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Hi, a strange question. I had been given an FC20 many years ago by a ham now sadly SK and it seems to have had a mini melt down. Inside near the control port there’s a sensing inductor and the surrounding parts have burned out. As it’s on the input I can only assume it’s been driven with excessive power somehow or some other issue. There is a 20pf trimmer and on the schematic it claims to be Null adjust. I believe it’s in the VSWR forward and VSWR reverse sampling however it’s on the transceiver side so I’m trying to get my head around why the parts burned out. It seems a resistor 27ohm took the brunt but melted TC1001 in the process and much of the PCB tracks. I’m replacing all surrounding components regardless as they amount to pennies but can anyone clarify what null adjust as I can only assume it’s a reference to 50ohm and FSD on reverse.? As it’s coupled to TP1008 a test point I assume one hooks up equipment here to adjust null.
If anyone has a service manual about as I’m not sure one was ever issued. Any information on what null adjust is would be helpful if it’s in the service manual.
Many thanks in advanced,
De Spence M0STO
Sent while portable! please excuse typos.
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This may help, I have not found set up instructions yet
BR
Andrew
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Hi Andrew, the information is spot on and I really appreciate it.
? Just waiting for a callback or email from Yaesu UK. They’re pretty good chaps there so normally turn things around quickly.
? As soon as I’m in receipt of my bits I shall go through your alignment tips. I’ve got a really accurate Bird Termaline and a few very good SWR meters too and can use two Bird 43’s one in FWD and one in REV.
? Many thanks and will report back when all is done. Just wish I had a foil layout but can reverse engineer the tracks.
? 
Kind regards Spence de M0STO? Sent while portable! please excuse typos.
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On 23 Feb 2022, at 15:23, Andrew Lenton < a@...> wrote: This may help, I have not found set up instructions yet
BR
Andrew
<yaesu_fc-20.pdf>
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Hi Spence,
A good site to find manuals etc. for Yaesu is either the main Yaesu site, or the site.? On the FT site, look at the right side of the page and scroll down a little bit, you will find the main manual site.? Click on it and it'll take you over to all of the pages they have with manuals, service manual, and schematics if they can be found.? Sometimes no one ever got the the tech supplicant, so it's not to be found.? Also on our site here, go to the files section, I had uploaded everything I had on the FC-20 along with the FT-847.? I have the service manual on both print and disc if I remember right, but I had to buy the FC-20 form another person and no manual or anything with it.?
73
Russ Abbey, N4MAV
Floyd County, Virginia
EM97ua
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Hi if you used a Bird through line, make sure the element power is low i.e. 50 Watts when using on reflected, as most SWR meters have a more sensitive scale on reflected! The Bird is the same scale in reverse, unless you change to a lower powered element, if you se what I am getting at, That is a bad burn up I suspect it was more than 100 Watts into an open circuit, lets hope the process or is still with us and the board is not too damaged. Bird is ideal for return loss, but not for a low SWR.
Change the Diodes to BAT46, I have some here I can make a matched pair for you
73
Andrew G8UUG in Hampshire
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If yoy need some close up photos of a not toasted FC-20. Let med know.
Nils
SM7DVO
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Hi Andrew, I’ve got a good stock of BAT46 and BAT85’s (used in the FT847) so thank you for the offer.
? Fortunately I have a few decent SWR meters and 50w and 100w elements and also aware of the shortcomings of the thruline so thanks for the heads up. I have two bird meters so easy to put a 50H element in reverse and 100H in forward.
? The good news is the tuner still works as expected. It still tunes on all bands! As strange as it sounds the processor isn’t affected as far as I can tell but it is in direct connection to the null adjustment circuit however some protection exists.
? I’ve put in a small order with Yaesu as mentioned so just waiting for that confirmation.?
Will keep you updated. Also noticed the gas discharge tube on the tuning board looks a little smokey. Not put a meter on it yet and doubt it’s taken a hit but they are available from RS Components for about ?6 and I’m a business customer so no postage fortunately otherwise this would start becoming a small but very expensive repair when compared to the cost of a second user ?tuner.?
? Many thanks and please keep the thread going guys as the information so far is absolutely dynamite. It’s really appreciated.
The very kindest regards,
De Spence M0STO? Sent while portable! please excuse typos.
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On 23 Feb 2022, at 15:54, Andrew Lenton < a@...> wrote: Hi if you used a Bird through line, make sure the element power is low i.e. 50 Watts when using on reflected, as most SWR meters have a more sensitive scale on reflected! The Bird is the same scale in reverse, unless you change to a lower powered element, if you se what I am getting at, That is a bad burn up I suspect it was more than 100 Watts into an open circuit, lets hope the process or is still with us and the board is not too damaged. Bird is ideal for return loss, but not for a low SWR.
Change the Diodes to BAT46, I have some here I can make a matched pair for you
73
Andrew G8UUG in Hampshire
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Hi Nina, I have two FT847’s, two FC20’s and two MD100 microphones. Sad I know but also two G5500’s. I went though a phase of buying everything twice when the opportunity came up so can take some close up snaps of my known good FC20.
