Posted: 8/24/2008 1:34:42 PM EDT
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Hi Folks: I am having some trouble with my backup radio, a Yeasu FT-77. I am hoping that I can get some advice here on how to start to fix it. I learned the very basics of electronics in studying for the General exam, but I am afraid I don't know a lot beyond that. Here is the problem: The FT-77 works on all bands except 75/80M. When the band switch in the 75/80M position, I get no numerals on the display, just the decimals. If I change it to 40 or 20 or any band but 75/80 meters, it works great. Additionally, it seems as if it really isn't working on 75/80, in that if I twirl the tuning dial I hear no stations, or even changes in the background static. This problem had been intermittant, and initially, a flick to the 40M setting and back would nearly always bring up the 75/80M band. This trick worked less and less frequently, until it simply won't anymore. As to diagnostic tools, I am afraid all I have is a set of jewler's screwdrivers and a digital multimeter. The repro manual I bought (which I subsequently found online) has a schematic, which I can may be able to post, if it's helpful. My initial thought was to open the case and squirt the band selector switch with some De-Oxit. Any other ideas on a direction in which to proceed? Thanks for any advice you may be able to provide. Stay Safe, AGreyMan KB9*** |
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My guess is someone tuned around alot and used the band selector as a handrest, or it may have just worn out. Have you tried using the continuity function on the mutimeter to test the switch? You'll have to read the schematic to do that. I wonder if one of the contacts isnt bent out of position or broken? You'll want four hands for that job. |
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That's a fine looking classic set. I'd give the de-oxidizer another try. Have a look in the back of QST for guys who specialize in repairing these old sets. E-ham opinions will also have some input for you. Sweet looking radios need tender loving care. Good luck. |
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Thanks guys. I am hoping that I get a chance to play with it a bit further later this week. It is a manual switch (if you look in the first photo, the metal rod that is parallel to the red spray nozzle is the rod from the face all the way back to the actual switches) and I think I will try to get in there and make certain the contacts are actually contacting. Maybe a light touch of crocus cloth to the contacts, and a gently push with a jewler's screwdriver tp the little metal tab to make sure the tab isn't "floating" above the contact, and not actually making the circuit. Thanks for the advice and encouragement. Stay Safe, AGreyMan |
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It could be a Phase Lock Loop circuit not locking up. The Kenwood TS440 radios had this problem due to some adhesive used around some transistors in the PLL circuits, that eventually broke down with age and became conductive. The same symptom of dots on the display were indicative of the problem. Not saying that is your problem, just very similar with that model Kenwood. I'll look around and try to find some info for your paticular rig and get back to you on it. I'd also closely examine the circuit board with magnification and good lighting around the band switch for any possible cold solder joints that may be failing under mechanical stresses. |
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If you decide to do repairs, Turner Radio in Lancaster, CA has good reviews. I spoke to several people on the air who mentioned his shop in high regard. Turner Radio Eham Review |