My FT-980 is series 04. So I guess all service notes needed in early versions were done.
After fixing the PA, next day I found that LSB reception was... strange, like added AC, tremolo when listening CW in LSB mode... in short very bad. All other modes were OK as much as I remember. After some 10 minutes LSB reception was normal, and I made a one hour QSO with very good reports on my modulation, I received all OMs with no problems. But the problem is there. Only in LSB and only the first 10 minutes.
I read about and thought about TC01 in PLL unit. A well known candidate. So I checked as per service instructions. USB, Witdh CCW, and no voltage at all. Whatever I do cero voltage in TP. The radio was receiving OK in USB, but still horrible sound in LSB. I was sure I was doing something wrong, and check and check and changed meters, they show 0,00V.
Until it got warm. And LSB sound became normal. Not a believer, I rechecked voltage in TP, and I had voltage, but out of range. USB and WIDTH CCW about 3V. LSB and WIDTH CW 1.5V. Exactly half what the manual says (6V-3V/4V)I hope my meter is OK. That is why I opened a new thread, works after 10 minutes and voltage ratio USB/LSB 2:1 is almost exact. Just it does not exist in cold and when appears is half the normal value.
As I told in the PA problem thread this radio has been sleeping for more than 25 years. And as today I have not realigned anything. So I guess I should do something with my limited means.?
BTW I hope the large metal cover of PLL/VCO units lifts just pulling. I dont have good test equipment, but I have a frequency meter, good ceramic trimming screwdrivers, and a RF probe I have never used. And null experience in PLL or similar.
Neither the user manual nor the service, explains the signal path or function. In my old FT-101ZD the operation manual described with detail how the radio worked.
Well, if I wait 10 minutes before I use it in LSB it is a nice radio. But I would like to understand what is happening.
73 EA1FC
