RL02 Tracking

shadoooo shadoooo at gmail.com
Tue Dec 22 16:17:10 CST 2020

> The ready lamp flashes not when the servo burst is >visible, but when the
heads are just before it.
> Why? Well, I probably set the gain too high on the read/write module.

I'm sure you read the manual, however I add some explanation to be sure.
The best head position is not where a servo track is at maximum amplitude
(head is exactly centered to a servo track), but where you read two servo
tracks with the same amplitude (so head is exactly between two servo
tracks, in middle position).
Comparative measurement of two servo tracks allow the servo control to
understand the position of the head in respect to data track.
If the best position for data track is not where servo have same amplitude
probably the head is misaligned or the spring support of the head bent /
To analyze head circuits you need a good oscilloscope, you should be able
to see burst of servo tracks and data tracks too, with two channels you can
understand if analog to digital threshold / pulses signal conversions do
work as expected.
Time ago I fixed an RL02 having a malfunctioning head amplifier circuit.
The gain was too low. When I increased it rotating variable resistor, the
circuit begun to ring (barely auto-oscillate), so was nearly unstable. Data
and servo signals were corrupted, but this was visible only zooming on
oscilloscope after careful trigger alignment.
I don't remember exactly what I did, but some capacitors needed
replacement, then I tuned head gain while loading a platter to the best
position for operation, maybe slightly lower than manual recommendations.
Then it worked perfectly.


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