Can someone make suggestions for this PCB?

[dirkies]

closer up: https://lh4.googleusercontent.com/-H...221_132901.jpg


This PCB comes from an external no-name 5.25" drive for Amiga I bought around 1989, which died long time ago (the drive, it was more and more unreliable to read floppies correctly)

Now with all gotek/hxc and other hacks out there, I thought I could maybe use this one to house an external pseudo floppy in it.

However close but no cigar!

If a 3.5" drive is connected to it:
>It shows up in early boot menu as DF1:
>Workbench will see a DF1: drive
>first the drive will make a short usual noise when the Amiga boots from DF0 (heads parking to position 40 I guess)
>but then the led will blink fast (with or without floppy), mechanism is silent
>Workbench will say that there is a NDOS disk in the drive.

>I also tried to hook a PC floppy drive onto it, same thing.
>I even tried a GOTEK on it but same thing.

the cable from Amiga to the PCB is the same as the ones I see in normal working external 3.5" drives, so that is not the issue. (connected to P2 on PCB)
the 4 dipswitches only indicate on 2 of them: "40 / 80 tracks" and "DS" and are set to that. Changing the others does not do anything, I guess they are not connected.

there is a further external socket to daisy chain another drive (never tested that one)

PCB only references 542C-C and underneath 010988 (most likely date of design signoff). Sticker says RF542C which does give some google hits indicating this was a ROCTEC drive.

4 chips in there, some familiar ones, looked it up in google:

SN74LS74AN - dual D-type positive edge-tirggered flip-flops
(>have this first one also in my Alfa-Data ext 3.5" drive)
SN74LS86N - Quad 2-input exclusive or gate (low power Shottky)
SN74LS123N - IC switching regulator
HD7438P - Quad 2-input positive NAND buffer with open-collector output (low power Shottky)

Looks like this PCB was initially intended for something else, as a lot of empty space on it with circuits and holes not being used at all.

Has someone with enough electro background an idea what makes this different from a 3.5" external drive?

Any ideas what I could try as a mod/hack to make it work?
Or some suggestions what to measure?

Or should it just be binned?

[hooverphonique]

74LS123 is a monostable multivibrator, but that's not important..

did you orient the cable connected to P2 correctly?

all the unpopulated area on the right looks like power stuff, so maybe it's used for drives that need an external power supply, or something?

if the board is intended for a pc drive and not an amiga drive (most likely), it could be designed for a pc-drive configured for device select 0 instead of 1 (pc drives default to use device select 1).. On your pc drive, check for "DS0"/"DS1" jumpers, and see if you can switch them around; it can be either a solder jumper or a traditional removable one.

[dirkies]

yes, cable P2 oriented correctly

No idea about the unused part of the PCB, could well be for some PSU related thing, not needed for Amiga. The unused holes in the back of the casing were taped, only DIP switches were not covered.

The board is not intended for PC, it was sold specifically as for Amiga, PC floppies did not work on it. It was sold in Amiga magazines as a ROCTEC RF542C external drive. It mimicked completely a 3.5" 880KB drive, the Amiga was not aware this was a 5.25" drive.

[hooverphonique]

i'm not talking about pc floppies, but pc floppy drives.. amiga internal dd drives are essentially the same as pc ones, just configured a bit differently.. for external ones, you have the pcb to take care of some or all configuration differences, so there would be no point in not using a cheap off-the-shelf pc one..

[pandy71]

123 is dual monovibrator and it is used to generate pulses with particular time length - sometimes used as crude window/bit slicer (recovering clock from MFM). 86 is used frequently to double frequency.
Side to this 5 1/4 usually spinning with 360 rpm where 3 1/2 with 300 rpm - all this may suggested that board doing something more than just regular latch (74 + 38).

[Magic]

I remember building an interface like this years ago to work with a Teac 3.5" pc floppy drive. It required several jumpers on the drive itself to be re-configured before it would work. It was Double Density only. Perhaps the floppy drives that you tried could be jumpered differently?