Tics of Transistors the Emitter Is Not Quite As Posi- Tive, and the Collector Is Far More %

ana aescrmea how to troubleshoot I I I I transistorized circuits. Incorporated into the text was a description of a simple in-circuit transistor checker that utilized the X-Y display capabilities of an oscilloscope. la. NPN silicon transistor typical bias lb. PNP germanium transistor typical We have received many requests for conditions bias conditions copies of this article and especially Figure 1. Transistor bias examples information about the transistor showing the “on” condition checker. So, by popular demand, here is a repeat of “How to Troubleshoot In a PNP transistor, the base must saturated germanium transistor Transistorized Circuits Faster,” by be more negative than the emitter in may have as low as 0.05 volts be- George Stanley, based mostly on his order for current to flow. tween its emitter and collector, book, Transistor Basics: A Short So “on” bias voltages for a transistor while a saturated silicon transistor Course. Copyright @ 1967, 1975 by can be summed up by referring to may have 0.5 volts or less between Hayden Book Company, Inc. All Figure 1 and the following two rules: these leads. rights reserved. This material is - For a PNP, the base is negative, printed with the permission of 0 the emitter is not quite as nega- Hayden Book Co., Inc., Rochelle n, tive, and the collector is far more Park, N.J. 72 negative. 0 -76 0 Fundamental Characteris- - For an NPN, the base is positive, tics of Transistors the emitter is not quite as positive, and the collector is far more %

