Hallicrafters Sr-2000 Operating instructions

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

REPAIR & RESTORATION

HALLICRAFTERS

SR-2000

CAUTION: FATAL VOLTAGES ARE OPEN AND EXPOSED ONCE

THE COVERS OR CASE IS REMOVED. OBSERVE THE FREE

HAND RULE. THAT IS, ANY TIME THE POWER IS APPLIED, IF

YOU ARE RIGHT HANDED YOUR LEFT HAND IS IN YOUR HIP

POCKET. IF YOU ARE LEFT HANDED YOUR RIGHT HAND IS

IN YOUR HIP POCKET. YOU PROCEED AT YOUR OWN RISK.

This document is the intellectual property of the author, Walter A. Cates, WDØGOF. Unless specifically

credited to a contributor, all processes, ideas, drawings, data sheets and opinions contained here-in are the

intellectual property of the author. Any reproduction of this document for profit will be vigorously pursued.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

INTRODUCTION

This is not a “restore to museum” quality guide. Cleaning, painting and front panel touchup are not covered.

There are reams of documents that cover those actions. There are very few documents that delve into the inner

workings of these radios. This document does. This document applies directly to the production run reflected by

the 155-000348C schematic. Earlier or later production run units may vary slightly in signal levels and

measurements. There have been many post production modifications recommended for the 2000 and they effect

the trouble shooting very little.

This document takes a systematic approach to rehab. In all discussions the word manual refers to:

OPERATING AND

SERVICE INSTRUCTIONS

FOR

COMMUNICATIONS

TRANSCEIVER

MODEL SR-2000

If this procedure is followed, in the order presented, you will minimize the frustration of restarts and backups

and chasing red herrings. It assumes a working knowledge of radio and tube circuit theory. For the most part it

will lead you to the stage or stages where faults have occurred. At this point you must have the skills to locate

the failed component. Each step of this process assumes all proceeding steps have been successfully completed.

If you try to jump into the middle of the process you may end up in confusion.

You have obviously elected to spend time and effort in this restoration. So, I high y recommend that you

do a dry run with the schematic, manual and this document. As you read this document follow it through the

schematic and the manual. A wealth of knowledge will be gained by doing so.

This document is the intellectual property of the author, Walter A. Cates, WDØGOF, unless specifically

credited to a contributor. All processes, ideas, drawings, data sheets and opinions contained here-in are

the intellectual property of the author. Any reproduction of this document for profit will be vigorously

pursued.

CAUTION: FATAL VOLTAGES ARE OPEN AND EXPOSED ONCE

THE COVERS OR CASE IS REMOVED. OBSERVE THE FREE

HAND RULE. THAT IS, ANY TIME THE POWER IS APPLIED, IF

YOU ARE RIGHT HANDED YOUR LEFT HAND IS IN YOUR HIP

POCKET. IF YOU ARE LEFT HANDED YOUR RIGHT HAND IS

IN YOUR HIP POCKET. YOU PROCEED AT YOUR OWN RISK.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

TABLE OF CONTENTS

INTRODUCTION .................................................................................................................................................. 2

1. SR-2000 INITIAL INSPECTION AND TESTING........................................................................................... 5

1-1. VISUAL AND MECHANICAL INSPECTION......................................................................................... 5

1-2. RECAPPING;.............................................................................................................................................. 5

1-3. AFTER MARKET MODIFICATIONS ...................................................................................................... 5

1-4. INITIAL POWER UP ................................................................................................................................. 6

1-4-1. TEST EQUIPMENT REQUIRED ....................................................................................................... 6

1-4-2. POWER UP PRE-SET CONDITIONS................................................................................................ 6

1-4-3. INITIAL POWER UP TESTS ............................................................................................................. 6

1-5. CHECK AND ADJUSTMENT OF OSCILLATORS: ............................................................................... 6

1-5-1 TEST EQUIPMENT REQUIRED ........................................................................................................ 7

