Hallicrafters Sr-400 cyclone ii User manual

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

REPAIR & RESTORATION

HALLICRAFTERS

SR-400 CYCLONE II

SR-400A CYCLONE III

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-400

WDØGOF 6/22/20014

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 does. This document applies only to the Cyclone II and Cyclone III. The first

question you might ask is “why did I not include the SR-400 Cyclone”? The first generation 400 had too many

things not quite correct. Mr. Orwin (Hallicrafters engineer) fixed those when he designed the Cyclone II. The

best advice I can offer to owners of the original SR-400 is to upgrade it to the Cyclone II level. A document for

upgrading a Cyclone to the Cyclone II is available. Contact me and I will send you the document. Just to clear

the air I am not a fan of the Cyclone III either. I use my Cyclone II. I turn on my Cyclone III once a month for 2

or 3 hours just to keep it dry.

This document takes a systematic approach to rehab. Unless otherwise noted all discussions apply to either the

Cyclone II or III. It is designed to be used in conjunction with the original equipment manual. In all discussions

the word manual refers to:

OPERATING AND

SERVICE INSTRUCTIONS

FOR

COMMUNICATIONS

TRANSCEIVER

MODEL SR-400(X)

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-400

WDØGOF 6/22/20014

TABLE OF CONTENTS

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

1. SR-400 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: ............................................................................... 7

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

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

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

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

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

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

1-5-4-3. VFO ALIGNMENT...................................................................................................................... 8

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

2-7-1. CYCLONE II TEST........................................................................................................................... 12

2-7-2. CYCLONE III TEST ......................................................................................................................... 12

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

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

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

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

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

3-4-1 TRANSMITTER POWER TEST ....................................................................................................... 14

3-5, TRANSMITTER FAULT ISOLATION ................................................................................................... 15

3-5-1, DRIVER CAPACITIVE PICKUP TOOL ......................................................................................... 15

3-5-2, LOW OR NO POWER ACROSS ALL BANDS .............................................................................. 16

3-5-3, NO OR LOW POWER ON A SINGLE BAND. ............................................................................... 16

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

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

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

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

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

4-7. V6 RX FAULT ISOLATION.................................................................................................................... 17

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. TECH NOTES .................................................................................................................................................. 19

5-1. BASIC TUNE UP...................................................................................................................................... 19

5-1-1. THE PROBLEM: ............................................................................................................................... 19

5-1-2. WHY IS THIS IMPORTANT?.......................................................................................................... 19

5-1-3. A SIMPLE SOLUTION..................................................................................................................... 19

5-1-4. SUMMATION: .................................................................................................................................. 19

5-1-5. MANUAL SECTION 5-4 MARK UP:............................................................................................... 20

5-2 PA NEUTRALIZATION ........................................................................................................................... 22

5-3. OPTIONAL 6 MEG IF ALIGNMENT ..................................................................................................... 23

5-x. ADDITIONAL TECHNICAL INFORMATION SOURCES:.................................................................. 23

6. DATA SHEETS................................................................................................................................................ 24

6-1. VFO FREQUENCY CORRECTION........................................................................................................ 24

6.2 PERFORMANCE DATA........................................................................................................................... 25

6-2-1. RECEIVER PERFORMANCE DATA.............................................................................................. 25

6-2-2. TRANSMITTER PERFORMANCE ................................................................................................. 26

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

1. SR-400 INITIAL INSPECTION AND TESTING.

SO YOU JUST GOT AN SR-400 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-400. 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 60 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.

1-2. RECAPPING;

There are only six capacitors that are considered must replace components. They are: C70 and C218, 5 uf/25v;

C46, 25 uf/25v; C147, 2 X 30 uf/350v; C240, 175 uf/25v and C244, 500 uf/6v. C240 and C244 are found only

in the SR-400A. 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 remove them and return the rig to the original

configuration. For valid circuit modifications see k9axn in section 5-3.

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

1-4. INITIAL POWER UP

Note: When bench testing the SR-400 set the antenna switch (S2) to SEPARATE. Connect the load and

wattmeter to ANTENNA (J1 or J2). Connect the signal generator to REC ONLY (J3). This will eliminate the

possibility of transmitting into the signal generator. It will also speed up the transition from RX to TX while

testing.

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 temporarily replace the 5 amp slo-

blow fuse with a 4 amp normal delay fuse. 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-400. 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-400 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, NOTCH

pressed in and fully counterclockwise. Preset the PRESELECTOR to the approximate position in the band you

will be operating, set the LOAD and PLATE tuning to the appropriate settings corresponding to the chart in the

original manual (the chart is located in section 5). Set the FUNCTION switch to either USB or LSB depending

upon which band you will be testing the default is LSB. Insure that a jumper plug in installed in J4 on the rear

of the radio. The jumper plug should have a jumper between pins 4 and 10.

