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Hardware => Lynx EtherDongle => Topic started by: twooly on April 04, 2012,
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So long story short I got 2 etherdongles in the lastest coop. Got them both built and only one works.
It will flash ok (verify checks out ok) and the led comes on during the flash but when connected to power the led doesn't come on and no lights on the ethernet jack either.
So here is what I've checked and I'm not sure what is going on.
Getting 8.55 in from the power connector
Seeing 5.0 and 3.3 on the voltage regulators
Pin 1 - 8.55, Pin 2 - 0, Pin 3 - 5 on the 5v regulator
Pin 1 - 0, Pin 2 - 3.3, Pin 3 - 5 on the 3.3 v regulator
50MHZ Oscillator - 3.3v between pin 4 and 8
50 MHZ Oscillator 1.6v between pin 4 and 5
So I got those readings and wanted to double check them so I started going through them all again when I noticed the power on the connector has now dropped to 6.02 instead of the 8.55 like before and the 3.3v regulator was extremely hot (my dad jumped really quick when he touched it :) ) and saw readings from it of like 0.32. The 5v I was now seeing 4.97
I'm going to go through and retouch everything just seemed wierd that all of a sudden the power dropped and now all the readings are off
Any thoughts?
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Pics
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The output of the power adapter should be 6V.
8.5V seems a bit high. I checked the output on mine and they are around 9V with nothing connected.
If the regulator is getting hot, it could be getting shorted. I cannot tell in your picture but it looks like the corner of the heat sink is very close to one of the small capacitors. Make sure that the heatsink is not touching any other components
Also, check for any solder bridges.
It may be a typo but you listed two 50MHz oscillators. One should be 50MHz and one should be 8MHz.
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So I did a retouch on everything last night and the power in is showing 7.98
Heatsink is not touching anything.
I only gave numbers for the one 50MHZ oscillator, showed between the different pins.
Ill have to get readings on everything else tonight.
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Pic of the board after touch up
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I don't see any obvious issues from your pictures and your original voltages seem to be correct.
Did you test it again after doing the touch ups?
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Here they are
Getting 7.37 in from the power connector
Pin 1 - 7.34, Pin 2 - 0, Pin 3 - 4.87 on the 5v regulator
Pin 1 - 0, Pin 2 - 320mv, Pin 3 - 4.74 on the 3.3 v regulator
50MHZ Oscillator - 50mv between pin 4 and 8
50 MHZ Oscillator 250mv between pin 4 and 5
So we think the 3.3v regulator is toast?
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So we think the 3.3v regulator is toast?
It's possible, but since you were getting 3.3V initially, it would be unusual for it to suddenly go bad. You didn't happen to touch it against something as your were checking the voltages? Or touch the meter probe against two of the pins at the same time?
Check the legs of the regulator to make sure solder didn't wick through and short out on the top side of the board. If you can't find any place that is shorting out, then I would guess the regulator is bad.
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I'll check them. Don't remember ever crossing it but anything is possible.
I had someone else here locally look also and the don't see a solder bridge either.
I'll say that I never noticed it being hot after the build because I never touched it. Went over it with someone else here locally and after getting the readings he touched it and it was extremely hot ( first time we touched it second time plugged in )
I'll probably get a new one to see if that does it.
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So I did a retouch on everything last night and the power in is showing 7.98
Heatsink is not touching anything.
I only gave numbers for the one 50MHZ oscillator, showed between the different pins.
Ill have to get readings on everything else tonight.
7.98 is what I got on mine so that should be OK. I would replace the 3.3 volt regulator and go from there.
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Yes check careful for bridges first and then try changing it. try to carefully cut the legs off and then remove each leg on at a time. Heat the leg with your iro turned up hot and give it time to heat all the way throught the pcb. Do not pull on it if it is not coming easy it is still semi soldered and you will pull a trace off the pcb. So be patient with it and on ease it our when it will come on its on with very little effort.
RJ
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Twooly handed this off to me to take a look at it. The problem manifests itself as a short in the 3.3v side of the circuit. I have checked and rechecked multiple times for any solder bridges and found nothing. There is approximately a 0.5 ohms of resistance differences between the probes touching themselves and what is displayed across pins 1 (ground) and pin 2 (+3.3v) of the 117v33 voltage regulator. So if my premise is correct there is something with very low resistance causing a short and thus why the 3.3 voltage regulator was "burning" hot.
Here's what I did to try and located the short.
1. I removed one end of all the capacitors on the board that showed continuity across the capacitors. There were 11 of them as shown in the picture. The short was still present.
2. I removed the removed the 8mhz and 50mhz oscillators. The short was still present.
3. I removed the "Magjack". The short was still present.
4. I then checked the resistors still soldered into the circuit and all of them checked out OK. The short was still present.
5. I removed the four(4) optocouplers (6N137) from their sockets. The short was still present.
6. Although the 5v regulator didn't appear to be the problem I removed it because of was running out of options. The short was still present.
7. I believe the only two things remain in the +3.3v circuit; the Ethernet and PIC chips. Both of them look OK when I look at them with a light on the backside of the board. I don't see any bridges on any of the pins.
I'm out of options and things to try.
Any other ideas of thoughts?
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What about the 100uF capacitor?
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It looks like one of the 100uF caps is on the 6v input and the other one is on the 5v output of the 7805 regulator I'll remove them and then report back.
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Both 100uF caps have been removed and the short is still there.
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Traces?
Larry
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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.
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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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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
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Are there any 0.1 UF capacitors in the 3.3V rail that could be shorted?
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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
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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?
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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
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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.
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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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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
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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
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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
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Did you mean to upload a picture?
Why yes, yes I did, sorry brain fart.
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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