HP Car 3490A manual CPrBr/o, Pbeliminarytroubleshooting, ACCESSF0RSERVtCtNG, Troubleshootingtrees

Model3490A SectionVII

SECTIONVII

TBOUBTESHOOTINGAND

C I R C U IDT I A G R A M S

7 . T .INTBODUCTION .

7-2- This section contains information necessaryfor repairing the Model 3490A. Schematicdiagrams,trouble- shooting trees, and other troubleshootingand repair information are included. Figure 7-17 showsthe location of assemblieswithin the 34904. Additional trouble- shootingnotes arelocatedon schematics.

7 . 3 .PBELIMINARYTROUBLESHOOTING .

74.lf the Model 3490A operatesincorrectly and the trouble cannot be correctedby the Adjustment Proce- dures,the following troubleshootinginformation should be used.Check for loosewires or other obvioussources of trouble, such as burned or loosecomponents.Make sureprinted circuit boardsare seatedfirmly in connec- tors.Also make sure those microcircuit packagesthat mount in socketsarefilmly seated.

7 - 7 .ACCESSF0RSERVtCtNG .

7-8. Accessto most areasof the instrument may be gained by removing the top cover and the top guard cover;It should not be necessaryto remoyethe bottom coversunlesscomponentson the Main Circuit Assembly, Al , must be replaced. Removethe top trim strip to gain accessto the DisplayAssembly.The threeverticalscrews which secure the Display Assembly heat sink to the guard shield must be removedin order to remove the Dsplay Assembly.

The High Impedance,AC Converter and the Ohms Converter printed circuit boards and components must be kept clean and free from fingerprints or other contamination, or performance may be degraded.Handle these assembliesby the board extractors.

7 - 5 .TROUBLESHOOTINGTREES .

7-6. Troubleshooting information for variouscircuits or operationsof the 3490A is containedin severaltrouble- shooting trees and associatedinformation. The General TroubleshootingTree,Figure7-4,may be usedto isolate the problem to a particularareaof the instrument.The following list indicates the circuits to which each tree applies:

Troubleshooting Tree Title	Figure No.
Standard3490A Circuits
General	14
DC Analog	n <
AC Converter	7-6
OhmsConverter	7.7
Display	7-8
Logic Test	7-9

7.9.POWERSUPPLYCHECKS.

7-10. Check the power supply voltagesat the points listed in Table 7-1 usingan oscilloscopeand a dc digital voltmeter with 4digit resolution. Voltage and ripple specificationsare as shown. All ripple measurementsare to be madewith the samplerate in the HOLD position. Voltages are listed following the supply used as its reference.Therefore, power supply voltagesshould be checked in this order. The first supply checked wtrich fails to meet the voltage specified is the faulty supply. All supplies referenced to the faulty supply will also

,indicate readings out of specification. With the faulty supplyidentified proceedto troubleshootasfollows:

a.Pull opticns and install requiredjumper boards.If problem disappears,determine which option is at fault and proceedto its troubleshootingsection.

Table7-1. PowerSupplyVoltagesandGurrentLimit Values.

hgic Clock	7-ro
Option 021
Data Output	7-lr
Option 022
Remote	7-12
Option 030
cPrBr/o	t - 13
Option040or 045

		BaseSupply
	A 1 A , I
Test Point		Volrage	Ripple
+ 1 7V		16.99 to + 17.0'lV	< 50 mV p-p
+	5 V	4.995 to + 5.075 V	( 60 mV p-p
+ 3 0 V		3 0 . 1 0 t o + 3 O . 9 O V	< 25 mV p-p
- 1 7 V		' 1 6 . 9 t o - 1 7 . 1 V	< 5 0 m V p f
-	5 V	5.00 to - 5.85 V	< 60 mV p-p
- 3 0 v		3 0 . 1 0 r o - 3 0 . 9 0 V	< 25 mV p-p

Raw S0pply

Current Limit {Applox. Voltag€sl

Al Rl04 = .434 V

A1R'l = .448 V A l R 1 1' l= 1 . 3 4 v

A 1 R 1 1 8= . 5 4 V

4 1 R 1 2 5 = 1 . 3 0 V

Sample/HoldGeneral	1-14
Sample/HoldLogic	7-r5
Option080

Ratio1 - 16

			Ripple
Test Poinl	Supply	Voltage	{Approx. Voltag€)
TPD	24V	2 4 t o + 2 8 V	I vp - p
	24V	2 4 t o - 2 8 V	t . 2 v pf
	3 8 V	3 8 t o + 4 4 V	. 5 V F p
TPA	3 8 V	3 8 t o - 4 4 V	.5 v p-p
TPC	9 V	9 t o + 1 1 V	1 . 5V p - p

1-l