General Category > Lisa Troubleshooting and Repair

Two sick Widgets

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stepleton:
Widget 1 continues to behave as it has last time. Following the instructions linked above, I found that the LED current was low and replaced the coarse adjustment resistor with a lower value, then adjusted as directed, but this then increased the amplitude of the POS_A and POS_B signals considerably. Even before the adjustment (and still afterwards), in the X/Y plot, these signals appeared to have a 1V offset from being centred around 0V,0V. I made adjustments, and this was about the best I could get:

https://photos.app.goo.gl/aJCD7Uu7Nwi7bK8j7

(The video shows repeated attempts at a data recal as commanded by a UsbWidEx in the servo debugger mode.)

The encoder gain adjustment was quite sensitive and nonlinear, and I probably ought to have exercised some contact cleaner into the pots ahead of time.

I noticed that one of the two L165 amplifiers on Widget 1's servo board seems to get pretty warm, warmer than I remember these parts getting for Widget 2. I put heat sinks on the amplifiers temporarily while I was adjusting the encoder gains. The attached thermal image shows that the one furthest from the card-edge connector gets up to about 60 degrees C this way after a few minutes. I'm not sure if this indicates a fault or if the arm is just stiff.

To finish on a happier note, here's a video of what I think is a healthier servo on Widget 2:

https://photos.app.goo.gl/mVcNxuQQjZ55d5hWA

I could adjust the tach gain pot so that the action goes to 35ms as recommended (instead of around 30ms as shown), but given that the problem now seems to be related to Head 1's ability to read, I think I'll focus my attention there instead. My next strategy will probably be to swap parts around between the boards of these Widgets (and perhaps some working Widgets as well) to try and isolate a fault.

rayarachelian:
Good to know (about 56K, etc.) thanks.

compu_85:
The head voice coil can not make much torque. Unplug the head wires, and voice coil wires, and with the drive spinning try to move the heads by hand. (As Patrick noted - the platters must be spinning - don't drag the heads across the stationary disk!)

It should feel completely smooth with little resistance, and no bumps / detends. If you feel any, you can try moving the heads back and forth a whole bunch by hand to "work out" the sticky spot.

cheesestraws:
Hello!  I am belatedly making myself known as per the first post :-).  I didn't realise there was a thread here about these, so I will watch with interest.  These are the Widgets that came with my Lisa: the person who sold it to me said they hadn't been working when he got them, either, so they have been dead for a while, and have pretty much just sat in a box since I got them.  I'm really glad SCIENCE (or at least ENGINEERING) is now happening to them :-)

patrick:
If you are interested in some internals of these drives, you can read this article: http://john.ccac.rwth-aachen.de:8000/patrick/UsbWidLA.htm
Many technical documents originating from the Apple Drive Division can be found at bitsavers: http://bitsavers.org/pdf/apple/disk/widget/
There you will also find the widget firmware, in a form that can be modified and reassembled (e.g. with the "as" assembler). This could be used to bypass faulty areas on the hard disk surface or to implement further debugging functions.

Here are some examples of working with UsbWidEx http://john.ccac.rwth-aachen.de:8000/patrick/UsbWidExamples.htm. This is the tool that Tom currently uses with your drives.

NeoWidEx https://github.com/stepleton/NeoWidEx you can use yourself by simply running it on your Lisa.

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