Tektronix 494AP service manual Selectorswttch

o
o
o
o	1. !{iust		Low Vottagepower Suppty
o	(R6028							power
		andR6061
					onthe				Su'pljlyboard)
o	This high-efficiencypower supply uses an internal
o
	oscillatorwith a frequencyof 66 i<fiz. The frequency
o	adjustmentis normally-requiredonly after replacin!
	oscillatorcomponents;therefore,pari t is the normal
o	adjustmentand check procedure,part ll of this step
o	shouldonlybe requiredafterrepairof the assembly.
o
a	Since the SpectrumAnalyer uses a high
o
	efficiencypower supply, with the primjry
o	ground potentialdifferentfrom chassisoi
	earth		ground,		an		isolation transform€r
o	should be used betweenthe power source
o	and the Spectrum Analyzer power input
	receptacle.
o	The transformer must have a three-wire
O	input and output connector with ground
	throug.hthe			input and output. n tumper
o
	shouldalso be connectedbetweenitre pri-
	mary		ground		side		to chassis qround
o	(emitterof e2061 and the groundterminal
o	of the inputfitterFL301.)
	lf the power supplyis separated
o	instrument and operated on								from the
									the bench,
o	hazardouspotentials
							exist withinthe supply
	for several secondsafter power is discon_
o	nected. This is due						to the slow discharge
	of capacitors
o				C6101and C6111. A retaxl_
	tionosciilatortightsDs5112(nextto c6111)
o	whenthe potentialexceedsg0 V.
,	Partl: Checkand Adjust Low Voltages
o
	a. Connecta voltage-variable
o								transformerin ,ine
	with the SpectrumAnalyzerpower input and set									the
	transformerfor l17Vac.					Remove
o
	Z-AxisandSweepboards.							the cover over the
a	b. Monitor
	(Figure		the +15 V test pointon the Z_Axisboard
o	5-1b)with a vottmeter(DVM).
	c. Removethe power						Supplycover screw located
o	belowthe	'10
			MHz lF OUTPUTjack on the rear panel
o	(seeFigure5-1a). This wilt provide
								accessto the +5 V
	Referenceadjustment,R6O2g.
a	d. AdjustR6028for +15 V on the vottmeter.R602g
o	is accessed by inserting a narrow_bitscrewdriver
	throughthe screw hole that was removed
O	this step.								in part c of
o
o

o o o o o

AdjustmentProcedure- 494A/4g4ApServiceVol. 1

^e. Vary the input voltagefrom 90 Vac to 132Vac. Check that the +1SV supply remainsregulated,and inputpowerdoesnot exceed210W.

f.Checkthe othersupplyvoltagesat the test points indicated in Figure 5-.1b,against toleranceslisied in Table5-2.

Table 5-2

POWERSUPPLYTOLERANCES

+8.92V to +10.1V -4.96 V to -5.0S V -7 V to -8.5 v

-14.84 V to -15.16 V

+4.73V to +5.29V

+16.81V to +18.6V

+95 V to +105V

+280V to +310V

S.Remove the voltage-variabletransformerandreconnectthe Spectrum Analyzerdirectly to the power source.

Part lt Adjust OscillatorFrequency

a, Removethe power Supplymodule,as described in the Maintenancesection, then remove the power Supplymodulecoverand disconnectpg045.

b.Plugthe powercord into the powerinputrecep_ tacle andconnectit to a suitablepowersource(11SVac or 230Vac, dependingon the position of the LNE

SELECTORSWTTCH).

c.Use a plastic or insulatedtuning tool or equivalent,to insert between the two on/off power switches(3300)to closetheseswitches(Figure5-1a).

d, Connect a test oscilloscope probe, with a deflection sensitivityof 5 V/div and sweep rate of 10ps/div to TP6053(Figure5-1a). Noteth€ amplitude of the output waveform, of the oscillatorU60S9,is approximately10V,

e.Adjust R6061 {Osciilator Freq Adj) for a waveformperiodof 15 ps (66kHz).

f, ReconnectP3045, replace the power Supply module cover, and re-installthe moduleon the Spec- trum Analyzer.

5-3