Modifications for the Kenwood TS-520

These mods where written bt Greg Weremey N1JFE
Electronic Service Pros.
TS-520, TS-820 CW filter select control

In the TS-520SE, the heater switch has been replaced with a CW WIDE/NARROW select switch. For those operators who desire this type feture for their transceiver, the following information may be considered as a guideline.

TS-520S series transceivers
  1. A minature SPDT switch may be installed at the operators preference, on the rear side, or bottom panel. Use this to switch the CW or SSB filters by wiring the BROWN lead, which normally is transferred to the CW terminal on the IF unit, between the SSB filter, for WIDE , and CW for NARROW.
  2. A Traditional solution has been to use the FIX CH switch, position 3 and 4 for filter switching. This may be donw by completely rewireing the switch, or by leaving the switch wiring and the filter wiring as for normal operation, and bridging the following terminals:

         A.   FIX CH C terminal to IF SSB Terminal
         B.   FIX CH 4 terminal to IF CW terminal
              Placing the FIX CH switch to 4 will operate the SSB filter 
                      in CW mode.

TS-820S Series Transceivers
  1. Similar to the TS-520 series, a miniature SPDT toggle switch may be installed at the operators preference a the rear or on the obttom cover.
  2. The FIX CH switch, or Digital Hold switch may be rewired to control the CW wide/narrow function

On the MODE switch, S6-1, the SSB filter control is GREEN, and the CW filter control line is GREY. Break the GREY line and connect it from the MODE switch to the SPDT common terminal. Connect the GREY line to the IF unit ot one terminal, and bridge tht GREEN SSB line to the other Switch terminal.
DG-5 Standard Service Procedure

(Supplement to the DG-5 Service Manual)


A majority of DG-1 failures are caused by nothing more than an intermittent opening of a plated-through hole connecting top and bottom foil paths of the PC board.

Before any component level service is attempted, it is advisable to eliminate the possibility of an intermittent connection causing or complicating counter failure.

  1. Disconnect all cables.
  2. Remove cabinet: 2 screws at the rear, 2 screws with star washers on the bottom.
  3. Disassemble display from chassis; 4 countersunk screws on the side rals.
  4. The display unit has 2 through holes without leads, and the Counter main board has 82 through holes without leads passing through them. Ideal service would be to first remove all solder from these holdes using vacuum desoldering devices, or WIK-IT braid. Then, pass a length of #24 tinned bare wire into each clean through hole, solder, and clip flush. For 10 holes listed under IC's solder sparingly so as not to create a solder bridge under the component. For the remaining 72 holes, inspect each "pinned" connection from both sides to ensure (1) no bridge and (2) a good solder joint.
  5. Wash the display to counter Board PC board connectors (male and female) with FRESH trichlorethelyne. Heat dry and inspect for flux residue. Spray the connectorrs with silicone.
  6. Similarly, clean and coat the rear panel RCA jacks as in step 5.
  7. Reassemble, reversing steps 3,2,1.
How to solder on the DG-5 pc board.
  1. Use a low power pencil iron of 35 watts or less.
  2. Use rosin core solder, small diameter.
  3. Do Not create solder bridges or splotches.
  4. Do Not overheat or otherwise lift the foil from the board.
  5. Wash excess flux away with FRESH trichlor, and a small flux brush.
Neatness counts - it's your radio.

Through Hole Accounting

Display unit - 2
Counter unit -82
Total -84

A.   Under; IC2,4,13,20-25,34,  1 each
     Total 10

B.   Adjacent or between; IC3,13-14,15-16,22-23 1 1 each
                          IC1-2,6,18              2 each
                          IC12                    3 each
     Total 13

C.   Located between rows: IC13-18,20-25  - 5
                           20-25, 26-31   - 10
                           IC26-31, 32-37 - 15
                           IC32-37, 38-39 - 25
     Total 55

D.   At rear panel: FS7805 regulator - 1
                    2SD235 transistor- 3
     Total 4

E.   Display unit - 2
Additional Ponts

  1. R126 &129 are power resistors located at the left rear corner of the PCB. Remove the tubing from their outside legs and resolder each lead to the top foil path. Specific symptom for this failure is no display, and no decimals.

  2. For counters which roll, random count, or inject hash noise back into the TS-520/520S especially when hot, install an additional .1uF @ 12v bypass cap across the FS7805 regulator on the foil side of the PCB from the center ground lead to the outside leg, across C89.

