3 Oct
2011
3 Oct
'11
7:14 p.m.
From: ard at p850ug1.demon.co.uk
Hi Tony
I did enough experiments to see that I had no problems reading floppies
other than those that were recoreded near the monitor.
My guess is that it upset the bias so that it shifted the depth over time,
enough to upset the read of the data. The recoding is all through
the depth were as the reading is more of a surface thing. To read
it is the spacing of the edges of the NS-SN fields. Singe the recording takes
place over a larger volume of the media, it can effect the NS-SN
transitions because of the depths of the fields.
Dwight
I have found that floppies are sensitive to the
stray fields
of things like monitor deflection coils while they are being recoded.
I've never seen similar fields cause any problem while reading.
Even moving the monitor as little as another 6 inches was enough
to stop the problem.
I am supriset it affected writing and not reading. Had it been the other
way round, I would have suspected interfecent pickup in the read
amplifier (seen that often enough), this does not damage the disk though.
I assume your disks written when the drive was too close to the monitor
were not readable elsewhere, the data on the disk was genuinely
corrupted. But I don;t see why a disk would be more susceptable to
external mangetic fields when writing than at any other time.
It also may not have been the defleciton coils. There are plenty of other
magnetic devices in CRT nonitors -- PSU transformer, flyback transformer,
degausisng coil (if a colour CRT), etc.
-tony