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ana aescrmea how to troubleshoottransistorized circuits. Incorporatedinto the text was a description of asimple in-circuit transistor checkerthat utilized the X-Y displaycapabilities of an oscilloscope.We have received many requests forcopies of this article and especiallyinformation about the transistorchecker. So, by popular demand, hereis a repeat of “How to TroubleshootTransistorized Circuits Faster,” byGeorge Stanley, based mostly on hisbook, Transistor Basics: A ShortCourse. Copyright @ 1967, 1975 byHayden Book Company, Inc. Allrights reserved. T h i s material isprinted w i t h the permission ofHayden Book Co., Inc., RochellePark, N.J.Fundamental Characteristics of TransistorsBefore describing specific troubleshooting tips, let’s take a momentand review several important transistor characteristics.Conventional PNP or NPN transistors are basically ccofl”devices andmust be biased “on” to their operating point. This is done by forwardbiasing the base-emitter diode tomake the transistor conduct. Referto Figure 1 for examples of forwardbias on NPN/PNP silicon and gernsistors.Figure 1, an NPN tranhave its base more posile emitter in order forow.IIIIlb. PNP germanium transistor typicall a . NPN silicon transistor typical biasconditionsbias conditionsFigure 1. Transistor bias examplesshowing the “on” conditionIn a PNP transistor, the base mustbe more negative than the emitter inorder for current to flow.So “on” bias voltages for a transistorcan be summed up by referring toFigure 1 and the following two rules:- For a PNP, the base is negative,the emitter is not quite as negative, and the collector is far morenegative.- For an NPN, the base is positive,the emitter is not quite as positive, and the collector is far morepositive.There is a distinct difference between a transistor being turned “on”and being “saturated.” When a transistor is saturated, it’s generallythought of as being almost a short,that is, the IR drop across the emitter and collector resistors equals thesupply voltage as shown in Figure 2.Naturally this means that there ispractically no voltage drop betweenthe collector and emitter of the transistor. In this condition, both thebase-emitter and base-collector diodes are forward biased (where inthe “on” condition only the baseemitter is forward biased - thebase-collector is reverse biased). AWWIW&WMRGHIYWOMsaturated germanium transistormay have as low as 0.05 volts between its emitter and collector,while a saturated silicon transistormay have 0.5 volts or less betweenthese leads.0n,720-760%00Figure 2. Transistor bias exampleshowing the “saturated” condition1

“Saturated” or “off” are the usualconditions found in digital circuits.In ac circuits where transistors areused as amplifiers instead ofswitches, the amount the transistoris turned on depends upon currentgain (beta) of the transistor, the resistors in series with the collectorand emitter, and the supply voltage.remove the forward bias as shown inFigure 3. The collector voltageshould then rise to the approximatelevel of the supply voltage. (Any difference is caused by ICO,thecollector-to-base leakage current.)The higher the collector voltagerises, the lower ICO,and the betterthe transistor.Basic Troubleshooting TipsI1fIOV1In troubleshooting transistor circuits, the most important area toexamine is the base-emitter junctionas this is the control point of thetransistor.Tip #IMeasure the base-emitter voltage. From this decide how thetransistor should be behaving.Then look at the collector voltageand see if the transistor is behaving as it should be.Figure 3. Amplifier with forward biasremovedIIIf the collector voltage doesn’t rise asexpected, we’ve identified a badtransistor. This technique is perfectly safe in AC coupled circuits.However, in some DC coupled circuits, we could cause damage ifbase-emitter shorts a r e appliedaround high power levels (e.g., suchas the output stage of a poweramplifier).Tip #2Modify the control signals present and see if the circuit responds accordingly.Now, back to ICO,the collector-tobase leakage current mentionedpreviously. As we implied, if thetransistor was perfect it would haveleakage current. Look at Figno ICOure l a again. Note the collector voltage is more positive than the basevoltage. In this “on” condition thebase-collector diode junction is reverse biased. This reverse biaseddiode should be off, but because wehave never been able to make a perfect diode, there is a very small current leaking across