HP-Service-Note-400D-2C 电路图.pdf

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1、 MODELS 400D, 400H, AND 400L VACUUM TUBE VOLTMETERS TEST, ADJUSTMENT, AND CERTIFICATTON METHODS These Service Notes have been prepared as an aid in testing and adjusting all Model 400D, 400H, and 400L Vacuum Tube Voltmeters. The procedures that follow supersede those in other Service Notes or Op- er

2、ating and Servicing Manuals for these instruments. All circuit references apply to one of the three ref- erence schematic diagrams in these Service Notes. No attempt should be made to make an instrument agree completely with any one of these schematics. All recommended circuit changes are described

3、in Section I of these Service Notes. Voltages mentioned herein are measured between the indicated points and the chassis unless specified otherwise. The voltmeter power supply should al- ways be tested before undertaking repair and adjust- ment of any other section of the instrument. These Service N

4、otes are divided into five sections as follows: Section Page I MODIFICATIONS 1 I1 TUBE *CW* U Y W O R T *-I000 r(Mc.0 *db.,A. E* RadioFans.CN 收音机爱 好者资料库 Page 2 v- 400D-2C D. MODEL 400D SERIAL NO. 5130 AND BELOW Transpose the connections to electrolytic capa- citor C30 so that C30B is 20 pf and C3OC

5、is 40 pf. This transposition will reduce power supply ripple. E. MODEL 400D SERIAL NO. 14770 AND BELOW MODEL 400H S ERIAL NO. 1137 AND BELOW Replacement of control R29 or three-section resistor R28 in the amplifier feedback circuit will necessitate revising and rewiring the feedback circuit. The par

6、ts for this circuit revision are supplied as a kit with complete instructions under Stock No. 400D-95A. The revised feedback circuit is recommended for all 400D and 400H instruments whenever repair of the feedback circuit is necessary. The revised circuit is superior to earlier circuitry but does no

7、t offer suf- ficient advantages to warrant modification merely to include the new circuit in an instrument. The problem of adjusting frequency response following any changes in the feedback circuit would also make it advisable to avoid making unnecessary changes, F. MODEL 400D SERIAL NO. 16371 AND A

8、BOVE The regulated power supply was changed. Series regulator tube V7 was changed from a 6AU5 toa 12B4A. Control tube V8 was changed from a 6CB6 to a 6U8 and reference tube V9 was changed from an OB2 to a type 5651. The circuit differences can be determined by referring to the schematic diagrams inc

9、luded in these Service Notes. Field modification to incorporate this change is im- practical and is not recommended. SECTION II - TUBE stop when pointer is right on zero, If pointer overshoots zero, repeat this adjustment. 3) When pointer is exactly on zero, rotateadjustment screw approximately 15 d

10、egrees counterclockwise. This is enough to free adjustment screw from the meter suspension, If pointer moves during this step repeat entire adjustment. B. SETTING MECHANICAL ZERO IN MODEL 400L The special meter in the 400L is adjusted with the vtvm turned on since the meter pointer rests against the

11、 stop at the left end of the scale when the instrument is turned off. RadioFans.CN 收音机爱 好者资料库 Page 4 I In most 400L instruments the mechanical zero is pre- set during manufacture of the meter movement, The adjustment screw in such meters is inoperative. Most 400L instruments will have no adjusting s

12、crew on the front of the meter case. The following procedure is for use only with those instruments in which the mechanical adjustment screw is effective. 1) Connect a 1.0 volt rms, 400 cps signal from the Voltage Calibration Generator to the 400L INPUT terminals. Set the 400L to the 1-volt range an

13、d adjust the feedback control (R29) for a full scale meter reading of 1.0 volt. Any convenient range could also be used along with a corresponding change in input signal level. The input signal frequency is also not critical. 2) Switch the Calibration Generator todeliver a signal of 0.3 volt, or 0.3

14、 of the signal level used in step 1. Set the meter mechanical zero adjusting screw to ob- tain a reading that is 0.3 of the reference reading in step 1. Use the same vtvm rangefor both steps 1 and 2. If you overshoot, continue to rotate the screw clockwise and again approach the 0.3 point from the h

15、igh side of the scale, The screw should not be turned counterclockwise during this procedure. 3) Repeat steps 1 and 2 until no further improvement can be noted. Compromise adjustment of themechani- cal zero can be made for optimum tracking. After final adjustment, cover the screw with a small piece

16、of black tape. 1 I C. CHECK REGULATED POWER SUPPLY 1) The B+ voltage at the output of the regulated power supply should be 250 volts i5 volts. Measure this voltage between the chassis and the cathode of the series regulator tube with the line voltage set to 115 volts. 2) Vary the line voltage betwee

17、n 103 and 127 volts. The regulated B+ will usually change no more than 2 volts from one extreme to the other, Ripple volt- age in the regulated B+ is usually 3millivolts or less under these same test conditions. The dc voltage at the plate of the series regulator tube or at the cathode of the rectif