Before describing specific trouble- positive. 0 0 shooting tips, let’s take a moment There is a distinct difference be- and review several important tran- tween a transistor being turned “on” Figure 2. Transistor bias example sistor characteristics. and being “saturated.” When a tran- showing the “saturated” condition 1 Conventional PNP or NPN transis- sistor is saturated, it’s generally tors are basically ccofl”devices and thought of as being almost a short, must be biased “on” to their operat- that is, the IR drop across the emit- ing point. This is done by forward ter and collector resistors equals the biasing the base-emitter diode to supply voltage as shown in Figure 2. make the transistor conduct. Refer Naturally this means that there is to Figure 1 for examples of forward practically no voltage drop between bias on NPN/PNP silicon and ger- the collector and emitter of the tran- nsistors. sistor. In this condition, both the base-emitter and base-collector di- Figure 1, an NPN tran- odes are forward biased (where in have its base more posi- the “on” condition only the base- le emitter in order for emitter is forward biased - the ow. base-collector is reverse biased). A WWIW&WMRGHIYWOM “Saturated” or “off” are the usual remove the forward bias as shown in amplifier stage, excessive leakage conditions found in digital circuits. Figure 3. The collector voltage current can cause clipping distortion In ac circuits where transistors are should then rise to the approximate because of the shift in the quiescent used as amplifiers instead of level of the supply voltage. (Any dif- operating point. switches, the amount the transistor ference is caused by ICO,the is turned on depends upon current collector-to-base leakage current.) Tip #3 gain (beta) of the transistor, the re- The higher the collector voltage In an amplifier with clipping dis- sistors in series with the collector rises, the lower ICO,and the better tortion, try cooling each transis- the transistor. and emitter, and the supply voltage. tor with spray coolant. Quite likely you will find that when the Basic Troubleshooting Tips I 1 f IOV 1 leaky transistor is cooled the clipping distortion disappears. In troubleshooting transistor cir- Conversely, heating a leaky tran- cuits, the most important area to sistor will make the problem examine is the base-emitter junction much worse by greatly increas- as this is the control point of the ing the ICOleakage. transistor. Basic Circuit Analysis If the base-emitter junction is forward biased, the transistor would An interesting problem is illustrated normally be “on.” Figure 3. Amplifier with forward bias removed in Figure 4. In this circuit, both transistors are of the NPN type. Note If the base-emitter junction has zero I I If the collector voltage doesn’t rise as that Q2 has 0.8 V reverse bias on its bias or reverse bias, it should be emitter-base junction, but the 2.0 turned off. If it is not off under these expected, we’ve identified a bad transistor. This technique is per- volts on the emitter means that there conditions, it is either shorted or ,- is 2 mA of emitter current. Now, leaky. fectly safe in AC coupled circuits. ”p However, in some DC coupled cir- since the emitter-base junction is not cuits, we could cause damage if shorted, this 2 mA of current also Tip #I base-emitter shorts are applied flows through the 8K resistor in the Measure the base-emitter volt- around high power levels (e.g., such collector of Q2. Therefore, the age. From this decide how the as the output stage of a power collector voltage, Vcc, is: transistor should be behaving. amplifier). 18V - (8K) x (2 mA) = 2V Then look at the collector voltage Thus, it would appear that Q2 has a and see if the transistor is behav- Now, back to ICO,the collector-to- short between collector and emitter. ing as it should be. base leakage current mentioned previously. As we implied, if the For example, if the base-emitter transistor was perfect it would have voltage is 0.6 volts forward biased no ICOleakage current. Look at Fig- and the collector voltage is the same ure la again. Note the collector volt- as the supply voltage, something is age is more positive than the base wrong. Probably the collector-base voltage. In this “on” condition the junction is open. base-collector diode junction is reverse biased. This reverse biased Expanding on the above idea leads diode should be off, but because we to our second troubleshooting tip. have never been able to make a perfect diode, there is a very small cur- Fig. 4. Direct coupled two-stage rent leaking across it. This leakage example circuit Tip #2 current flows through the collector- ~~ ~ Modify the control signals pre- base junction and part of it goes Another interesting problem in sent and see if the circuit re- through the base-emitter (control troubleshooting illustrated in sponds accordingly. point) junction. Figure 5. Although the emitter ‘ 3 current of Q1 is 1 mA, the collector For example, if the transistor is for- Since leakage current is extremely current is only 0.52 mA (i.e., ward biased as shown in Figure 1, temperature sensitive, we can use 5.2V+10K). Stage Q2 shows 5 mA see if it is behaving as an amplifier. this to our advantage in trou- flowing in both the emitter and Short the emitter to the base to bleshooting. For example, in an collector circuits, so Q2 is either WWW.HPARCHIVE.COM associated resistance and capaci- I I I I 0 Figure 6 shows a simplified schema- tance. The loop is caused by the tic of the transistor checker and the capacitance (probably a coupling Fig. 5. Capacitive coupled two-stage ideal voltage vs. current waveforms capacitor), and the fact that the example circuit you can expect to see. waveform is not a perfect "right" angle is because of the associated shorted or saturated. The one voltage resistance (probably bias or load that would answer this question is resistors). not given; i.e., the voltage on the base of Q2. If everything were working correctly, this voltage would be approximately 1.5V.

t H"rll (15V) x (10K) VB = 90K + 10K Figure 6. Transistor checker and ideal waveforms

VB = 1.5v Since the transistor checker puts out What appears to have happened is Figure 8. Ideal waveforms for a good a sine wave that has alternatively that C3 is shorted. This would ex- diode positive and negative half cycles, we' plain why there is only 0.52 mA flow- would expect a perfect diode to being through resistor R4. The other have as shown in Figure 7. 0.48 mA is flowing through C3 and resistor R6. If C3 were shorted, it NOTE: All references to a diode also would also explain the voltages on imply the base-emitter or base- Q2. The 5.2 V on the base produces collector diode junctions of a 5.0 volts on the emitter, which, in transistor. turn, causes the 5 mA of d-c current to flow and Q2 to saturate. In actual practice, the waveforms shown in Figure 7 are all possible If capacitor C3 were replaced, the because the test leads are not base voltage of Q2 would be 1.5 V dc, and the voltage on the emitter would be about 1.3 V dc. This, in turn, Figure 9. Typical in-circuit waveform for a good transistor would cause about 1.3 mA of dc to flow. The resultant collector voltage would be 12.4 V dc. The schematic of the tester shows a switch that shorts out a 5.6K resis- In-CircuitTransistor Tester tor. This switch is primarily for current limiting so you don't damage Even though all the above tips are sensitive transistors. You can also good ones, there is a transistor tester use it for in-circuit vs. out-of-circuit that will speed up troubleshooting testing. even more. This tester works on the known fact that PNP and NPN tran- Figure 7. Ideal waveform of good This transistor tester leads to our diode sie ;tors are made up of two diodes. next troubleshooting tip.

