Pete
Site Admin
Joined: 23 Apr 2011
Posts: 3
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 Posted: Sat Apr 23, 2011 7:14 pm Post subject: Resistor blown on pcb |
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I have already emailed this out but lets put it up here for easier viewing.
What we have on site:
USV06 50kw running on a KWB supplied inverter.
The boiler pump and mixing valve are controlled by external relays.
The story behind the mother board:
At first switch on, the boiler kept tripping the 3 phase invertor rcd.
Each plug on the mother board was taken out and put back in to try and find the cause, still tripped.
The neutrals at the boiler isolator were taken out and re-inserted, after this the rcd in the 3 phase inverter stayed on.
Boiler powered up but ext1 was not connected at this time.
Fuel was taken into the burner by relay tests but no other relay tests were done.
Ext1 was made and boiler fired.
After approx. 2 minutes it was noticed that the exhaust fan wasn't on and it was very warm.
The fan was tested with an external 240v supplied and it worked.
After this the boiler kept tripping the 3 phase inverter rcd.
Upon my visit on yesterday I removed the pcb, took off the metal casing and noticed a resistor with scorch marks.
Fitted the pcb back and plugged in components one at a time.
When I got round to the fan this seemed fine, spinning slowly.
Knowing that there were previous concerns about this I decided to do a relay test on it, putting around half power to the fan - this didn't change the speed.
I increased the % and the fan increased. What seemed like a few seconds after this, burning and smoke started from around the same resistor area.
I took away the board and you can see the resistor in question in the photos. |
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