My son has an FT-891 that he has mounted as a base radio in his shack.  He's had it for several months now.

Yesterday, he noticed that the fans seemed to be coming on more often when he was just leaving it powered on without transmitting.  He felt the heat sink and the chassis, and it was warm to the touch.

He turned down the brightness of the display, and that didn't seem to affect anything.  He dismounted the radio from the shelf (its mounted to the bottom of a computer desk hutch and open on all sides) and noticed the ground wire had been knocked off, but he hasn't been transmitting with it, so that shouldn't have made a difference.

After reconnecting the ground wire and remounting the radio on the shelf, after sitting for a couple of minutes, it would get hot again and the fans kick on.

We both did google searches, and didn't find anything.  I'm really stumped at why this radio gets this hot when its not transmitting.

If you have an FT-891, does it get hot and the fans kick on when its just only receiving?

This may not help much, but can you dig through the menu and find temperature displays for various parts of the radio?  For instance, my K3 has a temperature readout for the amp, and also for the front panel display.  It might help locate what is getting hot.

Echo above and ask these questions.

Does he live in a dusty environment, does he have pets, does he smoke.

If yes to any of the above, he may need to clean the interior of the radio.

This is probably a stupid question but what is the radio sitting on? Is there anything sitting on top of it? Blocking air vents and/or putting the radio on something else that might be getting hot will certainly cause that to happen. Also check the input voltage to the radio from whatever power supply he's using.

Time for an amp clamp.

I have one and have not noticed it getting warm on receive.

Its attached to the underside of the computer desk hutch using the bracket that came with the radio.  Its wide open on the back, bottom and sides, and has about a 3/4 inch gap between the top of the radio and the hutch.  Its been this way since it was installed months ago.

No on smoking, but yes on pets.  Normal household dust.  We opened up the radio case, and the inside is pretty clean (no dust found.)

Power supply is an Astron 35 amp power supply.  Its the same on that he's been using with that radio and the Icom 735 that was replaced by the FT-891.

I have not noticed that with mine.

Time to borrow a thermal camera.

The heat from the radio will go upward. Perhaps a small fan to push the air around the radio when it's on will solve the problem.
73,
Rob

Mine definitely doesn't get warm while it's just sitting there receiving. I also have a headset plugged in so it's not using the on-board speaker.

Were you able to check the voltage coming from the power supply? (Not likely to be the problem but I don't have any other ideas). I'm assuming from your description of the way it's mounted, it's not the sun beating down on it nor is it getting heat from some other piece of gear nearby, particularly something underneath the radio on the desk itself (since it sounds like the radio is elevated).

We haven't had a chance to check the voltage yet - probably do it tomorrow night.  FWIW, there is a dual band 2m/70cm radio and the auto tuner that uses the same power supply and neither of them have had any problems like this.  They've both been hooked up to the same power supply since the FT-891 was installed.  And, the 891 has gotten hot with the dual bander and tuner off.

Also, he uses that radio for FT-8, and its hooked up to a Signal Link USB.  But, its been hooked up to that Signal Link and used for FT-8 since it was installed back in January.

My son brought up the problem with his FT-891 at our ARES meeting last night and everyone was pretty well stumped.  The only suggestion they had was to do a hard reset on it.  Other than that, the only option is to contact Yaesu.

Its not in direct sunlight - in fact, when we've noticed the problem its been after sunset.

There is a small flat screen monitor below the radio, but the monitor has been in that location since the radio was installed.   Regarding the shack hardware nothing configuration-wise has changed since that radio was installed.  Everything is the same and mounted in the same location.

Check your AMP draw into the radio also.

I can't remember which but there are some electrical components (gates?  MOSFETs?) which when fail, can fail closed.  If the radio is drawing power like it's transmitting, without actually transmitting, that'd be a good place to look.

I was finally able to check the volts and amps.   Its showing 13.85 volts DC.  The ameperage started off with the radio pulling 2.8 amps.  It kept going up until the fans kicked on.  I stopped measuring when the radio was pulling 4.61 amps and my fingers and hands got tired holding the probes

I did talk to a Yaesu rep., and he said that on receive it should pull around 2amps.

We're still stumped.

Might try pulling the covers off and poking around inside to see what's actually generating all that heat.

If you have an IR thermometer, that could also be useful.

It shouldnt be pulling that much .... I've never saw mine pull over 1.5 amp in rx.  Most of the time it pulls 0.95 Amps in rx with the settings I run .

The manual says 2.0 A current consumption when actively receiving an incoming signal.

Page 30

https://static.dxengineering.com/global/images/instructions/ysu-ft-891_sn.pdf

Seriously - time to open it up and see if you can isolate where it’s getting hot. (Or send it in I guess).

If the current draw is ramping up, I would guess there is a component in thermal runaway. Could be anything from a bad solder joint to a leaky cap conducting DC and changing a bias point.
73,
Rob

Thanks everyone.  I'm going to open up a ticket with Yaesu tonight and get it sent back in under warranty.

I'm really curious as to what has happened to it......