Tektronix 585 - Page 60

Maintenance — Type 585
Fig. 5-16. Location of the high voltage test point.
If the voltage at the HV Adj. Test Point is zero or ab 
normally low, replace the Oscillator tube V800 and the
Error-Signal Amplifier tube V814. If this does not restore
operation the Oscillator circuit should be checked.
A quick check on the operation of the Oscillator circuit
can be made by observing the heater glow in the 5642
rectifier tubes, located under the shield at the upper right
rear of the instrument. These tubes are visible through the
opening in the side of the shield. If no heater glow is visi 
ble the Oscillator circuit is inoperative. This could be due
to an open transformer T801, or to a defective component in
the circuit of V800 or V814.
If heater glow is visible in the rectifier tubes, the Os 
cillator circuit is operating. If the heater glow appears to
be dim, however, the output of the Oscillator may be in 
sufficient for proper operation. A more accurate check
on the Oscillator may be made by removing the shield
covering the high-voltage transformer and measuring the
bias at the grid of V800. This can be measured at the junc 
tion of the 100-k resistor R806 and the 0.01  f capacitor
C806. R806-C806 are located on the ceramic terminal strip
near the post that supports the front of the shield. The
voltage at this point should measure about — 65 volts.
WARNING
Do not let your hand or body touch the chassis
when making this check. Secondary reactions to
an otherwise harmless shock might result in a pain 
ful injury.
If the Oscillator circuit is operating properly, but the
voltage of the HV Adj. Test Point does not measure in the
vicinity of — 1350 volts, the 5642 rectifier tube V862 is
most likely defective.
Abnormal Intensity
If a trace is visible on the c rt, the intensity of the trace
may be used to identify trouble in either the negative bias
supply or the positive anode supply.
If the trace is excessively bright, and does not change as
the INTENSITY control is adjusted, check the negative bias
supply including the lead to pin 3 on the c rt socket. Check
for a defective rectifier tube V822, an open supply winding
or a filament winding, an open resistor including the IN 
TENSITY control, or a shorted or leaky capacitor. If trouble
is not found in any of these components, a defective c rt is
indicated.
If the intensity of the trace is extremely low, check for an
inoperative positive supply. Also check the anode con 
nection to the c rt, including R836 and C836.
If the accelerating potentials appear to be too high, as
evidenced by decreased deflection sensitivity, check the
Error-Signal Amplifier circuit.
If a badly distorted trace or spot is visible on the c rt,
check the Geom. Adj. control R861 and its connection to
the neck pin on the c rt. Also check the ASTIGMATISM
control R864 and its connection to the c rt base socket. If
the FOCUS control has no effect on the trace, check this
control (R856) and its connection to the c rt base socket.
IMPORTANT: If any components in the Oscillator, Error-
Signal Amplifier or — 1350-volt cathode supply circuit are
changed, or if the setting of the HV Adj. control is changed,
it will be necessary to check the calibration of the instrument.
In particular, sweep rates and vertical deflection factors
should be checked.
5-14