Hallo N9IB
Regarding the no reception, I have not clear the situation. Does it show frecuencies in display? How in GEN?. Only in HAM?. There can be some things. if it is only in Ham. I would first discard problems in the RF unit. I am not an expert, but there is some info regarding problems in the HAM band filters due to electrolytic capacitors in the 11 band filters losing capacity. Much easier is to check connectors J10 and J11 (push and pull) (they are close to Xtal filter). In general it may help to move out and in the connectors in this 40 y.o. radio.?
When you have the radio opened and upside down to show RF unit, check in RF J015 in radio front, between attenuator shaft and a large transistor, this transistor inhibites transmission in some logic circunstance. Red cable in J015 coming from RL01 (input to transistor)? should have 13.5V on transmission. White cable is TX13.5V to PA I have been talking about. Checking voltages in this J015 it is important. White cable (output to PA) has a lower voltage than red cable (input from RL01). In case of overcourrent in PA, the voltage can be low, and the relay? RL01 (switches 13.5V Rx/Tx) can be damaged.
If you look in youtube for a video on "Reparacion FT 980" (in Spanish) you can see some damage and repair in PA.
Overintensity in 13.5V PA can blast capacitors (video), and even trip the overintensity protection in 13,5V PS, where Q01 is some kind of constant intensity source to comparator. In this radio as the real power is in 24V, the 13.5V PS is not that powerful. That is why it is important measure voltage in white cable of J015 of RF unit when Tx allowed (HAM and no transverter). If the 13.5V PS is cut to very low voltage, all voltages are low, and the radio can make anything it likes. So... Check that voltage...
And closing the circle, the mod in PA so PA Q01 takes collector from TX13.5V instead from 13.5V, means some added ?200mA? intensity to RF Q01 and RL01 originally designed to handle only PA bias intensity, but it seems this mod has been made at factory. ?To avoid autoscillation of PA? Might be feedback between Q02 & Q03 to Q01 via the 13.5V path. So they changed Q01 to TX13.5V line, physically far from 13.5V path. Who knows... I keep in mind from the PA in video mentioned that the blasted capacitor C18 and the "cut and moved" (green wire) L05 choke are in Q01 power path. Changed from TX13.5V to 13.5V. ?Coincidence?
Unfortunately it is difficult to lift the PA board from the aluminium radiator to check/change capacitors in PA, like C30 330uF in 24V or the many tantalium in 13.5V and TX13.5 lines. It is all very compact. But the aluminium sides where 7808 is, can be easily dismounted to have lateral access and weld new capacitors on top wires of damaged capacitors (not easy in all cases)
73 EA1FC
