[wxsig] Help with T-238 failure

[Clay Cottingham]

Scott -

I have the original T238 and have spent some time mucking around with it
both in hardware and software. The heartbeat is software controlled so as
John said it should pretty much narrow it down to the crystal or the CPU.
The CPU is rated for 5V so there is a pretty good chance it is fried - the
good news is that a new one will set you back about $11 + s/h - you will
still need to load it though. As I understand it, the T238+ needs a
different crystal to run in debug mode which would be required to load the
software on an off-the-shelf CPU. Hopefully TAPR or Will or someone can
provide a programmed CPU for a nominal fee.

I would also check the MAX232E since there are varieties that are rated for
5V and 12V. Not sure what was used on the T238+

I haven't been able to find much on the specs for the LCD panel nor a
datasheet. The link on Will's site is no longer active. If anyone has info,
please let me know where to get it.

I ran into heat issues originally when I was using a 12V wall wart supply.
Got a 7.5V one from Radio Shack and can now safely touch the heat sink on
the regulator. The regulator is rated for a max of 35V input and has thermal
shutdown protection, so in theory it should not have failed due to heat, but
the extra heat dissipation may have caused the failure.

Hopefully Will or someone else can give you better news. :)

Clay

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of John Koster
Sent: Wednesday, June 29, 2005 4:32 AM
To: TAPR Weather Station SIG Mailing List
Subject: Re: [wxsig] Help with T-238 failure

I didn't think about the heartbeat.  That alone might narrow things down 
to the processor and the oscillator.  Of course once you get those going, 
there may be other problems. 


I was hoping that Will would chime in here, but I think he is on a trip at 
the moment.  

I have the same problem with the scope.  Not enough BW.  I do have a logic 
probe that helps in most cases.  

On Wed, 29 Jun 2005 Sct599 at aol.com wrote:

>  
> Hi John:
>  
> Thank you for the response. 
>  LCD: When I initially found the unit after the failure, the display had
> random unintelligible blocks of pixels. These pixels would change in
> response to pushing the "Select" button. After subsequent power ups, the
> display is blank of any pixels. The back light remains functional. With
> it showing the random pixels initially indicate that it may have
> survived the event?
>  
> Crystals: I will check these as soon as I can and report back. Believe it
or 
> not, my scope is only a 5Mhz!
>  PC port: I had thought about doing this but did not since there was no
> "heartbeat" LED activity. Heartbeat LED checked out OK. Should I give it
> a try anyway?
>  
> Thanks again,
> Scott
>  
>  
>  
>  
>  
> In a message dated 6/29/2005 10:43:26 A.M. Mountain Daylight Time,  
> w9ddd at tapr.org writes:
> 
> Any  indication that the LCD module survived?  For some reason that and
the  
> crystal modules would be the first suspects on my list.  You should  be 
> able to talk to the unit without the LCD though via the PC port.   
> 
> I'd start by verifying the oscillator works with either a scope or  logic 
> probe that's good to 32MHz.  Nothing happens with the 32MHz  clock
working.
> 
> On Wed, 29 Jun 2005 Sct599 at aol.com wrote:
> 
> >  Hello Group:
> >  
> > I am looking for any input you all may be  able to provide concerning a

> > failure with my T-238 (original  model).
> >  
> > Found that the U5 voltage regulator had failed  putting approx 11 volts
on  
> > the 5 volt buss. Replaced U5 and no  indication of unit coming back to 
> life.  
> > Performed the "Power up  and initial testing" procedure and all appears
to 
> be OK.  
> > Is it  safe to assume that the U3 microprocessor and possibly all 
> components   
> > powered by the 5 volt buss have been destroyed?  If so, is there  any
hope  
> in 
> > repairing this unit?
> >  
> >  73,
> > Scott - NØLNE
> >  _______________________________________________
> > wxsig mailing  list
> > wxsig at lists.tapr.org
> >  https://lists.tapr.org/cgi-bin/mailman/listinfo/wxsig
> > 
> 
> --  
> 73,
> John,  W9DDD
> 
> 
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> 
> 
> 
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> 

-- 
73,
John, W9DDD


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