TYT TH-9800 No 2M Power

Discussion in 'Radio Circuits, Repair & Performance' started by KJ7AGP, Sep 12, 2020.

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  1. KJ7AGP

    KJ7AGP Ham Member QRZ Page

    Hello all - first time posting here!

    I have a TYT TH-9800 quad-band radio, it's been around for a couple of years but has stopped working at some undetermined point while it was in my car. It's got some squeal on transmit and doesn't appear to output much power at all on the 2m band. I noticed it was broken when it wouldn't use any repeaters except those on the 70cm band.

    Has anyone had a problem like this before? I've tried a few things but I'm getting nowhere.
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    I guess you tried a factory reset ?

    You may want to check the Relay, It selects the RF path of UHF/VHF.

    If it still outputs on UHF, Chances are the relay has a problem. The RF output transistor is shared for all bands.

    Good Luck.
    KJ7AGP likes this.
  3. KJ7AGP

    KJ7AGP Ham Member QRZ Page

    Several factory resets, T4 or whatever the deepest reset was. I'm gonna check out that relay, I have the thing on the bench and I see it, my only problem is most/all of my equipment is sub 100Mhz and makes diagnosing VHF problems difficult.

    The squeal on the output is also giving me pause, it's present on at least 70cm and 2m, though I suppose it may be a near-field effect that isn't present on other people's repeaters. I did get a radio report through a repeater on 70cm and he said it was clear as crystal.

  4. KJ7AGP

    KJ7AGP Ham Member QRZ Page

    The relay was definitely part of the problem! I swapped the 10M and 2M relays after bench testing the 2m one and finding it was bad. These relays are kinda crappy so it makes sense that they die, hopefully this one lasts a while longer.

    People are saying there is a hum present on 2m transmissions, I'm not really sure what that'd be from. Additionally, the SWR on 2m output is higher than it should be. I have a little nanoVNA and it agrees that my antenna should have a sub 2:1 SWR on the entirety of the 2m band. The power meter I have claims the SWR is greater than 5:1 on transmit, so I don't know if everything is hunky-dory yet.

    I was able to do simplex on 70cm to ~25 miles away to a family member on top of a hill, but nothing came through at all on 2m. Surely 2M should be performing at least as well as 70cm in this case?

    Glad to have the radio at least useful again though, I can continue my development and experiments now in the higher bands.

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