Author Topic: No LED  (Read 6991 times)

Offline vairmoose

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No LED
« Reply #15 on: May 09, 2012, »
Traces?

Larry
3 today (standing at light switch, holding two lighters)
Going live in 2012

Offline rmp2917

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Re: No LED
« Reply #16 on: May 10, 2012, »
Pins 2 and 3 on the 6 pin ICSP header are 3.3V and ground. Also, pin 40 on the daughter board header is 3.3V.

I believe the only other 3.3V connections (besides the ones you've already checked) are on the two SMD chips. I can send you the pin numbers to check if you would like.

Offline jess_her

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Re: No LED
« Reply #17 on: May 10, 2012, »
This would be the last thing I would do.  Find half way on your 3.3V trace/buss cut it in a easy reparable place and keep halving it until you find the short. Solder bridge across the cuts for trace repair.
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Offline rm357

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No LED
« Reply #18 on: May 10, 2012, »
Cutting traces??
Really??

That would be the very last resort in my book.
Take some good pictures of both sides of the board and post them. Let us have a look before you start doing crazy stuff...

RM
Robert
Warner Robins, Georgia, USA

Offline pk

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Re: No LED
« Reply #19 on: May 10, 2012, »
Are there any 0.1 UF capacitors in the 3.3V rail that could be shorted?

Offline dcwehw99

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Re: No LED
« Reply #20 on: May 10, 2012, »
OK Guys, here's what we have now.

I removed the ICSP header as suggested by RMP since it was on the 3.3v trace and we still have the short.  I looked at the 48 pin connector (2 - 24pins) and figured that I probably wasn't going to get it removed without any damage so I checked for any continuity between pin 40 (3.3v) and the surrounding pins and found none.  Pin 33 on the connector is the closest ground and it and pin 40 show a short.  According to my mapping of the 3.3 trace the only other components on it are the two SMD chips as RMP has verified also.

PK I removed all 0.1uf capacitors on the 3.3v rail as my initial try going for the most likely thing.  There were 11 of them and I have circled them in red in the attached picture.

Maybe RJ could chime in on this one for any other suggestions or if you guys have any other options, please put them out on the table.

Thanks
Denny

Offline pk

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Re: No LED
« Reply #21 on: May 10, 2012, »
I am just throwing this out for what it is worth... are any of the blue 10 UF capacitors on the 3.3V rail?


Offline dcwehw99

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Re: No LED
« Reply #22 on: May 10, 2012, »
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I am just throwing this out for what it is worth... are any of the blue 10 UF capacitors on the 3.3V rail?



The four 0.1uf capacitors at the bottom of the board are in the +5v net and appears to be OK so I didn't remove them.  The three groups of a blue 10uf and the yellow 0.1uf capacitor are not on the +3.3v rail and don't show any problem when I check them with the meter.

All input is worth considering.  I appreciate all responses and suggestions since I'm at the end of my rope.

Thanks
Denny

Offline bisquit476

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Re: No LED
« Reply #23 on: May 10, 2012, »
Hi Denny,

I've circled what I believe to be pins 33 and 40, which you are saying shows a short. Those 2 pins are connected by resistors aren't they?(yellow arrows and blue circle) I may be wrong.

Offline twooly

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Re: No LED
« Reply #24 on: May 10, 2012, »
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Hi Denny,

I've circled what I believe to be pins 33 and 40, which you are saying shows a short. Those 2 pins are connected by resistors aren't they?(yellow arrows and blue circle) I may be wrong.

Did you mean to upload a picture?
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Offline dcwehw99

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Re: No LED
« Reply #25 on: May 10, 2012, »
Here's the latest thing I've done.

I've removed the three (3) 10uf capacitors and one leg of each 0.1uf capacitors with the exception of the four (4) 0.1uf capacitors below the four (4) 485 chips and the short is still present.  Those four (4) are on the +5v rail.  Here's a picture of the board as it stands now.

Denny

Offline t.jo13

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Re: No LED
« Reply #26 on: May 10, 2012, »
Not sure if it is bridged but take a look at the area I have circled. the arrow is pointing at it

Offline dcwehw99

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Re: No LED
« Reply #27 on: May 10, 2012, »
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Not sure if it is bridged but take a look at the area I have circled. the arrow is pointing at it

There was a small piece of solder sitting next to that pin but no bridge.  Must have gotten there from removing one of the other solder connections on the board.

Thanks
Denny

Offline bisquit476

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Re: No LED
« Reply #28 on: May 10, 2012, »

Did you mean to upload a picture?


Why yes, yes I did, sorry brain fart.

Offline dcwehw99

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Re: No LED
« Reply #29 on: May 10, 2012, »
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Hi Denny,

I've circled what I believe to be pins 33 and 40, which you are saying shows a short. Those 2 pins are connected by resistors aren't they?(yellow arrows and blue circle) I may be wrong.

No, those 2 pins aren't connected by resistors but they are connected via six (6) 0.1uf capacitors located at the right end of the four (4) optocouplers and 485 chips.  The top two (2) row of arrows, indicated by the blue circle, is the +3.3v rail where I removed one of the legs of each of the six (6) capacitors.  The bottom arrow is on the ground rail and is the other leg of three (3) of the capacitors.

Thanks for you input.
Denny