18、ier tube should be between 400 and 420 volts with a 115-volt line, Low voltage at this point may be from adefective rectifier tube, filter capacitor, or power transformer. To check the rectifier tube, connect a dc voltmeter be- tween chassis and the rectifier cathode. Reduce line voltage from 115 to

19、 103 volts. The voltmeter reading should drop as line voltage is reduced and then remain steady. If the dc voltage continues to drop at a slow rate, the rectifier tube is probably weak and should be replaced. If the regulated B+ voltage is not correct, replace- ment of any or all four tubes in the p

20、ower supply may be necessary. If tube replacement does not correct the dc voltage, precision resistors R62 and/or R64 may have changed value and should be replaced. Ab- normal current drain caused by component failure elsewhere in the vtvm can result in poor power sup- k ply regulation, 400D-2C Exce

21、ssive ac ripple may be from a defective tube in the power supply other than the rectifier tube, Ca- pacitor C36 may be open, D. SET DC HEATER VOLTAGE 1) Adjust control R66 to set the dc heater voltage for tubes V1 and V2 to 6.3 volts rt0.2 volt. The dc volt- ages across the heaters of tubes V3 and V

22、4 must also be 6.3 volts rt0.2 volt. DO NOT USE A VOLTMETER THAT IS CONNECTED TO A COMMON GROUND WITH THE VTVM UNDER TEST WHEN MEASURING THESE HEATER VOLTAGES. A SHORT CIRCUIT WILL RESULT. Slight readjustment of control R66 will often bring these two voltages within tolerance. 2) If both voltages ca

23、nnot be set to 6.3 volts, f 0.2 volt, adjust R66 to bring the lowest of the two voltages within tolerance. Connect a resistor in arallel with the two heaters with the highest voltage. )?he correct resistor value will enable you to bring bo* heater voltages within tolerance by readjusting control R66

24、. Use only one resistor in parallel with one pair of tubes at a time. A resistor value below 220 ohms 1 watt should not be used. 3) If you are unable to obtain the correct heater voltage after completing steps 1 and 2, checkelectro- lytic capacitors in the heater circuit. If both heater voltages are

25、 low, check selenium rectifier SR1. E. INPUT DIVIDER CIRCUIT IDENTIFICATION 1) An identification of the type of input circuit will enable you to select the proper test required for your instrument. Instruments are classified by type of input circuit into two general groups: a. Models 400D, serial 00

26、1-34370and below; Models 400H/L, serial 001-11226 and below , . , these instruments may have either a “capacitive input divider” or a “resistive input divider”. Com- plete steps 2 through 6 to determine which one is present. b. Models 400D/H/L with serials prefixed 017- and 048- . . , all these inst

27、ruments employ a “re- sistive divider”. Omit steps 2 through 6 and proceed with Section IV-F. 2) Set the vtvm to the 1.0 volt range and connect a 1.0 volt rms, 400 cps signal from the Calibration Generator to the INPUT terminals. Any convenient range higher than the 1-volt range can be used. The sig

28、nal frequency should be approximately 400 cps. 3) Rotate capacitor C4 (on input circuit board) one full turn while watching the vtvm meter reading. The meter reading will vary only about 547, in some instru- ments and approximately 5v0 in others. 4) If the meter indication varies approximately 5vo,

29、capacitor C4 is a Voltage Calibration Adjustment, This will be referred to as a “CAPACITIVE INPUT DIVIDER” circuit in the balance of the procedures in these Service Notes. 00665-3 400D-2C Page 5 5) If the meter indication varies approximately 547, capacitor C4 is a Frequency Response Adjustment. Thi

30、s will be referred to as a “RESISTIVE INPUT DIVIDER” circuit in the balance of the procedures in these Service Notes. i / 6) Mark the type of input circuit on the input circuit shield, This reference will be used in later steps of this Test Procedure. F. INPUT CIRCUIT PRELIMINARY FREQUENCY RESPONSE

31、ADJ USTMENT 2) For Models 400D/H/L with serials prefixed 017-: a. Connect a 1.0 volt rms, 400 cps, signal from Voltmeter Calibration Generator to INPUT of vtvm. Switch vtvm to 1.0 volt range. b. Adjust RlOl for a vtvm reading of 1.0 volt. I. MISCELLANEOUS CHECKS NOTE: All checks in this section are

32、made with the vtvm cabinet in place. This adjustment is for “RESISTIVE INPUT DIVIDER” circuits only: 1) Connect a 1 kc, 2 volt peak-to-peak, square wave signal to the INPUT o f the vtvm under test. Connect the OUTPUT terminals of the same vtvm to the vertical input of a high frequency oscilloscope s

33、uch as the Model 150A. 2) Switch the vtvm to the 1.0 volt range and adjust capacitor C4 for the best square wave pattern on the oscilloscope. G. BASIC CALIBRATION (SETTING AMPLIFIER GAIN) 1) For Models 400D serial 001-34370 and below and Models 400H/L serial 001-11226 and below: Connect a 0.3 volt r

