No 3volt or 5 volt LED on Power up

[austindave]

Hi Lineman,

Sounds like your regulators are right. 78c05 is the 5 volt one; and the one marked LD33cv is the 3.3v one (LD1117V33C) - you'll see in the LE manual, step 4 that these are the correct markings.

So from here, I'd suggest doing the following:

1. remove the RS-485 devices (2) and the optocoupler from the sockets. Try powering it now.
2. After removing power, check to see if any of the other components got warm / hot. In particular, check the capacitors.
3. While you're at it, check to see if one of the voltage regulators is getting warm. If so, which one?

Based on what you find from the above, the next step might be to use your ohm meter to see what's shorted.

Hope this helps.

--Dave

[lineman]

Hi Lineman,

Sounds like your regulators are right. 78c05 is the 5 volt one; and the one marked LD33cv is the 3.3v one (LD1117V33C) - you'll see in the LE manual, step 4 that these are the correct markings.

So from here, I'd suggest doing the following:

1. remove the RS-485 devices (2) and the optocoupler from the sockets. Try powering it now.
2. After removing power, check to see if any of the other components got warm / hot. In particular, check the capacitors.
3. While you're at it, check to see if one of the voltage regulators is getting warm. If so, which one?

Based on what you find from the above, the next step might be to use your ohm meter to see what's shorted.

Hope this helps.

--Dave

Removed the 2 485 chips and the H11aa chip this is tho opto right and the only thing that get hot is the round black bridge rectifier top left above 2700 uf and the trans. reg cool and the 2 100 uf cool to the touch

[RJ]

If it is not a solder bridge I am leaning to a bad diode in the bridge. Would be a first time I have seen this but not impossible I guess. You will need to desolder it and take it off. Then put your ohm meter on the pcb pad for + and the diagonal one for the ground. See if you have a short. If not then a new bridge would be called for. If you find a short there it is time to start looking for a solder bridge again.

I would look again for a solder bridge. 99% of the time it is not a bad part. Most of the parts used on this design is pretty tough.

RJ 

[Dennis Cherry]

Just a side comment.

Many years ago working as the lead technician in a electronic production department. I ran across a unit that would not work correctly and no amount of testing would find the problem.

Determined as I was in my youth, it took me a couple of hours to find the problem and not by using a meter or oscilloscope.

It took a good magnifying glass and a very close inspection of the PCB.  What I found was in the process of making the PCB circuit board, there must have been a scratch in the PCB or photo process and it left a VERY tiny bridge between 2 circuits.

Looking at it with just your eye you could not see it, only the magnifying glass and a good light would show it.

[lineman]

Would be a first time I have seen this but not impossible I guess. You will need to desolder it and take it off. Then put your ohm meter on the pcb pad for + and the diagonal one for the ground. See if you have a short.     OK I HAVE DESOLDERED THE RECT. OR SHOULD I SAY DESTROYED IT BUT NO HARM TO PCB, TOOK A OHM READING FROM THE + AND THE DIAGONAL AND GET A READING OF 20.00 THIS NORMAL I ASSUME BECAUSE A SHORT WOULD ZERO OUT RIGHT IF ALL IS GOOD THEN SHOULD I ORDER ANOTHER RECT. AND TRY IT OR IS THERE ANY OTHER TESTING I NEED TO DO BEFORE SOLDERING IN NEW RECT. IT IS A PAIN TO GET OUT I HAVE A SPARE IT CAME WITH THE OTHER LE KIT

[RJ]

If you are saying 20 ohms then it seems way to low.  This would calculate out to over .6 amps which the whole board does not draw that much current.

RJ

[lineman]

If you are saying 20 ohms then it seems way to low.  This would calculate out to over .6 amps which the whole board does not draw that much current.

RJ

Yes the ohms stop at actually 20.56 I will try another meter to verify also can I just put the Rect in and not solder just for a short test like plug in and unplug

[lineman]

If it is not a solder bridge I am leaning to a bad diode in the bridge. Would be a first time I have seen this but not impossible

 RJ now you have seen one I put the new bridge RECT in and get 3 volt and 5 volt LEDs thanks for everyones help well its to mouser to order a RECT for the other LE .

[austindave]

I put the new bridge RECT in and get 3 volt and 5 volt LEDs

Wow. Wild. I never would have imagined...

Sure glad you got it figured out!

--Dave

[RJ]

I am just glad you found the problem and got it working.

RJ