LGB 50110

[Lodgie_]

This is for reference for anyone who has a dead LGB 50110 transformer. My one packed up a few days ago and I found a replacement which will take a month to get here. Thinking that nothing ventured, nothing gained and even less to lose, I stripped it down and had a poke around. Unplug it first!

The first hurdle is splitting the base from the cover. These are held in with plastic rivets which have to be drilled out. There's nothing much to worry about on the other side of the rivets. Inside is a stonking great transformer, one side of which is connected to the neutral (blue) mains, the positive runs up inside to a small pcb at the top of the box. This needs to be removed. Undo the 4 large screws holding the transformer in place, carefully lift it free paying special attention to the output wires and connectors - this is a push fit in to the case. Once safely removed lift out the black plastic mounting for the top PCB, remove the two small screws and separate. There's not much to go wrong on here, a couple of LED's and a few discreet components plus a small black plastic unit which contains a bimetallic strip which (I think) prevents overheating by cutting out when it gets too warm. It can be tested with a meter, it should be closed when cold and show zero resistance on the meter. Mine didn't so I shorted the two legs and powered up and it worked. The switch was then removed and a temporary link soldered in its place. This works but it's not ideal as there is no overheating protection, so I hunted around for a replacement switch - couldn't find one so on eBay I located a cheap-as-chips modern equivalent, a few of which I have ordered as they come with various temperature settings. I'll report back in a few weeks when it arrives and is fitted.

 

[Paul2727]

Just a thought...
From experience, bimetallic strip switches rarely fail in the open position unless they have been subjected to considerable or frequent overheating. (Often caused by excessive power draw etc.)
Did you test the output voltage or check the temperature of the transformer after being powered up?
It is possible that if it has been regular overheating then there maybe damage to the the winding insulation.
A good sniff of the transformer. (Obviously when unplugged.) is a good way to check too. Any acrid smell indicates problems.
Regards,
Paul.

 

[Lodgie_]

That's a good point well made. I did measure input and output voltages and checked resistance at all points - (240v & 0v!)), the switch contacts were not in the best of health with pitting and verdigris - I purchased this second hand last year with no history, it may have had a hard life. The transformer itself is in fine order, zero smell and it looks factory fresh. It all looks remarkably well engineered. There is not a lot to go wrong on these units apart from the components in the auxiliary PCB and that switch wasn't the best engineered one I've seen, it looked a little lightweight for its function.
Cheers
John

 

[Paul2727]

That's a good point well made. I did measure input and output voltages and checked resistance at all points - (240v & 0v!)), the switch contacts were not in the best of health with pitting and verdigris - I purchased this second hand last year with no history, it may have had a hard life. The transformer itself is in fine order, zero smell and it looks factory fresh. It all looks remarkably well engineered. There is not a lot to go wrong on these units apart from the components in the auxiliary PCB and that switch wasn't the best engineered one I've seen, it looked a little lightweight for its function.
Cheers
John

That's good news.
The pitting and verdigris is interesting. Maybe it was regually used or stored in damp conditions.
The bad contact caused by the verdigris probably led to arcing causing the pitting (Like a baby arc welder.) Each pit would therefore not only have received a micro hot spot but loss of the material. Over time that would definitely cause a bimetallic strip failure.
You used to get the same thing happen inside under tightened 240 v plug terminals. (A common cause of household fires.)
The sealed plugs don't suffer from this as much.
Always a good thing to check for before running old transformers with unsealed 240 v plugs.
Regards,
Paul.