it. This leakagecurrent flows through the collectorbase junction and part of it goesthrough the base-emitter (controlpoint) junction.For example, if the transistor is forward biased as shown in Figure 1,see if it is behaving as an amplifier.Short the emitter to the base toSince leakage current is extremelytemperature sensitive, we can usethis to our advantage i n troubleshooting. For example, i n a nFor example, if the base-emittervoltage is 0.6 volts forward biasedand the collector voltage is the sameas the supply voltage, something iswrong. Probably the collector-basejunction is open.Expanding on the above idea leadsto our second troubleshooting tip.Tip #3In an amplifier with clipping distortion, try cooling each transistor with spray coolant. Quitelikely you will find that when theleaky transistor is cooled theclipping distortion disappears.Conversely, heating a leaky transistor will make the problemmuch worse by greatly increasing the ICOleakage.Basic Circuit AnalysisIf the base-emitter junction is forward biased, the transistor wouldnormally be “on.”If the base-emitter junction has zerobias or reverse bias, it should beturned off. If it is not off under theseconditions, it is either shorted o rleaky.amplifier stage, excessive leakagecurrent can cause clipping distortionbecause of the shift in the quiescentoperating point.WWW.HPARCHIVE.COMAn interesting problem is illustratedin Figure 4. In this circuit, bothtransistors are of the NPN type. Notethat Q2 has 0.8 V reverse bias on itsemitter-base junction, but the 2.0volts on the emitter means that thereis 2 mA of emitter current. Now,since the emitter-base junction is notshorted, this 2 mA of current alsoflows through the 8K resistor in thecollector of Q2. Therefore, t h ecollector voltage, Vcc, is:18V - (8K) x (2 mA) 2VThus, it would appear that Q2 has ashort between collector and emitter.,”pFig. 4. Direct coupled two-stageexample circuit Another interesting problem i ntroubleshooting illustrated i nFigure 5 . Although the emitter ‘current of Q1 is 1 mA, the collectorcurrent is only 0.52 mA (i.e.,5.2V 10K). Stage Q2 shows 5 mAflowing in both the emitter andcollector circuits, so Q2 is either3

II0IIFig. 5. Capacitive coupled two-stageexample circuitFigure 6 shows a simplified schematic of the transistor checker and theideal voltage vs. current waveformsyou can expect to see.shorted or saturated. The one voltagethat would answer this question isnot given; i.e., the voltage on the baseof Q2. If everything were workingcorrectly, this voltage would beapproximately 1.5V.VB (15V) x (10K)90K 10Ktassociated resistance and capacitance. The loop is caused by thecapacitance (probably a couplingcapacitor), and the fact t h a t t h ewaveform is not a perfect "right"angle is because of the associatedresistance (probably bias or loadresistors).H"rllFigure 6. Transistor checker and idealwaveformsVB 1.5vWhat appears to have happened isthat C3 is shorted. This would explain why there is only 0.52 mA flowing through resistor R4. The other0.48 mA is flowing through C3 andresistor R6. If C3 were shorted, itwould also explain the voltages onQ 2 . The 5.2 V on the base produces5.0 volts on the emitter, which, inturn, causes the 5 mA of d-c currentto flow and Q2 to saturate.If capacitor C3 were replaced, thebase voltage of Q2 would be 1.5 V dc,and the voltage on the emitter wouldbe about 1.3 V dc. This, in turn,would cause about 1.3 mA of dc toflow. The resultant collector voltagewould be 12.4 V dc.Since the transistor checker puts outa sine wave that has alternativelypositive and negative half cycles, we'would expect a perfect diode to behave as shown in Figure 7.NOTE: All references to a diode alsoimply the base-emitter or basecollector diode junctions of atransistor.In actual practice, the waveformsshown in Figure 7 are all possiblebecause t h e test leads a r e notFigure 9. Typical in-circuit waveformfor a good transistorThe schematic of the tester shows aswitch that shorts out a 5.6K resistor. This switch is primarily for current limiting so you don't damagesensitive transistors. You can alsouse it for in-circuit vs. out-of-circuittesting.In-CircuitTransistor TesterEven though all the above tips aregood ones, there is a transistor testerthat will speed up troubleshootingeven more. This tester works on theknown fact that PNP and NPN transie;tors are made up of two diodes.Figure 7. Ideal waveform of gooddiodeWWW.HPARCHIVE.COM--Figure 8. Ideal waveforms for a gooddiodeThis transistor tester leads to ournext troubleshooting tip.

