MY YAESU FT-991A IPO/ATT FAULT - Frontend gone Bye Bye...... 

Hi Mike, Thank you for posting the link to my article, and I'm super pleased that it did someone else some good. The friend who's radio I repaired operates multiple radios at the maximum legal limit and has not experienced a failure since I did the original repair that was documented in the article. For those who ask about leaving the radio on with a nearby transmitter active, this is not a good idea. The RF at the receiver front-end is half-wave rectified by D1004 and then the resulting DC bias drives Q1005 into saturation, activating the ATT circuit (and making it susceptible to burn-out). This vulnerability is discussed in the article. Q1005 was a good idea by Yaesu, but wasn't implemented quite correctly in that the resistor power rating in the attenuator was not up to the task. The goal of Q1005 was to have the attenuator kick in and protect the receiver front end from nearby RF sources. Had the attenuator not burned out, the circuit would have done just that. Cheers. W7CIA P.S. I've added a link back to this RU-vid video in the article.

I wonder Yaesu has corrected this problem on the 991A in 2021???

Good job ! That happened to me about 25 years ago - I had an IC-725 in my bedroom as a receiver. I had left it on with an antenna connected. I was in my shack working DX. When I came back to the bedroom, the front end of the IC-725 was damaged. Ever since then I have made absolutely sure I do not have other rigs switched on and connected to a nearby antenna while transmitting on a different HF rig.

Well done Mike for researching this and sharing the fix. Top Banana 🍌👍

Good job Mike! Thanks for sharing

Thanks for the video. My radio also suffered a failure while operating with a legal limit transmitter. On my radio, it did not matter if the attenuator was on or off, the receive would only pick up extremely strong signals. R1005 was split in half. In addition, pin diodes D1113 and D1089 also failed. For some reason D1090 was ok. I was lucky to find the diodes on digikey as they are now obsolete. The diodes are tiny and the only ones available are an even smaller form factor than the originals. Replacing them was like giving a flea a haircut. Anyway, just want to let people know that if the fix isn't successful, check the pin diodes following the resistor.

Another great video Mike,TNX!!! I'm really looking for the answer from Yaesu to you!! By the way, I have in plan to buy FT-991A in close future..however for my mobile & portable operation "old" FT-890AT is still OK. It is nothing new for multiple operator situation,but such "a mistake" in 2020 should NOT happen to Yaesu, who make otherwise great radios!!!

Thanks for this detailed instruction video, my 4 year old 991A has just developed the same problem.

Thank you very much for this. I own an 991A and this radio was bought exactly for fieldday, camping and so on. Will keep it away from other rigs. 73 Hermann DK2BE

If one must listen on another band while transmitting, external band pass filters are the way to go. If listening while transmitting is not required, some relays and XOR keying logic with the amplifier keying lines offers a lot of flexibility. I use the amplifier keying line from my transceiver to operate a pair of isolation relays for the SDRPlay receiver.

Great video! I would like to caution others to NOT use a wire wound resistor. Wire wound resistors can behave like coils in RF and audio circuits.

Great job mike.

Very Good.Thank,s.

Thanks Mike, my 991 for some reason stopped receiving in IPO, I calculate that due to high radio frequency nearby, how could I replace the 150 ohm resistor and solve the problem, thank you very much.

Hi mike I glad you posted this issue with 991A ,it just happen to my brand new yaesu 99A with less than 5 hrs use. I will examine mine , it looks pretty much the same issue ,I was trasmitting on 80M while the 991A was monitoring 20m , then i realize the front end was gone on my 991 ..over the years I have many radios set up the same way and never before happen anything like that, it is pretty upsetting since is a brand new radio ..I will try to fix it since I live in DR . HI6FMX thank you mike

Many thanks for the Great Video Mike I have a 991 With Same issue The Resistor does not look blown but it looks as if its got a bump on the top i never new this was a fault until i tested it against my mates 991 a brand new out of the box thanks again

'Should a £1,100 radio blow-up and stop working in 2020' .. no, and just one of the many reasons I am dubious about giving the Y company any hard earned. Good fix ! 73.

Seriously good video. The clarity of the images was superb. Thank you! I'm on the fence on buying a 991a. I have a IC-746 that works well but it doesn't have modern noise reduction filters. Do you think I can just add a DNR speaker (they cost nearly $200 US) to my 746, or would it be worth the investment going from a 20 year old radio to the 991a?

Hi thank you for this video, and i guess, have the same issue, can you please what is the website you are reffering to, what is the value of the resistor? Thanks

Interesting. I bought my FT-991A s/h from a reputable dealer and it had the IPO fault and also was deaf on VHF / UHF SSB only. It was a long repair job but finally tracked down to blown diodes (invisible) in the front end. Luckily, they repaired it FOC and Yaesu apparently paid the bill. Then I knew why the previous owner had traded it in!

Hi mike,many thanks for the vid, i have just bought a 2nd hand 991a and it has this problem, on examining the resistor its still in place but my radio has exactly the same problem as yours in the video, will removing the resistor and replacing it be the answer ???? or is there a way i can check the resistor before removing it ???? many thanks mate

Great fix! I have an issue with my 991a but I don't really know anyone local who might be able to fix it so may have to send it in. It works on HF fine and receives 2m/70cm fine but does not transmit correctly on 2m analog/2m c4fm/70cm c4fm. 70cm analog does seem to work. I got the unit as the third owner and I believe the first owner had some kind of issue with the radio and may not have understood what it was or what had happened. I really do like the radio in all other regards so far, seems to "hear" really well.

I did same Transmitted on 160m ant with kw while my 891 was connected to 80m dipole 891 was tuned off Didnt think it would harm it but now ipo/att gone It receives ok like before but turning on sigs drop 9 s units Anyone know what to check /replace ?