1-5-2. CARRIER OSCILLATOR:.................................................................................................................. 7

1-5-3. HETERODYNE OSCILLATOR:........................................................................................................ 7

1-5-3-1 Adjustment of L19 ......................................................................................................................... 7

1-5-4. VFO:..................................................................................................................................................... 8

1-5-4-1. VFO RIT/CAL .............................................................................................................................. 8

1-5-4-2. VFO CORRECTOR...................................................................................................................... 8

1-5-4-3-1 VFO STABILITY TEST ........................................................................................................ 9

2. RECEIVER FAULT ISOLATION................................................................................................................... 10

2-1. EQUIPMENT REQUIRED....................................................................................................................... 10

2-2. STANDARD TEST CONDITIONS ......................................................................................................... 10

2-3. PROCEDURE OVERVIEW & PRESET CONDITIONS ........................................................................ 10

2-4. RECEIVER FAULT ISOLATION CHART............................................................................................. 11

2-5 AGC TEST ................................................................................................................................................. 12

2-5-1. AGC FIGURE OF MERIT ................................................................................................................ 12

2-5-2. AGC THRESHOLD ADJUSTMENT ............................................................................................... 12

2-6. S-METER ZERO....................................................................................................................................... 12

2-7. CAL OSCILLATOR ................................................................................................................................. 12

3. TRANSMITTER TESTING............................................................................................................................. 13

3-1. TEST EQUIPMENT REQUIRED ............................................................................................................ 13

3-2. STANDARD TEST CONDITIONS ......................................................................................................... 13

3-3. INITIAL SETUP TESTS........................................................................................................................... 14

3-3-1 S-METER ZERO ADJUSTMENT ..................................................................................................... 14

3-3-2 BIAS ADJUST.................................................................................................................................... 14

3-3-3 TRANSMITTER PRETEST ............................................................................................................... 14

3-4 INITIAL TRANSMITTER TESTS............................................................................................................ 14

3-4-1 TRANSMITTER DRIVE TEST PROBE PICK UP........................................................................... 14

3-4-2 Driver output test................................................................................................................................. 15

3-4-2-1 PA FINAL PRETEST.................................................................................................................. 15

3-4-3 TX second mixer output test ............................................................................................................... 15

3-4-4 TX second mixer input test ................................................................................................................. 16

3-4-4-1 Het oscillator TX signal levels..................................................................................................... 16

3-4-4-2 6.5 MHz I.F. INJECTION ......................................................................................................... 16

4. RX SUBSYSTEM TROUBLESHOOTING AND TESTING ......................................................................... 17

4-1 VFO DRIFT................................................................................................................................................ 17

4-2. V15 RX FAULT ISOLATION.................................................................................................................. 17

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

4-3. V9B RX FAULT ISOLATION................................................................................................................. 17

4-4. V9A RX FAULT ISOLATION................................................................................................................. 17

4-5. V7A RX FAULT ISOLATION................................................................................................................. 17

4-6. XTAL RX FILTER/NOTCH FAULT ISOLATION ................................................................................ 17

4-7. V6 RX FAULT ISOLATION.................................................................................................................... 18

4-8. V4A RX FAULT ISOLATION................................................................................................................. 18

4-9. V3 RX FAULT ISOLATION.................................................................................................................... 18

4-10 V2 RX MIXER FAULT ISOLATION..................................................................................................... 18

4-11 V1 RX FAULT ISOLATION................................................................................................................... 18

5 TX SUBSYSTEM TROUBLESHOOTING AND TESTING .......................................................................... 19

5.1 CARRIER BALANCE ............................................................................................................................... 19

5.2 HET OSC LOW OR NO SIGNAL IN TX MODE..................................................................................... 19

5-3 TX 6.5 MHz LOW INJECTION TO 2

MIXER ..................................................................................... 20

5-4 TX DRIVER FAULT ................................................................................................................................. 20

5-5 FINAL PA FAULT .................................................................................................................................... 21

5-5 1 UNABLE TO SET PA BIAS. ............................................................................................................. 21

6. TECH NOTES .................................................................................................................................................. 22

6-1. BASIC TUNE UP.......................................................................................Error! Bookmark not defined.

