Help 0.8.5 Dead?

Phaedrux

@dc42 might have an idea on what has failed.

Both hot end and bed get very hot.

Are you saying that with no SD card in the socket the hotend and bed are heating as soon as power is applied?

dc42

@dave-parry does the 0.8.5 have a green 3.3V LED, if so is it lit?

Dave Parry

@dc42
yes it does have a 3.3v led, but its not lit. the first four led's are lit. (hot end, bed, Vin and 5v)
and yes the bed and the hot end heat up when no sd card in.
I was wondering if the mosfets may be blown.

dc42

@dave-parry the lack of +3.3V explains why the heater mosfets are turned on (because of the way the mosfets are driven in the 0.8.5) and why the board is unresponsive. So the question is why the 3.3V is missing. Most likely either the 3.3V regulator has failed or something is shorting it out. Have you disconnected everything from the board except for VIN and/or USB? Are any components on the board getting hot?

Dave Parry

@dc42 Thanks for the reply. Cant check now but will later today. Haven't disconnected anything other than the heaters.
If it is the 3.3v reg can I change this myself? I have very small soldering iron and heat gun and have changed components before ( not on the duet...).

dc42

@dave-parry it may well be that one of the endstops or the Z probe is shorting out the 3.3V rail, because the endstop and Z probe connectors have 3.3V on them. If the regulator does need replacing, then it's possible to remove it using either hot air or low melting point solder such as ChipQuik. It's easiest if you also heat the whole board to about 125C on a hotplate. After removal, it can be replace using a soldering iron.

Dave Parry

@dc42 Hi david,
Have disconnected everything off the board and still no 3.3v. So I guess the reg is dead.
I think its positioned just above where Duet is written on the board. Will try somewhere like RS to get some (I think I have to order 10..)

dc42

@dave-parry is anything on the board getting hot?

Dave Parry

@dc42 The only thing getting hot is that regulator.

Dave Parry

Have changed the 3.3v reg but still no 3.3v LED, but the reg is still getting hot and when connected to my PC, and the com port still isn't visible. This is with nothing connected.
May have to buy a new duet after all.

dc42

@dave-parry something is shorting the 3.3V rail out. It's likely be that whatever component is doing that is also getting warm, although probably not as hot as the regulator.

Dave Parry

@dc42 Thanks, checked the 2 caps adjacent to the reg, C4 and C95 and they both increase in temp when I power the board (from 25 to 51c). So will change them both. Can you tell me what values they are, I don't have smd ones but I have a reasonable selection of beads etc so may try tacking one of those in place. Not elegant I know but at least I would find out if that's the problem.

Dave Parry

@dave-parry It's ok found a components list, there 10u and 1u

Dave Parry

@dave-parry I think it's dead. I have taken the 3.3v reg and the 2 capacitors off the board, and there's still a short between Pins 1 & 2 and both sides of C4 all shorted to ground. Cant see anything that could be the cause. Maybe a track has shorted somewhere but no idea where. Dont understand why both sides of C4 are shorted to ground