I had the same problem after only two hours of installation, this is a design problem that I hope will solve at least for those who are not able to remedy. Thanks for the video and link

i havent looked at the schematic but the question is, can you leave this radio ON while transmitting on another radio? What about VHF? say I use the 991a as a VHF/UHF radio, it's turned ON and i'm transmitting on another HF rig, will this burn the resistor? ALSO what if the 991 is OFF and it's connected to an HF antenna while i'm transmitting on another radio? will that cook the resistor again?

Will this happen if I use a legal limit amplifier with my 991a? I also run 2 radios will it be ok if I disconnect the antenna and switch it off?

I had issues in the same zone around that relay but it was D1113 causing my PTT to switch the Power amp switching output to always switch to ground. Replacing D1113 fixed my remote PTT out.

hello great guide, by chance do you know how to expand the V and U?

Does Yaesu acknowledge this as a flaw they will fix, or is there some "put a choke in, or stay X meters away from another antenna" instruction somewhere?

I'd be cautious about adding a zener diode across D1002. Non-linearities, parasitic capacitance etc might create undesirable effects. Any conventional zener will try to conduct in forward direction at around 1V). Using a higher power rated R1005 (as shown) is a good choice although keep in mind that some conventional resistors have spiral cut film which can add an inductive component.. could that make attenuation vary with frequency on higher bands? I'd try to select a non-inductive part. Very careless of Yaesu to make such a mistake.

Hi Mike, I have a 991a with a slightly different issue but could be related. Everything seems to work as it should but i have a dead S-meter on SSB, On FM it flickers erratically. The TX side of the meter reads as it should but on RX it just sits at 0. No one seems to know or have heard of this issue. Any help greatly appreaciated. Lee M0RQX

MOst of the radios have very similar front end protection nowadays. FT-991 has a protector for 8KV/30A momentarily. In a club with several stations, a band pass filter is recommnded for each radio, especially if linears are used. And also a RF choke on the radio side.

Mike -- I think I have a similar problem. Incoming signals are distorted to the point that I cannot understand what the other party is saying. I don't know how this happened. Any thoughts?

Have you had anymore issues since putting in the larger resistor Thanks much

I also have an FT991A, it lives in my shack, so this problem is unlikely to rear its ugly head, but at least I now know what to fix if and when it happens, thanks for documenting this. 73 M7PDF

Hi Mike….just a simple question bearing in mind I know nothing about this hobby.. I’ve just bought a Ft991a as a receive station only and will not be transmitting on it - will I cause any damage to it if I run this off the same ariel as my ic705 which I use for receive only aswell?basically running two rigs off one ariel through a 3 way BNC connector?….much appreciated rep,y please…( please forgive my lack of knowledge on the subject!) Andy W

Just looking at radios to buy and that was on my shortlist. It isn't now though!

Thank you Mike, for this valuable contribution. I operated two KW transceivers in same shack. The FT-991 immediately failed, with the problem described. Thanks to your contribution, the matter was settled after one hour ... Thank you very much

Another fine job done in the kitchen ;o)

We all know that Yaesu will never admit one way or the other that this issue is a problem. One other reason that this failure occurs is static and lightning. Digikey does have a direct equivalent SM resistor that I figure is a better for replacement that a thru hole component. Digikey has it as (CPF-A-0805 B150RE).

Hi Mike, I have seen (and repaired) nearly identical damage to other models of rig. This is by no means a Yaesu or FT991A only problem, FWIW switching the radio off does not protect it from this type of damage. It is difficult to protect against this type of damage without affecting IMD performance. Unfortunately the attenuator is prior to the bandpass filters so the damage can readily occur even if the transmitter is on another band. Glad to see someone else fixing their own gear! 73

The deformed plastic on the relay has not made it "sticky" by any chance? Nice repair :)

Wouldnt have thought a tiny thing like that would cause that much destruction..certain!ey saved a few Bob than Sending it away

My dream radio

how many watts? how far away from other transmitter? what types of antennas? how far apart were the antennas? what frequency? any rigs front end can be blown; i'm curious as to the condition/situation that caused your failure

HI Mike I had this problem but have just received my 3 month old 991A back from Yaesu repair under warranty. all good now, many thanks for explanation. R1005 was blown, R1012 high, D1089 gone high resistance and a 47ohm resistor? so a bit different. 73 Rob G3RCE

Same happened on a 7610 of a friend

same issue with a ft891. Not sure if same cause. Works normal till ipo or att is turned on

Up to watching your film i was all for the ft991a think i will keep the icom 7300, ive heard a few lads who use the ft991a say when in contests they have problems with rx over load. Mike M1KEY M0FCG

The FT-891 has the same issue. 3 weeks new and already back at Y for repair.

Was this a 2nd attempt at repair as the relay looks melted as if touched by a soldering iron. Perhaps it was from you cleaning up the pads. Caution as this could cause the relay to fail mechanically.

you muuuulted the relay housing lol

Where you learned to do that ??

Troubling...... I've not heard of this. I will ask around.

How near?

Mine just burned up while in QSO with a friend of mine. I have an electrician coming in to search the house for problems.

Yaesu got that 1 horribly wrong!

Audio is not the best :( It can handel some boost/and a limeter music is way to loud.

These are the greatest pieces of junk I've ever seen and it's not that I haven't given them a chance. Like 5 chances. One they just refunded 1000$ of my money which was around $400 light. Other times they repair them only to find other problems rearing their heads. Like PL tones changing as well as tones changing freq.. I want this radio, I love this radio but it hates me. Why the JUNK? If anyone knows please tell me. I wish I could sell them for ICOM's but can't get it fixed or my money back.

Mine did this. And it was switched off.

Terribly weak audio, need to speak up.