apple Lisa2. Any advice on non-working floppy drives?

Tony Duell ard at p850ug1.demon.co.uk
Tue Dec 7 14:25:16 CST 2010


> 
> Hi Tony and others.  Progress and pin readings from the Lisa 2 project...
> 
> I've cleaned a couple of the 400k Drives thouroughly just in case the 
> machine was struggling with the mechanisms.  No change.  The drives still 

I assume you've checked the obvious -- that the spindle motor will turn 
freely by hand.

> sit there on boot in stubborn silence, although the LEDs inside are lit.  No 
> sound or attempt at disk ejection when there is a disk present.

How do these things detelct that a disk is inserted? I know the 800K Mac 
drive usese switches on the front of the PCB operated by the disk housing 
whern it is loaded. Does this do the same thing, or does it use 
photodetectors, or what? 

This is a really silly comment, but I'll make it anyway. You are using DD 
(and not HD) disks, right? The point is that in some drives (certainly 
some erly Sony full-height osnes), the disk-insered sensor lines up with 
the HD-detect hole in the latter disk tpye, so if you load such a disk 
the drive doesn't notice it.

> 
> I did some measurements on the Lisa Lite board input connector, and here's 
> what I found.  I used the circuit diagram at
> http://www.freeinfosociety.com/electronics/schemview.php?id=1417 . The 
> signals in brackets represent the corresponding pins on the sony floppy 
> drive.  A disk was in the drive at the time.
> 
> PH0 (CA0) - 0.2v but rises to 3.5v momentarily when the machine is first 
> switched on
> PH1 (CA1) - 0,2v normally but every 4-5 seconds this pulses to 3.5v
> PH2 (CA2) - Same as PH1
> PH3 (LSTRB) - 0.2v

I don;t knowwhere you'd find it, but I think one of the origianl Inside 
Macintosh books has some descrition of the floppy drive control protocol. 
It might explain how those lines are used.

> WRQ (WRTGATE) - 4.9v
> HDS (SEL) - 4.3v but pulses to 0.2 v every 4-5 seconds
> DEN (ENBL) - 0.2v
> RDA (RD) - 4.9v but pulses to 0.2 v every 4-5 seconds
> WRD (WRTDATA) - 0.2v
> MT (goes to Lite Adaptor circuitry) - 0.11    Returns to drive pin as PWR - 
> 3.6v

That suggests to me that the Lisalite board isdoing something sensible 
and producing a PWM signal. I asusme you don;t have a 'scope or logic 
analyser :-)(

> All 12v and 5v power and ground pins read what they should.

OK. So we now know it's not a  power problem. That is good in that it 
means you won;t be damaging any hardware :-)

> SNS - 4.9v but pulses to 0.2 v every 4-5 seconds
> 
> I''m still digesting what this all means using the Lisa hardware manual here
> http://lisa.sunder.net/LisaHardwareManual1983.pdf .  There is a 
> comprehensive  explanation of how the drive interface works in section 6 but 

Be careful. I don't know if that manual covers the Liaslite/Sony drive 
system or just the origianl Twiggy drives, but I could well believe there 
are differneces between them.

>From what I rememebr of the I/O board scheamtics, the floppy drive 
control lines come from some parallel interface chips (6522s?) on the I/O 
board, so their function and timing is determined by software. It's 
entirely possible (I would say 'quite likely') that these signals do 
different things when you use the Lisalite/Sony board.

I will take a look at the URL you mention and see if I can suggest anything.

> I'm still digesting this and trying to get my head around it.  Appreciate 
> that I'm not a techie and a lot of this stuff is new to me.

All I can say is that I remember that feeling all too well :-)

> As I see it at the moment, the drive is certainly getting power, and appears 
> to be getting signals.  Whether these signals are the right ones are another 
> question?

At this stage I think I'd concentrate on either trying to work out what 
the control signals are really doing (but this will be very hard without 
a logic analyser [1]) or I'd be looking at the drive itself to see if I 
could find anythig wrong there. It's a pity I've never actually seen one 
of these drives

[1] Yes, there are plenty of ways to manage without one, but as with most 
things it's a trade-off between equipment and experience. Ifyuo know what 
you are doing you can make do with a couple of chips from the juk box and 
a few LEDs. If you have less experience, having the test gear can help 
(provided you know enough to use it...)

-tony



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