Shugart SA405R drive - no head stepping. Service manual?

[philpem]

Hi all,
I'm trying to fix a Shugart SA405R full-height 5.25in drive.

Failure symptoms are that the drive selects and the main motor runs, but the drive will not seek.

I've already replaced the ULN2803 with no change to the symptoms (the new ULN2803 now gets a little warm).
The head stepper motor has about 60 Ohms between the coil ends, and about 30 Ohms between either end and the common (5th pin, black).

Does anyone have a service manual or schematic for this drive? The main PCB is a "25235-3 2332", which isn't in any of the Shugart manuals I found on Bitsavers.
I figured it was an SA400 variant and that seems to be partly true in that the general wiring is similar -- but the designators and pin wiring are very different.

Cheers
Phil.

 

[ldkraemer]

You should be able to use these pages from the SA400 Manual to test the Stepping. It shouldn't be hard to chase
the signals through to the Outputs for the Phase {A..D} low going Signals.

 

[philpem]

I've been trying to do that, but the SA400's head stepping driver design is radically different to the SA405R's. Notably the SA405R uses a 74LS08 and a 74LS74 to generate the phase signals for the motor. There's are a bodge-wire on the 74LS74 (from pin 4 to 10), the purpose of which I'm not certain.

 

[Chuck(G)]

Try this link for the SA460 manual. The 460 is essentially the 96 tpi version of the 450, so the circuitry should be identical.

 

[philpem]

Thanks for that Chuck, but the 405 seems to be very different to that design. The stepper seems to be unipolar - it has five wires. One is a permanent +5V while the others are coil windings fed from a ULN2803. On the PCB there's no "source" and "sink" driver -- just the ULN2803. The stepping motor drive logic seems to be similar, but at the same time very different.

 

[Chuck(G)]

Is this a 405 or 450? I'm getting confused. :shock:

 

[philpem]

I don't know where you got SA450 from. I said above that the drive is an SA405R!

 

[Chuck(G)]

I took 405 as a typo. My apologies. So, a relative of the SA400? Disk-and-follower positioning?

 

[philpem]

I don't know if it's an SA400 relative - both mechanically and electronically it's quite different.
Where the SA400 has two PCBs, this has one, and the chassis wiring uses four 0.1in-pitch connectors instead of the single edge connector.

From memory (the drive has the covers on at the moment), it has a stepping motor, spiral leadscrew and torque-limited screw follower to move the head.

It's quite a strange beastie.

 

[Chuck(G)]

So, probably closer to an SA410, then. The SA400 disk-and-follower was a terrible idea.

 

[tingo]

OP: you should probably take lots of pictures of the drive and the printed circuit boards, and make them available somewhere. Perhaps someone here would be able to figure out more details about the drive from the pictures.