WWW.HPARCHIVE.COM -- Tip #4 and RxlO scales, VOMs often have a resistance scales. These voltages Use the transistor checker for very high short circuit. This current also can damage delicate emitter- rapid testing. Make sure to test may be as high as several hundred base junctions. Usually the RxlK both the base-emitter and base- mA and can damage small delicate scales are safe for most meters but it collector diodes. transistors. On the other hand, is best to measure your own. Table 1 VOMs often have high open circuit shows the characteristics of several A little experimenting with a voltages (22.5V) on their high common ohmmeters. printed circuit board containing many transistors will rapidly show you the various waveforms you will encounter for’good transistors. The main point to look for is whether or The working technician is quite produce discrete pulses at several not the waveform has a “break” in it likely to encounter tunnel diodes in hundreds of MHz. the trigger circuits of scopes, fre- (Pt. A in Figure 9). If it does, the Due to very high impurity levels, the quency counter front ends, and transistor diode is good. Remember, diode’s quiescent forward voltage elsewhere. the lower the resistance of the bias drop is very low and its reverse resistors, the less defined the leakage current very high. This “break” (Pt. A Figure 9), and the In theory, these diodes have a nega- would lead your ohmmeter to con- more the waveform appears like a tive resistance slope in one portion of clude that the diode is shorted in “short”. Of course, when testing their characteristic curve, making both directions. A first glance with out-of-circuit, the “break” will be them capable of amplification and the transistor tester will give the very sharp -just like a true diode. oscillation. See Figure A. In actual same appearance. However, a little practice, however, we have a prob- extra effort and a closer look may This tester can also be used for test- lem if we try to look at this slope. reveal that at or near its rated cur- ing tunnel diodes. The waveform is Any simple circuit that we can de- rent the diode does, in fact, switch shown in Figure 10. vise to gradually increase the cur- states. If the transistor tester has a rent through the diode will have 100 ohm current limiting resistor, some internal resistance. Therefore, then 1 volt vertical deflection will it’s almost impossible to arrive at correspond to 10 mA of junction cur- point B because the diode will ab- rent. Any reasonable facsimile will ruptly switch from A to C and vice work so long as you can display versa on the decreasing swing. This about 0 to 30 mA vertically. The switch action results in about 0.5 curve on a good diode will be similar volt change across the diode and oc- to Figure 10 in the main article curs at nominally 5 to 15 mA cur- allowing you to discern the switch rent. The voltage change occurs very points and get a fair idea of the cur- rapidly. Circuits like Figure B can rent magnitude. Figure 10. Tunnel diode waveform 1 I When testing tunnel diodes, make Integrator i sure the switch is in the In-Circuit position as you need the higher current.

Transistor Tests with a VOM I

Another way to test transistors is to perform a forward and reverse ohmmeter check on the two transis- T tor diodes. It’s much slower than E with the transistor checker. Also you Figure A. Figure 0. have to be careful about the short- circuit current and open-circuit voltage of your ohmmeter. On Rxl

