[wxsig] T-238+ modem2 No Text on Display

[William Beals]

Charles:

Another possibility is that the MAX232 is not working quite right.  The LCD
needs the -9V supply from that chip to generate the bias voltage used by the
potentiomenter to adjust the screen contrast.  Check both sides of the
potentiometer with a volt meter, one side should be +5V, the other side
should be -9V.  Or, meausre Vlc on the LCD module and wiggling the pot
should adjust the voltage from +5V to -9V.

If you don't see the -9V, check all the caps around the MAX232.  If it does
check out, then we're back to hoping somewhere there is an open or short on
the seven control signals to the LCD.  Best bet in that case is to have the
LCD plugged in and the entire T238 powered off and measure continuity for
all the signals.

Let us know if that works.

will 

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of Charles Suhr
Sent: Sunday, April 22, 2007 8:57 AM
To: 'TAPR Weather Station SIG Mailing List'
Subject: RE: [wxsig] T-238+ modem2 No Text on Display


I'm running a 9vdc input.  And the unit was powered off before I started
this test.

Charles

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of Dave
Sent: Sunday, April 22, 2007 9:46 AM
To: TAPR Weather Station SIG Mailing List
Subject: Re: [wxsig] T-238+ modem2 No Text on Display

Are you supplying it 12 volts?  This sounds like the temperature problem a
lot of us had.  The voltage regulator in the 238 doesn't like 12 volts and
overheats.  We put in a voltage regulator to drop the 12 volts down to I
think 8, and then the regulator in the 238 knocked it down more to what it
liked.  I am sure the more techy people will give you more info.

Dave

----- Original Message -----
From: "Charles Suhr" <charles at ccsuhr.com>
To: <wxsig at lists.tapr.org>
Sent: Sunday, April 22, 2007 6:40 AM
Subject: [wxsig] T-238+ modem2 No Text on Display


>I having a problem get text to show on the display.  I just completed build
> my T-238 and Modem2.
>
> Working my way through the power up and testing everything was working 
> like
> a champ till I got to the point of connecting the LCD screen; I mid 
> position
> the contrast pot and had 4 rows of boxes no matter where I adjusted the 
> pot
> I got no text.
>
> Contrast varied from no boxes to the 4 rows of boxes.  Any Ideas?
>
> I check pin to pin from t-238 to LCD module looking for a open but got 
> good
> results.
>
> The Activity LED flashes just like it supposed to and voltage measurement
> on U1 and U2 are fine.
>
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