Trace SW4548E

[clivejo]

I'm currently working on a Trace SW4548E.  There is damage on the I/O Relay board around the generator relay.  Notice the damage is on the relay input (12V) supply tracks.  The inverter was not connected to the generator at the time of failure, has anyone seen this damage before or know what caused it?  I intend to bypass the damaged tracks but I'm concerned about what caused the fault in the first place.

[marcus]

relay coil shorted? check the coil resistance against nominal.

[camillitech]

Morning CJ,

I've a complete AC board with relays on it, in fact I've two complete inverters (possibly 3) https://lifeattheendoftheroad.wordpress.com/tag/trace-inverter-repair-trace-sw4548e/ there's something wrong with the board but the relays seem OK. PM me your address an I'll post it out.

Cheers, Paul

[clivejo]

I've just finished pulling out the FET board and it looks good.  As suspected the wee fuse has blown on the FET board.  Can anyone suggest a cheap replacement part, maybe even a fuse holder that can be more easily replaced?  Something like this? - http://uk.rs-online.com/web/p/pcb-mounts/3110015/

[jonesy]

 It takes a lot of heat to damage the fibre glass like that.  From the precise size of the burn on the underside, I'd say you have a multi layer board, with the right hand relay pin joining the planes together. The pin was a dry joint and there was a fair amount of current through the layers.
I reckon the relay wasn't energized as the small track feeding the other pin would fuse in an instant at high current, unless there is a thicker trace on top.

Can't really read the fuse. Looks like. T4A, time delay / slow blow 4a.  Does it protect the MOSFET drivers? They didn't expect it to fail given the location.

[clivejo]

Can't really read the fuse. Looks like. T4A, time delay / slow blow 4a.  Does it protect the MOSFET drivers? They didn't expect it to fail given the location.

The fuse is a T4A and exactly as you describe a Time delayed slow blow.  I have seen these fuses blow a lot, which is why, while the board is out, it might be a good idea to install a PCB mounted cartridge holder.

This particular fuse is the source of power for the entire inverter "brains".  The circuit drops the 48VDC to 12VDC which powers the relays etc.  Seeing the damage caused to the PCB under the relay I expected this fuse to have popped.  I am amazed by the amount of damage done to the PCB board and the tracks, as you said, it produced a lot of heat to do that!  I intend to replace the fuse and solder on some fly leads directly to the relays from the ribbon cable header, this should bypass the damaged tracks completely.

[jonesy]

This particular fuse is the source of power for the entire inverter "brains".  The circuit drops the 48VDC to 12VDC which powers the relays etc.  

Well, I have seen relay coils heat up when run on either over volts (2 x) or too much AC ripple on a DC coil, but not to the point of burning tracks, so probably a red herring for you.  However, check/replace the output cap on the 48/12V converter which is most likely a low ESR device. They age quickly and dry out.  They can swell/short out/go open circuit/leak goo or just sit there inert.