[CQ-Contest] Need help/guidance/advising to fix my TS-590s TX

[Yan (XV4Y)]

Hi,

I know this is a bit out of topic but as there are many skilled technician on this list I hope I will find some help.
My two transceivers (TS-590s and FT-100 as backup) are now unable to transmit.
I am left with QRP rigs which are not best suited for DXing and contesting…

I’ve tried anything that seems obvious to fix my TS-590s without success so far.
The problem is related to the ALC / Power Control circuitry. It is intermittent, but has worsen.
Everything work great except that the ALC bargraph goes crazy till the top and the power folds back to 50W and even lower.
I’ve been disconnecting/reconnecting the cables inside the transceiver checking for oxydation on the connections due to the tropical weather here (we’re in the midst of the rainy season).
I’ve done a "Final Unit » re-alignement thinking of a possible part value changing with aging and tropical weather.
New values are only slightly different from the original ones, so that was not the origin of the problem.
I’ve eliminated a possible PA transistors failure as while in Service Menu mode for the alignement the rig consistently put 100W out.
Checking the waveform with an oscilloscope shows no visible distortion while in Service Menu.

I am now thinking in disabling the ALC circuit altogether and using only the rig in CW with carefully set CAR level.
However before doing anything non-reversible I would like to have some help and check what can be done...

Thanks for your time.
73,
Yan.
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Yannick DEVOS - XV4Y
http://www.qscope.org/
http://xv4y.radioclub.asia/