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[wxsig] Problem with modem2 tx

William Beals will at beals5.com
Thu Apr 30 03:11:56 UTC 2009


Perdo:

All the power voltages look OK.

On P100 pin 6, the PTT line to your transceiver, it could end up doing something strange looking if the transceiver is turned off.  Usually the radios have a protection diode, so if you try to drive 5V into the unpowered radio, it clamps the voltage. 

By the way, my long message earlier I was assuming Pin 6 was on P102 (header to the T238), not P100 (connector to the radio), so that whole diagnosis doesn't make sense!

Can you provide a description of the wiring you did between the modem2 and the radio.  I looked up the IC706MK2g and it seems reasonably straight forward, the only thing that looked weird is they had two separate grounds, one for PTT and one for audio. Did you just short the two together?

I downloaded the manual for the TH-F6A and was surprised it did not have a description of how to hook up the microphone jack. Where did you find the documentation on how to hook it up?

will

-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of pedro.motilla at ono.com
Sent: Wednesday, April 29, 2009 2:42 PM
To: wxsig at tapr.org
Subject: Re: [wxsig] Problem with modem2 tx

Hi to everyone��

Investigation, act 1:

Power to the modem2 board looks ok. (J2 or p102), between pin 15 and 16, 5 volts.

Other tests points, (included suggested by Will)

Mx614, pin 11, 5 Volts., pin 16, 5 volts.

U101, pin 8, 5 Volts., Pin 5, 2.48 Volts., pin 3, 2,48 Volts.

Positive pin on C108 (voltaje divider) = 2.48 Volts.

C110 = 5 Volts.

P100, pin 9, 5 Volts. pin 6, 3.41 Volts.

Extrange circunstance: when I insert female connector db9 to p100 and switch on the transceiver, voltage on pin 6 goes to 4.7 Volts, when it switch to tx, voltage drops to 0.05 Volts, if it is switched off voltage drops to 3.4 Volts.

So it looks like  as if all ICs would have good power, and all the voltage test points i can guess from the schematic, would be ok.

As you said, I tested on mx614 pin 11 and there  are 5 volts, so, it is supposed i  have a connection issue, you mean a connection issue between modem2 and transceiver (wiring cable) or between modem2 and motherboard?

As far as i do not have an oscilloscope at home, those are the tests i can do today with a multimeter (any other suggested tests are welcome).

Next check points (investigation act 2):

1- Test with scope that ceramic resonator DOES his job.

2- Test with scope p100, pin 8, when it is on tx to check if it goes any audio signal.


Thanks in advance for your time and help.

Best regards.

EA5BFT.
Pedro.



----Mensaje original----
De: will at beals5.com
Fecha: 29/04/2009 4:13
Para: "TAPR Weather Station SIG Mailing List"
Asunto: Re: [wxsig] Problem with modem2 tx

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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