12 Oct
2020
12 Oct
'20
7:46 a.m.
One is for the solenoid that lowers the pad onto the
disk to allow
reads/writes.
One is for the sensor to detect track 1 (LED and detector)
One is for the sensor to detect sector pulse
One is for the servo motor that moves the head in and out
One is for the read/write head
One is for the 110v power to the drive motor itself that spins the belt
and the disk via the center spindle.
I did not move the 110v power wire because that is from a common harness
between the drives and it's pretty obvious the disk is spinning. :-) The
other five were switched between controller channel 0 and 1 (PD0: and PD1:)
At this point I think I'm onto the sector pulse LED not working due to
5v being applied to it. Will be working on that more this morning with a
better/more precise power supply.
Jumping in at this point...
In a 'real' RX01, each sensor LED (track 0 and index) has the cathode
grounded and the anode connected to +5V via a 68ohm series resistor.
If you measure the voltage across the pins with the LED disconnected
(or if the LED is open-circuit) with any reasonable meter, it'll read
5V. The meter will not draw enough current for the resistor to drop a
noticeable voltage.
Of course there is no reason why the resistor couldn't be between the
cathode and ground (with the anode connected to +5V). It's a simple
series circuit, the current is the same everywhere.
The thing that puzzles me is why you read 5V across an LED that seems
to work on the bench. I wonder if a connection is open somewhere.
-tony