Tip #4Use the transistor checker forrapid testing. Make sure to testboth the base-emitter and basecollector diodes.A little experimenting with aprinted circuit board containingmany transistors will rapidly showyou the various waveforms you willencounter for’good transistors. Themain point to look for is whether ornot the waveform has a “break” in it(Pt. A in Figure 9). If it does, thetransistor diode is good. Remember,the lower the resistance of the biasresistors, t h e less defined t h e“break” (Pt. A Figure 9), and themore the waveform appears like a“short”. Of course, when testingout-of-circuit, the “break” will bevery sharp -just like a true diode.This tester can also be used for testing tunnel diodes. The waveform isshown in Figure 10.Figure 10. Tunnel diode waveformand RxlO scales, VOMs often have avery high short circuit. This currentmay be as high as several hundredmA and can damage small delicatetransistors. On t h e other hand,VOMs often have high open circuitvoltages (22.5V) on t h e i r highresistance scales. These voltagesalso can damage delicate emitterbase junctions. Usually the RxlKscales are safe for most meters but itis best to measure your own. Table 1shows the characteristics of severalcommon ohmmeters.The working technician is quitelikely to encounter tunnel diodes inthe trigger circuits of scopes, frequency counter front ends, andelsewhere.produce discrete pulses at severalhundreds of MHz.In theory, these diodes have a negative resistance slope in one portion oftheir characteristic curve, makingthem capable of amplification andoscillation. See Figure A. In actualpractice, however, we have a problem if we try to look at this slope.Any simple circuit that we can devise to gradually increase the current through the diode will havesome internal resistance. Therefore,it’s almost impossible to arrive atpoint B because the diode will abruptly switch from A to C and viceversa on the decreasing swing. Thisswitch action results in about 0.5volt change across the diode and occurs at nominally 5 to 15 mA current. The voltage change occurs veryrapidly. Circuits like Figure B canDue to very high impurity levels, thediode’s quiescent forward voltagedrop is very low and its reverseleakage current very high. Thiswould lead your ohmmeter to conclude that the diode is shorted inboth directions. A first glance withthe transistor tester will give thesame appearance. However, a littleextra effort and a closer look mayreveal that at or near its rated current the diode does, in fact, switchstates. If the transistor tester has a100 ohm current limiting resistor,then 1 volt vertical deflection willcorrespond to 10 mA of junction current. Any reasonable facsimile willwork so long as you can displayabout 0 to 30 mA vertically. Thecurve on a good diode will be similarto Figure 10 in the main articleallowing you to discern the switchpoints and get a fair idea of the current magnitude.1IWhen testing tunnel diodes, makesure the switch is in the In-Circuitposition as you need the highercurrent.Transistor Tests with aVOMAnother way to test transistors is toperform a forward and reverseohmmeter check on the two transist o r diodes. It’s much slower thanwith the transistor checker. Also youhave to be careful about the shortcircuit current and open-circuitvoltage of your ohmmeter. On RxliTIntegratorIEFigure 0.Figure A.WWW.HPARCHIVE.COM -I-

IIiIiTABLE 1. CHARACTERISTICS OF COMMONOHMMETERSMake, Model,and RangeiOpen Circuit Short CircuitVoltageCurrentPolarityHP 412A (VTVM)IR x !-0.01 v0.1 vR y: 1UR RRRRRxxxxxx1001K10K100K1M10M8.0 m A10.0 .11.11.11.11.11.11.1vvvvvvv120 m A11 rnA1.1 rnA110.0 pA11.0 flA1.1 p A0.11 pA1.3VVR -Tn-crnArnA-BLACKpApAPApAHP 4108 (VTVM)R x 1R x 10R x 100R x 1KR x 10KR x lOOKR x 1MRED BLACKHP 410C (VTVM)xxxxxR xR xRRRRR101001K10K1.31.31.31.31.31.3lOOK1M10MVVVVV55 m A5.7 rnA0.57 rnA57 PA5.7 pA0.5 pA0.05 PAREDBLACK -SIMPSON 260 (VOM)R x 1R x 100R x 10K1.5 V1.5 V7.5 v125 m A1 rnA60 pARED -BLACKSIMPSON 269 (VOM)R X 1R x 10R x 100R x 1KR x 10KR x lOOK1.51.51.51.52430VVVVVV74 rnA8 rnA8 mA0.82 rnA1.3 m A13 /*ARED-BLACKTip #5Measure the short-circuit currentand open-circuit voltage for eachresistance scale on your VOM'sand VTVM's. Keep this information along with the polarity of theleads on a chart on the back ofthe ohmmeter.Tip #6If you are using a