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

William Beals will at beals5.com
Thu Apr 26 23:48:36 UTC 2007


Charles:

This REALLY does sound like an intermittent connection between the micro and
display.  I am wondering if it is a stealth-bad solder connection or
something.  Another possibility could be a short on one of the display lines
to something else.  From what you describe, the micro is pretty happy and
coming up reliably every time (from the LED).  It may not hurt to re-solder
all the pins in the LED signal path just to be sure, there aren't that many.
Another thing you may want to try is to GENTLY flex the main board a bit on
power-up to see if that has a dramatic effect.  That would point to an
intermittent connection.  

When you do try something, it is important to reboot (hit the reset button)
between each attempt.  The interface to the LCD is using a 4-bit mode that
if it gets out of sync, may not easily get back in sync unless you hit the
reset button.

will

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of Charles Suhr
Sent: Tuesday, April 24, 2007 7:48 AM
To: 'TAPR Weather Station SIG Mailing List'
Subject: RE: [wxsig] T-238+ modem2 No Text on Display

Ok maybe someone can shed a little light on this.  I measured the voltages
at v1 -9 and +5 both looked good and center pin was variable.  I had already
check the continuity of all the data paths before.  I got a bit curious and
tried a couple of resets using sw1 then went and cycled through the switches
one at a time.  Got to a point where I was getting weird characters on the
displays and each menu press would add more but at least I was getting
display now.  Then tried reset one more time and got normal boot screen
credits and in memory and the to the missing 1 wire device which is true not
attached yet. Red heartbeat led was flashing every second the whole time.
Plan is to let the unit set powered down for a couple of hours then go power
it up again an see if it powers up fine this time.  Any Ideas what was wrong
initial?

Thanks for all the help

Charles

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of William Beals
Sent: Sunday, April 22, 2007 2:03 PM
To: 'TAPR Weather Station SIG Mailing List'
Subject: RE: [wxsig] T-238+ modem2 No Text on Display

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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>
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