GM300 AUDIO ISSUE

[modatking]

Gents,

I have a Vhf Gm300, when I turn the volume up on a busy channel to hear, it produces a loud "feedback" noise, when I bring the volume down it goes away.It sounds as though I was standing infront of a PA loudspeaker with a microphone.



Any Ideas what may be causing it?

I am using the internal speaker, both pins 15 and 16 are jumped for internal speaker.

thanks

Dennis

[ledzep11]

There are pins which interconnect the RF board and the logic board. Try cleaning these pins...they are known to have corrosion issues.

[jackhackett]

Bad feedthru connector between the logic and RF boards.


Edit: Stardate 0911.25 supplemental...

Didn't see the previous answer the first time I posted, so I'll expand a bit..

The feedback problem is usually caused by the connector being physically broken, the connecto is actually a series of ceramic feedthru capacitors with the pin soldered to the inside plating, on the older style connectors the plating breaks away with the pin, and it ends up forming a nice little microphone that picks up vibration from the speaker causing feedback.

If the part number on the connector is not 2804637J01 it is the older style and should be replaced with one of that number.

Also, make sure the shields are all seated well.

[Will]

Can also be a bad RX VCO coil gone microphonic. Try a test with an external speaker.

[modatking]

Ok,

So in the meantime, till I get around to taking it apart. If I connect an external speaker I should be ok?

I mean now, the speaker is no longer in the housing with the bad cap.

[jackhackett]

Well... an external speaker will help with the feedback problem until you can get the cause fixed, but if it's the connector you can have other problems, such as the radio going off frequency quite a bit.

The VCO coil could also be the problem.. I've seen that a few times, but not nearly as much as the connector being bad.

If you've got the connector with the number I mentioned stamped on it, it's probably ok and you can just clean the pins and reseat it, if it's not that one, you WILL need to replace it.

good luck with it.

[modatking]

thanks for the help guys!