Transmit Problem HB1B Redux

After replacing the Final PS transistor as discussed in this thread, I thought the issue had been resolved.

But something weird happened this morning as I used the iambic keyer to call CQ, it appeared the box got ‘stuck’ on transmit, I saw the SWR climb to about 1:3.

I quickly switched off the device and tried again.

When it got stuck in transmit, I ‘jiggled’ the keyer by sending couple random dits and dahs and the transmit stopped.

I tried again. This time when it got stuck I looked at everything I could to gather as much dat as possible.:

  • SWR rises to 1:3
  • LCD does not show the ‘P’ indicator, but ‘S’ with a full receive signal.
  • Audio turned to a bit of a squealing distortion
  • Smoke came out of the unit and the screw that affixes the Final PA Transistor to the housing was very hot to the touch.
  • I opened the housing and verified visually that the transistor was damaged

So I replaced the transistor again, and again have full power on transmit, but am seeing it get stuck again and the SWR climbing with the squealing sound.

I switched the unit off and am posting this now to see if there are any ideas out there as to what I should look at as the culprit here.

As always, any feedback and input is highly appreciated.

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12 thoughts on “Transmit Problem HB1B Redux

  1. Adam,

    I will do my best to help you out, but I have to hit the road and head out to the show. I got the call that I have VIP passes waiting for me :)……. Don’t use the radio. It sounds like your PA is exhibiting instability and blowing up. Check grounding. Check screw tightness in the radio on ground points. Replace the final and see if it goes spurious into a dummy load. Check soldering on the board for cold or cracked solder. Look at the RF PA transformer soldering.

    That PA transistor is not really a device that was designed for RF, so I wonder what impact that has on stability.

    C Ya,

    Marc

  2. OK, another data point, I think you are right about the grounding being off.

    I opened the case, but left the battery connected (its internal)

    The only things connected were headphones and keyer. I turned the unit on, and started to connect a whip antenna, which had no other contact whatsoever, the only way it was connected to ground was through my body since I was holding on to it.. and I heard it key up (which was weird of course since I didn’t hit the keyer) and immediately….smoke. The transistor blew up again.

    So something must be loose somewhere. I’m going to do my best to see if I can find it.

  3. Getting spurious RF into the unit via headphone jack or key? Also..try a low VSWR dummy load and see if it behaves. A whip antenna generates a strong RF field in the proximity of the radio if you are connecting the whip with no feed line (i.e. right AT the radio). Just a thought……

  4. I fried another transistor before finally deciding to completely overhaul the whole device, took the PCB out, desoldered everything and really cleaned everything out. Then I tested all the remaining transistors I had and chose the one that appeared to have the right measurements. A bit of a crapshoot, but I certainly knew which ones where busted. then I carefully put it all back together again and really paid a lot of attention to the seating, soldering and heat screw/conducter/isolator materials of the transistor.

    Low and behold, its working well now, fingers crossed as we’ll see how it hold up…

    AC

  5. After 5 replacements of the final pa I gave up, something is seriously hosed with this rig and its blowing up the final when swr is even just a bit off, like 1:1.5 even

    I got a Yaesu ft-817nd and have been busy learning how to use it, pretty rugged and not even that much bigger than the chiner-rig!

    AC

  6. About the only thing I don’t have is the 817. I repaired one for a friend after Yaesuk service condemned the radio. It took me about 30 mins to fix it and I did have some play time with it. I thought it was cool and about the only thing I would consider buying from that company. If you want me to have a look at the Chickety China radio, contact me off of this blog.

    WR2i

  7. Adam,

    I have been following your posts on the Youkits rig. I spent too much time tuning my antenna and while the rig can be heard in a receiver there is no indication of power out on my SWR bridge. The P in the display shows no vertical bars. I replaced the final transistor and I still get no power out.
    It’s been a while since you posted anything on your problem and I wonder if it has been resolved and if so what did you find?

    Bob, W3ARA

  8. are you using a power adapter or just battery? what type of battery, what voltage, and what is the voltage readout on the screen before, and during transmit?

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