Problems modding an PC floppy drive to work with the Amiga 500

[Ariath]

Hi!

I'm trying modding a SFD-321B/LB PC floppy drive to work with my Amiga 500 (i also have a Gotek, but i want to also use floppies and my plans are putting the real drive as DF0 and the Gotek as DF1).

In various sites the people says that all that is required with this model is moving the resistor for DC to RDY, remove the bridge of DS1-Center and making a new between Center-DS0, and connect the pin 2 of the ribbon cable to the upper pad of DC.

I tried but... the drive seems unrecognized by the Amiga. The drive led is light and the motor spins endlessly (i don't remember now if after inserting a floppy disk or without it).
(due i lost the tiny resistor, i used a cable to bridge the two RDY pads)

The drive worked perfectly in a PC before being modded.

Any clues?

Thanks in advance

[MiaM]

Just to double check: Are you 100% sure that the ribbon cable works correctly and isn't inserted the wrong way around? Drive spinning constantly, LED on and the computer thingking that the drive is broken is a sure symptom of the wire being upside down or broken.

Also I don't think it's likely that this is the issue, but I would be a bit careful with how the added wires are routed, so that they don't lie directly above / near by a PCB trace that carries a signal that might be capacitively coupled to your added wire.

Bonus-unlikely: IIRC Amiga drives are supposed to have some termination on the signals, i.e. pull-up resistors to +5V. Could it be that this PC drive is missing those terminators? I doulb that this would make the LED and motor being constantly on, but still. (My studies back in the days found that an A500 isn't able to drive the low impedane terminators (iirc 150 ohm or so) on old 5.25" drives, but I think 1k or perhaps 2k worked fine. Fiddled with this to use the software on Aminet that can read 1541 disks using a regular 5.25" drive).

Otherwise check the voltage on the DS0 and MOTOR signals. If they are high but the LED and motor is on then something has gone wrong with the drive. If they are low figure out if the computer drives them low (disconnect the ribbon cable and measure directly on the computer side). Although a long shot, if your A500 were missing it's drive either since you got the computer or you don't remember exactly why it was removed, there could be something wrong with the A500 itself. (IIRC the DS signals are driven directly by one of the CIA chips while the MOTOR signal is generated using a latch combinign the MOTOR and DS signals from the CIA).

[Ariath]

https://www.youtube.com/shorts/Q7VoIdGzrdY

First, thanks for you response .

I have re-done the soldering work (also i found a new 000 resistor to replace the tiny wire i used to bridge the RDY pads) and, as long as i can see, there is no connection errors.

The multimeter reports that the pin number 2 connects with the upper DC pad and with the chip pin that follows, so this chain seems to be ok. Also i have tested the ribbon cable connector to be sure no pin was connected to his neigbours.

I have also re-done the DS0 bridge and the DS1 pad has no connection with it.

But the unit keeps "working" the same . The ribbon cable is OK, i have tested the Gotek and i can load games with it, and, since the ribbon cable connector can't be inserted wrong in the floppy drive, all the pins must be in their place.

Also, i forgot to mention that i have an ACA500+ accelerator card, but i have done the test after unplugging it with same results (again, the Gotek works perfectly).

I'm using a PC floppy disk with the HD "mod" so it can be read by the Amiga.

I bought the Amiga with the Gotek as DF0 and i don't have any other floppy drive to test, PC-type or not.

All i have left to do is voltage measurement, but i would be surprised if i find some wrong. The floppy drive worked perfect in a PC tower before being modded, and i am using the same floppy disk i used to test the drive in Windows 98 .

See ya!

[Jope]

Sometimes the floppy drives have their connectors keyed upside down. Try flipping the cable at the other end.

[Ariath]

You mean that, even if the ribbon cable works with the Gotek, maybe it needs to be flipped the side that is connected to the Amiga to make the floppy drive work?

I'll cross fingers and try that

Thanks for the suggestion

[Leon Besson]

Originally Posted by Jope

Sometimes the floppy drives have their connectors keyed upside down. Try flipping the cable at the other end.

Normally an indication that this happened the floppy drive light would stay permanently on as well

Have had plenty of trouble with drive mods. Sometimes it could the be the cable used to bridge that’s at fault.

[Ariath]

Originally Posted by Leon Besson

Normally an indication that this happened the floppy drive light would stay permanently on as well

The floppy drive led is on all time in the video.

Also there is something i don't understand, although it has to do with the Gotek instead the floppy drive, and is that the Amiga drive led, the orange one, doesn't lit when an ADF is being accessed.

If you look at the Gotek activity led when a ADF is loading, you can see the led blinking, as just the orange led on the Amiga should be, but it is off all time.

There has been a couple of times where, while checking connections in the Gotek, the orange led has blinked a bit when an ADF has started loading, but it keeps off afterwards.

I'll try flipping the Amiga end of the ribbon cable this afternoon.

See ya!

[Ariath]

I still can't believe It...

IT WORKS!!

I have flipped the ribbon cable end that connects to the Amiga and the floppy drive has finally been recognized!

I have booted Workbench 2.1 and successfully formatted the PC floppy disk .

I still have no clue of why the orange drive led on the Amiga don't blinks with floppy activity but at least i know now that the mod was well done.

Thanks a lot for your assistance .