Maintenance—485/R485 Service
TABLE 4-4 (cont)
Trouble Symptoms
Checks to Make
Comments
1 nverter starts then shuts o ff at fast
rate (10 Hz or faster).
Check comb connector " R " for proper
installation.
Overvoltage Stop circuit stops inverter
when connector is out.
Check
power from T1848 reaching
U1910
Stop monostable w ill stop inverter if
U1910 does not have power to function.
Pin 6 = +7.5
Pin 7 = - 2 V
Check secondary voltages for overvoltage.
Overvoltage Stop circuit stops inverter if
U 1910 does not regulate.
Excessive ripple on semi-regulated
supplies.
Look
for
an open rectifier diode.
Compare ripple frequency on the input
capacitor of each Semi-regulated Supply.
Due to symmetry of operation an open
rectifier on one supply w ill cause ripple
on all supplies.
See Table 4-3 for max output ripple
values.
Matching of the forward voltage drop of
the two rectifiers in a supply may be
necessary to avoid excess ripple.
Inverter w on't start.
Check
for blinking
neon
oscillator
DS1824 on Inverter board.
If DS1824 is blinking. Line Input circuit
is okay. If DS1824 is not blinking, check
for open line fuse or other malfunction.
Check for start pulse w ith AC-coupled
probe at TP 1835.
AC-coupled probe required due to lack of
ground reference in Inverter circuit. Start
pulse should occur each line cycle.
Check Q1900 and Q1902 for shorts.
If either transistor is shorted, the inverter
w ill not start.
Line fuse opens when power is
turned on.
Check Line Selector switch for correct
position.
If
Line Selector
is correct, check
semiconductors on Inverter board with
line cord disconnected and all capacitors
completely discharged.
No intensity control or poor focus
control (see Fig. 4-2).
Check DC restorer diodes in CRT circuit.
Check for proper levels at outputs of Z
Axis and Auto Focus circuits.
If diodes check okay compare circuit
waveforms to those given in Fig. 4-2.
No high voltage.
Check Cathode M ultiplier and Anode
Multiplier circuits.
The Transformer board can be removed
by first removing the Power board and
Inverter board, disconnect Line Cord and
wait five minutes for Line Storage
capacitors to discharge before removing
Inverter board.
NOTE
F or additional inform ation see circu it descriptions, Table 4-2, and c irc u it board connection
map a t the end o f this section. Waveforms fo r comparison are given in Fig. 4-2A through Fig. 4-2P.
4-8
REV. APR 1974
Summary of Contents for 485
Page 3: ...485 R485 rviice T h 5 0 Oscil oscope ...
Page 74: ...Rackmounting 485 R485 Service 6 6 ...
Page 128: ...485 R485 Service MAR 1979 5 m V B A L ADJ ...
Page 152: ... 0 iT s i ...
Page 164: ...2S2 n eKn s e s 5 4 85 Os c illo sc o p e REV F A U S 1 9 7 7 I 1 9 3 5B POWER SUPPLY 773 ...
Page 178: ......
Page 179: ...485 R485 OSCILLOSCOPE REV D MAR 1977 ...
Page 184: ...REV C MAR 1976 485 R485 OSCILLOSCOPE ...
Page 197: ......