Viewing card record tracks

The HP 97 Service Manual test procedure for the card reader calls for using MagnaSee to check the record track lengths. MagnaSee is hard to find or no longer available, and other magnetic developers are $35-$45 for 2 ounces. Iron filings as used in school magnetic experiments costs about $5 for a lifetime supply. This shows how it works:

Click here for photo

It's not good enough to read the individual line patterns, but the length is easy to see.

Now, I have to figure out why the tracks are so short when compared to the diagram in the Service Manual.

Comments/suggestions welcome.


Edited: 2 Oct 2010, 3:07 p.m.

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