Yaesu FT-920 Antenna Tuner Component Smoking Need Help

Discussion in 'Radio Circuits, Repair & Performance' started by W2GAS, May 6, 2017.

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  1. W2GAS

    W2GAS Ham Member QRZ Page

    Hi all today I was tuning up on 80 meters to practice some CW and when I pressed the auto tuner I smelled something burning. I opened the rig up to see what it was and to my surprise this component (pictured below) was fried! Anyone know what this is? I noticed there is 8 of them most likely 1 for each band? The number on it reads 201J10 We had rain today I usually never tune up with the full power but today I made the mistake of doing just that and that's what I get!! Anyway, if I just replace that part will it be fixed or did something else burnout before that stage? radio works fine only smokes when I use that band. I didn't do anything else until I know what caused this to happen. Thank you all for taking the time out to read this and your help is greatly appreciated.
    73's
    Tony
    W2GaS

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  2. KM5FL

    KM5FL Ham Member QRZ Page

    That is a dipped silver mica capacitor. Part number C5005 on the Tuner main unit schematic.. It's value is 200PF, 1KV. Over the years, I've owned 4 - 5 FT-920s and have never experienced a problem with the tuner... Your not being able to identify this component leads me to believe you lack the skills to properly troubleshoot the problem with your radio.. My best advice is place the radio in the hands of a competent technician..

    KM5FL
     
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    It may have just smoked that one. But it looks like the cap next to it has been hot too.

    I would replace them with something of better quality.

    Good Luck.
     
    Last edited: May 6, 2017
  4. W2GAS

    W2GAS Ham Member QRZ Page

    I would love to know what I could replace them with! They are very cheap looking!
    And You are right the next to it burnt a little too! that was from 160M
    If anyone knows what they could be replaced with I would love to hear!
     
  5. KA9JLM

    KA9JLM Ham Member QRZ Page

    Something like this should be good. http://www.newark.com/cornell-dubilier/cdv16ff201jo3/silver-mica-capacitor-200pf-1kv/dp/12C2736

    Check the data sheet to make sure the ones you get meet spec or better than the originals.

    I would not use it, Until repaired. 1 cap can affect many bands, Not just 1. They all get switched in and out, To obtain the capacitance needed to tune.
     
    Last edited: May 6, 2017
    W2GAS likes this.
  6. W2GAS

    W2GAS Ham Member QRZ Page

    I wonder how it blew out in the first place
     
  7. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Tuning at high power into a not well pruned 160m antenna can develop quite high voltages that are not typical for the higher bands. Very easy to exceed the voltage rating of the caps causing shorts and failure.

    We need to be aware of the voltages that can develop on the lower bands. Depending on the antenna design and installation, matching components/tuners and radio, it may not even be possible to transmit at full rated power e.g. 100W without causing arcing in a given transmitter. It may be necessary to reduce power.

    I recommend tuning at minimum power, then transmit at low power slow increasing and being alert for arcing in the radio and tuner (may be as benign sounding as faint "tics"). If there are coils/caps outside, check them for signs of arcing as well.
     
    Last edited: May 7, 2017
    G4COE and W2GAS like this.
  8. W2GAS

    W2GAS Ham Member QRZ Page

    Yeah, I didn't want to come to grips with that. But you confirmed what I thought was the issue. That was the first time I did that. Rain had to have some part too. I will take your advice for future tuneups!
     
  9. N7EKU

    N7EKU Ham Member QRZ Page

    Anyway,

    There was nothing wrong with the capacitors really. They are not cheap components, just their ratings were exceeded. Silver mica caps are the ideal part for antenna tuner capacitance due to their very good RF performance. It's possible to use higher voltage rated ones, but unless all the other components are also upgraded there could likely just be other failures (in other caps, relays, inductors, or the PCB tracks). I don't know what your antenna is, but it's really common that 160m is hard on tuners because the antenna are almost always comparatively really short.

    73,


    Mark.
     
    W2GAS likes this.
  10. VE3TMT

    VE3TMT XML Subscriber QRZ Page

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