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REPAIR AND RESTORATION OF THE SR-2000

 

19 

WDØGOF 3/7/20014 

 

5 TX SUBSYSTEM TROUBLESHOOTING AND TESTING 

 

5.1 CARRIER BALANCE 

The BALANCED MODULATOR is a very simple ckt but it is also a very difficult ckt to pinpoint faults in. 
Fortunately there are very few components to “guess at”. The variable cap C192 is the highest failure rate 
component in the ckt. Second is the diodes CR19 and CR20. These two diodes “should be a matched pair”. 
Great quantities of these diodes are still available and can be found for around $0.50 ea. Matched pairs go for 
around $30.00 a set. I purchase 10 to 15 at a time and match them myself. If you do not have a curve tracer a 
simple matching circuit can be made.

 

 

5.1.1 CW CARRIER INJECTION 

In CW mode S3A FRONT pin 10 supplies a gnd via two 10K resisters to the tie-point of CR19 and CR20. This 
unbalances the mixer. This gnd cuts off CR20 and biases CR19 full on feeding the carrier osc signal directly to 
V6 in CW and TUNE modes. A problem on this line could cause normal CW or TUNE modes but out of spec 
carrier rejection in SSB modes. With the radio turned off measure the resistance to gnd from C20 anode. It 
should be 20k in CW or TUNE modes and greater that 150K in LSB and USB modes. 

5.2 HET OSC LOW OR NO SIGNAL IN TX MODE 

Re-run the tests in section 1-5-3. If the results of the test rerun are incorrect then there is a fault in V12 or its 
associated circuitry. If the rerun tests are good then pull V4 and check the following:  

 

CR11 is the switch that routes the het signal to the 2

nd

 TX mixer V11A in transmit mode. For the following tests 

turn the RF and MIC gain controls fully counter clockwise and the band switch on the 80 meter band. There is 
RF present in the switching circuits so you will have to 

pull V12

 to get accurate dc measurements. In receive 

mode the anode of CR11should be 5.9 vdc and the cathode should be between 14.8 and 16.5 vdc. If there is no 
or erratic voltage on the cathode of CR11 then L20 is most likely open.  

 

When you key the transmitter (

with V12 still pulled

) the cathode should drop to less than 2 vdc. The anode 

should be about 0.3 vdc higher than the cathode. If these voltages measurements are correct then the diode and 
the switching are good. 
1, If when in the transmit mode the drop across CR11 is more than 0.4 vdc the diode is bad.  
2, If the cathode voltage in the receive mode is not above 14.8 vdc then replace V15.  
3, If in transmit mode the voltage on the cathode of CR11 does not drop below 2 vdc then there is a problem in 
the grid bias RX/TX switching of V15. 

Summary of Contents for SR-2000

Page 1: ...RE 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...

Page 2: ... 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 h...

Page 3: ...UIPMENT 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 ...

Page 4: ... CARRIER BALANCE 19 5 2 HET OSC LOW OR NO SIGNAL IN TX MODE 19 5 3 TX 6 5 MHz LOW INJECTION TO 2ND 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 SUBSTITU...

Page 5: ...rade 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 l...

Page 6: ...TS 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 suppl...

Page 7: ... 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 ...

Page 8: ...t 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 15o 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...

Page 9: ...ual 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 Th...

Page 10: ...els 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 ...

Page 11: ... 7 for details 7 V4A Pin 2 6 250 MHz 40 uv wt Problem is most likely V4A or associated circuitry See section 4 8 for details 8 V3A Pin 2 6 250 MHz 20 uv wt Problem is most likely V3 A or B or associated circuitry See section 4 9 for details 9 V2A Pin 9 7 250 MHz 40 uv wt Problem is most likely V2A or associated circuitry See section 4 10 for details 10 Junction C15 C20 7 250 MHz 25 uv wt Problem i...

Page 12: ... scope in DC mode using a 1 1 probe to the junction of R2 and C12 in the grid ckt of V1 Slowly turn the AGC THRESHOLD pot counter clockwise until the trace on the scope just starts to move in the negative direction If the adjustment is successful re run the tests in 2 5 1 if it fails either test there is a fault in the agc amp NOTE The procedure in the manual 8 4 D should not be used The manual pr...

Page 13: ...Y POINT the transmitter testing process assumes that the receiver has been tested and is operating to specs It is of the utmost importance that the receiver is operating to specifications ALL of the transmitter testing to follow is based on this assumption 3 1 TEST EQUIPMENT REQUIRED 1500 watt wattmeter dummy load 100 MHz scope Frequency counter Audio oscillator with 600 ohm output 600 ohm dynamic...

Page 14: ...to the key jack on the rear of the transceiver Then you can set the FUNCTION switch to the CW position and leave it there and press the key when you want drive This saves wear and tear on the FUNCTION switch and reduces the chances of leaving the transmitter keyed to long For the remainder of the tests when you are instructed to key the transmitter you will either switch the FUNCTION switch from L...

