Model3490A

7.40.DISPLAYTROUBTESHOOTING.

SectionVII

Table7-5. DataOutput TroubleshootingTips.

741."Ihe Display TroubleshootingTree, Figure 7-8,mav be used io troubleshoot a defective display'The nuäerical display units and the polarity unit may be most easilycheckedby substitutinga known goodunit' Accessto the Display Assembly is gained by removing the 3490A top trim strip and the tfuee vertical screws securingthe diiplay heat sink to the guardshield'

742 . LOGICTBOUBLESHOOTINGSUGGESTIONS.743.Severalmicrocircuits in the logic section may be

checked by observing the inputs and outputs of the device. The "Q" output of a D flip-flop, for example, should agreewith the "D" input if the flipflop is being

clocked.(See AlU6, 7, 71, 14, 17,20 md 22.) The output is changedby the "0" to "1" transition of the clock input. Also, the output of an inverter (AlU8 and 10)shouldbe the logicalinverseof its input.

744.lf incorrect readingsareobservedon the logic test, pull AlU2, 3, 9 and 16 andreinstate,taking careto seat leadsproperly in their sockets.AlU2,3, 9 and 16 may be checkedby substitutinga known good device.

Symptoms

Measurerent Intotmatioo: No data output

No dab output and no polarity, overload, or overrange

No odd numbers in any digit

N o 2 ' s , 3 ' s . 6 'osr, 7 ' si n a n y d i g i t N o 4 ' s , 5 ' s , 6 't!r, 7 ' sin a n y d i g i t No 8'sor 9'sin any digit

Range Intorrotion:

No range data output

No range and no funcion data output No odd numbered range data

Ranges 2,3, and 6 do not print correctly Ranges 4,5, and 6 do not print correctly

Fundion lnformation:

No {unction data output

No tunction and no range output

Functions 1, 3, 5, 7,9, -,A, and * not correct Functions 2, 3, 6. 7. +, -,O, and * not correct Functions4,5, 6,7, V. A, f, and' not correct Functions 8, 9, +, -,V, A, O, and i not corrrct

Polaritv, Overload, Overrange. Sample/Hold, and Remote Mode Intormtion:

None of the above outputs correct None oI the abow and no range output No polarity output

No overload outPJlt No overrange output

No Sample/Hold Mode outPüt No Remote Mode output

Probablo Cau$

A9U9

A9U6

A 1 0 U 1 , 2 , 3 , 7 A 1 0 U 1, 2 , 4 , 7 A 1 0 U 1 , 2 , 5 , 7 A10u1,2, 6,7

AgU7

AgU6

41OU3

AlOU4

A1OU5

AgU7

A9U6

A1OU3

A1OU4

A1OU5

AlOU6

A9U7

AgU6

A1OUs

A1OU6

A1OU3

AlOU6

A10U6

:i

l

ii

j;

:l

.:'

a;

,'

. , 1

,J

i

'745. Certain microcircuits may be associated with particular malfunctions.A1Ul9 utd 2l deal with pro- grammingthe 3490A rangeandfunction. AlUl5 and24 are associated with sampling and sample rate delays. AlUl5 alsodealswith function delays.

746.If decimal point or ranging problems cannot be located by using the troubleshootingtrees,the trouble may be in the display, the front panel switching, or the optional Remote Assembly. The decimal points in the display are switched during the LOW true enablesignals to the display units (seeFigure 7-8).

747.If the instrument does not sample, the logic circuits may be locked in a certain state or sequence. Turn the instrument off. While holding the manual pushbutton depressed,turn the instrument back on anil. observe the states of logic signalsYMA through YMG with an oscilloscope(seeFigure 7-24). Theseare found

at test points O, T, P, S, Q, N and J in the logic section of ,the main circuit board. Test point O should be a steadyHIGH, and all othersLOW. If theselevelsare.not correct, the Read Only Memory, AlU9, or one of the State Storage flip-flops may be defective. If all seven sigrals are correct, releasethe pushbutton and check the test points again with the oscilloscope.If all levels are the sameas before (TPO HIGH and all others LOW), the normally closed contacts of the pushbutton switch may not be making contact. Checkto seeif the pushbutton is binding in the center of the SampleRate knob.

7 . 48DATA.OUTPUTTROUBTESHOOTING (0ption021).

749.Ceftan typesof failuresin the output information may be traced to certain circuits in the Data Output Assemblies.Table 7-5 lists a number of svmptomsand

their probable causes.Refer also to the Data Output TroubleshootingTree,Figure7-1l.

7 . 50REMOTE.CONTROLTROUBLESHOOTING (0ption022).

7-51. Refer to the Remote TroubleshootingTree, Figure 7-12,for information for troubleshootinethe remote control circuits.

7-52cPlB.TROUBLESH00TtNc(0ption030).7-53.GeneralGhecks

7-54. lf the 34904 with Option 030 doesnot operate correctly, first determinewhether the trouble is in the I/O circuit or the main 3490A circuits.The performance checksin SectionV may be usedto determinewhether the instrumentoperatesproperly in standardmultimeter operation. Make sure the I/O plug-in printed circuit boardsare seatedproperly in their sockets,and that the ribbon cable connectors are inserted properly. Also make certain that all microcircuit packagesare seated firmly in the sockets.

7-55. TroubleshootingMethod.

7-56. The logic circuits which make up the GPIB option are very difficult to troublestroot by the normal component method of troubleshooting.Consequently,a GPIB Repair Kit, -hp-Part No. 03490-80009,has been made availableto facilitate fast and efficient on-siteand bench repair of the GPIB I/O Interface Option. The GPIB Repair Kit consists of five assemblies(*rp Part No.

0349G60613 46532, -66533,-66534and-66536),and

,

six parts kits (hp Part No. 03490€0013, {0031, -80032, -80033, -80034 and -80036), which are indi-

vidually available. See Table 6-1 for description of assembliesand parts kits. This table also provides a

7-5