Sudden Death of an Express - Resolved

[meman]

I tend to leave my 9 LEs powered up 24/7 during the season, and after 5 years of faithful service I discovered one of them DOA tonight.
Wife had called me earlier in the day saying that the circuit this LE was on had tripped and extension cord was hot, so I'm sure its related, but none of the other LEs on that
circuit were harmed.

No 3/5v leds lit, nothing. Fuse was blown so I replaced it....everything still dead. No burn marks or bad smells on the board...just a the usual yellowed flux from the soldering.  Got 120v at the transformer, but not sure I'm measuring tap on the other side right...not showing more than 2.9v DC if I measure between pin 6 and the rectifier leads. Swapped it out with a new one, but still same readings. Got nothing measuring from center lead to edge lead of either of the voltage regulators either. Not really sure how to test the rectifier.

Tomorrow is the big crowd, so pulling an all-nighter to get a spare LE kit soldered up, but would like to figure this one out when time permits. All suggestions welcome.

Thanks.
Mike E.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

[caretaker]

Check what voltage (if any) you are getting at the regulators.  My first guess would be the transformer went bad.

[therealbigjim]

I feel your pain . I am about of spare parts myself.

[Jeffl]

Check what voltage (if any) you are getting at the regulators.  My first guess would be the transformer went bad.

That would be my guess a well.  An Ohm meter should be able to test the primary side winding in the transformer.  I'm just not sure if it can be done in circuit.

[tbone321]

The primary side is only connected to the AC power so there is no issue checking it while in circuit.  Just put an ohm meter across the plug (while not plugged in) and see if there is continuity.  An open circuit is a blown transformer.

[meman]

Mystery solved....bad traic on channel 15.  Swapped it out and the board powered up normally.
I had a short circuit that fried a triac in a different LE a couple of years ago, but I didn't remember it killing the entire board this way.

Now to research the string of candy canes that was plugged into this channel so I don't blow it again.

Merry Christmas !!!
Mike E.
 

[meman]

And root cause analysis reveals that the wires in the male vampire plug attached to channel 15 had shorted in spectacular fusion of copper and plastic. The cords for this LE sit on the ground next to my arches, and I had not sealed the cut end of the SPT1 with liquid tape or insulated this plug with dielectric grease. I suspect water entered the vampire plug, shorted it, blew the triac and fuse in the LE.

Used the grease this time as I assembled a new vampire plug.

Mike E.

[therealbigjim]

Thank for posting the resolution

[caretaker]

Thank for posting the resolution

+1  This is the type of information that helps everyone.

[winwin]

Glad you found your problem and thanks for sharing your findings. 

Used the grease this time as I assembled a new vampire plug.

Do you intend to go back to all your vampire plugs to add grease to them? i have not used any either and I wonder if I should not do the same thing now; not a fun job but if it prevents having a repeat of your problem, I don't mind that much any more!