Really appreciated my good friend. Thanks but will take my other one apart when I receive my components.
Kind regards,
De Spence M0STO? Sent while portable! please excuse typos.
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On 23 Feb 2022, at 16:12, Nils Ostman < n.e.ostman@...> wrote: [Edited Message Follows]
If yoy need some close up photos of a not toasted FC-20. Let med know. Nils SM7DVO
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I have a business account with RS where do you live ? 73 ? Andrew ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Spence M0STO via groups.io
Sent: 23 February 2022 16:22
To: [email protected]
Subject: Re: [YaesuFT847] Yaesu FC20? Hi Andrew, I’ve got a good stock of BAT46 and BAT85’s (used in the FT847) so thank you for the offer. ? Fortunately I have a few decent SWR meters and 50w and 100w elements and also aware of the shortcomings of the thruline so thanks for the heads up. I have two bird meters so easy to put a 50H element in reverse and 100H in forward. ? The good news is the tuner still works as expected. It still tunes on all bands! As strange as it sounds the processor isn’t affected as far as I can tell but it is in direct connection to the null adjustment circuit however some protection exists. ? I’ve put in a small order with Yaesu as mentioned so just waiting for that confirmation.?
Will keep you updated. Also noticed the gas discharge tube on the tuning board looks a little smokey. Not put a meter on it yet and doubt it’s taken a hit but they are available from RS Components for about ?6 and I’m a business customer so no postage fortunately otherwise this would start becoming a small but very expensive repair when compared to the cost of a second user ?tuner.? ? Many thanks and please keep the thread going guys as the information so far is absolutely dynamite. It’s really appreciated. The very kindest regards, De Spence M0STO? Sent while portable! please excuse typos.
On 23 Feb 2022, at 15:54, Andrew Lenton <a@...> wrote:
Hi if you used a Bird through line, make sure the element power is low i.e. 50 Watts when using on reflected, as most SWR meters have a more sensitive scale on reflected! The Bird is the same scale in reverse, unless you change to a lower powered element, if you se what I am getting at, That is a bad burn up I suspect it was more than 100 Watts into an open circuit, lets hope the process or is still with us and the board is not too damaged. Bird is ideal for return loss, but not for a low SWR.
Change the Diodes to BAT46, I have some here I can make a matched pair for you
73
Andrew G8UUG in Hampshire
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Hi Andrew, I live in Stanford Le Hope, Essex and my nearest branch was Bow, Maverton way but that has long shut. I think my nearest is in South London but I always order online these days.
? De Spence M0STO? Sent while portable! please excuse typos.
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On 23 Feb 2022, at 20:50, Andrew Lenton < a@...> wrote: I have a business account with RS where do you live ? 73 ? Andrew ? ? Hi Andrew, I’ve got a good stock of BAT46 and BAT85’s (used in the FT847) so thank you for the offer. ? Fortunately I have a few decent SWR meters and 50w and 100w elements and also aware of the shortcomings of the thruline so thanks for the heads up. I have two bird meters so easy to put a 50H element in reverse and 100H in forward. ? The good news is the tuner still works as expected. It still tunes on all bands! As strange as it sounds the processor isn’t affected as far as I can tell but it is in direct connection to the null adjustment circuit however some protection exists. ? I’ve put in a small order with Yaesu as mentioned so just waiting for that confirmation.?
Will keep you updated. Also noticed the gas discharge tube on the tuning board looks a little smokey. Not put a meter on it yet and doubt it’s taken a hit but they are available from RS Components for about ?6 and I’m a business customer so no postage fortunately otherwise this would start becoming a small but very expensive repair when compared to the cost of a second user ?tuner.? ? Many thanks and please keep the thread going guys as the information so far is absolutely dynamite. It’s really appreciated. The very kindest regards, De Spence M0STO? Sent while portable! please excuse typos.
On 23 Feb 2022, at 15:54, Andrew Lenton <a@...> wrote:
Hi if you used a Bird through line, make sure the element power is low i.e. 50 Watts when using on reflected, as most SWR meters have a more sensitive scale on reflected! The Bird is the same scale in reverse, unless you change to a lower powered element, if you se what I am getting at, That is a bad burn up I suspect it was more than 100 Watts into an open circuit, lets hope the process or is still with us and the board is not too damaged. Bird is ideal for return loss, but not for a low SWR.
Change the Diodes to BAT46, I have some here I can make a matched pair for you
73
Andrew G8UUG in Hampshire
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Good morning, for those who are following this post and interested in the cure? Here are some snaps of the good working FC-20 I also own (this is like new inside).
Here is a list of the components I’m replacing and the associated Yaesu part numbers.