  3. For complaints of hum or digital noise from the DG-5 back into the TS- 520/s both during RX and TX, tighten the mounting screws which supply ground to the Carrier unit X50-0009-01 in the transceiver.
Please annotate your service manual.
Service notes on TS-520

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 21 (21-10-1977)


  1. No switching of final relay: Bad Q8 on X54-0001-00 2SA562Y.
  2. No drive: C3 100pf in final box is cold soldered.
  3. Low output: Check the plate load cap for touching plates.
  4. 3.5 MHz low output: Replace burned 47pf 3KV at load wafer.
  5. No TX: Final choke burned out in final VOX L8.
  6. No RX or TX: Bad common amp. Q1 3SK35GR in IF unit X48-1060-00.
  7. No ACC: No plate current Q2 3SK41 If unit X48-1060-00.
  8. No TX relay: Q8 2SA562Y on VOX unit. Also R18 1K resistor relay control.
  9. No TX or RX: Check 9 volt terminal on FIX AVR (X43-1100-00) is loose.
  10. No CW TX: Bad 9 volt regulator. Check D3 WZ061 on X43-1100-00.
  11. No TX: Solder touch between TIF and key terminal on X44-1080-00.
  12. No drive to TX: Check RL1 on GEN unit, small reed relay (X52-0010- 01).
  13. No ALC meter action on 10 meters: This is normal for TS-520.
  14. CW chirp: Q4 2SA606L on Fix channel AVR X43-1100-00.
  15. ALC meter to maximum when TX: RFI terminal at X44-1080-00 is not soldered.
  16. No TX output: 82pf 3KV in final is burned.
  17. No TX output: Q3 on RF unit 3SK41 X44-1080-00.
  18. No bias: 10 ohm cathode resistors burned in final VOX.
  19. No drive or TX output: R70-71 RF unit, R5 Rectifier unit.
  20. No VOX: Q8 in VOX unit X54-0001-00.
  21. No TX: 12BY7 is bad. Shorts and burns out. R71 and 70.
  22. No carrier output: Q1 on Carrier X50-0009-01.
  23. No drive - no screen voltage: R5 470 ohm open on rectifier X43-1090- 00.
  24. No drive - no ALC: Q2 3SK35Y IF unit. Q3 3SK41L RF unit.
  25. No RF output: C13 0.04uf at pin 1 of S2001A is bad.
  26. Low mic gain: Q1 2SC1000 on Gen unit.
  27. No TX: Misconnection of brown wire after installation of CW filter.
  1. Low Sensitivity: Touching RLT and 9V at function switch.
  2. Receiver sensitivity: No -6v at AVR: Q8 2SC735 on X43-1100-00 is bad.
  3. Frequency Shift: Bad carreir Xtal 3395 on carrier unit.
  4. VFO drift: C6 22pf, VFO unit.
  5. No receive: Bad Q4, 3rd IF amp 3SK35GR on X48-1060-00.
  6. Receiver sensitivity and bias current jump, -6v unstable: T1 oscillator transformer for -6v is bad on X43-1100-00.
  7. Erratic AGC action: C11 100uf 16Von X431100-00. Fix channel AVR is bad.
  8. Frequency shift when warmed up: Q1 in VFO 3SK22GR.
  9. No RX or TX: If unit C59 touch to T12 IF transformer.
  10. Receiver noise: Q5 3SK35Y X44-1080-00.
  11. Receiver sensitivity down: NBI terminal is pulled loose. Receiver at IF board.
  12. No S meter reading and RF gain CCW. No meter deflection: Q3 on IF unit. Q5 on RF unit.
  13. VFO frequency jumped: There is loose tension inside VFO.
  14. VFO frequency shift: Cold solder of VFO output lead to VFO output socket.
  15. Blows fuse when first on: Check Q1 and Q2 DC-DC converter transistor. One is possibly shorted.
  16. Noise blanker inoperative: R6 4.7K resistor is broken at Q2 on X54- 1080-10.
  17. Loud audio squeal: Q4 3SB473 on X49-0008-01 shorted.
  18. Low receiver sensitivity: Diode D4 1S1587 on RF unit.
  19. VFO intermittant: Wire to L1 in VFO is not soldered.
  20. No receive: Q4 3SK35Y, Q5 3SK35GR on RF unit.
  21. No receive: Q9 3SK35GR on IF unit.
  22. Hash noise in receiver: Q3 on RF unit 3SK41.
  23. Blows fuse: C31 power supply is shorted, 100uf 500v. Also check associated diode D3, D4.
  24. No RX on all bands: WWV switch is broken or a wire is loose or not soldered.
  25. Receiver sensitivity: Q5 on RF amp 3SK35Y.
  26. Receiver sensitivity: NBO terminal on X48-1060-00 is loose.
  27. Low audio: Check for purple wire touch to ground at 12 pin connector in rear panel.

