It is interesting to look at the shape of the output signal after such adjustments. And of course, I am sure that the thin probes of the cheapest Chinese multimeter dangling in the holes from the bolts show the true value of the current. An excellent guide to breaking your expensive transceiver!
Thank you for your comments. It is entirely up to the viewer whether they undertake this adjustment or not. The methods they use are entirely their decision. Any equipment used is whatever the person doing this check has to hand. If they have a professionally calibrated ammeter then they can use it if they so wish. No part of this video insists that people buy a cheap Chinese multi-meter to carry out this work, they can easily used a high-end professionally calibrated meter that costs hundreds if they own one. Anyone who is unsure of the methods used or lacks the skill required to undertake this work should consult someone who is knowledgeable. The probes were lodged in the contacts and shown as they are in the video for clarity - showing the probes being held in place by hand would make the video less clear. Finally my transceiver is not broken! See you on the air!
@@doktorvells3634 You must be responsible for creating a false impression of the simplicity of such manipulations, which encourages some people to repeat this and break their devices. My son once watched a video that was inspiring with its simplicity and decided that he could clean the laptop himself. I then had to repair what he broke. I know for sure that an incorrect bias current leads to a change in the operating mode of the transistors and signal distortion. Have you checked whether the signal shape has changed at different frequencies and at different power levels?
All the points you make are the responsibility of the person carrying out the process. If anyone has concerns about what they have been told then they either investigate for themselves (including looking at component datasheets) or simply do not do it. They must use their own judgment! Reducing the bias current will not break the radio and it can be increased again (with care) if the user so wishes. This information was provided for the experimenters of the amateur radio community. I do not have the time to discuss this further with you.
Hi, just went through the technical suplement of FT991a, page 27, HF PA unit adjustment and there is clearly written adjust to get 1,5A. Any idea why YAESU officially instructs to adjust to 1.5A? The technical supplement for this model is easy to get. Any idea?
No idea. I have seen somewhere that the original Yaesu recommended level of 1.5A is or was an error. Numerous people have had problems with the transistors blowing when biased at 1.5A. Transmission works OK when biased at 1.0A.
Got mine done, but if I pulled the jumper on 4001, it wouldn't read anything. With it on, it read 1.57 amps. I adjusted it as low as it would go (1.3 amps). I then pulled the jumper on 4002 and the reading went to 0 amps. I put it back on and was able to adjust the reading to exactly 1 amp. so, I adjusted 4001 reading to 1.25 amps, then brought it to down to 1 amp with the other. This 'balanced?' the adjustment of both sides to about the middle of their adjustments. In any case, if I put my meter back on, it will read 1.0 amps. Hope this works.
Hello, me again. Sorry. But since ind8d this, i could never get 100W again in HF, max 60 or 65. I returned bias to 1,5Amp and the power was back!!! Its ok to have 1Amp and low power? Some ideas? Thanks
hello, in my 991 I removed the Giampers one at a time and there is tension in both. why then do I have no power?? max 40w modulated in usb and 20 in fm.
Ok have not done this mod yet but will. My concern with the FT-991A is no USB connection. It did work fine for about 2 or 3 years and then no communication thorough the USB port. Sent it to the service center in California and they said it needed a new mother board for about $700 USD. Well I did not get it fixed but Have seen a repair of the USB circuit on you tube. Also low audio from the radio but I can live with that. Thanks for the great video and keep them coming.
Judging by what others have written and referring to the Mitsubishi datasheet then misalignment was probably the cause. Transmitting into a severely mismatched load (high SWR) can also cause the transistors to blow.
You forgot to say that you have to have the radio in SSB Mode, otherwise if you have it on FM you are going to get a really big current, also you don't need to get out your screwdriver if the current is 2 Amps then it is correct.
Some people have performed this on their brand-new FT-991A's. Whether you do this or not is entirely up to you and depends on many things including whether you want to void any warranty you may have on the radio.
Thanks for this!!! I will do it ASAP! Question... Have you reach to a solution for the FT 991A tuner issue? Ill tune it at low part of 40m band and in LSB as soon i pres PTT it puts carrier and infinite SWR. Thanks
@@doktorvells3634 service manual for 991 and 991a both say 1.5 amps. Sent rig back to service and asked to set idling current at 1 amp..seemed aggravated a bit and said he had done these for years and never a failure, but did not indicate his setting. We shall see, but I will ask where he set it when it returns. I sent to service for blown finals at 50 watts SSB, then did same at 35 watts. Frustrated. My ts 590sg works fine in it's place, as does my Paragon II.....same hook up.