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

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 ONLY. If it blows the

fuse you most likely have a short in the hi-voltage or the B+ locate the fault and repair before continuing. Now

let it sit there for 10 to 15 minutes. Locate R50, 2000 ohm, 10 watt resistor connected to V10. The voltage at

one end should 150vdc and 250 – 280vdc at the other if not; you have a fault in the wiring or the 150v regulator.

This fault must be cleared before you proceed. Otherwise the only thing we need to do at this time is rough set

the bias voltage. Some models of the PS-500 power supplies have a bias control on the rear of the chassis. If

yours has the bias control pot, proceed to Abelow. If it doesn’t, go to B.

A. On the underside of the Final tubes locate the grid side of R107 (100k). This is where we will measure the

bias voltage in the receive mode. Set your meter on the 200vdc range. Now adjust the bias adjust control on the

power supply for maximum negative voltage. Continue to step B.

B. Turn the power off; plug your meter into the red (+) and blue (-) test jacks on the power supply. Set the

meter on the 2vdc range. Set the function switch to LSB, Connect a mic and set the RF GAIN and MIC GAIN

to minimum. Turn the power back on. Let it warm up. Set the OPERATION switch to MOX. Key the mic.

Adjust the BIAS ADJ control on the front panel for 0.7 vdc on the test meter. If you cannot adjust it or it is very

high then you have a problem in the final PA or bias divider and this must be corrected before you proceed. If

all is well with the bias you are now ready to proceed to the CHECK AND ADJUSTMENT OF

OSCILLATORS section.

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

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.

1-5-1 TEST EQUIPMENT REQUIRED

Oscilloscope, 100MHz bandwidth and two probes, Frequency counter.

1-5-2. CARRIER OSCILLATOR:

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

Switch back and forth from USB to LSB to insure both oscillators start without any hesitation. In USB mode

adjust C139 for exactly 1652.800 KHz. Switch to LSB mode and adjust C136 for exactly 1650.000 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.

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. 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. With the four 10 meter xtals you are pretty much stuck with where ever

they are unless you have a bag of xtals to swap. For the 80, 40, 20 and 15 meter bands, each band has a loading

cap (C103, C102, C101 and C100 respectively). These loading caps can be swapped out to pull individual xtals

on to frequency. 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 use of the CAL ADJ and RIT CONTROL adjustments will be discussed later to compensate for

errors in the het osc.

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

1-5-4. VFO:

The VFO is comprised of V13, V4B and associated circuitry, the VFO correction circuitry and the RIT/CAL

circuitry.

From the manual:

Frequency Stability;

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-400 a more reasonable warm up time is 30 to 40 minutes.

1-5-4-1. RIT/CAL

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

corrections to the VFO 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 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 ccw and note the counter reading. Rotate the

CAL max cw and note the counter reading. The difference from ccw to cc rotation should be minimum 4 KHz;

most rigs will run approximately 6 KHz. Readjust the CAL pot for 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.

Connect the frequency counter to pin 3 of V4A. Set the function switch to LSB, 40 meter band and tune the

main tuning until the frequency counter reads 4.5530 MHz. Switch to USB and the frequency should drop 3000

Hz or to 4.5500 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. There are only 5 possibilities for this

fault. 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 -20 to -28 vdc. If the offset switching voltage is

correct and the offset is un-settable then R85 is possible but least likely. CR12, C126 and/or C127 are most

likely the cause. If the offset voltage is incorrect the most likely cause is the FUNCTION switch S3A. This fault

must be cleared before you proceed.

1-5-4-3. VFO ALIGNMENT

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. SUBSYSTEM

TROUBLESHOOTING AND TESTING for corrective action.

REPAIR AND RESTORATION OF THE SR-400

WDØGOF 6/22/20014

VFO ALIGNMENT CONTINUED:

Proceed to section 8-8-A of the original manual and perform the mechanical indexing adjustments before you

proceed.

When the mechanical indexing adjustments have been completed 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 4.35 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. Adjust the tuning dial to the black 500 and adjust L21 for

4.350 MHz. Adjust the dial to the black Ø and adjust C122 for 4.850 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 C32A is indicated

(I use 1 KHz for my shop spec). Knifing should never be attempted on the SR-400 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.

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-400

WDØGOF 6/22/20014

2. RECEIVER FAULT ISOLATION

YOU MUST HAVE ALL THE OSCILLATORS TESTED AND ALIGNED BEFORE PROCEEDING. SEE

SECTION 1-5.

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).

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 0.4 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)

CW OFF

NOTCH CCW

BAND SELECTOR 7.0

PRESELECTOR 40

AF GAIN MAX

RF GAIN MAX

NOISE BLANKER OFF

METER RFO/S

RF LEVEL CCW

MIC GAIN CCW

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. 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 R42 and R123. 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.

This manual suits for next models

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