TS-520S -6v Supply Failure

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 43 (9-8-1979)

When troubleshooting a TS-520S, check all power supply voltages, including the -6v DC supply. Symptoms such as dead, blown 2A DC fuse and now dead, low RX, no TX, or similar may occur after switching between 80 and 40M.

Cause of failure may be traced to an intermittent shorting between the 14v dc and -6 dc supplies as the band switch is rotated between 40 and 80 meters. This will weaken or destroy D8, a 6v zener on the FIX CH AVR unit.
To prevent repeat failures, break the White lead and install a 22 K ohm 1/2 watt resistor at the bandswitch S5-6, between the -6v supply line and switch terminal. An of course replace D8 on the FIX CH AVR unit, X43-1100-00.

New Part: 22 k ohm 1/2 W carbon resistor

Please notate your Service Manual.

TS-520/520S CW Frequency Shift

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 46 (6-8-1979)

Reports of intermittent frequency shift during CW operation, on the order of a few hundred cycles, may be traced directly to the Carrier Unit.

On the Carrier unit X50-0009-01, install a ground lead of #18 tinned wire or similar, between the cases of T1 transformer and X3, the LSB XTAL.
Recheck frequencies after installing this ground lead.

Please notate your service manual.
TS-520 Increased sensitivity, Better audio and Amplitude Modulation

1. Increased sensitivity.

On the RF board, Q5 is the RF RX amp. Notice that G2 is tied to the AGC line.
Bend G2 up from the socket, solder a 10k resistor to it and connect the other end of the resistor to the 9v line on the front of the board. This will allow the FET to run wide open, and you will have a better S/N ratio. You will gain about two S units in signal and you may want to adjust your S meter to compensate. I did this mod almost a year ago and have had no problems even with signals that were 40db over!

2. Better audio.

A few capacitors should be changed to accept a wider audio bandwidth.
These will only increase the BASS response and not the treble as it is limited by the IF filter. Change the following on the generator board;

C3 (1F) to 10F
C4 (4.7F) to 47F
C5 (1F) to 4.7F
C8 (.047F) to 4.7F
C9 (1F) to 10F
C11 (4.7F) to 47F
C10 (10F) to 22F

This will make the Tx audio flat. Make sure that the Local Oscilator is adjusted correctly or else you will have the bass attenuated by the IF SSB filter.

I also changed the caps on the AF board.

C14 (.47F) to 4.7F
C13 (.047F) to .47F
C1 (1F) to 4.7F

You will also want to use a good speaker. I have an old speaker box that got gutted.
I put in a 6x9 coaxial car speaker and it sounds great! Since the audio is limited to 4Khz anyway, don't go bonkers with tweeters. You may want to play with a few caps inside the speaker to roll off some of the very highs which will only be transistor noise anyway.

Along with changing the caps for flat audio, I installed two jacks for audio on the back of the 520. These are RCA female jacks that are used to connect to an equalizer.
Unwrap the wire on the generator board marked MA O. This is the output of the Microphone Amplifier. Connect some microphone coax from this terminal to your RCA socket on the back of the rig marked output. Remember to ground both ends of the cable so you won't have hum/RF problems. Now connect the other RCA socket via mic cable to the wire that you unwrapped from the MA O post.
Make up a jumper cable for those times you don't want to use the EQ.
I recommend an old Radio Shack 5 band EQ. I have no RF problems at all and I run 500w PEP with the amplifier sitting next to the Kenwood. Stay awayf from EQ's that use all IC's. I find regular transistors are better for handling RF.

3. Amplitude Modulation

This radio can talk AM in a pinch. You will be limited to SSB reception though. That's OK if you don't mind playing with the RIT to get rid of the beat tones.
I decided it was degrading the specs when I put in a regular AM detector so I pulled it out. Here is how you make it talk.
Get a DPDT relay (12v) and connect it inline with the fixed channel selector switch, so that when you select crystal 4 the relay energizes.
Now lets take the relay in two sections. The first is connecting the ouptut of the mic amp into a matching transformer via this relay. You want it connected so that the MA O is on the wiper and the relay NC1 is connected to the Balanced Modulator. Connect the other relay terminal NO1 to the low impedance side of the transformer. Connect the other lead of this winding to ground. So when you select fix channel 4, the relay energizes, and disconnects the mic from the balanced modulator and connectes it through the transformer to ground.