It doesn't matter because the configuration described in the video puts the radio into 'transmit' with the final transistors in 'stand-by' mode due to the fact that USB is used with no audio to modulate the suppressed carrier. Just to be on the safe side I would set it to 5W.
@@doktorvells3634 Thank you very much. I just wanted to be sure before attempting this. I see when I transmit 100W it only shows 90W on my SWR/Watt meter. Want to nip this in the butt before it presents itself as a problem later on.
That's perfectly understandable. I wrecked many a radio (and other things) when I first started in electronics because I didn't know how to approach taking things apart then reassembling. Now I know that a methodical approach is necessary and to be in the right mood is also important. My biggest tip is don't try to rush the job because that is when mistakes can happen the most.
Is this procedure valid on the FT 991 NOT A? Are they being biased wrong at factory, or does technical specs tell repair services to bias them incorrectly? I just got new finals, and using 35 watts on ssb mine blew. again! NO issues with station as I have other rigs and swapped cables and switches with those on other rigs and other rigs are fine. Antenna fine, P.S. fine, &190 dollars a pair is getting expensive.
Procedure IS valid for 991A. Biased incorrectly at factory. I can't explain why yours keep blowing. If you bias yours as shown in the video you SHOULD be OK unless something else is wrong.
Just checked mine, properly biased from the factory. purchased in the US in 2021. Zero issues with this rig
It is interesting to look at the shape of the output signal after such adjustments. And of course, I am sure that the thin probes of the cheapest Chinese multimeter dangling in the holes from the bolts show the true value of the current. An excellent guide to breaking your expensive transceiver!
Thank you for your comments. It is entirely up to the viewer whether they undertake this adjustment or not. The methods they use are entirely their decision. Any equipment used is whatever the person doing this check has to hand. If they have a professionally calibrated ammeter then they can use it if they so wish. No part of this video insists that people buy a cheap Chinese multi-meter to carry out this work, they can easily used a high-end professionally calibrated meter that costs hundreds if they own one. Anyone who is unsure of the methods used or lacks the skill required to undertake this work should consult someone who is knowledgeable. The probes were lodged in the contacts and shown as they are in the video for clarity - showing the probes being held in place by hand would make the video less clear. Finally my transceiver is not broken! See you on the air!
@@doktorvells3634 You must be responsible for creating a false impression of the simplicity of such manipulations, which encourages some people to repeat this and break their devices. My son once watched a video that was inspiring with its simplicity and decided that he could clean the laptop himself. I then had to repair what he broke. I know for sure that an incorrect bias current leads to a change in the operating mode of the transistors and signal distortion. Have you checked whether the signal shape has changed at different frequencies and at different power levels?
All the points you make are the responsibility of the person carrying out the process. If anyone has concerns about what they have been told then they either investigate for themselves (including looking at component datasheets) or simply do not do it. They must use their own judgment! Reducing the bias current will not break the radio and it can be increased again (with care) if the user so wishes. This information was provided for the experimenters of the amateur radio community. I do not have the time to discuss this further with you.
I recommend adjusting the Bias current from the service manual 1.5 amp.
Adjusting 1 amp ALC may operate incorrectly in some frequencies
Hi, just went through the technical suplement of FT991a, page 27, HF PA unit adjustment and there is clearly written adjust to get 1,5A. Any idea why YAESU officially instructs to adjust to 1.5A? The technical supplement for this model is easy to get. Any idea?
No idea. I have seen somewhere that the original Yaesu recommended level of 1.5A is or was an error. Numerous people have had problems with the transistors blowing when biased at 1.5A. Transmission works OK when biased at 1.0A.
Got mine done, but if I pulled the jumper on 4001, it wouldn't read anything. With it on, it read 1.57 amps. I adjusted it as low as it would go (1.3 amps). I then pulled the jumper on 4002 and the reading went to 0 amps. I put it back on and was able to adjust the reading to exactly 1 amp. so, I adjusted 4001 reading to 1.25 amps, then brought it to down to 1 amp with the other. This 'balanced?' the adjustment of both sides to about the middle of their adjustments. In any case, if I put my meter back on, it will read 1.0 amps. Hope this works.
