No LED

[twooly]

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?

[twooly]

Pics

[rmp2917]

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.

[twooly]

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.

[twooly]

Pic of the board after touch up

[rmp2917]

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?

[twooly]

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?

[rmp2917]

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.

[twooly]

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.

[caretaker]

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. 

[RJ]

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

[dcwehw99]

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?

[rmp2917]

What about the 100uF capacitor?

[dcwehw99]

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. 

[dcwehw99]

Both 100uF caps have been removed and the short is still there.