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[wxsig] Crashing and random characters

John Koster w9ddd at tapr.org
Tue Jul 1 01:28:28 UTC 2008


A cheap and dirty way to test if this is a heat problem, is put in say a
47 ohm 1 watt or so resistor.  I don't recall what the current draw is on
the T238+ is, but if it's around 100 mA, that would get you down to a
little under 10 VDC going into the T238+.  Tweak the value as needed.  
This takes approximately half the regulator heat away from the board.  Of 
course the further the resistor is away from the T238+ the better.  

If you choose the resistor method as a permanent solution, then mount it 
outside any enclosure you might mount the T238 inside of.  



On Mon, 30 Jun 2008, William Beals wrote:

> Guy (and all):
> 
> I forgot about the switching regulators!  Another good solution if that is
> the problem.
> 
> Guy: If you power supply is putting out 13.4 volts then I'm more confident
> that is your problem.
> 
> will
> 
> -----Original Message-----
> From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
> Behalf Of Mark Patton
> Sent: Monday, June 30, 2008 8:43 AM
> To: TAPR Weather Station SIG Mailing List
> Subject: Re: [wxsig] Crashing and random characters
> 
> I replaced mine with a 3-terminal switching regulator made by TI.  I got 
> it from Digi-Key.  I think the one I used was 78SR105HC-ND.  It 
> physically is much larger but pin compatible.  I used epoxy and mounted 
> it to the back of the main PB board.  I just fit (insulate it first 
> though...).  It's been working perfectly for the past 2.5 years.  I'm 
> sure there are others that would work just as well.
> 
> Mark
> 
> Ken Brown wrote:
> > A couple of years ago someone posted a message about this subject and
> > he said he replaced the voltage regulators with drop in replacement
> > TI switching regulators.  I have done the same thing and my original
> > T-238s are now quite stable.  They are three terminal drop in
> > replacements for the 7805 regulators. They cost about $10 at the time.
> > Unfortunately I don't have the part number at hand here but could look
> > it up this evening.  I got them from Mouser.
> >
> > Ken
> >
> > Guy Story KC5GOI wrote:
> >   
> >> William Beals wrote:
> >>     
> >>> Guy:
> >>>
> >>> Ouch, that doesn't sound good.  It also doesn't sound familiar
> >>> unfortunately.
> >>>
> >>> You definitely want the 1.15.8 firmware, it is a lot better and more
> stable
> >>> than 1.15.4.
> >>>
> >>> Any chance the voltage regulator is overheating?  It can happen reliably
> if
> >>> your incoming supply is much over 12V and your backlight is on.  For a
> >>> lightly loaded and unregulated wall wart, that voltage can easily get up
> to
> >>> 14 or more volts.  The regulator handles it for a while, but then starts
> >>> going into thermal shutdown which isn't a graceful on/off shutdown.
> >>>
> >>> will
> >>>
> >>>
> >>>   
> >>>       
> >> Will, the heat sink for the voltage regulator is getting too hot to 
> >> touch.  I do not require the back light.  I will check the schematic 
> >> tonight for the trace the backlight is on and cut the trace.  I remember 
> >> we had to do that on the original kit year ago due to a short on that 
> >> trace.  The power supply is putting about 13.3, and I am running 4 
> >> instruments.
> >>
> >> Thanks.
> >>
> >> Guy
> >>
> >> _______________________________________________
> >> wxsig mailing list
> >> wxsig at lists.tapr.org
> >> https://lists.tapr.org/cgi-bin/mailman/listinfo/wxsig
> >>     
> >
> > _______________________________________________
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> > https://lists.tapr.org/cgi-bin/mailman/listinfo/wxsig
> >
> >
> >
> >   
> 
> 
> 
> 
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> 
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-- 
73,
John, W9DDD





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