Sunday, June 07, 2015

FT-707 repair (9) No external VFO

Looking back, this is the 9th issue found between the two sets, hopefully will be the last!

The problem with the "blue" FT-707 was that the external VFO was not working with the set, it was working with the other set so the VFO is ok.

I started looking at the diagram, for sure the issue is in the connection to the external VFO, the VFO ligt's and controls the radio if you press the RX but no frequency, only the 91Mhz symptoms of no VFO:

Started by testing the switch inside the plug with a make shift adapter (the shield of a plug):

One of the poles in the plug swithc put's inline a 50 ohm resistor so it's easy to test from the RF board, pin 3 of J05 "memo out".

All the connections were tested and all with continuity....what is going one here? Something is not right!

Let's bring the heavy troubleshooting stuff.... the oscilloscope, before that,  just powered on the radio once more and the external VFO was working!... Hum!?, probably the contact creaner I aplied on the swithc changed things... good, let's close the lid before it breaks again.... then is when it stops again, ahhh, a broken cable for sure, some touches on the cables and voila the culpit (external vfo in):

The press of the lid against the cable would disconnect and that's why when I did the testing it was all ok. live and learn!

For now this will end the FT-707 repair series, they only need a god tuning and some cleanup, if something major "arrives" will post here.

Have a nice week!

No comments: