Yaesu-FT-991-group AM Transmit Audio

Yaesu-FT-991-group AM Transmit Audio

I purchased a new FT-991 late December 2015. Everything seemed OK with the radio until I tried AM. I wanted to participate in a local 6 meter AM net. The audio is distorted to the point where no one can understand me. I tried setting the power to 5 watts into a dummy load, lowering mic gain, turning off min-EQ, all with no success. I also noted downward modulation only. And yes I did a factory reset.

I checked with 3 other people who recently purchased the 991 and they all sound horrible just like mine. I am afraid this radio design is broken on AM. Good thing I kept the boxes. Anyone else seeing (hearing) this problem?

Updated  ::
I do not know if someone had already mentioned but I think I found how to solve your problem : go to this link , at middle of poge , where it is explained step by step how to do I hope to help you

Updated : :
I went to service menu and adjusted menu 18-02 from 77 to 52, and now I have reports of "almost FM quality audio".

Carrier power droped to 25W without audio input (RF POWER set to 40), I could find "power up and down" to peaks from 15W to 40W with modulation.

MIC Gain was raised from 30 to 65 with reports saying nothing but "Excelent".

Yaesu FT-991 AM Issue Resolution

Glenn/WA3LAB found the fix below on the net to resolve the issue with the Yaesu FT-991 in AM mode. The techs at Yaesu they said they’re aware of it, but Yaesu has not put out a bulletin on it.

Both Glenn & I have followed this procedure and it appears to work. I wouldn’t want it put out there without letting people know that they should proceed with care, and not to change anything else unless they really know what they’re doing. Since there’s not many people running AM anymore most people have no idea there’s a problem.

– Leonard / WV3P

(Warning: once you put the radio into the service mode you can really screw things up, so do this at your own risk.)

AM Transmission Audio Trouble

The problem:
20160205 – Information can be found about the bad transmitted AM audio quality on the internet. To be sure that’s true, I verified this with my FT-991. And the AM audio quality is indeed quite bad. The FET’s from the HF power amplifier of my FT-991 are already replaced (at the Yaesu service centre) and therefore there isn’t a relation between the bad finals and bad AM audio quality. Based on my “research” I can conclude that the solution is quite simple and can be done yourself.

Here is a supposed fix for the AM issue. 


  1. I sent my FT-991 back to Yaesu Service in Cypress, CA. They did an AM alignment and sent the FT991 back to me. AM quality sounds acceptable on HF BUT the AM audio quality is still very poor on 6 meters. I also checked AM on 2 meters and it is even worse. I actually was told to send the rig back to Yaesu service again. I am extremely dissatisfied with the poor interaction I had with the technical staff from their service center. I specifically asked them to document what they did and send test results. They totally ignored me. Whenever I asked for further in depth information about what they did to my FT991, they basically ignored me request. I called their technical support line and asked to speak to their service manager and requested he call me back but he never did. In all my interactions with Yaesu, I have been respectful to them but they have avoided answering my requests. My AM transmit audio issue is unresolved. I have no intentions to forgetting about this until Yaesu fully resolves this issue.

  2. Here is a supposed fix for the AM issue. http://www.paarc.net/yaesu-ft-991-am-issue-resolution/


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