Tektronix 503

Maintenance— Type 503
Fl»- «-6 location of D611 and C61J |unction lo ti point, (right
lido of Intlru nto nl).
To check the secondary circuit of T601, measure the volt
age at the junction of D612 and C612 (Fig. 4-6). This voltage
should be approximately +500 volts. Check the secondary
winding of T601 and the voltage doubler circuit if the volt
age is not correct. A reading of approximately 600 volts or
more at the junction of D612 and C612 indicates the oscil
lator circuit [V620, T620) is inoperative or the line voltage
is too high. Before replacing V620, check for defective parts
associated with V620. Some of the parts to check, for ex
ample, ore T620, C620, C621, and R621.
If the proper output voltage is obtained from at least
one of the power supplies, the oscillator circuit need not be
checked. In this case, check the rectifier and components
associated with the inoperative supply.
Failure to Regulate at the Correct Voltage. If the
supplies fail to regulate at the proper voltages, first check
the line voltage. The supplies are designed to regulate
between an input voltage of 105 and 125 volts (or 210 ond
250 volts), with the design center at 117 volts (or 234 volts),
RMS Improper line voltage may cause the supply voltages
to be off.
If the output of any of the supplies is off by only a small
amount, it may be possible to readjust the — 100 ADJ. con
trol to obtain the proper voltage. It should be noted that
when the setting of the —100 ADJ. control is changed, the
entire instrument must be recalibrated according to the
procedure given in Section 6 of this manual.
If the supplies fail to regulate, check the lubes (if this
has not already been dono). Then make sure that the volt
age at the junction of D612 and C612 is approximately
+ 500 volts. Check for off-value resistors, especially in the
dividers, and for open or leaky capacitors associated with
V634.
4-6
©
Fig. 4-7 . Checking (he Vertical A m plifier for an unbalance condition.