Hello, me again. Sorry. But since ind8d this, i could never get 100W again in HF, max 60 or 65. I returned bias to 1,5Amp and the power was back!!! Its ok to have 1Amp and low power? Some ideas? Thanks
That is strange Martin. I can get 100W on HF with 1Amp no problem.
hello, in my 991 I removed the Giampers one at a time and there is tension in both. why then do I have no power?? max 40w modulated in usb and 20 in fm.
Ok have not done this mod yet but will. My concern with the FT-991A is no USB connection. It did work fine for about 2 or 3 years and then no communication thorough the USB port. Sent it to the service center in California and they said it needed a new mother board for about $700 USD. Well I did not get it fixed but Have seen a repair of the USB circuit on you tube. Also low audio from the radio but I can live with that. Thanks for the great video and keep them coming.
Thanks for the kind comments. I hope you get your USB connection repaired soon.
If I find one of my blown finals to be at more than 1 amp, would it be safe to safe Yaesu misaligned them and thats why they blew?
Judging by what others have written and referring to the Mitsubishi datasheet then misalignment was probably the cause. Transmitting into a severely mismatched load (high SWR) can also cause the transistors to blow.
You forgot to say that you have to have the radio in SSB Mode, otherwise if you have it on FM you are going to get a really big current, also you don't need to get out your screwdriver if the current is 2 Amps then it is correct.
I also reviewed the service manual and it does say to adjust to 1.5amp, does the output reach 100 watts when using 1.0amp?
Yes.
Im just about to buy a brand new 991A in 2024, are you suggesting I should have to do this on a brand new radio from manufacturer?
Some people have performed this on their brand-new FT-991A's. Whether you do this or not is entirely up to you and depends on many things including whether you want to void any warranty you may have on the radio.
@@doktorvells3634 but if I buy one brand new it will have three years Yaesu warranty so if it goes pop wont this be covered under the warranty?
Thanks for this!!! I will do it ASAP!
Question... Have you reach to a solution for the FT 991A tuner issue? Ill tune it at low part of 40m band and in LSB as soon i pres PTT it puts carrier and infinite SWR. Thanks
Sorry Martin I do not low about that problem. Glad you like the video anyway. One of my transistors was biased at 1.5A!
I did it! Also with 1,5A in my unit. Procedure accomplished! Thanks
You are welcome.
@@doktorvells3634 service manual for 991 and 991a both say 1.5 amps. Sent rig back to service and asked to set idling current at 1 amp..seemed aggravated a bit and said he had done these for years and never a failure, but did not indicate his setting. We shall see, but I will ask where he set it when it returns. I sent to service for blown finals at 50 watts SSB, then did same at 35 watts. Frustrated. My ts 590sg works fine in it's place, as does my Paragon II.....same hook up.
Any specific Power Output needed when doing this? 10 watts? 25 watts? 35 watts? or does it not matter? Thank you
It doesn't matter because the configuration described in the video puts the radio into 'transmit' with the final transistors in 'stand-by' mode due to the fact that USB is used with no audio to modulate the suppressed carrier. Just to be on the safe side I would set it to 5W.
@@doktorvells3634 Thank you very much. I just wanted to be sure before attempting this. I see when I transmit 100W it only shows 90W on my SWR/Watt meter.
Want to nip this in the butt before it presents itself as a problem later on.
I thought this problem was taken care of by Yaesu when they went to the FT-991 A model. Apparently not. Ridiculous.
10W into indoor dipole? BOSS! 😊
Thanks! I mainly run 10W or less into it. It isn't a perfect antenna but it works quite well under good conditions.
Thanks
You're welcome.
I don't have the guts to do this on a perfectly working radio.
I guess I would rather risk doing nothing than taking the risk of my causing problems.
That's perfectly understandable. I wrecked many a radio (and other things) when I first started in electronics because I didn't know how to approach taking things apart then reassembling. Now I know that a methodical approach is necessary and to be in the right mood is also important. My biggest tip is don't try to rush the job because that is when mistakes can happen the most.
Is this procedure valid on the FT 991 NOT A? Are they being biased wrong at factory, or does technical specs tell repair services to bias them incorrectly? I just got new finals, and using 35 watts on ssb mine blew. again! NO issues with station as I have other rigs and swapped cables and switches with those on other rigs and other rigs are fine. Antenna fine, P.S. fine, &190 dollars a pair is getting expensive.
Procedure IS valid for 991A. Biased incorrectly at factory. I can't explain why yours keep blowing. If you bias yours as shown in the video you SHOULD be OK unless something else is wrong.