6-1-1. THE PROBLEM: ................................................................................Error! Bookmark not defined.

6-1-2. WHY IS THIS IMPORTANT?...........................................................Error! Bookmark not defined.

6-2 PA NEUTRALIZATION ........................................................................................................................... 22

6-3. AUDIO POWER METER SUBSTITUTE................................................................................................ 23

6-99. ADDITIONAL TECHNICAL INFORMATION SOURCES: ............................................................... 24

7. DATA SHEETS................................................................................................................................................ 25

7-1. VFO FREQUENCY CORRECTION........................................................................................................ 25

7.2 PERFORMANCE DATA........................................................................................................................... 26

7-2-1. RECEIVER PERFORMANCE DATA.............................................................................................. 26

7-2-2. TRANSMITTER PERFORMANCE ................................................................................................. 27

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

1. SR-2000 INITIAL INSPECTION AND TESTING.

SO YOU JUST GOT AN SR-2000 FROM E-BAY OR SOMEONE THAT

SAID “IT WORKED FINE THE LAST TIME I TURNED IT ON”. NOW

WHERE DO YOU START? THE FOLLOWING PROCESS HAS

EVOLVED OVER YEARS OF REFURBISHING THE SR SERIES

EQUIPMENT. IT SHOULD BE FOLLOWED IN THE ORDER IT IS

WRITTEN. THIS PROCEDURE IS DESIGNED TO PROGRESS IN AN

ORDERLY MANNER TO MINIMIZE RUNNING IN CIRCLES. YOU

MUST HAVE THE MINIMUM OF TEST EQUIPMENT LISTED TO

PROPERLY REHAB OR REPAIR THIS EQUIPMENT. BE AWARE THIS

IS NOT SOMETHING THAT WILL BE ACCOMPLISHED WITH GREAT

SPEED. THE AVERAGE TIME TO COMPLETION IS AROUND 80

HOURS. SOME HAVE TAKEN AS MUCH AS 200 HOURS, SOME AS

FEW AS 20 HOURS.

1-1. VISUAL AND MECHANICAL INSPECTION

Complete chassis cleaning and mechanical inspection are always advised. Cleaning of the controls, rotary

switches and the relays is of particular importance. Look closely for broken or burned components. Check the

rotation of the controls and mechanical stops of the main tuning dial (Section 8-8-A in the manual). Try to

eliminate the mechanical problem first. If you are going to upgrade to a higher production run complete those

upgrades before you start the electrical tests. If your rig is paired with an HA-20 disconnect it and install a

jumper from pin 2 to pin 10 of J2. Test pin 10, it should be grounded.

1-2. RECAPPING;

There are only 2 capacitors that are considered must replace components. They are C146, 25 uf/25v and C147,

2 X 30 uf/350v. Capacitor C147 carries a heavy current load. Therefore the ESR rating of its replacement is

important. They should have an ESR rating of 1.0 ohm or less. ESR’s less than 0.3 ohm are available. This is

not a place to save money. C147 is a dual cap. There are sources for this capacitor, but be careful. Some

manufactures of these parts use inexpensive low quality parts. Don't buy from suppliers who will not quote or

guarantee the ESR rating. Very low ESR individual capacitors are readily available. So replacing the dual cap

with two capacitors under the chassis is sometimes a better solution. Generally speaking shotgun replacement of

the paper caps is not recommended at this stage of refurbishment.

1-3. AFTER MARKET MODIFICATIONS

If you find any modifications, re-wirings or added components evaluate the mods closely. The best on line

source for proper modifications is k9axn.com. If the authenticity of the mods cannot be verified remove them

and return the rig to the original configuration.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

1-4. INITIAL POWER UP

Note: Initial assumption is, the power supply has been fully restored and meets original specifications.