34、ms, 400 cps signal from the Cali- bration Generator to vtvm INPUT. Switch the vtvm to 0.3 volt range and adjust the feedback control, R29, to obtain a reading of 0.3 volt. 2) For Models 400D/H/L with serials prefixed 017-: Connect a 0.001 volt rms, 400 cps signal from the Calibration Generator to vt

35、vm INPUT. Switch the vtvm to the 0.001 volt range and adjust the feedback control, R107, to obtain a reading of 0.001 volt. i / H. BASIC CALIBRATION (SETTING INPUT DIVIDER) 1) For Models 400D serial 001-34370 and below and Models 400H/L serial 001-11226 and below: a. Connect a 1.0 volt rms, 400 cps,

36、 signal from Voltmeter Calibration Generator to INPUT of vtvm. Switch vtvm to 1.0 volt range. b. For “CAPACITIVE INPUT DIVIDER” circuits, adjust C4 for a reading of 1.0 volt. c. For “RESISTIVE INPUT DIVIDER” circuits, the vtvm indication will normally be 1.0 volt. If reading is high, decrease value

37、of pad (R87) in L/ parallel with R3. If reading is low, increase value of pad (R87). Resistor R3 and pad R87 are on input circuit board. 00665-2 1) Noise and Switching Transients - This check will vary with the voltmeter model. Models 400Dand 400H have one method while the 400L has a different metho

38、d. a. For 400D and 400H VOLTMETERS - Plug a shielded connector (8 Stock No. 1251-0019) over the INPUT terhinals of the vtvm under test, A lO0,OQO ohm resistor should be connected be- tween the terminals inside this shielded plug. The residual reading on the 0.001 volt scale will normally not be more

39、 than 0.00005 volt (5% of full scale). b. For 400L VOLTMETER - Connect a 0.0003 volt rrns (0.3 millivolt) signal of about 400 cps from the Calibration Generator to the INPUT termi- nals, The voltmeter reading should be steady with the range switch in the 0.001 position. Noise in V1 or V2 will cause

40、this reading to vary erratically. c. Connect the 100,000 ohm shielded resistor (see step a) between the INPUT termirials. Rotate the range switch through all 12 positions in both directions. The meter needle may be momen- tarily d e f l e w as high as full scale between some switch positions. The me

41、ter pointer should always drop back to zero at a uniform rate with- out pause or a sudden change in the rate of fall. d. Remove the shielded 100,000 ohm resistor and connect a 0.001 volt rms, 400cps signal from the Calibration Generator to the INPUT terminals, The voltmeter reading should be steady

42、with the range switch in the 0.001 position. If the results obtained in this test are not satisfactory, check tubes V1 and V2, all coupling capacitors, elec- trolytic capacitors in screen and plate circuits, V2 plate load resistor, and cathode bypass capacitors. a. Connect a 0.001 volt rms, ac signa

43、l to the INPUT terminals and set the vtvm to the 0,001 volt range. Hold your hand palm-upward and sharply rap the front of the meter case with your knuckle. b J The pointer will usually not move more than,. about 1/8 inch along the meter scale. b. Repeat step a at 300 volts on the300-volt range. The

44、 results obtained should be the same. 2) Check for Microphonics Page 6 Replace V1 and/or V2 to remove excessive micro- phonics. Pre-selected tubes are available from for V1 and V2. See Section I1 of these Service Notes for details, 3) Check Output vs Shock a. Connect a 1.0 volt rms, ac signal to the

45、 INPUT and set the vtvm to the 1-volt range. Connect the vtvm OUTPUT to an oscilloscope and adjust oscilloscope to display several cycles. b. Strike either top front corner of the instrument with the palm of your hand, There should be no sudden change in amplitude nor a momentary collapse of the pat

46、tern. This test will detect another type of microphonic tube or poor elec- trical connections within the vtvm. 4) Check Beat Notes at 60 and 120 Cycles a. Connect a battery operated oscillator to the IN- PUT terminals of the vtvm. Set the range switch to the 1-volt range, Adjust the oscillator outpu

47、t to provide a vtvm reading of 0.9 volt at about 58 cps. Adjust the oscillator frequency toobtain maximum meter swing which will normally not be more than about 1/8 in. along the meter scale. b. Repeat step a at 120 cps. The maximum meter swing will usually not be more than about 1/8 in. along the m

48、eter scale. High beat notes are usually caused by defective tubes anywhere in the instrument. J. RECHECKDCHEATERVOLTAGE Check the dc heater voltage by the method given in paragraph D. If either electrolytic capacitor in the heater circuit has been replaced, a heat-run of several hours should be allo

49、wed. After the heat-run to form the capacitor plates, reset the heater voltage. K. CHECK CALIBRATION AND TRACKING 1). Check full scale accuracy of each voltmeter range. Use the Voltmeter Calibration Generator. The cali- bration should be within *2% of full scale for a 400D Voltmeter or ilg of full scale for a 400H or 400L Voltmeter, The test voltage should be between 50 cps and 500 kc. Avoid using the power line frequency or a harmonic of the power line. Refer to the accuracy specific