal FDD flat cable; I'm using a straight cable (no twisted pair). This will allow me to make some tests with a 3.5" fdd later (I'm wondering if the computer bios supports a two external FDD config...)

This is the wiring schematics I used.

The PC detects the drive during the boot phase, asks if I want to use it as A: or C: ; if you choose the A: option, it will boot from the external drive.

Troubleshooting:

If the PC detects the drive but will refuse to boot from the internal drive, check if you remove the TERM jumper.
If the PC can't detect the drive, check if you connected the READY signal (pin 34 on FDD)

cheers,
Giovi

p.s. in the following schematics, the pin 34 on the FDD connector isn't marked as READY; but it is...
 

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Since it's raining and I can't have a ride on my bike :blush:, I also tried to connect the drive to my Zenith Supersport portable PC (same era of the Bondwell PRO8T).
It seems to work fine, but I experienced some trouble formatting, and probably it disaligned the FDD. I will check it tomorrow... maybe. I only did some read test, not writing, but it should work.

The drive must to be set as DS2 (and TERM=open).

The Zenith doesn't boot from the external drive, though.

Follow the cable pinout.

cheers,
Giovi

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It doesn't really change the drive to 360K, since the drive is still 96 tpi not 48 tpi. All it enables you to do is use a 5.25" HD drive as a 720K on a system that doesn't support the PC AT standard rate of 300 KHz. In that case, it's unlikely that the host supports 500KHz high-density either, so I don't quite see the point of the switch.
 
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