TS-520 Transmit Problem

Discussion in '"Boat Anchor" & Classic Equipment' started by KE0EP, Jul 6, 2019.

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  1. KE0EP

    KE0EP XML Subscriber QRZ Page

    Just got a 520 and need help tracking down some trouble. No carrier in TUNE or CW modes but getting output in sideband.

    How should I start hunting down the cause?

  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    I assume you've tried turning up the Gain control which impacts drive level in Tune and CW modes but not in SSB mode.

    How did you tune the rig in SSB mode if you have no drive or output power in Tune or CW modes? Did you peak the preselector then dip the plate current and adjust loading all while whistling into the mic or something?

    I'd probably start by monitoring with a second receiver tuned to the operating frequency, do you hear a signal when you key the transmitter in Tune mode with the Carrier setting all the way up and does that sound audibly peak when you adjust the preselector? That would validate that the rig is actually generating a carrier signal in Tune mode even if it's not strong enough to produce an ALC meter reading per the tune up procedure.

    A related question would be whether you see normal ALC meter movement in SSB mode. IOW, you could have a weak driver tube that does not provide enough drive to get an ALC meter reading but still be generating carrier or your rig may not be generating carrier at all in Tune and CW modes. A properly adjusted ALC meter doesn't start to deflect until you've reached very near full drive power into the finals so low drive can show up as no ALC meter movement even when there is some carrier at a lower level.

    There's a resistive divider that lowers the screen voltage when in Tune mode to reduce the output power level. I've seen these fail in a couple of Kenwood hybrids and when they do you get no power in Tune mode. That doesn't explain lack of power in CW mode but it's a common enough failure that it's worth checking. The resistors are R5 and R6 on the HV unit and divide down the 210V line when in Tune mode.
  3. W5RKL

    W5RKL Ham Member QRZ Page

    Sounds like the CW 3395.0Khz CAR UNIT crystal may not be oscillating.

    You can check this by measuring the CAR UNIT RF output signal in TUNE
    or CW modes by connecting a frequency counter to the CAR UNIT "OUT"
    terminal. The counter should display approximately 3395.0Khz in TUNE or
    CW mode. A receiver tuned to +/- 3395.0Khz can also be used instead of a frequency

    The CAR UNIT board is mounted below the chassis next to the AF UNIT board.
    You can see the location of the PC boards in the TS-520S operator's manual. If
    you don't have that manual you can download it from my website by clicking the
    link below.


    Once the manual downloads, go to Bottom View FIGURE 39 in the manual.

    I also have the TS-520S service manual on my website. Click the link below to
    download the service manual


    If the CAR UNIT is producing a 3395.0Khz output signal then check, as one response
    has stated, the HV Unit R5 and R6 resistors, each are 56K 1/2 watt.

    Mike W5RKL
    Last edited: Jul 6, 2019
    WQ4G and KE0EP like this.
  4. KE0EP

    KE0EP XML Subscriber QRZ Page

    Yes, GAIN control adjusted.

    There's enough noise being generated during SSB transmit to tune using external receiver. Full power out in SSB.

    When set to TUNE or CW, there's an initial "pop" (perhaps from a relay?) audible on external receiver, then power quickly drops off.

    ALC meter deflection is normal in SSB.
  5. KE0EP

    KE0EP XML Subscriber QRZ Page

    Your manuals are nice and clear, Mike. Do you have them for the 520? There's no CAR OUT on the 520, just on the 520s.
  6. KE0EP

    KE0EP XML Subscriber QRZ Page

    There's a 3395.0 kHz signal present on the OUT pin of the CAR board in all modes.
  7. KE0EP

    KE0EP XML Subscriber QRZ Page

    R5 and R6 on HV unit appear to be good. Tested in-circuit: fluctuate from about 30k to 42k over a period of about 10 seconds. I'm assuming that's because of caps charging.
    Last edited: Jul 7, 2019
  8. KE0EP

    KE0EP XML Subscriber QRZ Page

    I'm going to check the relay on the GENERATOR board.
  9. KE0EP

    KE0EP XML Subscriber QRZ Page

    Carrier signal is present at the input to RL-1 but does not appear at the output terminal when relay is energized.
  10. W5RKL

    W5RKL Ham Member QRZ Page

    Yes, click the link below for the Operator and Service manuals for the TS-520.

    TS-520 Operators Manual

    TS-520 Service Manual

    There's no way any transmit Mode will work if there's no CAR UNIT signal at the output of
    Generator Unit board's RL1 in transmit (RL1 on the Generator Unit board is energized).
    The Generator Unit board's RL1 relay is the signal path for ALL CAR UNIT signals to
    pass through to the BM in transmit. The output of RL1 connects directly to the BM (Balance
    Modulator) through CAR NULL pot VR2 on the Generator Unit board. RL1 on the Generator
    Unit board is a simple SPST N.O. relay. Recheck your measurements for the CAR UNIT
    signal on the Generator Unit board. The output of the Generator Unit board is at its "GEN"
    terminal. That terminal connects through a piece of RG174 coax to the IF Unit board's
    "GEN" terminal so you should see the CAR UNIT signal at both "GEN" terminals.

    You also should not have 3395.0Khz output frequency from the CAR Unit board in ALL modes!

    The CAR UNIT output frequency in TUNE and CW modes is 3395.0Khz.

    The CAR UNIT output frequency in LSB should be 3393.5Khz and in USB 3396.5Khz.

    Mike W5RKL

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