IBM 01 Maintenance Manual page 419

CIO
MACHINE
TROUBLE
Tube filament
does not light
No conduction
at any time
Excessive
arcing at Tab
lever contact,
points burned
POSSIBLE CAUSE
Fuse blown
Open filament of 2D21 tube
lOOK
ohm (brown, black, yellow)
resistor to 72 volt line open
IN-92 diode across magnet coil
open, or high forward resistance
DIAGNOSTIC TECHNIQUE
Check fuse visually or measure across fuse with
voltmeter. If 115V A.C. is indicated, the fuse is
blown, if good, zero volts will be indicated. If a
neon tester is used, a glow will occur on a blown
fuse but will not glow on a good fuse.
Check across pins 3 and 4 of tube with ohmmeter
for open filament. If open, replace tube. Correct
resistance is one to two ohms.
NOTE: (A faint violet glow will be visible in the
tube when it is conducting. Check for glow by
shorting contacts on contact plate together and
closing tab contact.) Unsolder one end of resistor,
check with ohmmeter for open or proper resistance.
Unsolder one end of diode, check for open and/or
proper forward resistance.
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