Phototransistor - IBM System/34 Maintenance Manual

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23-270
PHOTOTRANSISTOR
Old Style File Control Card!
Service Check
OOOD
•
Erase Current
1.
2.
3.
4.
5.
6.
7.
8.
Set Power to 0 (operator panel).
Remove the 33FD from the machine and
disconnect the drive motor plug (see paragraph
23-100).
Attach the positive probe of the volt ohm meter
(15 Vdc scale) to the +5 Vdc test point and the
negative probe to the phototransistor current test
point on the file control card located on the 33FD.
Close the diskette drive cover, and set Power to I
(operator panel). The volt ohm meter should read
3.5 Vdc to 5.5 Vdc.
Open the diskette drive cover and insert a diskette
backward and close the cover. The volt ohm
meter should read 0.0 Vdc to 0.5 Vdc.
Connect the drive motor plug.
If a scope is available, connect the probe to
'+Index'. Check for an index pulse width of 1.7 to
8.0 ms. Check for approximately 160 ms between
index pulses.
Set the Power to
0
(operator pane!), check that
the cables are connected; then install the 33FD in
the machine.
E
u
-
>
N
+24 Vdc
+ Write Gate •
+ Low Current
•
+ Index
•
Phototransistor
Current (yellow)
+ Access 1/2
.
.
+ Access 3/0
t
-5 Vdc
0
•
New Style File Control Card!
Phototrallsistor Current
Normal Position
*See Note
Position 1
+ Index
•
+5Vdc
0 0
Preamp TP2
- Head Load
+ Head Engage
+ Write Data
MC-1
MC-2
0
•
•
MC-3
,
MC-O
•
•
PreampTP1
Ground
•
LED Current
+
Access 0
+5Vdc
Ground
500 ps/cm
I
On t~e old style file control card (2 wide, 3 high), test
points are located randomly on the component side of
the card. On the new style file control card (2 wide,
2 high)
I
test points are brought out to two rows of pins
labeled TPA and TPB.
Note:
If a problem is experienced with multiple index due to shine-through, the threshold level of the
index amplifier can be increased by paralleling input resistance. Position 1 will increase the threshold by
a factor of 5; position 2 will increase the threshold by a factor of 25. The threshold level should not be
raised more than is necessary to ensure proper operation.
23-270
33FD Diskette Drive 25
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