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[wxsig] Crashing and random characters

Guy Story KC5GOI kc5goi at gmail.com
Tue Jul 1 01:53:37 UTC 2008


John Koster wrote:
> 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
>>>>
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>>>>     
>>>>         
>>> _______________________________________________
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>>>
>>>
>>>
>>>   
>>>       
>>
>>
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>>     
>
>   
I have bent back pin 15 on the header that connects to the display for 
now.  The heat sink is still getting warm but not like it was.  I like 
the voltage regulator idea.  I will talk to someone I know at Tanners in 
Dallas about the part.  I have had it running for about 40 minutes now 
and so far it seems ok. 

Guy




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