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~___- - _I---- I Tip #5 TABLE 1. CHARACTERISTICS OF COMMON Measure the short-circuit current I OHMMETERS and open-circuit voltage for each i resistance scale on your VOM's Make, Model, Open Circuit Short Circuit and VTVM's. Keep this informa- I and Range Voltage Current Polarity tion along with the polarity of the i leads on a chart on the back of i HP 412A (VTVM) the ohmmeter. I R x !- 0.01 v 8.0 mA R y: 1U 0.1 v 10.0 rnA RTn-- -c Tip #6 R x 100 1.0 v io.0 rnA +R x 1K 1.0 v 1.0 rnA BLACK - If you are using a VTVM, make R x 10K 1.0 v 100.0 pA R x 100K 1.0 v 10.0 pA sure the range you are using has R x 1M 1.0 v 1.0 PA enough open-circuit voltage to R x 10M 1.0 v 0.1 pA overcome the 0.2V for germanium and 0.6V for silicon. HP 4108 (VTVM) Otherwise you will get an un- Rx1 1.1 v 120 mA satisfactory reading. R x 10 1.1 v 11 rnA RED - R x 100 1.1 v 1.1 rnA R x 1K 1.1 v 110.0 pA BLACK + Since leakage does not show up well R x 10K 1.1 v 11.0 flA R x lOOK 1.1 v 1.1 pA on the transistor checker of Figure 6, R x 1M 1.1 v 0.11 pA nor on the ohmmeter tests, it is best to have an inexpensive beta/leakage tester on hand. There are many HP 410C (VTVM) available and some of the best are in R x 10 1.3 V 55 mA kit form. If a leakage current tester R x 100 1.3 V 5.7 rnA RED + R x 1K 1.3 V 0.57 rnA BLACK - is unavailable, you can try shorting R x 10K 1.3 V 57 PA out the emitter-base junction while R x lOOK 1.3 V 5.7 pA R x 1M 1.3 V 0.5 pA simultaneously measuring the volt- R x 10M 1.3 V 0.05 PA age drop across the collector load resistor. SIMPSON 260 (VOM) Tip #7 Rx1 1.5 V 125 mA RED + R x 100 1.5 V 1 rnA Measure ICBO by shorting the R x 10K 7.5 v 60 pA BLACK - emitter-base junction and monitoring the voltage across the SIMPSON 269 (VOM) collector lead resistor. RX1 1.5 V 74 rnA R x 10 1.5 V 8 rnA RED - R x 100 1.5 V 8 mA BLACK + R x 1K 1.5 V 0.82 rnA R x 10K 24 V 1.3 mA R x lOOK 30 V 13 /*A For example, if you measured 30 mV across a 10K load resistor, your leakage current would be TRIPLEll 630 (VOM) Rx1 1.5 V 320 rnA RED - R x 10 1.5 V 32 rnA BLACK + R x 100 1.5 V 3.25 rnA (Varies with R x 1K 1.5 V 325 pA serial This would be about right for a ger- R x lOOK 22.5 V 70 pA nurn ber) manium transistor at room temperature, but a little high for a silicon TRlPLElT 310 (VOM) surface-passivated transistor. Rx1 1.5 V 7.5 rnA RED - R x 10 1.5 V 750 pA BLACK + One of the most common mistakes in R x 100 1.5 V 75 pA (Varies with R x 10K 1.5 V 75 PA serial analyzing transistor circuits is to number) miscalculate the gain of one stage in a multi-stage amplifier. The error O Numbers in bold type indicate safe range. usually occurs in miscalculating the real value of the load resistor for

