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TS530SP blown fuse after transmitting

Discussion in '"Boat Anchor" & Classic Equipment' started by NJ3T, Nov 5, 2019 at 6:20 AM.

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  1. NJ3T

    NJ3T Subscriber QRZ Page

    By the way, now that I think about it, I don't think I noticed the frequency drift until after I started transmitting.
    Both time the fuse blew was just after unkeying the mic.
    Thanks all,
  2. WR2E

    WR2E Ham Member QRZ Page

    Mike RKL, is it a relay that switches between operating bias and cutoff bias? Maybe that’s in need of cleaning?
  3. N8YX

    N8YX Ham Member QRZ Page

    I'm not Mike but there is a relay in the '530's PA cage. Handles T/R antenna changeover and a few other things. The other relay in question is on the IF Board and is a 4PDT Omron type. That one's known to be problematic at times. The OEM version is no longer available but Ken, K4EAA stocks a suitable replacement part.

    Looking at the schematics, the PA relay doesn't appear to switch bias.
    Last edited: Nov 8, 2019 at 2:45 PM
  4. WR2E

    WR2E Ham Member QRZ Page

    I've got one of those in my 830 actually.

    Does that relay control bias to the final? (I can't recall and don't have schematics handy)

    Just a thought...
  5. N8YX

    N8YX Ham Member QRZ Page

    And I have 2x in my 2x 830s. ;)

    I believe that one is the bias control relay. See post (edited) above re: PA compartment relay.
  6. W5RKL

    W5RKL Ham Member QRZ Page

    Q31 on the AF Unit board controls the final amp "FG" pin grid voltage during receive and transmit switching.
    The SG switch is an SPDT mechanical switch that controls the final amplifier's screen voltage polarity, no relay. The only
    Kenwood hybrid, TS-520, TS-530, TS-820, or TS-830 that uses a relay to control the final amplifier screen voltage
    polarity switching is the TS-830. The TS-830 Rectifier Unit relay is an SPDT relay mounted
    on the TS-830's Rectifier Unit board.

    Okay let's see what the OP did and said

    After the OP powered up the 530, turned the HEATER switch ON, and listened for about 5 minutes for the net to start, no transmitting
    occurred and the fuse did NOT blow.

    Next, he changed frequency, about 7Khz, to tune up the 530, again no indication of a problem. Unfortunately, we still do
    not know if the sideband transmit IP idling current is stable at 60ma or not. We need to know this. Still, the fuse has still not
    blown. At this point the OP had tuned up the 530, getting ready for the net. He then said this:

    I then returned to the net frequency and after about a half-hour the net control called me. I answered and transmitted for maybe 20 seconds.

    Note the "half-hour" period he was NOT transmitting, only receiving, and the fuse did NOT blow!!. This clearly indicates the -C bias supply
    had not failed and it not the source of the problem.

    The next time the OP transmitted was when he was called by net control, and his transmission was kept short, approximately 20 seconds. Still,
    the fuse did not blow. We are over a half-hour without the fuse blowing with only a couple of short periods of transmitting.

    Next, the OP said the following which is where he started noticing the problem again:

    When the net was over (total of 45 minutes from initial power-up) I started talking to some of the fellas that hung around after the net. It was then that everything went south. I talked for maybe 20 or 25 minutes (on and off) before the fuse blew.

    During the 45 minutes, the OP chatted with other stations after the net ended, the time the 530 was in transmit would more than likely vary from
    a few seconds to possibly a minute or two, maybe longer. Prior to this period of time, the fuse did not blow since 95% of the time was spent
    "receiving" not "transmitting". If the idling current in transmit is unstable, it could easily rise above 60ma, even peg fully to the right, causing
    the fuse to blow. During receive, the final tubes are biased to cut off so there is zero current flowing in the final tubes, hence no fuse blowing.

    Unless the OP has other information we don't know of, I believe the source of the problem is/are one or both final tubes. If the OP has a spare
    set of 6146Bs, replace them and test for proper operation and stable idling current at any transmit time period.

    Mike W5RKL
    Last edited: Nov 8, 2019 at 8:05 PM
    WR2E likes this.
  7. W5RKL

    W5RKL Ham Member QRZ Page

    Hi Jim,

    I wonder if you have spent some time to look into the 530's side band no RF drive transmit idling current (60ma) stability?

    Unless there are other factors we don't know about, I still am focusing more on the final tubes as being the source of your
    soaring plate current that's causing the fuse to blow.

    Mike W5RKL Moderator

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