IBM 1627 Manual page 14

Table 2. Trouble Analysis Guide
SYMPTOM PROBABLE CAUSE
Unit inoperotive; neon power indicator does not light
1.
Fuse Fl blown; check for short circuit, then replace fU5e
2.
Defective Power switch 53
3 •.
Defective wiring or connector P5
Unit inoperative neon power indicator lights
1.
Fuse 2 blown; check for short circuit then replace fuse
2. Defective power transformer T 1
3. Defective power supply component; make voltage and
continuity checks; see Fig. 3-5.
Both chart drive motors inoperative
1.
Defective Chart Drive switch 54
2.
Defective AC wiring
One chart drive motor inoperative 1. Defective motor; check continuity of windings
2. Defective phase-shift component, R6-C8 or R7-C9
Drum step motor inoperative but carriage operation normal; 1. Defective step motor; check continuity of windings
or carriage motor inoperative but drum operation normal 2. Open current limiting resistor or shorted diode; check
continuity; see Fig. 3-5.
3.
Defective drive transistor or ring counter stage; check
waveforms per Fig. 3-4.
Drum step motor or carriage step motor inoperative in one
1.
Defective 5 ing Ie Shot; check waveforms
direction only; operation normal in opposite direction 2. Defective input trigger circuit; check waveforms and
continuity
Discontinuities in plotting, or inaccurate plotting 1. Improper adjustment of step motor;
see Removols, Replocements,
and Ad justments
2.
Double stepping due to noise on input signal line; check for
excessive power supply ripple; check for defective switching
fi Iter components, loose connections, bad solder joints
Operation normal on automatic plot but abnormal on manual Defective control switch or associated wiring
operation
Operation normal on manual but abnormal on automatic plot Defective input trigger circuit or associated wiring
Pen control circuit inoperative 1. Defective solenoid; check continuity between key pins on
pen assembly
2. Defective trigger or current control circuit; check waveforms
waveforms, most defective components can be loca-
ted by using an ohmmeter to check for an open or
shorted condition. Be sure to consider parallel
components when testing with an ohmmeter. An ex-
cellent method of determining the correct reading is
to compare the readings of an identical component
with another, identical, circuit on the board (drum
and carriage circuits are identical). Specific com-
ponent checks are given in the following paragraphs.
two back-to-back diodes arranged in PNP or NPN
configuration. Check the forward and reverse re-
sistance of each diode with an ohmmeter adjusted to
the XIOO ohm scale (Figure 2-2).
NOTE: Before removing and discarding the tran-
sistor as a result of this test, check the printed card
to establish that a shorted transistor junction is not
the result of its being shunted by a low-resistance
component. The XIOO scale of the ohmmeter should
always be used to protect transistors from excessive
currents.
Transistors. A good-bad test to indicate open or
shorted transistor junctions can be performed on
transistors without removing them from the circuit
board. For this test, transistors are considered as
Diodes. Test diodes with an ohmmeter in the same
way that transistors are tested,
2,3