WWW.HPARCHIVE.COM that stage. Figure 11 shows a two- here is a list of important points re- leakage current then equals the /”1 stage amplifier. The correct value lating to the troubleshooting tips voltage across the load resistor for RL1 is not the actual listed value and characteristics previously divided by its resistance. (Make of the resistor, but rather the paral- described. sure the collector is not DC lel combination of RL1, Ra, Rb and - NPN and PNP transistors are coupled to the next stage.) Rin of Q2. Usually the Rin of Q2 is basically “off’ devices while vac- - Abnormal increases in room the most dominant factor in this uum tubes are basically “on” temperature leakage current combination. devices. (e.g., 10 times normal) often in- - Transistors are made up of two dicate contamination of the diodes: a base-emitter diode and base-collector junction (possibly a base-collector diode. In normal due to a cracked or broken (amplifier) operation, the base- hermetic seal). The result is a emitter diode is forward biased shift in the normal bias operat- and the base-collector diode is ing point. Trouble will only be reverse biased. experienced if the driving signal drives the transistor to or near - Shorting the base to emitter cutoff. The transistor will not turns off transistors while for- properly turn off and the result * ward biasing base-emitter junc- may be clipping or distortion due tions turns on transistors. Figure 11. Two-stage amplifier to the residual leakage current - All transistors have leakage cur- flowing through the external re- rent across their reverse biased sistors. Heating and cooling a Tip #8 base-collector diodes. For surface transistor aggravates this condi- When calculating the gain of a passivated silicon transistors, tion and sometimes shows up stage, be sure and include the this current is usually no more marginal operation. parallel loading effects of the than several nanoamperes. Since - Shorting collector to emitter ”) next stage bias resistors and germanium transistors cannot be simulates saturation as the tran- input impedance. surface passivated, this leakage sistor behaves like a closed current normally may be several switch. microamperes. Summary Much information on transistors is - Leakage current increases with available from HP on video tape in All of the above tips relate back to heat (a law of physics) and dou- the Practical Transistor Series, HP the fundamental characteristics of bles about every 10°C. Part Number 90100D, Trou- transistors described at the begin- - Leakage current may be easily bleshooting Transistor Circuits Fas- ning of this article. To summarize, measured by shorting the base- ter, HP Part Number 90030 683 and emitter junction and measuring Troubleshooting FET Circuits Fas- between the transistor collector ter, HP Part Number 90030 726. and the supply voltage. The Contact your local HP office for more information or call direct to Hewlett-Packard Video Products, (415) 857-2381.

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HP-IB VERIFICATION PROGRAMS

Many Hewlett-Packard instruments with HP-IB fully documented with instructions, listing, flow- capability have calculator-controlled test programs chart, check points, etc. The verification programs available that can save you considerable time in listed below can be ordered from your local HP verifying instrument operation. Each program is office.

