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What to Expect When Increasing the AC Voltage to the TV
Observe:
AC Current (degaussing coil
Current will rise to 1 amp at about 12Volts AC, then
unplugged)
drop down to 0.34Amps
Oscillator's DC supply
Will increase proportional to the AC voltage being
voltage at R606
increased.
Collector of IC601-1
Must be half the DC voltage measured at R606. If
not, a part is still defective.
Normal Testing Results
Below is a chart that shows the converter/TV operation as AC is increased
slowly to the TV that is OFF. The Degaussing coil is unplugged during
this test.
In the 27" BA-4 chassis, the converter can be tested by temporarily jump-
ing the TV's ON/OFF relay contacts and removing the load by unsoldering
a series inductor L504. Do not disconnect the B+ regulating stage (IC603,
DM-58) or the TV will draw an abnormally high current as the AC voltage
is increased.
Increasing Voltages with TV OFF – Model KV20M40
AC
DC at R606
7 Vac
8 Vdc
11 Vac
11 Vdc
22 Vac
25 Vdc
40 Vac
50 Vdc
75 Vac
100 Vdc
110 Vac
150 Vdc
120 Vac
166 Vdc
Normal on a 20" BA-4 chassis TV
Converter IC601-2/E
Vp-p
Freq.
20 Vp-p
55kHz
22Vdc
28 Vp-p (w
49kHz
108Vdc
spikes)
35 Vp-p
51kHz
116Vdc
60 Vp-p
54kHz
116Vdc
100 Vp-p
61kHz
116Vdc
150 Vp-p
78.5kHz
116Vdc
170 Vp-p
104kHz
116Vdc
25
When beginning to increase the AC voltage to the set under test, the AC
current will increase sharply until the B+ reaches the correct voltage for
that set (116Vdc or 135Vdc) and then drops gradually as AC voltage is
increased. The degaussing coil is unplugged during this test.
Model
KV20M40
KV27S45
Above 12Vac, the B+ has reached its maximum and the regulation stage
changes the converter frequency to supply sufficient TV current to main-
tain a steady B+ voltage. As the input AC is being increased toward
120Vac, the current continues to drop toward the normal operating level.
This TV power supply can run unloaded, but the regulation circuit must
remain intact or the unit will damage the converter IC601 and blow a
fuse.
B+
Peak AC Current Consumption
AC Voltage
AC Current
12Vac
0.8 Amps
11Vac
1.3 Amps
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