Ok now the second part of the AM mod.
Take the HIGH impedance winding of the transformer and connect one leg to ground. Take the other leg and connect it to a 47uF cap.(neg lead) Connect the positive side of the cap to an 820 ohm resistor.
Connect the resistor to the 9v terminal (on the RF board or most any other board) Connect the junction of the resistor/capacitor to the NO2 terminal of the relay.
Connect the wiper of the relay to S on Q3 on the RF board. I found R17 to have its exposed wire connected to S on Q3. Simply scratch the paint away on R17 and solder to the resistor.

Since this design modulates after the IF, you will have full fidelity and bandwidth of your audio. If you use an EQ, don't be excessive with the highs or you will have enemys from the splash you create. Also, there is no limiter here. If you have access to one, install it in the EQ loop.

Have fun on 80M!!
Kenwood TS-520S for QRP

The TS-520S can be operated QRP down to a few milliwatts with simple modification. Apply negative voltage on the ALC pin of the ancillary socket.

Modification consists of a 220K Ohm pot and a 9V battery.

Kenwood TS-520S for QRP

Maximum of 34 microamps drawn so battery should last a long time.

Bob Wilder, W4RHW
TS-520S MARS Mod for 4.0-4.6MHz

After trying for several months, I have finally come across a modification for the Kenwood TS-520S that will allow this rig to be operated in the 4.0 to 4.6 MHz range in MARS operation. The modification came originally from Jim, WB4WBL (AF MARS AFA2FN) in Tampa, Florida.

The modification consists of moving the 12.395 MHz crystal from the Band Switch to a small DPDT toggle switch mounted on the bottom of the case. An additional 12.895 MHz crystal is added to the switch for the new range needed.

This new crystal can be obtained from International Crystal Manufacturing Company. The crystal is 20pf, wire lead type.

A short piece of RG-174 coax is used to connect the new switch with its attached crystals back to the Band Switch position from which the 12.395 MHz crystal was moved from.

Once the crystals are in place, the 3.5 MHz coils are retuned to a new center frequency of 4.100 MHz. The normal tuning of all the 3.5 MHz band coils are tuned to 3.750 MHz.

The new switch is mounted between the front of the radio and the hetrodyne oscillator board.

Jim says that he still has a TS-520 with the mod in it and it still works great after almost 20 years. He has modified several 520's over the years they all worked great.

73 Bob Wilder, W4RHW
TS-520 Novice Operation (75 watts)

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 2 (10-01-1975)
HV UNIT (X43-1100-00)

  1. Cut wire (See figure 1) .... red color.
  2. Insert 33kohm resistor in series between red wire and pin 210.
  3. readjust bias current to 60mA.

Figure 1 (Bottom side)

AM Broadcarst interference in TS-520

Author: Trio-Kenwood Communication, inc.

Service bulletin no. 4 (June 3 1975)

We have found a few instances of customers who live near an AM broadcast station hearing that station on the 3.5 MHz band of theire TS-520. Shown below is a filter that may be installed if this occurs.
1300 KHz22uH680pF
1000 KHz200uH220pF
700 KHz100uH470pF

A Suggested located for the filter is on a small terminal strip that is then mounted on a mounting screw of the RF unit. This screw is located at the front corner next to the VFO. The cable between S-9 (WWV switch) and terminal NAT of the RF unit is removed from terminal NAT and connected to one side of the filter. A short piece of RG-174/U is then connected from the other side of the filter to the terminal NAT. This hould prevent the AM broadcast interference.
TS-520/520S BS-5 Sweep interference

Author: Trio-Kenwood Communication, inc.

Service Bulletin no. 52 (10-8-1979)

BS-5 users may report ignition-like interference on 80 & 40 M from their SM-220 with BS-5. noise will be heard between 3850-3870 KHz, and 7245-7260 KHz any time the scope is on.

The sweep signal mixes with the IF (carrier) frequency. This derived signal, or its second harmonic will usually be less than an S1 signal, unless the coax ground to the scope is opened, in which case S9 may be indicated.

On the SM-220 PCB X65-1240-00, change the BS-5 +11V DC supply point:

  1. Cut the foil path between connector P110 pin 6 and Connector P103 pin 2.
  2. Install a 1S1555 diode between Connector P110 pin 6 and Connector P103 pin 1.
New Part: 1S1555 V11-0076-05

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