PROGRAM INSTRUMENT MODEL TAPE P/N DOCUMENTATION 5150A Thermal Printer Service Note 5150A-4 5312A ASCII Interface Module (5300B) Service Note 5312A-2 5328A Universal Counter (Opt. 011,020,021,030 Service Note 5328A-17 031, 040, 041) 5328A Universal Counter (Opt. H99) 5328MH99 Manual 5328A Universal Counter (Opt. 096/H42) 5328MH42 Manual 5335A Universal Counter 5335A Manual 5340A Frequency Counter (Opt. 011) Service Note 5340A-11 5341A Frequency Counter (Opt. 011) 5341A Manual 5342A Microwave Frequency Counter (Opt. 011) 5342A Manual 5343A Microwave Frequency Counter (Opt. 011) 5343A Manual 5345A Electronic Counter (Opt. 011) Service Note 5345A-9A 5345A Electronic Counter (Opt. 012) Service Note 5345A-12A 5353A Channel C Plug-In 59300-10001 (9825A) Service Note 5353A-1 5354A 4 GHz Frequency Converter Service Note 5354A-6 5355A Automatic Frequency Converter 5355A Manual 5358A Measurement Storage Plug-In 5358A Manual 5359A Time Synthesizer 5359A Manual 5363A Time Interval Probes Service Note 5363A-2 5363B Time Interval Probes 5363B Manual 5370A Universal Time Interval Counter Service Note 5370A-1A 59301A ASCII/Parallel Converter Service Note 59301-2 59303A Digital-to-Analog Converter Service Note 59303A-1 59304A Numeric Display Service Note 59304A-1 59306A Relay Actuator Service Note 59306A-4 59307A VHF Switch Service Note 59307A-3 59308A Timing Generator Service Note 59308A-1 59309A Digital Clock Service Note 59309A-3 59313A Analog-to-Digital Converter 59313A Manual 436A Power Meter 00436-10006 (9830A) 436A Manual 00436-10007 (9825A) Service Note 436A-2 8409B Automatic Network Analyzer 11863-10004 (9835/45) 11863D Manual 8409B Manual 8672A Synth. Sig. Gen. 11712-10001 (9830A) Kit Manual 11712-90001 11712-10002 (9825A) Kit Manual 11712-90001 8409B Network Analyzer 11863-10004 (9835/45) 11863D Manual 8409B Manual 8566A Spectrum Analyzer 08566-60002 (9825A) 8566A Manual 8568A Spectrum Analyzer 08568-60002 (9825A) 8568A Manual 8507A Network Analyzer 85030-10002 (9830A) 85030A Manual 8507A Manual 8507B Network Analyzer 85030-10007 (9825A) 85030B Manual 8507B Manual 3042A Network Analyzer 03042-90211 (9825A) 3042A Manual 3045A Spectrum Analyzer 03045-10001 (9825A) 3045A Manual 3582A Spectrum Analyzer 03582-10001 (9825A) 3582 Manual 3585A Spectrum Analyzer 03585-10001 (9825A) 3585 Manual 3050B Voltmeter System 03050-90230 (9825A) 3050B Manual 03050-90212 (9830A) 3050B Manual 3052A Voltmeter System 03052-90011 (9825A) 3052A Manual 3437A System DVM 0343 7- 10001 (9825A) 3052A Manual 3455A System DVM 03455-10001 (9830A) 3052A Manual 03455-10002 (9825A) 3052A Manual 3495A Scanner 03495-10001 (9830A) 3495A Manual 03495-10002 (9825A) 3495A Manual WWW.HPARCHIVE.COM

1, I

model number sequence for all instruments (including obsolete mod- els) in the "Service Note Index" - also available free of charge.

Please be aware that we can only supply free back issues on a limited basis. For those customers that d- (I W require large numbers of Service Notes for many different instruments, HP has a complete mi- crofiche library and automatic up- dating service available for a nomi- nal charge. reliability, improve performance, How Do I Obtain Service Notes or extend their usefulness. Inside Bench Briefs is an abstract of Service Notes are used to inform all the current Service Notes issued you of a revised adjustment pro- over the last 2-3 months. At the cedure, recommended parts re- rear of Bench Briefs is a Service placements, and new trou- Note order form. bleshooting procedures. Look in the abstract list for the Safety Service Notes communi- 1. model number of your cate potentially hazardous condi- instrument. tions related to the use of instruments. 2. Read the abstract to get an idea of what the note is about.

What Are The Benefits To Me? 3. If you want the note (or notes - You can create a history file on each many times there is more than HP instrument you own. Service one), check the appropriate For one thing they are free. Notes describe modifications to in- numbers on the order form and struments out in the field and are mail it to one of the listed For another they provide an after- the only way you have of keeping addresses. sales support link to Hewlett- your operating and service manual Packard for a continuous flow of up-to-date. 4. If you want back issues of Serv- service-related information about ice Notes (or notes that are not your instrument. Are Back Issues Available? listed in the current issue of Yes! Copies of all service notes ever Bench Briefs), simply write the What Do Service Notes Say? issued for an instrument are avail- model number (or Service Note Service Notes recommend modifi- able in both hardcopy or micro- number if known) across the face cations to instruments to increase fiche. These notes are listed in of the order form.

