TS-130S Receive Behavior (Intermittent Desense?)

Discussion in 'General Technical Questions and Answers' started by KF8KI, Jun 28, 2020.

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  1. KF8KI

    KF8KI Ham Member QRZ Page

    Morning all. I hope your Field Day is going well. I have a Kenwood TS-130s that I've had for years. Easily 20 or more. I don't use it a lot, but it's performed well over the time I've had it.

    I went for a while without being on HF, so she sat unused. In the last 6 months or so, I've become active on HF again and so the dust has been blown off of the radio.

    I've noticed an anomaly in her receive behavior since I started using her again. It was not there previously. I don't know if it's just that the bands are that wonky, or if I really have a receive problem. I'd like a second opinion before I open the case.

    Generally, in a intermittent fashion, the radio seems to suffer from a desensitization of the receiver. It's almost as if a protective receive attenuator is kicking in and out when it shouldn't be. It manifests as notably weakened receive signals. One minute some operator is S9 plus. Another, the same operator is barely coming out of the mud and I have to turn up the volume to hear him.

    Transmit power does not seem to be affected.

    It happens on occasion after transmit, but not always. There's also no rhyme or reason to when it comes and goes. I originally thought it was perhaps a response to bad SWR on transmit, but I've measured, swapped and changed everything from the transmitter on to see if I can reliably reproduce it, and I can't. This is making me wonder if it's just the bands that are that weird.

    One thing I have noticed though, is often if the receive is attenuated, starting to disconnect the antenna connector will often restore the receive level. This is what makes me wonder if it's the radio.

    A quick flip over to CW and transmit to tune the antenna will sometimes correct the problem as well. Not always though.

    Thoughts? I'm not sure if the TS-130s has automated receiver protection or not. There is a switch controlled RF attenuator. It seems to work as I'd expect, but switching it off and on doesn't seem to affect the problem.

    In absence of a better idea, I plan to see if I can find a service manual for the radio and investigate to see if there's an automatic attenuator which could be malfunctioning. Failing that, I thought I might just pull the covers and see what I see. It's well within my technical capabilities to fix anything that might be wrong with the radio. I guess I'm just trying to avoid pulling the cover without a better theory on what might be wrong.

    Thoughts?

    Thanks!
    ~Steve, KF8KI
     
  2. K7JEM

    K7JEM Ham Member QRZ Page

    Sounds like it could be dirty relay contacts on the rf switching relay. Years ago I had a similar problem with a TS-430. I could pulse the PTT and usually clear the problem.
     
    WQ4G, KA0HCP and KF8KI like this.
  3. KF8KI

    KF8KI Ham Member QRZ Page

    So is that the way you continued to solve the problem, or did you actually then try to clean the relay somehow?
     
  4. K7JEM

    K7JEM Ham Member QRZ Page

    As I recall, the problem kind of fixed itself after using it, when it did recur, I just toggled the PTT.
     
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  5. KF8KI

    KF8KI Ham Member QRZ Page

    If the contacts on the relay are my problem I'm going to have to work harder than that unfortunately. Whatever is causing the desense, when it goes away, it doesn't stay gone long. I found the service manual for the radio, so I'm reviewing that.
     
  6. K7JEM

    K7JEM Ham Member QRZ Page

    There is a T/R relay, and one for the attenuator. Either of those could be causing the problem. Does it do it on all bands? Cycle the attenuator switch many times to try and clean its relay.

    RX signal paths that go though relay or switch contacts often have this problem. There is no "power" to speak of passing through them to keep them clean. On telephone company relays, sometimes a small current is run through those paths to help keep them working properly:

    https://en.wikipedia.org/wiki/Wetting_current
     
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  7. KL7KN

    KL7KN Ham Member QRZ Page

    Could it be out of band/nearby station causing 'AGC pumping'?

    BTW - this is why I'm a fan of relay free radios. Had my fill when working on Collins equip.
     
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  8. AB9LZ

    AB9LZ Ham Member QRZ Page

    On some kenwood, a wetting current is applied to the RX relay contacts to get them to do a slight "weld" on contact, it makes them "self cleaning". I dont believe the 120 or 130 has that feature. You have to go after the relays and clean the contacts with sheets of paper.

    My 130 had a similar symptoms, but it turns out the culprit (in mine) was the mode switch.

    73 m/4
     
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  9. N3PM

    N3PM Ham Member QRZ Page

    This fix is in the same vein. It works on a 430, and may be adaptable to a 130
    https://www.qsl.net/wb4kdi/Kenwood/TS-430S/Service Bulletins/asb0902.html
    Mike N3PM
     
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  10. WQ4G

    WQ4G Ham Member QRZ Page

    Don't know too much about the TS-130s, but dirty relay contact would be my first guess. Dirty band switch contact or dirty capacitor wiper also come to mind. I would also verify that there are no issues with the feed line.

    Dan WQ4G
     
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