Tektronix 1705A instruction manual Low Volts Supply, Maintenance Power Supply Fault Symptoms

Maintenance

Table 6- 2: Power Supply Fault Symptoms (Cont.)

Power Supply cycles OFF/ON	Output Check (Low Volts),
	or High Voltage Oscillator Check (High Volts)
Does not power up	Control Circuit Check (Low Volts)
5 V not regulating	Error Amplifier Check (Low Volts)
Improper crt display	High Volts Supply

Low Volts Supply

NOTE. A 20Ω, 2 watt resistor should be used as a load for the Low Volts Supply. Disconnect J4 and connect the 20Ω resistor between W1 (+5 V) and TP1 (secondary ground).

1.Preliminary Checks

a.A properly functioning and loaded Low Volts Supply will output the voltages listed in Table 6-3. Use the DMM to measure the voltages between TP1 and the voltage test points. If the supply is not regulating properly, continue with the procedure.

Table 6- 3: Low Volts Supply Voltages

Test Point		Voltage
W1	-- (+5 V)	+4.88 to +5.12 V
W4	-- (+15 V)	+14.0 to +16.0 V
W3	-- (--15 V)	--14.0 to --16.0 V
W2	-- (+40 V)	+39.0 to +41.0 V

NOTE. The Low Volts Power Supply troubleshooting is performed without applying ac power.

b.Disconnect ac power from the instrument. Disconnect the instrument from the Power Supply by removing the jumper from J4.

c.Use the digital multimeter to measure the voltage between TP2 and the tab (drain) of Q9. Be sure the voltage is near 0 V before proceeding.

1705A Spectrum Monitor 6- 13