[R-390] 3MC issue updated

[Curt Nixon]

Steve Quinn wrote:
> I posted this a while back, when I shift to 3MC I hear signals then they fade 
> but not all the way out.
>
> OR I hear signals for about 30 secs then the band goes dead, dead as a door 
> nail.  I have cleaned the xtal and it worked when I put it in my 75S-1
>
> Question:  are the R390A xtals different from the other xtals used in other 
> Collins?
>
> I have heard from all to clean this or that, well this unit was taken apart and 
> everything was refurbished but the dang 3MC and the related 20MC don't want to 
> play nice
>
> Thanks
>
> Steve Quinn
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>   
GA All:

To me, this sounds like a bad cap that is only in-circuit for this 
position.  I would be studying the "map" and looking to see where the 
signal dies.  Use a scope or the buzz test...this should localize the area.

Crystals don't "fade out"..tubes can but they all work for other 
positions. 

a resistor could..possibly, but those don't usually get switched in and 
out for frequency specific use. 

Some freeze spray could also be your friend in finding a problem like 
this.  Don't overlook newly replaced caps or mica, ceramic, also.  
Perhaps a dirty wiper on one of the inside-can- trimmers also.  A 
micro-drop of Deoxit on every trimmer will help especially if done prior 
to any alignment--but could help anyway even if you don't subsequently 
move the trimmer.

FWIW

Curt
KU8L