435Al436A POWER METERS 1610A-9. Serials 194OA-01704 to 194OA-01764. Mod- 435A-5. Serials Prefixed 1629A and below, and serial ification to improve power supply regulation. numbers 2004U-05330 and below. N connector modification to allow POWER REF OUTPUT com- 1611A LOGIC ANALYZER patibility with 8481 8 and 84828. 161 1A-8A. Serials 1837A-02232 and below. Modifica- 436A-3. Serials 1629A01131 and below, and tion to eliminate bright spot on CRT after turn off. 1943UOO880 and below. N connector modification to allow POWER REF OUTPUT compatibility with 1615A LOGIC ANALYZER 84818 and 84828. 1615A-2. Serials 1937A-03487 and below. Modifica- tion to eliminate bright spot on CRT after turn off. 546A LOGIC PULSER 546A-1. Serials 1732A and below. Modification to im- 1822A TIME BASE AND prove performance. DELAY GENERATOR 1822A-2A. Serials 0907A- and below. Modification to 1302N1304A DISPLAYS improve reliability. 3 Here's the latest listing of Service 1302A-3. Serials 1721A and below. Preferred replacement for astigmatism potentiometer. 3325A SYNTHESIZER/ Notes available for Hewlett-Packard 1304A-3. Serials 1715A and below. Preferred re- FUNCTION GENERATOR products. To obtain information for placement for astigmatism potentiometer. 3325A-SA. Serials 1748A02350 and below. Modifica- instruments you own, remove the tion to improve square wave phase control. 1610A LOGIC ANALYZER 3325A-7. Serials 1748A02350 and below. Adjustment order form and mail it to the HP 1610A-8. Serials 1836AO1319 and below. Modification to mixer driver to improve reliability. distribution center nearest you. to improve reliability. 3325A-8. All serials. Relay cleaning procedure.

WWW.HPARCHIVE.COM 9551A-13. AH senais. +i2 volt regulator replacement cations to prevent intermittent single Channel inter- itication to improve third order intermodulation instructions. face operation while running A-D measurements. performance. 37798-18. All serials. Field installation of 37798 Option 8568A-30. IF section serials 2003A and below. Mcdifi- 35558 TRANSMISSION AND 002 into 37798 Option 001 instruments. cation to improve third order intermodulation NOISE MEASURING SET performance. 355552E. Serials 0992A06760 and below. Improved 4140A pA METERlDC 8568A-31. RF section serials 1943A and below. Rec- power supply reliability. VOLTAGE SOURCE ommended component changes to prevent signal 414OA-3. Serials 1917J00270 and below. Modification level fluctuations. 3570A NETWORK ANALYZER to improve operation of key controls. 8568A-32A. All serials. Adjustment procedure to im- 357OA-10. Serials 1331A01615 and below. Modifica- prove amplitude drift vs. temperature. tion to improve performance during HP-IB 4942A TlMS 8568A-34. All serials. Procedure to select A13C22 operation. 4943A-5. Serial numbers affected: capacitor whenever IC A13U13 is changed. 3570A-11. Serials 1331A01595 and below. Modifica- 4942A - All serials: tion to improve low amplitude phase 4943A - Serials 1731A00290 and below: 8614AIB SIGNAL GENERATOR measurements. 4944A - Serials 1737A00570 and below: 8614A-18-S. Serials 1748A and below. Procedure for A6 or A17 RF cable replacement compatibility. checking front-panel grounding. 3585A SPECTRUM ANALYZER 86148-10-5. All serials. Procedure for checking front- 3585A-3. Serials 1750A00570 and below. Modification 4943A TlMS panel grounding. to improve 75fl input return loss. 4943A-5. Serial numbers affected: 4942A - All serials: 8616AIB SIGNAL GENERATOR 3702B IFlBB RECEIVER 4943A - Serials 1731A00290 and below: 8616A-164. Serials 1739A and below. Procedure for 37026-42. All serials. Preferred replacement for NPN 4944A - Serials 1737A00570 and below: checking front-panel grounding. transistor (1 854-0071). A6 or A17 RF cable replacement compatibility. 86168-10-S. All serials. Procedure for checking front- panel grounding. 37038 IFlBB RECEIVER 4944A TlMS 37038-6. All serials. Preferred replacement for NPN 4943A-5. Serial numbers affected: 8620C SWEEP OSCILLATOR transistor (1 854-0071). 4942A - All serials: 862OC-5. Serials 1933A and below. Elimination of fre- 4943A - Serials 1731A00290 and below: quency shift in 8620C HP-I8 Option 001 plug-ins. 3705A IFlBB RECEIVER 4944A - Serials 1737A00570 and below: 3705A-7. All serials. Preferred replacement for NPN A6 or A17 RF cable replacement compatibility. 8671A SYNTHESIZER transistor (1854-0071). 4944A-6. Serials 1737A00481 and below. Modification 8671A-1. Serials 2006A and below. Modification to im- to prevent intermittent level dropout. prove performance of Reference Oscillator. 3710A lF/BB RECEIVER 3710A-22. All serials. Preferred replacement for NPN 5315AIB UNIVERSAL COUNTER 8672A SYNTHESIZED transistor (1854-0071 ). 5315NB-2. All serials. Replacement part numbers for SIGNAL GENERATOR yellow LED displays. 8672A-2A. S€?rials 1719A and below. Preferrebd re- 3712A IF/BB RECEIVER placement for 1853-0050 transistor. 3712A-3. All serials. Preferred replacement for NPN 5342A MICROWAVE FREQUENCY 8672A-8. Seriiils 2006A and below. Modification lo im- COUNTER transistor (1854-0071). prove perfcirmance of Reference.. Oscillator...... 5342A-9A. Serials 1812 and below. Procedure to cor- 8672A-9. Serials. ~^^-.iwiA mu Luu/A.^^^_. Mmiricarion.. to 3715A IFlBB RECEIVER rect A2 false frequency readout, and to eliminate improve amplitu,de recovery time. f 3715A-2. All serials. Preferred replacement for NPN ground at U19(8). transistor (1854-0071). IE71A DTS-70 5391A FREQUENCY STABILITY 9571A-1 0. All seriaIs. Recommended replaceinent for 3716A IFlBB RECEIVER ANALYZER SYSTEM 62605J Power :;upply. 3716A-11. All serials. Preferred replacement for NPN 5391A-1. All serials. Software bugs and fixes. transistor (1 854-0071).

