Heathkit IM-4100 - Page 51

Gag HEATHKIT® aint
Troubleshooting Chart
CONDITION POSSIBLE CAUSE
One readout does not reset to
zero with the input shorted.
: Check associated decade counter
and decoder/driver IC's.
Readouts will not reset to zero iE Q6.
in the kHz or MHz range. Pa 1C18.
3. 1G2771C2351G24:
4. 1C17.
1C13.
2 Switch SW2.
1C19, 1C20, 1C21.
Display will not light. Power supply.
1C27.
One or more display tubes will
not light.
Counter functions normal in MHz
range but not in kHz range.
Check associated decoder/driver
IC’s (IC8 through IC12).
Check associated decade counter
and decoder/driver IC's.
One display tube does not indicate
correct numeral from known frequency
source.
Counter resets to zero but will 1. Range switch not firmly pressed to
not count. correct position.
2: Insufficient amplitude of input
signal.
a Transistors Q1 through O04, IC1, IC2,
1C15.
OVER (overrange) lamp does not
function or is on continuously.
Counting sequence is displayed
during gating.
Memory transfer line, O6.
iC18.
Resistor R102.
2: Interchange D104 with another
display.
Random count with input cable ; Scrape paint under BNC connector
disconnected. on back of panel.
+5 volt supply too high. t: C27.
Decimal point does not light.