Is itpossible to test this SMC semiconductor in circuit?

Discussion in 'General Technical Questions and Answers' started by 2E0ILY, Jul 8, 2018.

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  1. 2E0ILY

    2E0ILY Ham Member QRZ Page

    I managed to feed 1kW of 137kHz RF up the RX antenna socket of my Kenwood TS-590S (please don't ask..... [​IMG]) I cast it aside as the damage seemed terminal, but having a fairly quiet day today I decided to do some probing. I believe the damage is limited to the RX/TX RF board and relatively localized. Some damage to surge absorption components, a 150nF SMC inductor, a few HVC131 Pin Diodes (gee, they are seriously TINY), and a 0.01 chip cap that's literally disappeared taking a plated through hole with it.

    I am a bit stuck about how to test a semiconductor in the BPF switching section though. I am paranoid about damaging the PCB so do NOT want to remove SMC components without VERY good reason as I am not very good at it! Could someone tell me if there's enough info in the attached excerpt from the schematics to say if I can test Q132 (highlighted in blue and a switching semiconductor for the BPF that was in use at the time of the "accident") in circuit, or what's the minimum to remove to so do please?

    Thanks. If more of the schematic is needed please ask!

    If the schematic excerpt doesn't load it's also at

    Attached Files:

    • test.jpg
      File size:
      575.7 KB
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Can you power it up and measure voltage on components ?

    See if it is turning on and off ?
  3. N1OOQ

    N1OOQ Ham Member QRZ Page

    Seconded. If you can measure the DC voltage at the collector, the schematic says it should be 0.4 with that filter selected, 13.5 when it's not.
  4. KK5JY

    KK5JY Ham Member QRZ Page

    :eek:, I say, :eek:!

    If your station details are such that such accidents are still possible, I would highly suggest you invest in a device such as this:

    Whether you buy or build one, it's very cheap insurance, especially if you build it from the very simple components, mostly Schottky diodes. I built one into an aluminum project box for around $10 US.
  5. 2E0ILY

    2E0ILY Ham Member QRZ Page

    Max 10 Watts input, lowest frequency 500kHz. thanks for the link, but one kilowatt of RF direct into it at 136kHz would almost certainly not be within its spec. My antenna change over relay had a glitch, so the amp's output went straight into the 590's RX antenna port.
  6. 2E0ILY

    2E0ILY Ham Member QRZ Page

    I have the board out of the transceiver and so far all testing has been done without power to the board. I should have made myself clearer, I am wondering what the least amount of things need removing (if any....) to test this device with the board still out of the rig. Thanks for the replies :)
  7. N1OOQ

    N1OOQ Ham Member QRZ Page

    Well of course the least amount to remove is nothing... Which is what testing in circuit allows you to do. Fixing any large amount of damage might require several cycles of assemly/disassembly, because the final tests have to be done fully assembled.
  8. KA9JLM

    KA9JLM Ham Member QRZ Page

    I think it can be done with the board out of the radio.

    But in the radio would be better. Unless a power supply has a problem, Fire it up Smoky. ;)

    There are many same circuits on that board for different bands.

    Compare the other transistors using the Diode Check function on your meter.

    Looking at the schematic can give a clue of what on the board will affect your readings.

    Have Fun. Save some smoke for later and share with a friend. :)
  9. 2E0ILY

    2E0ILY Ham Member QRZ Page

    I believe I see light at the end of the tunnel, no thanks to Kenwood,
    this has left me with a somewhat jaundiced view of Kenwood's service
    support, to say the least. The 590 is hardly a legacy radio, surely?
    The lack of any direct replies at all from Kenwood UK or Kenwood East
    USA has left me unlikely to buy another Kenwood product, and saying
    the RF board of a TS-590S is obsolete to three of their recommended
    UK service centres is madness, they aren't that old!

    I have replaced some blown chip ceramic caps, several front end
    protection diode devices, several (minute) PIN diodes and am about to replace
    several collector current limiting resistors in the BPF switching
    digital transistors circuitry. I can transmit and receive perfectly on all but
    three bands now, and these three bands are unable to switch in the
    relevant BPF due to high value resistors, up from 68 Ohms to circa 7k
    Ohms in the collectors of the digital transistors switched by the
    shift register IC's. It's been a learning curve for an elderly 2E0,
    (UK intermediate licence holder call) but I believe this will live again.
    To quote the well known phrase from the UK's Dad's Army series,
    They don't like it up `em (Especially a kilowatt up `em).

    By the way, kudos to the Ebay seller of Kenwood and the other top
    three ham radio makers' spares, "bijkker" who has been extremely
    helpful with parts and advice as to where to source bits Kenwood are
    unable or unwilling to supply themselves, and that he does not stock.
    A great guy!
  10. KA5IPF

    KA5IPF Ham Member QRZ Page

    I don't have a clue about the support you get on the other side of the pond but Kenwood East is no longer a Kenwood Service Center and hasn't been for a while. Maybe that explains their non-response. I looked at the pictures of your "fiasco" and realized that a detailed list of things to check would be impossible. I could tell you replace all the burned parts but after that you are on your own. It's just a matter of going thru and replacing parts as needed. Just exactly what you are doing.

    How is that Kenwood's fault?

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