1-4-1. TEST EQUIPMENT REQUIRED

DVM or VTVM

1-4-2. POWER UP PRE-SET CONDITIONS

First and of critical importance, you must have a power supply that has been tested and meets all the original

specifications. You will not be transmitting power until late in this process so there is no need to activate the

high voltage. The power supply front panel switch should be in the SSB LOW POWER position. Do not turn

on the High Voltage until you get to the Transmitter PA tests. It is not necessary to start with a low AC voltage

and increase the voltage over time to cook the rig. There are no domino circuits in the SR-2000. If you have a

short somewhere, you may cook a resistor and it will smell bad but it will lead you straight to the problem. So,

set all the gain and drive controls to minimum. Every time you turn on your SR-2000 all these controls

should be at minimum. The STANDARD PRE-POWER UP CONFIGURATION will always be: all gain

controls set to minimum, RIT off, RIT CONTROL at mid-range, CAL ADJ at mid-range, CAL OFF, NOISE

BLANKER OFF, Preset the PRESELECTOR to the approximate position in the band you will be operating. Set

the FUNCTION switch to either USB or LSB depending upon which band you will be testing the default is 80

meters LSB @3.900MHz. Insure that a jumper plug in installed in J2 on the rear of the radio. The jumper plug

should have a jumper between pins 2 and 10.

CAUTION: FATAL VOLTAGES ARE OPEN AND EXPOSED ONCE THE COVERS OR CASE IS

REMOVED.

1-4-3. INITIAL POWER UP TESTS

Ok it is time apply power. It is assumed that you have a fully recapped power supply that meets all

specifications. Attach the power supply and plug it in. Set the operation switch to REC. Now let it sit there for

10 to 15 minutes. Locate R50, 3300 ohm, 10 watt resistor connected to V10. The voltage at one end should

150vdc and 280vdc at the other. If you do not have the 280vdc assuming your power supply has been proven

functional then there is a wiring error between J6 and R50. If you do not have the 150vdc you have a fault in the

wiring or the 150v regulator. This fault must be cleared before you proceed. Now the only thing we need to do

at this time is rough set the bias voltage.

Measure the voltage on the wiper tab of R114 (BIAS ADJ control). The control should be set for -68 to -70vdc.

This is a setup setting done in the receive mode, a rough adjustment and will be precisely set later. If you cannot

set this voltage then you have a fault in the power supply or the bias divider network, R114, C182 and R113.

Insure that you have -90vdc on pin 4 of J6 and -20vdc on pin 3 of J6. This fault must be cleared before you

continue.

1-5. CHECK AND ADJUSTMENT OF OSCILLATORS:

Before starting any receiver or transmitter troubleshooting or the RF or I.F. alignment it is imperative that the

xtal oscillators and the VFO are precisely on frequency. If you will devote the time to these considerations you

will be rewarded with a rig that performs as well as any modern rig. A frequency counter and scope are

required. The procedure in the book will work ok, but will compound errors. If you get all the oscillators “on

freq” with proper output levels individually, then all else will fall into place. Do not make any adjustments until

the rig has been on for at least 30 minutes. Optimize the VFO last to insure it is stable. Do not hurry. Take your

time, these processes are critical.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

1-5-1 TEST EQUIPMENT REQUIRED

Oscilloscope, 100MHz bandwidth with X1 and X10 probes, Frequency counter.

1-5-2. CARRIER OSCILLATOR:

The carrier oscillator is comprised of V14A and its associated circuitry. The carrier oscillator has three modes

of operation. They are: LSB, USB and USB/CW off-set. First thing is to check the output of the carrier osc in

both USB and LSB modes. After warm up you should have approximately 6 vpp on pin 8 of V9A (test point

D). Now adjust T4 for max. The voltage on pin 4 or 3 of T4 should be 8 Vpp. If these voltages are more than

15% low then you most likely have a fault in the oscillator and this fault must be corrected before you proceed.

