bob85 or another HF radio repair man

[TonyV225]

My kids HF rig on there bench loses output on 10 meters. The power almost folds in half seems the longer the radio is used the faster it decreases or loses power.

It gives the full 100 watts on 20 17 15 I thnk it loses slightly on 12 meters this was checked into a dummy load so its not a tuner or antenna issue why is this thing doing this on 10 meters?

Ive tuned the radio to the service manual specs and instructions tuned on 14.200.00 I just dont get the power drop thats even with an auto tuner this is driving me nuts :headbang

 

[Happy_Hamer]

What kind of radio is it?

 

[TonyV225]

Bill this is one of the kids Yaesu FT-840

 

[Captain Kilowatt]

Has this radio been used on 11m by any chance? Check the bandpass filters in the PA section. Look for signs of overheating, bad connections etc.

 

[TonyV225]

CK this radio has 11 meters in it thats the way I bought it years ago. Like I said it seems ok then after awhile it folds back a little at a time.

Ill try it again today to confirm and then will have to open it again and look at the bandpass filtering area.

 

[RatsoW8]

CK this radio has 11 meters in it thats the way I bought it years ago. Like I said it seems ok then after awhile it folds back a little at a time.

Ill try it again today to confirm and then will have to open it again and look at the bandpass filtering area.

Tony...you might want to try the Ft-840 Yahoo forum. The out of band mod for the FT-840 didn't require snipping or removing any parts so I doubt thats the issue. I'd say it's a bad or dirty relay. I had similar issues on a Knwd TS-430 I revived. With the 430 it was a matter or running 12 volts through a resistor into the antenna jack and cycling the band switch to burn off the crud on the relays. Worked like a charm but I'm not sure of the process for the FT-840.

 

[TonyV225]

Yes Im familiar with that relay cleaning on the -TS430 I believe it was also posted here at one time maybe Mack posted it if I remember correctly. The radio sounds fine and I made a few contacts on 10 meters with it without complaints. I notice the longer Im on it that power starts fading or folding back. I checked it on 10 11 and 12 meters but once I hit 15 meters on up she jumps back up to 100 watts with a quick push of the outboard tuner and stays there.

 

[Captain Kilowatt]

Tony...you might want to try the Ft-840 Yahoo forum. The out of band mod for the FT-840 didn't require snipping or removing any parts so I doubt thats the issue. I'd say it's a bad or dirty relay. I had similar issues on a Knwd TS-430 I revived. With the 430 it was a matter or running 12 volts through a resistor into the antenna jack and cycling the band switch to burn off the crud on the relays. Worked like a charm but I'm not sure of the process for the FT-840.

It's not the method of modding, it's what can happen after. The reason I asked about 11m is that some radios have a pretty tight bandpass filter and heat will develop in the 10m bandpass filter when operated on 11m. This results in either burned components, loose connections from melted solder due to heat build up, or changes in component values, all of which can effect the output on a single band (or adjacent bands using the same filter) while others are fine.

 

[TonyV225]

Thats kind of what I am thinking aswell I know I use to run this particular radio myself and it worked fine for a few years Ill have to look into it.