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Kenwood TS-930S, No transmit

Discussion in 'Radio Circuits, Repair & Performance' started by W9MAS, Jul 15, 2013.

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  1. W9MAS

    W9MAS Ham Member QRZ Page

    Hi All

    I have a TS-930S that does not transmit. The meter reads about 1A collector current on transmit. That's all I get out of it.

    The drivers, finals, and bias appear OK. Supply voltages are all OK.

    This is a later serial number unit, so it does not have the digital board issues of older ones.

    Any ideas?

    I am an electronics tech by trade (20+ years exp. component level) but do not have a whole lot of the time to troubleshoot this thing. It's a side project, so that's why I'm posting my question here.

    Thanks to all for the help resolving the first issue I had with this!

    Last edited: Jul 15, 2013
  2. G4COE

    G4COE Ham Member QRZ Page

    Whats the drive input like to the PA department, is there drive there? I reckon this is the first port of call, a service manual could be had freely from many sources.

    For the standing current with NO drive in TX mode driver pair should be 70mA set with VR2 and final pair set to 1.3A with VR1, allowing 30 seconds for the current to stabilize according to the manual in both cases.

    This is set in TX mode with NO RF drive, obviously RF drive will cause the current to rise, also no RF drive will equate to no rf output.

  3. AG6JU

    AG6JU Ham Member QRZ Page

    if you can isolate transistor of driver, and final, usually simple PN junction test with multimeter can tell if that transistor is bad or not. also, TS-930 often lose regulation of power supply, if display light flicker or voltage change a lot during transmit, power supply regulation can be problem.
  4. G4COE

    G4COE Ham Member QRZ Page

    What good will that do if there's no RF drive?

    With no TX the first step is to check the RF drive to the PA module..... that's the way I would do it, rather than go disconnecting things, the input lead only unplugs.

    With no test equipment such as a scope or RF voltmeter/detector, disconnecting the RF input lead and loose coupling to another receiver ought provide clues when tuned to the same TX frequency and mode if drive is present or not.

  5. W9GB

    W9GB Ham Member QRZ Page

    Jose, EA5AGV restoration/repair of TS-930S

    WA4NVA - Kenwood TS-930S restoration.

    Eric Hidle, N2JBE -- did a number of repairs for his TS-930S (digital board rebuild/rework)
    that he described here on QRZ.
    You can ask him about his power supply:

    Kenwood TS-930S Service Manual

    TS-930S resources
    Last edited: Jul 16, 2013
  6. AG6JU

    AG6JU Ham Member QRZ Page

    check PN junction voltage drop. I found out that is quickest way to test transistor in amplifier. all of the transistor failed either complete short or open B -> C or B -> E

  7. G4COE

    G4COE Ham Member QRZ Page


    I agree transistors do fail but *is* going straight for the transistors a logical approach? I would have thought checking the drive first was even more logical.

    The OP stated 'No Tx', he checked the current in the finals being about 1 Amp.... in my manual it states 1.3A for the finals and 70mA for the drivers, so to me it looked about right.

    If the devices were leaky or collector emitter short then the bias would be uncontrollable, if they were o/c then there would be no current through them.... I stand to be corrected.

    No harm in checking the bias current first, much easier than 'lifting their legs'.

    If it should be the PA there a mod somewhere where one guy swapped them for FET's, I used the very devices in TV switch-mode power supplies (chopper FET), these are TO220 casings just like the tabbed voltage regulators.

    Here's the link Never tried them myself.

  8. W9MAS

    W9MAS Ham Member QRZ Page

    Thanks for the replies . . .

    I agree G4COE Dave, the next logical step is to check for signal drive to the PA. Was wondering if I should attempt to set the idle currents (VR1, VR2) first?

    And I'll have to dig out my RF probe . . . have not used in in a long time!

    Side Note: When troubleshooting my first checks are always the most fundamental ones - Quick go/no-go check of the driver, bias and PA xsistors. (My Fluke DVM never fails me!). Then a quick check of the supply/bias voltages.

    I had three problems with this rig when I first got it several weeks ago - (1) R19 and R20 on PS board burned open (2) Connector for Q3 was toasted (3) Had to tweak L77 (courtesy KA5IPF) to bring up level of Het. Osc. in order to get PLL lock

    So, it seems to be working now in all other respects . . .

    I'll keep ya posted!

    Thanks again,
    Mike W9MAS
  9. KE3WD

    KE3WD Ham Member QRZ Page

    It is my advice to not attempt adjustment of anything until you have ruled out all the other possible causes for the failure. Re-adjustment can not only mask symptoms, but in the case of bias current settings, might sere to destroy component$ that weren't bad to begin with.

    Find out where the RF stops first.

    Pulling the input to the PA and checking for Rf there is a good thing for starters.

    As already mentioned on this thread, you don't even need the RF probe to do that, just attach a short piece of wire to the hot of that pulled input line and use another receiver to see if the thing is transmitting from there without the PA involved.

    If it is, then it is time to troubleshoot the PA components, not adjust settings.

    First thing I would do then is to check all DC voltages against the schematic. Often is the case that a problem like this may not even be in the PA itself, but in the power supply, such as a lower regulated voltage that the PA needs. These can sometimes turn a headscratcher into an easy repair, the ubiquitous three-terminal regulator going out, or leaky electrolytics in the power supply, of if it uses discrete components, perhaps a leaky pass transistor, bad zener, etc.

    Sometimes, when stumped, I will move the idle current pots just to see what moving them a little bit does, which can also yield clues. Good idea to mark where they started, thus bheing able to return them to the original position, or at least into the ballpark.

  10. G4COE

    G4COE Ham Member QRZ Page

    Always get the clues first, saves a lot of time.

    One good piece of test equipment funny enough.... is the nose! Many a time mi' nose saved me troubleshooting, especially when things burn up or go 'pop', learned that years ago in the servicing trade.

    Should there be no drive when you check it, forget about the PA stage and work back towards where the drive comes from, should there be drive then we know which way to start paddling.

    Yeah, I forgot the voltages sorry!!!!
    You did say the transistors drew about 1 Amp so I imagined that being right AND that the bias was switching 'ON' when you pressed the TX button, that kinda 'threw me'..... just that I was inquisitive about there being any drive before condemning anything else.

    Been stumped many a time, I put it to one side get a couple more jobs done or until the next day perhaps.... got it working in no time, sometimes it makes you wanna bury yourself, you're never caught out the same way again!

    Last edited: Jul 17, 2013
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