Puma 100e - burnt modulation board (pcb)

[martinbristol]

Potterton Puma 100e "died" yesterday - no lights or response. There was a funny hot electrical smell round the boiler.

Mains fuse (3 amp) ok but internal 2 amp glass fuse blown. Checked inside and found main modultion board badly charred at the edges round the top left corner. I removed the board.

Burning had clearly happened at the soldered pin connectors and 2 of these were completely burnt out. Worst charring at the live and neutral mains connection. Also milder burning on pins connecting fan, air pressure switch, pump and "full sequence control panel" (these are in descending order of severity and also increasing distance from mains connection pins). Silver tracks on the board also burnt but charring concentrated at pin solder points.

Board is obviously beyond repair and must be replaced. However, I don't know if the board burnt out due to bad solder joints - as often discussed on this forum (I resoldered 1 bad 240 volt solder joint about 2 years ago) - OR if a fault elsewhere caused the problem. If a fault elsewhere (eg fan) can I test this with the board out of the boiler, using a meter, and if so how and what should I look for?

Really grateful for any avice. I will call an engineer if necessary but would prefer not to.

TIA
Martin

 

[martinbristol]

For anyone else with this problem the following may be useful:-
Bought new board £87. Spoke to heating engineer who recognised the problem and named the boiler model just from looking at the damaged pcb. Board runs hot, dries solder joints which arc and burn out. Mostly on the neutral side. He told me he has replaced lots of these.

He advised checking there is some resistance across live and neutral on the pump and the fan supply. Also to put a quick blow fuse in board, replace all connectors except the pump and fan connectors, turn on the power and then add each of these one by one (turning the power off each time). If the fuse does not blow then these devices are probably ok. As I expected the fuse did blow when I started the boiler but all seems to be well with the standard 2 amp fuse.

I measured the temperature at the board and was surprised to find 2 resistors (right beside and below the damaged area on my old board) which run at 103c. Potterton Tech support did not have any figures but they confirmed that these resistors run hot and newer boards have been strengthened to help with this.