1.44 floppy upgrade issue with DD disks

[Cwiiis]

So I managed to get the drive apart and I could see what looks like an obvious point to run a wire from - highlighted in the attached picture. Unfortunately, the behaviour is exactly the same, ~4.7V with no or an HD disk inserted, ~3.38V with a DD disk inserted...

Running out of ideas to be honest, maybe it just can't work with this drive :(

IMG_20230925_132618.jpg

IMG_20230925_132625_highlight.jpg

[exxos]

What voltages do you get on the switch with just the power cable plugged in ? I mean one side should be 0V..

[Cwiiis]

What voltages do you get on the switch with just the power cable plugged in ? I mean one side should be 0V..

If I don't connect the wire to the floppy board (so just the power cable attached, or the power and drive cable - no difference in results), I get 4.67V with no disk or an HD disk inserted and 0.005V with a DD disk inserted.

When I was testing the board outside of the ST and unpowered, testing between ground and where I soldered, a voltage registers and slowly lowers when I touch the probe initially (presumably a capacitor getting a charge and draining) and pushing the switch in immediately lowers it to 0V. Releasing the switch then repeats the behaviour.

[Cwiiis]

I'm thinking that perhaps connecting another input has meant that the pull down resistor which looks to be 1K (R63 - 102, visible in the photo) might need to be reduced, perhaps?

I don't have the knowledge to pick a sensible value, but given a short to ground ought to work(?), I guess I can just experiment a bit...

[frank.lukas]

Check the HD Out Signal from the Floppy ...

EPSON / SONY
DD = Low (0 Volt)
HD = High (5 Volt)
no Disk = High

TEAC
DD = High
HD = Low
no Disk = Low

Newer TEAC Drives -> http://www.wrsonline.de/teac.html

[exxos]

I'm thinking that perhaps connecting another input has meant that the pull down resistor which looks to be 1K (R63 - 102, visible in the photo) might need to be reduced, perhaps?

I did wonder if it was a pull down rather than a pullup as on "normal" drives. It could explain the 3.3V he is seeing. I don't recall the pullup on the HD7.

TEAC
DD = High
HD = Low
no Disk = Low

Could be his switch output is inverted then. So simply isn't going to work.

[Cwiiis]

The output isn't inverted, I see high for HD/empty and low for DD - but it's a pull-down resistor. If I soldered another 1K in parallel to make it 500 ohms, would that reduce the voltage I'm seeing for low? Is it likely to be enough? I don't have a huge variety of surface mount resistors handy, but I could always bodge a through-hole there, there looks to be plenty of room. Or is it the case that this just can't work when it's pull-down instead of pull-up?

[exxos]

The output isn't inverted, I see high for HD/empty and low for DD - but it's a pull-down resistor.

If its a pull down, then a open switch would be low, not high. The switch would have to switch to 5V directly. So it doesn't make sense.

I think you need to trace both sides of the switch and see exactly where they are going. One side of the switch would normally be connected to GND, the other side a pullup resistor to 5V.

[Cwiiis]

The output isn't inverted, I see high for HD/empty and low for DD - but it's a pull-down resistor.

If its a pull down, then a open switch would be low, not high. The switch would have to switch to 5V directly. So it doesn't make sense.

I think you need to trace both sides of the switch and see exactly where they are going. One side of the switch would normally be connected to GND, the other side a pullup resistor to 5V.

I have it apart and I was incorrect, it is a pull-up resistor. R63 shows continuity with the ground input at 1.6ohm resistance. So I don't know what makes sense anymore... If it's pull-up, isn't 1K way too low for 5V? My previous voltage readings are still correct - 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.

[exxos]

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.