VTVM, makesure the range you are using hasenough open-circuit voltage toovercome the 0.2V for germanium and 0.6V for silicon.Otherwise you will get an unsatisfactory reading.Since leakage does not show up wellon the transistor checker of Figure 6,nor on the ohmmeter tests, it is bestto have an inexpensive beta/leakagetester on hand. There a r e manyavailable and some of the best are inkit form. If a leakage current testeris unavailable, you can try shortingout the emitter-base junction whilesimultaneously measuring the voltage drop across the collector loadresistor.Tip #7Measure ICBO by shorting theemitter-base junctionandmonitoringthe voltage across thecollector lead resistor. For example, if you measured 30 mVacross a 10K load resistor, yourleakage current would beTRIPLEll 630 (VOM)R x 1R x 10R x 100R x 1KR x lOOK1.51.51.51.522.5VVVVV320REDrnA- 32 rnA3.25 rnA325 p A70 pABLACK(Varies withserialnurn ber)7.5 rnA750 p A75 pA75 PAREDTRlPLElT 310 (VOM)R x 1x 10R x 100R x 10KRO1.51.51.51.5VVVV- BLACK(Varies withserialnumber)Numbers in bold type indicate safe range.WWW.HPARCHIVE.COMThis would be about right for a germanium transistor a t room temperature, but a little high for a siliconsurface-passivated transistor.One of the most common mistakes inanalyzing transistor circuits is t omiscalculate the gain of one stage ina multi-stage amplifier. The errorusually occurs in miscalculating thereal value of the load resistor for

that stage. Figure 11 shows a twostage amplifier. The correct valuefor RL1 is not the actual listed valueof the resistor, but rather the parallel combination of RL1, Ra, Rb andRin of Q2. Usually the Rin of Q2 isthe most dominant factor in thiscombination.here is a list of important points relating to the troubleshooting tipsand characteristics previouslydescribed.- NPN and PNP transistors arebasically “off’ devices while vacuum tubes a r e basically “on”devices.- Transistors are made up of two*Figure 11. Two-stage amplifierdiodes: a base-emitter diode anda base-collector diode. In normal(amplifier) operation, the baseemitter diode is forward biasedand the base-collector diode isreverse biased.- Shorting t h e base t o emitterturns off transistors while forward biasing base-emitter junctions turns on transistors.- All transistors have leakage current across their reverse biasedbase-collector diodes. For surfacepassivated silicon transistors,this current is usually no morethan several nanoamperes. Sincegermanium transistors cannot besurface passivated, this leakagecurrent normally may be severalmicroamperes.Tip #8When calculating the gain of astage, be sure and include theparallel loading effects of thenext stage bias resistors andinput impedance.Summary- Leakage current increases withAll of the above tips relate back tothe fundamental characteristics oftransistors described at the beginning of this article. To summarize,heat (a law of physics) and doubles about every 10 C.-Leakage current may be easilymeasured by shorting the baseemitter junction and measuringbetween the transistor collectorand t h e supply voltage. TheWWW.HPARCHIVE.COMleakage current then equals thevoltage across the load resistordivided by its resistance. (Makesure t h e collector is not DCcoupled to the next stage.)/”1- Abnormal increases i n roomtemperature leakage current(e.g., 10 times normal) often indicate contamination of t h ebase-collector junction (possiblydue t o a cracked or brokenhermetic seal). The result is ashift in the normal bias operating point. Trouble will only beexperienced if the driving signaldrives the transistor to or nearcutoff. The transistor will notproperly turn off and the resultmay be clipping or distortion dueto the residual leakage currentflowing through the external resistors. Heating and cooling atransistor aggravates this condition and sometimes shows upmarginal operation.- Shorting collector t o emittersimulates saturation as the transistor behaves like a closedswitch.Much information on transistors isavailable from HP on video tape inthe Practical Transistor Series, HPPart Number 90100D, Troubleshooting Transistor Circuits Faster, HP Part Number 90030 683 andTroubleshooting FET Circuits Faster, H P Part Number 90030 726.Contact your local H P office formore information or call direct toHewlett-Packard Video Products,(415) 857-2381.”)

