Lpc2000

topandurangs wrote:

>--- In lpc2000@yahoogroups.com, "Leon Heller" <leon.heller@...> 
>wrote:
>  
>
>>----- Original Message ----- 
>>From: "Pandurang Shinde" <pandurang@...>
>>To: <lpc2000@yahoogroups.com>
>>Sent: Wednesday, March 22, 2006 11:35 AM
>>Subject: RE: [lpc2000] Re: RTC problem in 2136
>>
>>
>>    
>>
>>>thanks for immediate reply.
>>>Yes i am using external watch crystal of 32 khz. I have also 
>>>      
>>>
>found that i 
>  
>
>>>am not getting oscillation on that board(the board in which i am 
>>>      
>>>
>not 
>  
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>>>getting RTC updaed value ). But when i used same crystal on 
>>>      
>>>
>other board 
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>>>it( crystal ) seems working,so crystal is fine.
>>>What are the possible reason that i am not getting oscillation 
>>>      
>>>
>with 
>  
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>>>working crystal
>>>      
>>>
>>Are you *sure* the leads are properly soldered to the pads? Remove 
>>    
>>
>any flux, 
>  
>
>>it might be conductive. Chip might be faulty.
>>
>>Leon
>>--
>>Leon Heller, G1HSM
>>leon.heller@...
>>http://www.geocities.com/leon_heller
>>
>>    
>>
>
>
>hi,
>       Thanks once again.
>       Chip might be faulty.
>       Is there is any chance of this thing.
>       Because out of 50 boards i am facing this problem on nearly 
>more than 5 boards. 
>
>  
>

That sounds like a manufacturing problem more than an engineering 
issue.  In your situation, assuming the circuit is designed correctly, I 
would carefully inspect the boards visually under a microscope to see 
how clean the solder joints are.  I have seen boards which were not 
properly reflowed leaving debris around the pins: tiny little clusters 
of solder balls which have not melted properly nor have been cleaned off.

I had one manufacturer have me inspect some boards they had gotten from 
the assembly house which did not run.  Again, it was a small but 
significant number of boards.  Under a 20X microscope, you could clearly 
see the solder debris which was shorting pins out.  The debris was 
between the pins and back inside from the end of the leads: poor job of 
reflow + cleaning.

TomW


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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