TC1001??????????? K91000029????? TRIMMER CAP. ECV1ZW20X53T C1057 ???????????? K26270045? ? ? 200PF 500WV CERAMIC CAPACITOR D1008? ??????????? G2090244?????? DIODE? ISS106-E L1035 ??????????? L1790164??????? M.RFC LAL03VB102K R1053 ???????????? J07225270?????? CARBON FILM RES. RD16TPJ270 R1054 ???????????? J07225270?????? CARBON FILM RES. RD16TPJ270
Hope this helps anyone with similar issues.
Regards,
Sent while portable! please excuse typos. Hi Andrew, I live in Stanford Le Hope, Essex and my nearest branch was Bow, Maverton way but that has long shut. I think my nearest is in South London but I always order online these days.
? De Spence M0STO? Sent while portable! please excuse typos. On 23 Feb 2022, at 20:50, Andrew Lenton < a@...> wrote: I have a business account with RS where do you live ? 73 ? Andrew ? ? Hi Andrew, I’ve got a good stock of BAT46 and BAT85’s (used in the FT847) so thank you for the offer. ? Fortunately I have a few decent SWR meters and 50w and 100w elements and also aware of the shortcomings of the thruline so thanks for the heads up. I have two bird meters so easy to put a 50H element in reverse and 100H in forward. ? The good news is the tuner still works as expected. It still tunes on all bands! As strange as it sounds the processor isn’t affected as far as I can tell but it is in direct connection to the null adjustment circuit however some protection exists. ? I’ve put in a small order with Yaesu as mentioned so just waiting for that confirmation.?
Will keep you updated. Also noticed the gas discharge tube on the tuning board looks a little smokey. Not put a meter on it yet and doubt it’s taken a hit but they are available from RS Components for about ?6 and I’m a business customer so no postage fortunately otherwise this would start becoming a small but very expensive repair when compared to the cost of a second user ?tuner.? ? Many thanks and please keep the thread going guys as the information so far is absolutely dynamite. It’s really appreciated. The very kindest regards, De Spence M0STO? Sent while portable! please excuse typos.
On 23 Feb 2022, at 15:54, Andrew Lenton <a@...> wrote:
Hi if you used a Bird through line, make sure the element power is low i.e. 50 Watts when using on reflected, as most SWR meters have a more sensitive scale on reflected! The Bird is the same scale in reverse, unless you change to a lower powered element, if you se what I am getting at, That is a bad burn up I suspect it was more than 100 Watts into an open circuit, lets hope the process or is still with us and the board is not too damaged. Bird is ideal for return loss, but not for a low SWR.
Change the Diodes to BAT46, I have some here I can make a matched pair for you
73
Andrew G8UUG in Hampshire
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I can have RS deliver anywhere, I was just checking you were no 20 miles away! ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Spence M0STO via groups.io
Sent: 23 February 2022 21:14
To: [email protected]
Subject: Re: [YaesuFT847] Yaesu FC20? Hi Andrew, I live in Stanford Le Hope, Essex and my nearest branch was Bow, Maverton way but that has long shut. I think my nearest is in South London but I always order online these days. ? De Spence M0STO? Sent while portable! please excuse typos.
On 23 Feb 2022, at 20:50, Andrew Lenton <a@...> wrote:
I have a business account with RS where do you live ? 73 ? Andrew ? ? Hi Andrew, I’ve got a good stock of BAT46 and BAT85’s (used in the FT847) so thank you for the offer. ? Fortunately I have a few decent SWR meters and 50w and 100w elements and also aware of the shortcomings of the thruline so thanks for the heads up. I have two bird meters so easy to put a 50H element in reverse and 100H in forward. ? The good news is the tuner still works as expected. It still tunes on all bands! As strange as it sounds the processor isn’t affected as far as I can tell but it is in direct connection to the null adjustment circuit however some protection exists. ? I’ve put in a small order with Yaesu as mentioned so just waiting for that confirmation.?
Will keep you updated. Also noticed the gas discharge tube on the tuning board looks a little smokey. Not put a meter on it yet and doubt it’s taken a hit but they are available from RS Components for about ?6 and I’m a business customer so no postage fortunately otherwise this would start becoming a small but very expensive repair when compared to the cost of a second user ?tuner.? ? Many thanks and please keep the thread going guys as the information so far is absolutely dynamite. It’s really appreciated. The very kindest regards, De Spence M0STO? Sent while portable! please excuse typos.
On 23 Feb 2022, at 15:54, Andrew Lenton <a@...> wrote:
Hi if you used a Bird through line, make sure the element power is low i.e. 50 Watts when using on reflected, as most SWR meters have a more sensitive scale on reflected! The Bird is the same scale in reverse, unless you change to a lower powered element, if you se what I am getting at, That is a bad burn up I suspect it was more than 100 Watts into an open circuit, lets hope the process or is still with us and the board is not too damaged. Bird is ideal for return loss, but not for a low SWR.
Change the Diodes to BAT46, I have some here I can make a matched pair for you
73
Andrew G8UUG in Hampshire
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Spence G5STO
Andrew Lenton
Nils Ostman