A bit of a story here with the conclusion being: The "Mute Rx" transistor had failed short circuit and reduced high band Rx performance but didn't kill it completely - so if you suspect yours, it might be worth checking. Trust your instincts if you buy one second hand from a dealer & you suspect this, and ask for a meaningful (i.e. vs another FT450) a/b test at the least. So I've had my FT-450 for over a year now. When I first got it (second hand from a dealer) I found it very quiet on the higher bands but had nothing to compare it to and it was my first transceiver at my new QTH after a 6 year break from the hobby, so I rationalised it as being lucky to live in a QRM-free zone. I did take it back to the shop and compare with another receiver on one antenna, and was convinced it was OK. Any differences I put down to the other transceiver being superior and it was hard to tell anyway because of the high QRM around the shop (so band noise beat Rx noise on all bands and "S-meters aren't calibrated are they?"). However, now that the higher bands have been opening up again the nagging feeling came back & I verified that band noise wouldn't beat receiver noise on 28MHz. Then I read this https://www.wirehead.be/index.php/2018/10/10/yaesu-ft-450-deaf-on-higher-bands/. I decided to measure those two protection diodes and found them to be failed open circuit, not short. So a fault, but not one that would cause poor sensitivity. A bit more poking around revealed that Q2005 - the "Mute Rx" transistor - had failed short circuit between base and collector. I carefully removed it from the board and, yep, higher bands are now normal and much more lively with noise and signals on average maybe 4 S-points above where they were. I replaced Q2005 with a spare RF signal transistor from my stock. So - it's fixed. However: The two diodes are still open circuit and I guess I should replace them - though they've been like it for over a year. On the other hand the Rx is not now protected by the shorted Q2005. My repair isn't pretty as I used a TO92 case transistor with legs bent carefully to line up with where the SOT-23 SM pads are. I wonder what would happen if I simply removed this transistor? I know it mutes the Rx input on Tx, but for what purpose given there is also a Tx/Rx relay? Is it needed to mop up stray signal leaking through the relay? (Similar question - what happens if my ugly repair fails e.g. emitter / collector soldering goes open circuit?) I'm posting this as I said in case anyone else suspects their Rx on the higher bands, and I wonder what people would do next: Leave it - it works Replace the o/c diodes Replace the o/c diodes and attempt a better repair by buying a genuine replacement Q2005? Try to find a spare RF-IF board and play at the above knowing I can swap the board if it goes wrong? Buy another rig, sell this one with this story in the advert? All of the options are part of the fun of the hobby!