Saturday, 10 March 2012

Yaesu FRG7700 AF Gain pot wanted

There is a very nice Yaesu FRG 7700 comunications receiver sitting on my desk, I can see that the BBC World Service is broadcasting, as the S meter is working on 17,639khz, that should be 17,640khz but the memory is 2khz off station.

That is not the bother, the audio pot control has failed, which is a great pity as I can now hear nothing!

Bought off my good friend Willie from the  Lello 34, Bucaneer. The set is a 1982 model,  so some 30 years old now.

The audio pot has stopped working, on the net I found some advice on using Q20 spray oil, the result was fine for a short while, then silence, I was worse off than when I started, so can not advise that idea.

This is the Potentiometer I need a replacement for, its a duel action type, being the AF Gain and also the Tone. The owners handbook on page 25 tells me its symbol number VR1 and the part number is J6280009, with a description of DM10A638A-10kb-10ka

click on the picture for a larger view.

Note, this is not the part number as above, its the M Fine/Squelch control but looks the same as the Audio/Tone control. Does anyone have a spare for me.

Note, I have emailed Yaesu GB ( England) with no reply, also Yaesu Japan, same again, no reply, at least a reply to advise no stock, would have advised me they can not help.  Would you buy a new radio from such a company?

Update:  I have a spare pot, which pin connects to what is the question, Notty and Justin advised I use this method.

I used small shrink tubes to allow me to fit the meters test pins, worked a treat!

You need this type of meter, the digital type will not work, there are three connections on the pot, the center is a common, while the outer ones are basically left or right, the knob is turned fully clockwise right now, so this will be full audio.

I now need to isolate the audio from the tone, leave the tone wires alone and then wire in this new pot, that can be either left remote or mabye fitted into the phone jack or recording hole position for now?

How hard can this be?


News from the shack:

Hello Justin,

Well well, each day I turn on the Yaesu FRG 7700 and hope and hope I can hear some sound.

Today and on BBCs 12,095khz, I found sound at the full clockwise postition as normal, I then turn it down untill the sound drops off as its really just noise. This morning was no different, excepting each time I turned the audio down,the sound came back and as the volume setting became lower the audio was becoming clearer, so much so that I have the BBC news on for the first time in years!

Right now the audio pot is set quite low, about position two, there is clear sound right the way across now, I assume I have burnt it back in, the years of sitting on a shelf, left on frequency but the audio pot turned right down may have done the damage?

So I can now do the required ground wire and a long wire antenna through the roof  I think.



Note, the FRG 7700 does get very hot when using a 220 volt supply and left on all the time, so much so that some wax in parts of the set melted and dripped down. I would advise the fitting of a small ventilation fan in the area left hand of the front face and near the top of the set, there is a transformer there? I assume if we use the 12 volt supply option this are will not heat up?