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NAME Service Note Index COMPANY NAME, 0 Yes, I want a printed copy.

STATE ZIP

0 435A-5 0 34658-2A 0 377OB-20 0 8568A-19 0 436A-3 0 3551A-98 0 37708-21 8568A-20A 0 546A-1 0 3551A-12-S 0 3771A-2A 8568A-21 0 1302A-3 0 3551A-13 0 3771AIB-l1A 0 8568A-25 0 1304A-3 0 3555B-2E 0 3771AIB-17 0 8568A-28

0 161OA-8 0 3570A-10 0 3779A-15A 0 8568A-29 0 1610A-9 0 3570A-11 0 37798-15A 0 8568A-30 1611A-8A 0 3585A-3 0 37798-18 0 8568A-31 0 1615A-2 0 3702B-42 0 41408-3 P558A-32A 0 1822A-2A 0 37038-6 0 4943A-5 0 8568A-34

0 3325A-5A 0 3705A-7 0 4944A-6 0 8614A-18-S 3325A-7 0 3710A-22 0 5315AIB-2 0 86148-10-S 0 3325A-8 0 3715A-2 0 5342A-9A 8616A-164 0 333OAIB-11A 0 3716A-11 0 5391A-1 0 8616B-104 0 3335A-4 0 372CA-3B-S 0 5526A-5A 0 8620C-5

0 3335A-5 0 3721A-14B-S 0 855886A 0 8671A-1 0 3336AIBIC-2 0 3736A-3 0 8566A-5 0 8672A-2A 0 3455A-17A 0 377OA-39 0 8566A-6 0 8672A-8 0 3455A-18 0 3770A-40 0 8566A-7A 0 8672A-9 0 3465A-5A 37708-19 0 F'" 'A-1lA-S 0 9571A-10