For Selected HP-IB InstrumentsHP-IB VERIFICATION PROGRAMSMany Hewlett-Packard instruments with HP-IBcapability have calculator-controlled test programsavailable that can save you considerable time inverifying instrument operation. Each program isINSTRUMENT MODELfully documented with instructions, listing, flowchart, check points, etc. The verification programslisted below can be ordered from your local HPoffice.TAPE P/NService Note 5150A-4Service Note 5312A-2Service Note al PrinterASCII Interface Module (5300B)Universal Counter (Opt. 011,020,021,030031, 040, 041)Universal Counter (Opt. H99)Universal Counter (Opt. 096/H42)Universal CounterFrequency Counter (Opt. 011)Frequency Counter (Opt. 011)Microwave Frequency Counter (Opt. 011)Microwave Frequency Counter (Opt. 011)Electronic Counter (Opt. 011)Electronic Counter (Opt. 012)Channel C Plug-In4 GHz Frequency ConverterAutomatic Frequency ConverterMeasurement Storage Plug-InTime SynthesizerTime Interval ProbesTime Interval ProbesUniversal Time Interval CounterASCII/Parallel ConverterDigital-to-Analog ConverterNumeric DisplayRelay ActuatorVHF SwitchTiming GeneratorDigital ClockAnalog-to-Digital ConverterPower Meter8409BAutomatic Network Analyzer8672ASynth. Sig. Gen.8409BNetwork Analyzer11712-10001 (9830A)11712-10002 (9825A)11863-10004 (9835/45)8566A8568A8507ASpectrum AnalyzerSpectrum AnalyzerNetwork Analyzer08566-60002 (9825A)08568-60002 (9825A)85030-10002 (9830A)8507BNetwork Analyzer85030-10007 (9825A)3042A3045A3582A3585A3050BNetwork AnalyzerSpectrum AnalyzerSpectrum AnalyzerSpectrum AnalyzerVoltmeter System3052A3437A3455AVoltmeter SystemSystem DVMSystem DVM3495AScanner03042-90211 (9825A)03045-10001 (9825A)03582-10001 (9825A)03585-10001 (9825A)03050-90230 (9825A)03050-90212 (9830A)03052-90011 (9825A)03437-10001 (9825A)03455-10001 (9830A)03455-10002 (9825A)03495-10001 (9830A)03495-10002 001 (9825A)00436-10006 (9830A)00436-10007 (9825A)11863-10004 (9835/45)WWW.HPARCHIVE.COM5328MH99 Manual5328MH42 Manual5335A ManualService Note 5340A-115341A Manual5342A Manual5343A ManualService Note 5345A-9AService Note 5345A-12AService Note 5353A-1Service Note 5354A-65355A Manual5358A Manual5359A ManualService Note 5363A-25363B ManualService Note 5370A-1AService Note 59301-2Service Note 59303A-1Service Note 59304A-1Service Note 59306A-4Service Note 59307A-3Service Note 59308A-1Service Note 59309A-359313A Manual436A ManualService Note 436A-211863D Manual8409B ManualKit Manual 11712-90001Kit Manual 11712-9000111863D Manual8409B Manual8566A Manual8568A Manual85030A Manual8507A Manual85030B Manual8507B Manual3042A Manual3045A Manual3582 Manual3585 Manual3050B Manual3050B Manual3052A Manual3052A Manual3052A Manual3052A Manual3495A Manual3495A Manual

1,Imodel number sequence for all instruments (including obsolete models) in the "Service Note Index" also available free of charge.d-(IWreliability, improve performance,or extend their usefulness.Service Notes are used to informyou of a revised adjustment procedure, recommended parts replacements, and new troubleshooting procedures.Safety Service Notes communicate potentially hazardous conditions related t o the use ofinstruments.For one thing they are free.For another they provide an aftersales support link to HewlettPackard for a continuous flow ofservice-related information aboutyour instrument.What Do Service Notes Say?Service Notes recommend modifications to instruments to increaseWhat Are The Benefits To Me?You can create a history file on eachHP instrument you own. ServiceNotes describe modifications to instruments out in the field and arethe only way you have of keepingyour operating and service manualup-to-date.Are Back Issues Available?Yes! Copies of all service notes everissued for an instrument are available in both hardcopy or microfiche. These notes a r e listed in435Al436A POWER METERS435A-5. Serials Prefixed 1629A and below, and serialnumbers 2004U-05330 and below. N connectormodification to allow POWER REF OUTPUT compatibility with 84818 and 84828.436A-3. Serials 