Page 15: ... Any misstep from this point on could cost you a set of 1600 final tubes If you are unable to get normal power out you have a fault in the PA sub circuits VOLTAGES IN THE PA SUB CIRCUITS ARE LETHAL IF YOU ARE NOT EXPERIENCED IN HIGH VOLTAGE RF TROUBLESHOOTING IT IS TIME TO FIND A MENTOR Go to section 5 5 for PA fault isolation NOTE 18vpp on any band will drive Blue Burle tubes to saturation and th...

Page 16: ...5 2 Het osc low or no signal This fault must be cleared before proceeding to the next section Reinstall V4 when fault is cleared If all is well with the het osc injection levels go to the next step 3 4 4 2 6 5 MHz I F INJECTION With V4 reinstalled pull V12 Set the VFO to 250 on the black dial scale any band With the scope connected to pin 2 of V11 key the transmitter You should have 3 0vpp Will va...

Page 17: ...RX FAULT ISOLATION This circuit is pretty straight forward Check the voltages and resistances against the charts in the manual If they are correct then the options are few V9 C78 C77 or R48 are the most likely cause of the fault 4 4 V9A RX FAULT ISOLATION Power up and set the standard test conditions In LSB mode you should have a 6 vpp signal injection from the carrier oscillator on pin 8 of V9A M...

Page 18: ...he voltage on the socket pin 6 it should be 260 vdc If there is no 260 vdc then suspect T2 C42 or R23 With V3 pulled inject 6 25 MHz at 150uv into V3 socket pin 6 Tune the main tuning to approximately 250 on the black scale and peek the audio output If you do not get watt audio out then suspect C42 C44 or T2 If the proceeding checks are good there is a bias problem or V3 is bad If V3 is known to b...

Page 19: ...odes and greater that 150K in LSB and USB modes 5 2 HET OSC LOW OR NO SIGNAL IN TX MODE Re run the tests in section 1 5 3 If the results of the test rerun are incorrect then there is a fault in V12 or its associated circuitry If the rerun tests are good then pull V4 and check the following CR11 is the switch that routes the het signal to the 2nd TX mixer V11A in transmit mode For the following tes...

Page 20: ...its Go to section 3 4 2 in this document and run the driver tests 5 3 TX 6 5 MHz LOW INJECTION TO 2ND MIXER Once again the prerequisite is that the receiver has been debugged and is working at or near spec If the receiver is working properly and the 6 5 IF injection is low then C97 or the wire to C97 is the most likely cause 5 4 TX DRIVER FAULT Verify on all bands that the proper drive signal is p...

Page 21: ...check the bias switching You will not need to turn on the high voltage for this test Set up the standard conditions as per paragraph 2 2 of this document Connect a dummy load to the antenna connection of the radio In the following test you may see a slight difference in the voltages you measure The BIAS 90v and the FINAL BIAS 20v will vary slightly from one power supply to another The actual value...

Page 22: ... tuning up be careful not to move the preselector load or plate controls throughout the rest of this process Power down 1 Disconnect the plate and screen voltage by disconnecting J5 2 Connect the transmitter output to the scope or RF voltmeter An RF sampling T should be used between the TX output and dummy load to maintain a 50 ohm load on the TX output 3 Turn on the rig and let it heat up for at ...

Page 23: ... speaker If you use the audio power meter or the substitute in the figure below you do not have to listen to the constant tone while testing the rig My repair bench has a plug wired to a switch so I can select a speaker or the audio power meter This speeds up tuning and measurement considerably Power Voltage rms 2 Resistance Peak to Peak voltage X 0 3535 rms watt across 3 3 ohms 1 2845 v rms or 3 ...

Page 24: ...s an open to all site When you get to the site scroll down the left side to Technical Info and pick a category I do not know what the total membership to the reflector is but any post to hallicrafters mailman qth net will get almost immediate results https groups yahoo com neo groups HallicraftersRadios info This is a member only site It is free to join and I strongly recommend joining if you are ...

Page 25: ...TION OF THE SR 2000 25 WDØGOF 3 7 20014 7 DATA SHEETS 7 1 VFO FREQUENCY CORRECTION BLACK DIAL SPEC MHz TEST 1 TEST 2 TEST 3 TEST 4 TEST 5 TEST 6 0 4 851450 100 4 751450 200 4 651450 300 4 551450 400 4 451450 500 4 351450 ...

Page 26: ... 1 10 std 10 opt 2 10 opt 3 Tests performed only if options are installed Overall Sensitivity S N N A 1 0uv signal at the antenna terminal will produce a minimum 20db s n n BAND TEST FREQ SIGNAL LEVEL S N N MEASURED 80 40 20 15 10 opt 1 10 std 10 opt 2 10 opt 3 Tests performed only if options are installed AGC Figure of merit With a signal at the antenna terminal from 1uv to 60db no more than a 10...

Page 27: ...Mic gain set at max clockwise FREQ MIN SPEC low power PEP LOW MIN SPEC High power PEP HIGH Mic input level 5mv max 3 8mhz 500 watts 950 watts 7 3mhz 450 watts 850 watts 14 3mhz 450 watts 850 watts 21 3mhz 450 watts 850 watts 28 8mhz 400 watts 750 watts Avg RF power output with 1KHZ 5mv at mic input jack measured with Bird or equivalent CW power output with RF level set just to saturation level FRE...

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