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[wxsig] Problem with modem2 tx

William Beals will at beals5.com
Wed Apr 29 02:13:58 UTC 2009


Pedro:

Both earlier suggestions are good, either decreasing R101 or increasing C111.

My concern with your statements though is that you are saying NO audio, not LOW audio.  The above two fixes are to better handle not enough audio instead of none at all.  If it truly is no audio at all I am worried it may be something bigger.  With no audio at all (and no real receive capabilities coded), it could be a symptom of the MX614 not being operational at all.  Good on checking the chip, so that means something else.

The voltage you mention on pin 6 is a good indicator.  It should go very close to 5V.  I do drive an LED with it, but have the current limiting resistor there to not drag down the output pin of the microcontroller.  3.5V is roughly the trigger voltage for the MX614 to decide if it is in transmit mode or not, so it could explain things nicely if it turn out to be the case.  To try and isolate the issue, put a voltmeter on pin 11 of the micro and check the voltage there.  If it is 5V, then you have a connection issue.  If it is 3.5V, then it could be a solder bridge to another pin and you have two shorted outputs.  A quick way to isolate it if so is to pull the modem board off and re-measure the voltage when the LED is supposed to be on.  If it goes to 5V, then the short is on the modem board, if it stays at 3.5V, then the issue is on the main board.

Also, do check things like the crystal.  I'm not sure if you have or have access to an oscilloscope, but that is about the only easy way to check a crystal.  If you do, that is also a great way to see if any audio is coming out of pin 7 of the MX614.

So, lots of suggestions!  Not sure if any will pan out, but with feedback on what you measure, I'm sure we can isolate the problem for you within a few more emails.

will

-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of Mark Patton
Sent: Tuesday, April 28, 2009 3:55 PM
To: pedro.motilla at ono.com; TAPR Weather Station SIG Mailing List
Subject: Re: [wxsig] Problem with modem2 tx

It's been a couple of years but I seem to recall having a similar 
problem.  The problem was that the audio level was too low going into 
the radio.  I remember changing out the serial resistor labeled R101 in 
the schematic for something smaller than a 10K.   I'm traveling this 
week so I don't have access to may marked-up schematics until later this 
week to tell you exactly what I did. 

You might try searching the forum archive for "low audio" or something 
similar.  I recall that I wrote up my findings on the forum.

Mark

pedro.motilla at ono.com wrote:
> Hi people��
>
> First of all, i enjoyed very much with the kit, it is really cute and nice, just one frustrating thing:
>
> I have a problem with tx. 
>
> The motherboard has sw 1.15.4R
>
> All the wxstn seems to work properly. (temp., communication with pc, menus, etc.)
>
> The modem board seems to be correctly assembled. Components are (at least seems) to be ok.
>
> All the tests from the manual are ok, only one gives a difference, but I think it is a mistake in the manual, it says that pin6 from modem2 should show 5V. Actually it shows 3,5 but I think is ok as far as 5 volts run trhought a led and i think it is normal a small voltage drop.
>
> Tx happens, so Q100 should be ok.
>
> The problem is that no audio gets out. When it is switched to tx, nothing is heard.
>
> Tests has been done with 2 transceivers, Icom mk2g and ht Kenwood thf6, with 2 transceivers the same happens.
>
> I changed the mx614p, but the problems does not fix.
>
> The RV100, has been put on several positions and the problem is the same.
>
> Just in case, I changed rx to tx pins (just to eliminate a wiring mistake).
>
> Any idea?
>
> Thanks in advance for help.
>
> Best Regards.
>
> EA5BFT
> Pedro.
>
> _______________________________________________
> wxsig mailing list
> wxsig at tapr.org
> https://www.tapr.org/cgi-bin/mailman/listinfo/wxsig
>   




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