Once you are satisfied with the oscillator output set the function switch to USB. Connect a scope to pin 8 of

V9A to monitor the output voltage of the osc. Connect the frequency counter to either pin 4 or 3 of T4.

You will find that if you adjust T4 in one direction from the peak the signal drops off very fast. In the other

direction it falls more slowly. T4 should be adjusted about 2% to 5% off peak toward the slow fall off side. The

manual states that the signal level should be adjusted off peak to 80% of the max voltage. This will cause a

reduction in the max power in CW or TUNE functions. This is a stable circuit and at 2% to 5% of peak to the

slow roll-off side functions quite well. Switch back and forth from USB to LSB to insure both oscillators start

without any hesitation. In USB mode adjust C139 for exactly 1651.550 KHz. Switch to LSB mode and adjust

C136 for exactly 1648.550 KHz. Adjustment of T4 and C136 and C139 can interact. Re-check the output

voltage and re-check the frequency back and forth several times to insure that everything is stable and there is

no hesitation in the oscillator startup.

To check the USB/CW off set, set the function switch to USB and monitor the frequency of the carrier

oscillator. Then switch the function switch to CW. The frequency should rise at least 50 HZ. If it does not

suspect C135 or its control line.

1-5-3. HETERODYNE OSCILLATOR:

The Het Osc is comprised of V12 and its associated circuitry. This oscillator is the most troublesome of the

three. There are no adjustments to pull the frequency of each xtal. So if you do not have a box of spare xtals you

are rather limited in what you can do to put it precisely on frequency. First thing, check the oscillator output.

Connect the scope to pin 8 of V2. The minimum peak to peak voltages for each band should be: 80 meters 4

Vpp, 40 meters 4 Vpp, 20 meters 2.5 Vpp, 15 meters 2.5 Vpp, 10 meters (all 4 bands) 2 Vpp.

Adjustment of L19 may be required.

1-5-3-1 Adjustment of L19

Remove V4 to remove the VFO injection signal. Insure the HIGH VOLTAGE is off (both meters on the P2000

indicate ZERO).Connect the scope to test point B (V11 pin 2). Turn the OPERATION control to MOX and the

FUNCTION control to TUNE. Adjust L19 to get at least 5.5vpp on 80 and 40 meters and 2.0vpp on 10 meters.

If you get 5.5vpp on 80 and 40 meters and 2.0vpp on 10 meters then 20 and 15 meters should be 2.0vpp or

better. Turn the FUNCTION control to USB or LSB and reinstall V4. If the output does not meet these

minimums this fault must be cleared before proceeding. Once you are satisfied with the oscillator output signal

levels, disconnect the scope and connect the frequency counter to pin 8 of V2A and check the frequency on

each band. If the xtal frequencies are all high or all low then swapping out C104 and/or C105 may bring them

back in spec. The end unit frequency spec is + or – 3 KHz at any dial point across any band. With the VFO and

Carrier oscillators dead on whatever error you have in the heterodyne oscillator is what you will have to live

with. The CAL ADJ and the RIT CONTROL will correct for these errors. The use of the CAL ADJ and RIT

CONTROL adjustments to compensate for errors will be discussed later in the VFO discussions.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

1-5-4. VFO:

The VFO is comprised of:

V13 and associated circuitry;

V4B and associated circuitry;

The VFO correction circuitry;

The RIT and CAL circuitry.

From the manual:

Frequency Stability is; Less than 250 cycles drift in the first hour, after a fifteen

minute warm-up, and less than 100 cycles per hour thereafter.

Due to the age of the SR-2000 a more reasonable warm up time is 20 to 30 minutes.

