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[QCX40] And the beat goes on.....

Jess Gypin <ontarget1911@...>
 

Ok, I'm just not as sharp or something as I used to be😛
Got this out together a bit ago. Turned it on, no smoke. Q1 got really hot in about 3 seconds. No display. Pulled Q3, got good input to look at Q6 and so on to see what was turning on the PA. Q6 was shorted. Changed that and all 3 BS170s in the PA for good measure. I believe the technical term is shotgunning. I can desolder and solder pretty well still. Not too worried about damaging the board.
Turned it on. No smoke, no heat. Tweaked the LCD and boot screen. Walked through the alignment, not a lot of adjustment on some things, not clear how what specifically. Band pass tweaked right to the center of the cap. Receiver worked great. All menu items working, so no logic or display problems. Thought I found it.
Tried transmitting. Got side tone and receiver quieted. No power outlet all. PA finals got really hot fast when key down, like seconds. So, sort of the same as the original problem. Been all over the board. Verified values, no bad solder joints or toroid wire problems found. A couple of stray solder things that might have been an issue, but not obvious. Cleaned a couple of things, touched up all joints, fixed iffy looking or stray solder things. No obvious bridges or issues. Checked all toroids for continuity and clean, well made connections. Looked at T1. The only thing I have not chased down is the middle 5 wrap secondary is showing a no ohm relationship with the primary. "Shorted to" but have not examined the schematic close enough to know if that is normal path between them through the circuit somewhere. No continuity between the other two secondaries and the primary.
I can't keep it on any time at all without the PA finals getting hot now again. So transmitting or something put me back to square one I think. I never did transmit the first time on purpose so not sure they are the same cause.
So, I was going to check the nand hate to see if the final is just "on" from a DC perspective, but now cannot power it up without the PA getting hot immediately. So, that is where I am. The board has been over inspected. I might be forest for the trees now. Cannot do any dynamic testing, don't want to cook something else. As far as I know the logic and receiver should be fine. I was going to go down the PA and sig gen path to see if they were stuck "on" as was well advised, but now can't. I could pull Q6 or something, but probably not advisable. Q6 is NOT shorted like the first time, probably not been turned on long enough to blow this time.
My only hunch is that it may be the final and receiver transmit, receive switch stuck, or sig gen and tx lines from the nand gate both active or stuck high, or Q? in the key shaping turned on all the time, or can you tell I pretty much don't have a clue right now??
I am kinda stuck cause I can't leave it on to troubleshoot. But I will keep looking. It is obvious that if the receiver works/worked, and I got through the alignment, transmitting causes the problem and it just stays that way.
Thoughts?? I am putting it down for now. Don't want to get frustrated beyond the enjoyment factor. Too nice a radio for that, and the receiver and other toys are too cool!

Jess AE0CW

And yes I am supposed to know electronics😵. And no oscilloscope available. Just a DVM. We are full time RV and no workshop anymore.

Al Holt
 

Sorry to hear you're still having troubles. If you pull the finals (remove them) you should be able to troubleshoot the board easier. From what I can tell, having them out of circuit won't harm anything.

That should give you the opportunity to poke around to see what's going on.

From the looks of it, T1 is only used only for receive. L4 is used for transmit.

--Al

Jess Gypin <ontarget1911@...>
 

good thoughts. Thanks

On Thu, Dec 28, 2017 at 5:58 AM, Al Holt <grovekid2@...> wrote:
Sorry to hear you're still having troubles. If you pull the finals (remove them) you should be able to troubleshoot the board easier. From what I can tell, having them out of circuit won't harm anything.

That should give you the opportunity to poke around to see what's going on.

From the looks of it, T1 is only used only for receive. L4 is used for transmit.

--Al