1629A01131 and below, and1943UOO880 and below. N connector modificationto allow POWER REF OUTPUT compatibility with84818 and 84828.546A LOGIC PULSER3 Here's the latest listing of ServiceNotes available for Hewlett-Packardproducts. To obtain information forinstruments you own, remove theorder form and mail it to the HPdistribution center nearest you.Please be aware that we can onlysupply free back issues on a limitedbasis. For those customers t h a trequire large numbers of ServiceNotes for many different instruments, HP has a complete microfiche library and automatic updating service available for a nominal charge.How Do I Obtain Service NotesInside Bench Briefs is an abstract ofall the current Service Notes issuedover the last 2-3 months. At therear of Bench Briefs is a ServiceNote order form.1. Look in the abstract list for theofyourmodelnumberinstrument.2. Read the abstract to get an ideaof what the note is about.3. If you want the note (or notes many times there is more thanone), check the appropriatenumbers on the order form andmail i t to one of the listedaddresses.4. If you want back issues of Serv-ice Notes (or notes that are notlisted i n the current issue ofBench Briefs), simply write themodel number (or Service Notenumber if known) across the faceof the order form.1610A-9. Serials 194OA-01704 to 194OA-01764. Modification to improve power supply regulation.1611A LOGIC ANALYZER161 1A-8A. Serials 1837A-02232 and below. Modification to eliminate bright spot on CRT after turn off.1615A LOGIC ANALYZER1615A-2. Serials 1937A-03487 and below. Modification to eliminate bright spot on CRT after turn off.546A-1. Serials 1732A and below. Modificationto improve performance.1822A TIME BASE ANDDELAY GENERATOR1302N1304A DISPLAYS1822A-2A. Serials 0907A- and below. Modification toimprove reliability.1302A-3. Serials 1721A and below. Preferred replacement for astigmatism potentiometer.1304A-3. Serials 1715A and below. Preferred replacement for astigmatism potentiometer.1610A LOGIC ANALYZER1610A-8. Serials 1836AO1319 and below. Modificationto improve reliability.WWW.HPARCHIVE.COM3325A SYNTHESIZER/FUNCTION GENERATOR3325A-SA. Serials 1748A02350 and below. Modification to improve square wave phase control.3325A-7. Serials 1748A02350 and below. Adjustmentto mixer driver to improve reliability.3325A-8. All serials. Relay cleaning procedure.

9551A-13. AH senais. i 2 volt regulator replacementinstructions.35558 TRANSMISSION ANDNOISE MEASURING SET355552E. Serials 0992A06760 and below. Improvedpower supply reliability.3570A NETWORK ANALYZER357OA-10. Serials 1331A01615 and below. Modification to improve performance during HP-IBoperation.3570A-11. Serials 1331A01595 and below. Modification to improve low amplitude phasemeasurements.3585A SPECTRUM ANALYZER3585A-3. Serials 1750A00570 and below. Modificationto improve 75fl input return loss.3702B IFlBB RECEIVER37026-42. All serials. Preferred replacement for NPNtransistor (1854-0071).cations to prevent intermittent single Channel interface operation while running A-D measurements.37798-18. All serials. Field installation of 37798 Option002 into 37798 Option 001 instruments.4140A pA METERlDCVOLTAGE SOURCE414OA-3. Serials 1917J00270 and below. Modificationto improve operation of key controls.4942A TlMS4943A-5. Serial numbers affected:4942A - All serials:4943A - Serials 1731A00290 and below:4944A - Serials 1737A00570 and below:A6 or A17 RF cable replacement compatibility.4943A TlMS4943A-5. Serial numbers affected:4942A - All serials:4943A - Serials 1731A00290 and below:4944A - Serials 1737A00570 and below:A6 or A17 RF cable replacement compatibility.37038 IFlBB RECEIVER4944A TlMS37038-6. All serials. Preferred replacement for NPNtransistor (1854-0071).4943A-5. Serial numbers affected:4942A - All serials:4943A - Serials 1731A00290 and below:4944A - Serials 1737A00570 and below:A6 or A17 RF cable replacement compatibility.4944A-6. Serials 1737A00481 and below. Modificationto prevent intermittent level dropout.3705A IFlBB