1-5-4-1. VFO RIT/CAL

The RIT/CAL ckts are used to change the bias voltage on a varicap in the VFO. The CAL is used to make

minor corrections to the VFO frequency. The RIT when turned on allows for minor corrections in the

RECEIVER without changing the transmit frequency. In cw mode with the RIT turned on the RIT CONTROL

functions as the BFO.

Set the RIT lever switch to off, adjust the RIT control to the center of its rotation. Set the CAL control to the

center of its rotation. This is the setting for these controls throughout all testing unless otherwise noted. Set the

main tuning to near 300 on the black scale. Connect the frequency counter to pin 3 of V4A. Fine tune the main

tuning for 4550.0 on the counter. Rotate the CAL control to max counter clockwise and note the counter

reading. Rotate the CAL max clockwise and note the counter reading. The difference from counter clockwise to

cc rotation should be minimum 4 KHz; most rigs will run approximately 6 KHz. Readjust the CAL pot back to

4550 Hz on the counter. Turn the RIT on. Adjust the RIT CONTROL for 4550Hz on the counter. The RIT

CONTROL should be at the center of its rotation and not more than 10 to 15

off the center of its rotation. If it

is off too far then you have a dirty switch (S7) or a fault in the voltage divider network. Clear this fault before

proceeding. When the RIT CONTROL is rotated min to max you should see the same swing in frequency as

when you rotated the CAL control earlier.

1-5-4-2. VFO CORRECTOR

The VFO correction ckt adjusts for the frequency off set between USB and LSB (NOTE: CW operates in the

USB MODE). Before the VFO is aligned it must be established that the correction ckts are working properly.

NOTE: RIT OFF, CAL ADJ and RIT CONTROL both in center of rotation. Connect the frequency

counter to pin 3 of V4A. Set the function switch to LSB, any band and tune the main tuning until the frequency

counter reads 4.5530 MHz (approximately 300 on the black scale). Switch to USB and the frequency should

drop 3000 Hz or to 4.550 MHz. If not adjust C127 for exactly 4.5500. If you cannot then there is a fault in the

corrector ckt that must be repaired before you can continue with the VFO alignment. First check the offset

switching voltage on pin 4 of J4 (the ACCESSORY PLUG). In USB it should be 150 vdc. In LSB it should be a

negative voltage in the range of -10 to -28 vdc. If the voltage is switching properly yet there is no shift in

frequency R85 is possible but least likely. CR12, C125, C126 and/or C127 are most likely the cause. If the

offset voltage is not correct then S3A rear, R125, R124 or a wiring problem are the most likely fault.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

VFO ALIGNMENT CONTINUED:

1-5-4-3. VFO ALIGNMENT

1-5-4-3-1 VFO STABILITY TEST

NOTE: RIT OFF, CAL ADJ and RIT CONTROL both in center of rotation.

If you have not already done so proceed to section 8-8-A of the original manual and perform the mechanical

indexing adjustments before you proceed.

Before starting the VFO alignment perform a VFO stability test. Connect the frequency counter to V4A pin 3.

Power up and warm up for 30 minutes. Record the VFO frequency every 10 minutes for one hour. In the one

hour test it should meet the requirements of paragraph 1-5-4 above. After 1 hour perform a short term drift test

by recording the freq every minute for 5 minutes. The short term drift should not exceed 100 cycles. If either of

these tests does not meet specifications go to the VFO DRIFT subsection of section 4. RX SUBSYSTEM

TROUBLESHOOTING AND TESTING for corrective action.

NOTE: RIT OFF, CAL ADJ and RIT CONTROL both in center of rotation.

Assuming the that mechanical indexing adjustments have been completed (section 8-8-A) connect the

frequency counter to V4A pin 3. Record the VFO frequency every 100 KHz from 0 to 500 (black scale). A data

sheet is provided in the DATA SHEET section with the data points and the spec frequencies. You may want to

make several copies of the data sheet.

