I must be living under a black cloud. After getting the rig up and running I found that the PA output transformer had three of the ferrite toroidal cores cracked. I assume it overheated, possibly when I tested the unit by keying down CW into a dummy load at 30 watts on 80 meters for about 20 seconds. Is a replacement available? Maybe if I dismantled it and got new toroids I could make a new one, but that would be heavy duty desolder/resolver job. Or perhaps I could make a more robust replacement with new materials, possibly larger toroids.

Has anyone else seen this failure?

Jack
N6LN

开云体育

The same thing happen to my unit. Two toroids on one side broke off. It was happen during adjusting the drive current. I think it was a from of ps motor boating. There was a buzz coming from the unit when the drive current hit a certain level. The current jump from ~1A to about 3A. Still looking into how to fix it.

Also, there were two separate episodes, a few weeks back, where the power output shot up for at least a few seconds, spontaneously, to 69 and 77 watts. I don’t know why that happened, but perhaps the toroids were saturated and overheated. I only saw the damage this morning, but the output the past day or so was strangely down, especially on 80 meters. I had previously restricted output on 80, 40 and 30 to 30 watts via hw_settings.ini, but yesterday I only got 9 watts on 80, but increased the scaling factor to bring it up to 30 watts again. Again, I’m not sure when the ferrite cracks occurred.
Jack
N6LN

I saw a post in the past year about the construction of this transformer but I can’t find it. Does anybody have a link to ?it? I might find new toroids but I don’t know what mix to get.

By chance I had some new FT37-43 toroids (I’m assuming that’s the right mix) and I found that removing T8 was easier than I thought, so this afternoon I rebuilt the transformer. ?Why the transformer failed in the first place is another question.
Wish me luck!

Jack
N6LN

Thanks Mick. I knew the description was somewhere.
And for Jerry and anyone else who has this problem I hope my photos are helpful, if only to show that it’s possible to fix with a little effort and care.?

If it happens again I have eight FT50-43 toroids in my junk box and I’ll build a new, bigger transformer. I’m assuming that mine failed during normal operation but with bad luck, and that a bigger one with 3 turns of Teflon wire would perform similarly but with a greater safety margin. If that’s not a reasonable assumption I’d appreciate further advice. The larger transformer would not fit in the same space and would require a few millimeters of standoff space and therefore longer leads, but with luck it might not cause any additional problem—after all it’s not a VHF device…at least not intentionally!
Jack
N6LN

As Ashhar pointed out on another thread regarding a T8 failure, the real question is, why did it fail? So after repairing T8 I did some testing. First, power output on all bands was low—about 1 watt or less. Then one of the finals shorted. Before replacing it I removed both and tested the drivers. The voltages on the collector of Q15 on CW key down was 19V P-P on 80M, 22.5V on 40, then decreasing by band to 4V on 12 M and 2.4V on 10M. These voltages were with Drive=100 and decreased with decreasing drive, and are of appropriate frequency according to the bands.

Then the collector voltage suddenly dropped to zero with no ac. The receiver still works and goes silent on key down, and CW side tone persists, but there is zero voltage on the TX line (gate to Q10) on key down. I still see the appropriate CLK2 sine wave at the input (pin 6) of U5, but zero voltage at the output of U5, and no ac, at the output, pins1or 3, and no signal at C68 either on key down or key up.?

Then forcing the gate of Q10 to +3.3V gives a oscillation on the collector of Q15 with a DC peak about +14V (the input voltage from my linear power supply) and an rf signal of about 4-5V P-P at an unstable frequency of about 59-73 MHz. This doesn’t change whether or not I press PTT (key down) on CW mode. I understand that forcing Q10 on without any proper rf to the drivers may be causing self oscillation. Please see the oscilloscope screen shot.

What should the output of U5 look like? Shouldn’t there be some signal? Does the lack of signal output from this mixer on CW key down suggest that U5 failed? As it happens I already ordered and have replacement FSA3157 parts because I previously saw one burn out (U3) but that was before upgrade #2 with the T/R board, which makes U3 unnecessary. But it’s an SMD part and I don’t want to replace U5 it if it’s working.
Thanks
Jack
N6LN