[App_rpt-users] CM108 modification

[Doug Bade]

That explains it...I did not look there :-)

I need to see if my new Chinese versions have it ... it looks like 
lots more parts on the board but very similar otherwise... some other 
buttons added for mute and volume up down on the fob itself... 
assuming we do not need core.... I am wondering if I can isolate the 
4th pin on the speaker and  mic jack and just push ptt out that jack 
instead of cutting it all out as seems like the other 3 leads do not 
need to be changed...

I am considering replacing the npn transistor with a 2n7000 series 
fet as a series resistor is not needed on the gate side... as long as 
all runs at logic levels etc...

Doug



At 10:29 AM 7/8/2009, Stephen Rodgers wrote:
>Doug Bade wrote:
> > The schematic looks logically correct...
> >
> > C2 and C3 are in the usbfob.pdf picture..
> >
> > C1 does not appear to be.. It seems C1 is on the schematic but not
> > the construction picture.... I would think it should be there... as
> > to avoid DC coupling between the stages...
> >
> > I just recently got some CM109 based adapters from China that are
> > currently available and will be making some notes on them as I
> > perfect a mod..electrically they are the same.... the chip is 
> really tiny :-)
> >
> > Doug
> >
> >
> > At 08:24 PM 7/7/2009, you wrote:
> >> Ok, I'm modifying a CM108 USB adapter, and though I've done it
> >> before I can't remember if whether the picture or the schematics are
> >> correct in the pdf file.  In the picture, I see that for the mic
> >> input (RX Audio) has the twisted (or just soldered) end of the 68K
> >> and 470K attached to the 9 pin connector.  In the schematic, the
> >> twisted end is attached to a capacitor (which isn't in the picture
> >> and directions) and then to the mic input on the USB adapter.
> >>
> >> Can anybody tell me which way is the correct way to hook this up?
> >>
> >> Thanks,
> >> Jeff
> >> _______________________________________________
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> >
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> >
>As the previous post states, a coupling capacitor is required, however,
>it is already included in the SMT parts on the USB fob. The pictures
>don't show it because it is already mounted on the fob.
>
>C1 is a 4.7uF multilayer ceramic chip capacitor which is part of the
>original circuit as noted at the bottom of the schematic with an *.  An
>additional 4.7uF capacitor is not required,
>
>Steve
>WA6ZFT