The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

This radio worked great until my friend tried a new antenna with it now it squeals on transmit ( only on the am side) but not really a squeal that varies , more like a constant tone on the carrier, it does not vary with the modulation . anyone have any ideas as to what could cause this ?
Thanks

First check the mic,,if the shield gets shorted with the
audio wire it can cause a squeal..If youve checked the
mic and it is o.k..Then next id check the voltages
at TR-51 the AM Mod Amp..If TR-51 shorts you dead key
will be wide open, no forward modulation..And often it
will cause a high pitched squeal.TR-51 is located on the
right chassis rail,the transistor closes to rear of unit..It
should be a 2SB-754

Thanks for the suggestion , I will check it out , it would be helpfull if I could find a schematic for this radio would make trouble shooting a little easier, is there any where on the web I could find one?

I should have mentioned the radio will still transmit with mod, but the tone is super-imposed with the signal and I have tried different mics with same result.

Do you have an oscilloscope or a signal tracer? If so, I would look through the audio sections, and the transmit chain to see where the signal originates.

Don't know if this will help or not, but there is a wire wound choke on the mic. socket board that will sometimes burn or become open that will cause a squeal or hum in transmit when mic is keyed even with the mic gain turned down and talk back turned off. hope this helps.

Thanks but the mic board does not have a coil on it only a couple small caps, does anyone know where I could find a schematic for this radio? sure would make it easier to troubleshoot the audio section as no matter where I touch the scope to the squeal is present

cb tricks,,,look under the galaxy 77hml exact same as general lee
minus the fancy faceplate..another thing you might want to check
the diodes around the audio transformer..reason i say,,i have a cobra
148 gtl i bought off fleabay..and it does the same thing..and i discovered
some dumdum hooked it up reversed..fried the reverse polarity diode.
so they just took a pair of needlenose pliers and broke out the
shorted diode,,then apparently hooked it up reversed again..this time
fring the chokes on the power wires,,the diodes around the audio
transformer,,melted several wires around the transformer,,
gees what a mess...and that what it does,,it still receives good
and has good dead carrier,but with a constant squeal in audio.