Re: Apple 400k drive

Contemporary messages sorted: [ by date ] [ by thread ] [ by subject ] [ by author ] [ by messages with attachments ]

From: Terry Stewart <terry_at_email.domain.hidden>
Date: Tue, 8 Mar 2011 09:18:44 +1300

This is the issue with my 400k Lisa drives Phil alluded to. Actually there are TWO malfunctioning drives and they show the same symptom.

Often the drive doesn't spin the disk on either insertion or activation through a mouse click via the GUI. Whether or not the drive is activated depends on the exact position of the spindle. If you manually turn the spindle a little, it will activate. If the spindle stops on a "dead spot" it won't turn the next time the disk is inserted or activated. If I'm lucky enough to insert the disk and have it spin first time, one of the drives will load software but only very slowly and not always. I'm sure there are a lot of read-retrys going on. The second drive doesn't load software at all even if it does spin. There may be other issues with this one.

I've been in discussion with folk on the classic computer mailing list about this. The feeling was it could have either been the TA7259 motor controller IC, the associated caps or on of the hall-effect devices in the motor controller IC itself. The evidence for this is as follows...

I measured the voltages on the TA7259 pins when the drive under the following two states, manually pushing down the disk-detection lever to simulate a drive being inserted....

detector switch pressed and spindle starts to spin (this is what SHOULD happen)

detector switch pressed and the spindle does not move at all

What seemed to differ between 1 (spin) and 2 (no spin) was pin 6 (c-phase drive output terminal), pin 7 (b-phase drive output terminal) and pin 9 (a phase drive output terminal). Where the motor refused to turn with the switch on, these values were almost zero (with switch on or off). When the motor DID turn on switch on these were around 12v (again either with the switch on and off).

There is more. If I measured the voltage (switch off) and slowly rotated the wheel manually values on the three pins stayed mainly at 12v. but occasionally dropped to zero for a few degrees of turn, then quickly back to 12 as I rotated. In a 360 deg rotation, there were four of these "dead" (0V) areas at right angles to each other (approx 3, 6, 9 and 12 oclock). Whenever the wheel was positioned so the voltage was zero on these pins, switching the drive on (depressing the drive detect lever) had no effect. When it was 12v, the motor sprang into life when the disk detect switch was pressed.

I figure the reason that the disk keeps spining if it happens to start up is the momentum keeps it going over the dead spots. It's not good for keeping the proper speed though, which is why software loading takes so long.

I've replaced the TA7259 and associated caps with no improvement. Major suspicion is on one of the hall-effect devices. The next step is to see if I can identify which hall-effect devices are faulty and which are ok from both drives, and cobble together one drive with known good hall-effect devices.

That is the theory, and that is where I'm up to. If you think I'm on the wrong track, please say so. I'd be interested to know if anyone else has come across this symptom (and what you did about it). It's a coincidence that two out of the three drives I have are afflicted with this.

Cheers

Terry (Tez)

-- 
-----
You received this message because you are a member of the LisaList group.
The group FAQ is at http://lowendmac.com/lists/lisa.html
To post to this group, send email to lisalist_at_email.domain.hidden
To leave this group, send email to lisalist+unsubscribe_at_email.domain.hidden
For more options, visit this group at http://groups.google.com/group/lisalist

Received on 2015-07-15 16:52:53