757gx recieve dropping out

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757gx recieve dropping out

Postby KD4VPC » Wed Oct 08, 2008 11:25 pm

i have a 757gx, the recieve drops out after a couple minutes, i can mess with the rfamp button it will come back and go out. i have checked the lamp fuse,it measure's 8ohms, its not bad, but i dont know where else to go with this, and can help please let me know, or know a good technician i can send it to,
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Intermittent Receive FT-757GX and RF Amplifier

Postby Ghostwriter » Thu Oct 09, 2008 6:28 pm

Hello Art,

First disconnect the Antenna Coax from the RF Amplifier Output connector and disconnect the RF Amplifier's Coax to the FT-757GX transceiver's Antenna connector. Take the Antenna Coax and connect it Directly to the FT-757GX transceiver's SO-239 Antenna connector. Now turn the FT-757GX transceiver "ON" and see if the receiver has the Intermottent or No Receive condition.

After roughly 10 minutes which should be enough time to evaluate the Intermittent Receive problem which will indicate whether the problem is located in the Transceiver or the RF amplifier.

Since you do not sound like you are technical and the Intermittent Receive problem indicates the FT-757GX transceiver maybe at Fault, I will suggest to find another experienced General, Advanced or Extra Class (licensed for 10-15 years) Ham Operator in the Oakboro, NC surrounding area to assist you as an "Elmer" while troubleshooting and perfoemming the repairs on the FT-757GX transceiver. You will also need the YAESU Manual with Schematics, Circuit Desription and a Parts List.

Go to this Fox Tanco Yaesu web page and download the appropriate Service and Supplement Manuals for your FT-757GX H.F. Transceiver:

http://www.securesystemsnw.com/ft/ft-library/Eighties/Eighties.htm

ALL of the FT-757GX PDF Manuals are about half way down the web page.

Now IF the Intermittent Receive indicates that the FT-757GX transceiver is not at fault then the problem is in your RF amplifier. Make Absolutely Sure that the Power Switch is OFF and the Primary Power 120 / 240V AC Plug is removed from the wall socket before Openning the RF amplifier case for Servicing! If you are confident enough to look inside the RF amplifier providing you've got an Owner's Manual, Schematic Diagram and Parts List, then find the Transmit / Receive Relay(s) which may be at Fault.

The T / R Relay(s) can be RF Coaxial or look like an Open Standard Relay. In either case these relay contacts could be Arced / Burnt / Pitted or Just Plain Dirty "OR" the Relay Coils may have become Magnatized. If the contacts are Arced / Burnt / Pitted or Just Plain Dirty you will need a Relay Burnishing Tool to properly clean the contacts. If the Relay(s) is and/or are Magnatized you maybe able to purchse new Coils like on a Dow-Key Coaxial Relay or in the case of an Open Frame Relay purchase new Relays and install.

IF you are not confident to do the required task alone, then I will suggest to find another experienced General, Advanced or Extra Class (licensed for 10-15 years) Ham Operator in the Oakboro, NC surrounding area to assist you as an "Elmer" while troubleshooting and performming the repairs.

73,

Dan
WA9WVX
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Postby KevinL » Tue Oct 14, 2008 2:24 am

Hello Art, Dan

Art mentioned that fooling with the RF Amp button will bring the receive back on..
My guess is that the RF Amp Relay is dirty. It is accessable with the covers off, lift off the relay cover, give it a light shot of cleaner and your back in bussiness.
It worked on my rig, the problem is that there is no current going through the contacts to keep them clean.

Kevin
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Postby Ghostwriter » Tue Oct 14, 2008 8:13 pm

Hi Kevin

The reason I worded my reply to Art the way I did, was to provide him a simple way to evaluate or troubleshoot the actual failure, Is it in the transceiver or in the external RF tube amplifier.

Secondly, with all of the new hams becoming licensed many of these people fail to realize that in a RF tube amplifier (non-solid state) there are Very High Voltages present that can KILL a person. That's why I painstakingly wrote what to disconnect before openning the RF amplifier's cabinet for servicing.

I don't know if you have seen the ARRL Motto: Switch To Safety or Safety First! but there's a lot of truth behind those words. Equipment can be repaired or replaced but the individual people can not.

And third, I'd be very careful about recommending the use of spraying contact cleaner into relays and/or switch contacts because if the individual purchases an off the shelf lubricant spray contact cleaner, this may add in the future a build up of dirt on the contacts. I preferr to use a Burnishing Tool and Denatured Alcohol applied with a miniature stiff brush to minimize premature failures in the future.

I also recommended the help of another "experienced ham" as an Elmer to assist Art through his repair process. Some times having another pair of eyes will provide advice about how to perform the repairs. Art seemed to be questionable about going through the procedures, even asking for a technical person to perform the repairs.

I knew where the problem was instantly but I wanted Art to understand the troubleshooting process of elimination and then proceed to the RF Tube Amplifier's relay(s) at fault. You never learn anything by just repairing or changing the component at fault.

73,

Dan
WA9WVX

Forty years with the same Callsign and Fifty Nine years with the same Name. Some things never change!
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Hi Dan, Ghostwriter

Postby W4CLM » Thu Oct 16, 2008 4:02 pm

HI Dan,
Great to hear from you. I'm sorry for the long delay in my reply. I'm working on a ship (Currently in Seattle) and won't be home until December.

Yes you're right the price of everything especially parts for older equipment has gone through the roof. We have RF switches for the FL-2100 series but not the "Z" model. The "Z" model has been most difficult to located a suitable replacement.

Anyway Dan, I need to write to everyone on the forum. I'LL look forward to talking to you down the line. stay in touch.
Best 73
Carol Maher W4CLM
In Port Seattle WA. October 16th, 2008
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