400K floppy problems

[mitchW]

I just finished fixing up a Mac 512K. It works like new, including the internal floppy drive.

But the external 400K drive is making me mad. It is a SONY OA-D34V-22.

At first, the mechanism was stuck. This was easy to remedy. I also noticed that the pressure pad was missing.

But then, when I inserted the disk, it immediately says it is unreadable.

I found out that the motor doesn't even spin. Even if I took the floppy out and used a screwdriver to press down on the optical interrupter, the motor didn't spin.

But in the 1 of 10 attempts, I did managed to spin the motor for about 2-3 seconds. Once I even got a floppy to read (using a makeshift pressure pad) and it mounted on the desktop.

So essentially, there must be something wrong with a motor or a motor control. Perhaps something else?

Any ideas?

EDIT: I discovered that if I spin the motor with hand, and press on the optical interrupter while it is still spinning from inertia, the motor will spin on its own for a sec or two.

 

[unity]

It could be a voltage issue. It could be a motherboard issue. Or it could be a the drive. For me, step one is usually parts swapping. You have a working internal drive, so you could swap them. But that I mean open both cases, remove the external floppy cable and insert it into the internal. This way you dont even have to remove the internal drive, its just hooked up to the external port. If it works, you can rule out any motherboard issue/connector/cable/etc. If it does not, you can focus on other issues.

 

[mitchW]

I swapped the drives, but it does the same if connected to the internal port.

I played with the drive some more and found out that the motor will start by its own if it is rotated in some positions.

I took some voltage measurements that confirmed this, as sometimes there is 12V present on the one green 3-pin cable that goes from PCB to the motor. If the 12V is present, then the motor will start.

The presence of 12V varies on the rotation of the motor, so it comes and goes about 6 times in one rev. It looks like there are some hall sensors that detect the position of the rotor.

 

[CC_333]

I have a 400k drive like this, except it will just flat out die when it warms up some (I got it to work for a few minutes, but it became unresponsive and crashed the system). By trial an error swapping parts from a known working drive led me to a somehow faulty motor controller. Not saying that's your problem, but it could be?

Try swapping PCBs around from a known working drive and see what happens.

c

 

[mitchW]

Yup, I also believe that the motor control circuitry might be acting up. Perhaps is there someone on the forum that knows something about these three phase motor controllers, as they were used on pretty much every floppy drive. It might be a dried-up capacitor on the PCB, however, I checked them with an ESR meter and found no obvious faults.

I Googled and found this blog that someone also had acting-up floppy drive and he fixed it by replacing the hall sensor. However, there is very little other information about the diagnosing of these motors.