1.44 floppy upgrade issue with DD disks

[Cwiiis]

it's high for HD and low for DD and reads as 4.6V/0V when not connected to the HD board and 4.6V/3.3V when it is.

Afraid I don't know how that is even possible. The pullups on the HD7 are to 5V the same as your switch. So putting them both together should work.

I think it would just be monumentally easier just to use the proper drive.

Monumentally easier if I had the spare cash :) Given the drive does work as both HD and DD, it'd be really great to get it working rather than consign it to landfill. Worst case scenario, I guess I can just install a density switch, or perhaps I can make up some kind of intermediary circuit... I'd still love to know why this doesn't work.

I'll keep an eye on eBay for an MPF920, they do seem to go cheap occasionally.

[Cwiiis]

Something that occurred to me, does it make a difference that the resistor is connected through a diode? The continuity only registers in one direction...

[exxos]

Something that occurred to me, does it make a difference that the resistor is connected through a diode? The continuity only registers in one direction...

I don't know why there would be a diode anywhere near a switch.

As long as you got the HD7 wire on the switch it shouldn't matter. A switch will short the wire to 0V.

[Cwiiis]

My curiosity got the better of me and I traced all the connections. One one side of the switch is a 102 resistor to the 5V rail, on the other side of the switch it goes to where I originally connected the wire on the 0ohm resistor into that IC on the main board - so it's switching between whatever that is and 5V. Apologies for my wavering and vague answers, it would appear my multi-meter is on the way out and has been misleading me at various points...

So the switch looks something like this:

Screenshot 2023-09-25 223312.png

And I guess if I put a resistor to ground between the IC and R2 (or between R2 and point 2 on the switch, whichever) with a value greater than 1K, that ought to bias it towards ground?

[exxos]

There should be no bias in the first place. HD7 board has 5V to a resistor..

Capture.PNG

What you should have is 10K and 1K in parallel making maybe 900R pullup to 5V.

It looks to me your not even getting GND on your switch to start with.

But that would be inverted. When the switch is CLOSED it should be 0v! With what you posted, its 5V when CLOSED and floating otherwise. If thats really how the switch is wired up, that drive really sucks. Basically there is no switch to 0v which means DSDD mode will never work.

[Cwiiis]

There should be no bias in the first place. HD7 board has 5V to a resistor..


Capture.PNG


What you should have is 10K and 1K in parallel making maybe 900R pullup to 5V.

It looks to me your not even getting GND on your switch to start with.

But that would be inverted. When the switch is CLOSED it should be 0v! With what you posted, its 5V when CLOSED and floating otherwise. If thats really how the switch is wired up, that drive really sucks. Basically there is no switch to 0v which means DSDD mode will never work.

Yes, I believe that's how it's wired up and I don't disagree it sucks!

I tried what I suggested with a 10K resistor and that has changed the 'ground' to 2V... So I guess if I use a lower value of resistor, but still greater than 1K, I ought to get it close enough to ground that the switching will work(?) Trying that next.

[exxos]

I'm half asleep now, but this is probably the only way.

Screenshot 2023-09-25 223312.png

[Cwiiis]

I tried switching to a 2K resistor and it worked! I don't know if this will cause issues over time, but HD and DD now working correctly, tested copying and deleting files, all good :)

[exxos]

This would be simple to do.

Screenshot 2023-09-25 223312.png

EDIT
Actually that might not work because the base would limit the voltage to 0.7v.. So I small logic level mostfet would be needed.

[Cwiiis]

Just to recap, because I think I misread your comment - and thank you for your time exxos (and everyone else's)!

The switch works inverted - so when the switch is released (as it is with no disk or an HD disk), it acts as if it's closed and bridges to a 1K resistor to 5V. When the switch is closed (as it is with a DD disk), it acts as if it's open and leaves the input floating. My fix was to put a 2K resistor to ground so that the floating state is biased towards ground rather than leaving it floating. This allows the board to work correctly.

I don't know if it'll have any impact on the floppy drive long-term, but if it does, we can all agree it's a piece of crap drive and I'll get a new one at that point!