RECEIVER3705A-7. All serials. Preferred replacement for NPNtransistor (1854-0071).3710A lF/BB RECEIVER3710A-22. All serials. Preferred replacement for NPNtransistor (1854-0071).3712A IF/BB RECEIVER5315AIB UNIVERSAL COUNTER5315NB-2. All serials. Replacement part numbers foryellow LED displays.3712A-3. All serials. Preferred replacement for NPNtransistor (1854-0071).5342A MICROWAVE FREQUENCYCOUNTER3715A IFlBB RECEIVER5342A-9A. Serials 1812 and below. Procedure to correct A2 false frequency readout, and to eliminateground at U19(8).3715A-2. All serials. Preferred replacement for NPNtransistor (1854-0071).3716A IFlBB RECEIVER3716A-11. All serials. Preferred replacement for NPNtransistor (1854-0071).5391A FREQUENCY STABILITYANALYZER SYSTEM5391A-1. All serials. Software bugs and fixes.WWW.HPARCHIVE.COMitication to improve third order intermodulationperformance.8568A-30. IF section serials 2003A and below. Mcdification to improve third order intermodulationperformance.8568A-31. RF section serials 1943A and below. Recommended component changes to prevent signallevel fluctuations.8568A-32A. All serials. Adjustment procedure to improve amplitude drift vs. temperature.8568A-34. All serials. Procedure to select A13C22capacitor whenever IC A13U13 is changed.8614AIB SIGNAL GENERATOR8614A-18-S. Serials 1748A and below. Procedure forchecking front-panel grounding.86148-10-5. All serials. Procedure for checking frontpanel grounding.8616AIB SIGNAL GENERATOR8616A-164. Serials 1739A and below. Procedure forchecking front-panel grounding.86168-10-S. All serials. Procedure for checking frontpanel grounding.8620C SWEEP OSCILLATOR862OC-5. Serials 1933A and below. Elimination of frequency shift in 8620C HP-I8 Option 001 plug-ins.8671A SYNTHESIZER8671A-1. Serials 2006A and below. Modification to improve performance of Reference Oscillator.8672A SYNTHESIZEDSIGNAL GENERATOR8672A-2A. S ?rials 1719A and below. Preferrebd replacement for 1853-0050 transistor.8672A-8. Seriiils 2006A and below. Modification lo improve perfcirmance of Reference Oscillator. .8672A-9. Serials i w i A m u Luu/A. Mmiricarion toimprove amplitu,de recovery time. - . .IE71A DTS-709571A-1 0. All seriaIs. Recommended replaceinent for62605J Power :;upply.f

instructions1. If you want service notes, pleasecheck t h e appropriate boxesbelow and return this form to oneof the following addresses.2. If you want a printed copy of theservice note index, please markthe box below and return thisform to one of the followingaddresses.For European customers (ONLY)All other customersHewlett-PackardCentral Mailing Dept.P. 0. Box 529Van Hueven Goedhartlaan 121AMSTELVEEN-1134NetherlandsHewlett-Packard1820 Embarcadero RoadPalo Alto, California 94303Our highly trained staff and moderntabulating equipment are anxiouslyawaiting your reply.NAMEService Note Index0COMPANY NAME,Yes, I want a printed copy.ZIPSTATE0 435A-50 436A-30 546A-10 1302A-30 1304A-30 34658-2A0 3551A-980 3551A-12-S0 3551A-130 3555B-2E0 377OB-200 37708-210 3771A-2A0 3771AIB-l1A0 3771AIB-170 8568A-190 161OA-80 1610A-90 3570A-100 3570A-110 3585A-30 3702B-420 37038-60 3779A-15A0 37798-15A0 37798-180 41408-30 4943A-50 8568A-290 3705A-70 3710A-220 3715A-20 3716A-110 372CA-3B-S0 4944A-60 5315AIB-20 5342A-9A0 5391A-10 5526A-5A0 8614A-18-S0 86148-10-S0 3721A-14B-S000 3736A-30 377OA-390 3770A-400 8566A-50 8566A-60 8566A-7A0 F'" 'A-1lA-S1611A-8A0 1615A-20 1822A-2A0 3325A-5A3325A-70 3325A-80 333OAIB-11A0 3335A-40 3335A-50 3336AIBIC-20 3455A-17A0 3455A-180 568A-210 8568A-250 8568A-2808568A-300 8568A-31P558A-32A0 8568A-348616A-1640 8616B-1040 8620C-58671A-10 8672A-2A0 8672A-80 8672A-90 9571A-10

Jul 08, 1980 · In troubleshooting transistor cir- cuits, the most important area to examine is the base-emitter junction as this is the control point of the transistor. If the base-emitter junction is for- ward biased, the transistor would normally be “on.” If the base-emitter junction has zero bias or reverse bias, it should be turned off.

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