If the actual frequency consistently falls above or below the spec frequency adjustment of trimmer C122 is

indicated. Move the dial to the black 500 index mark (be sure you are looking head on at the dial to eliminate

parallax error). Adjust C122 for exactly 4.351450 MHZ.

Rerun and record the 6 data points again. If at the Ø or the 500 index mark you are more than 1 KHz off,

tracking of C122 and L21 is required. The original manual spec at this point is 2 KHZ. But it is normally not

difficult to get it less than 500 Hz. So why not try. Set the tuning dial to the black 500 and adjust L21 for

4.35145 MHz. Tune the dial to the black Ø and adjust C122 for 4.851450 MHZ. You may have to repeat this

several times to get it correct. Under correcting or overcorrecting at one end or the other is sometimes required

to get it to fall in.

Rerun and record the data. If any of the mid points fall more than 2 KHz from spec knifing of C120 is indicated

(I use 1 KHz for my shop spec). Knifing should never be attempted on the SR-2000 unless you are very

skilled at knifing. C120 is fragile and can be destroyed very easily. If you have a uniform distribution of the

error you can split the difference by adjusting C122. That is move the end points half the max error in the

opposite direction of the error. Once again you may have to go back and forth adjusting C122 and L21 to

equalize the error at both ends.

This completes the oscillator test and adjustment process. Again let me stress that diligence in getting the

oscillators correct will pay max benefits in the end product.

REPAIR AND RESTORATION OF THE SR-2000

WDØGOF 3/7/20014

2. RECEIVER FAULT ISOLATION

2-1. EQUIPMENT REQUIRED.

HF RF signal generator capable of 0.5 microvolts to 300 millivolts and covering 1600 KHZ to 30 MHZ

Audio output meter (similar to General Radio 1840A). [See TECH NOTES 6-3 for substitute]

Scope 100 MHZ or better with 1:1 and 10:1 probes or switchable probe.

Audio oscillator with 600 ohm output Z

capable of from 0.7 millivolts to 30v peak to peak output.

2-2. STANDARD TEST CONDITIONS

For the RECEIVER FAULT ISOLATION tests the following preset conditions are required.

OPERATION REC

FUNCTION LSB

CAL OFF

CAL ADJ MID RANGE

MAIN TUNING 250 (BLACK SCALE)

BAND SELECTOR 7.0

PRESELECTOR 40

AF GAIN MAX

RF GAIN MAX

NOISE BLANKER OFF

METER RFO/S

RF LEVEL COUNTER CLOCKWISE

MIC GAIN COUNTER CLOCKWISE

RIT OFF

RIT CONTROL MID RANGE

LOAD & PLATE N/A

2-3. PROCEDURE OVERVIEW & PRESET CONDITIONS

This test is a standard progression from output to input of a receiver. It assumes the probability of multiple

faults. At any point in the procedure if a fault is detected it must be cleared before you can go the next step. The

signal levels were derived from years of testing. The levels are not absolute in that an individual receiver may

vary as much as 10%. Any deviation of more than that should be considered a fault. In the case where post

production modifications have been installed as much as 25% differences may occur.

AGC problems can be difficult to localize particularly if there are other faults in the system. So for the 13 step

FAULT ISOLATION procedure that follows we will disable the agc. Locate the junction of R32 (2.2meg) and

R33 (1 Meg). Place a clip lead from that junction to ground. Once the fault isolation is complete and the

receiver is working properly tests of the agc circuit will be performed. A 10:1 scope probe will be used to

inject signals. Some measurements will require a 1:1 scope probe and these measurements will be noted.

The signal levels on the chart are injected signal levels therefore, when using the 10:1 probe the source will

be set for 10 times the level stated in the chart. The first two audio signals are measured peak to peak using a

tee connector on the audio oscillator. One side of the tee connects directly to the scope the other to the 1:1

injection probe. The remaining signals are RMS values as set on the RF signal generator output meter. NOTE:

Section 4 contains individual ckt and sub-ckt fault isolation tests.

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