Tait T855 - T858 Power Control

M850-00 T858/859 Fault Finding D4.9
Copyright TEL 31/09/98
4.6.2 T858 Power Control
Approximate voltages under normal operating conditions:
Measurement
Output Power
20W 50W
forward power at "FWD-PWR" pad (beside IC3)
RV63/R64 (RV63 wiper)
2.5V
1.4V
4V
2.1V
Does power control work?
Check 12V DC present
on IC1 pin 14.
Check sense volta
g
es
from directional coupler.
Check IC3 pins 7 & 1.
Check Q10 & Q11.
Check IC1 pin 1 >12V DC
when forward power low.
Does forward power
alarm output work?
Does reverse power
alarm output work?
Check Q12 & Q13.
Check IC1 pin 7 >12V DC
when reverse power hi
g
h.
Heat R72 with tip
of solderin
g
iron.
Power control OK.
N
N
N
Y
Y
Y
Y
Heat R72 with tip
of solderin
g
iron.
Check IC1 pin 13 is 0 to 1.4V
as set by RV69.
Check IC1 pin 14
g
oes from
hi
g
h to low as R72 heats up.
Check D17.
Does temperature
shutdown circuit
turn down output power?
N