Can I rescue my Duet?

After much modification & experimentation my Ormerod has been printing perfectly - with the occasional failure to stick properly.

However last week I saw the signs of a short circuit, I killed the power as quickly as I could but I could see horrid wisps of smoke. I can only think I'd shorted the bed as I put the clips on. There were obvious signs of a short on the Duet board but these were electrical rather than electronic.

When I power the board now with 5v all responds as it always did - the board is connected & T0 shows the expected temperatures.

However as soon as I switch the 12v supply the bed led lights without me setting it & after a short time I have wisps of smoke again. These wisps appear to come from the top left of the board, in the region of the bed & hot end outputs. In the short time between I can control the motors etc. The board has discoloured in places & the lacquer has obviously been affected. I can see no obvious damage to any electronic parts. I'm not going to leave it powered to see exactly what's cooking in case I do even more damage.

Does the board appear repairable? Any help & advice would be most welcome. I can't afford to renew the board if it could be fixed with a tuppenny part.

regards
CUA 193

It sounds like the bed heater mosfet needs to be replaced. That may be all.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

dc42,

Thanks for replying.

Sadly I don't really know a mosfet from a moo-cow. Looking through other threads has left me just as confused.

I rather assume the mosfet concerned is tr2, between the two terminals. When I typed the part number 035N04L at RS components it showed an 8 pin surface mount mosfet. I found BSS138 on the other threads which shows as 0.22 watts, which can't be right.

Being a bear of astonishingly little brain, could I simply ask:- what do I need, where do I buy it & where do I place it?

After this little problem I intend to put a relay between the duet & the hot bed & have a separate supply for the bed; would this be a good idea?

regards
CUA193

Yes, TR2 is the part that has probably gone short-circuit. On my Duet it is a IPD036N04L (RS part number 825-9364). There is a small possibility that your short also took out TR1, which is a BSH105 (RS part number 509-273), and it might be an idea to replace that while you have the board out as the price is insignificant.

If your Duet is not too badly burned they are not that difficult to replace, but use a hot fairly high-wattage soldering iron to melt the large tab of TR2 quickly. I find the easiest method is to use a small pair of sidecutters (e.g. RS part 606-490) to cut the two small leads of TR2 close to the body of the device, then melt the large tab and remove the device. Then melt & remove the two lead stubs you previously cut. Do *not* use a large thick-bladed sidecutter, a blunt cutter or a scissor action cutter as that is likely to impart forces that lift the pads. Afterwards, use solder wick (e.g. RS part 314-0993) to clean up all the pads before fitting the replacement. Instead of cutting you can melt the solder of each lead in turn and bend the lead upwards off the board using the iron tip or a small screwdriver, though this needs a bit of experience to get it done quickly without overheating & lifting the pads. You can also use a hot-air gun to melt all the pads at once and lift the part off with tweezers, but on the Duet this is not advisable because it will melt the plastic of the nearby connectors - heat from below if you want to use that method.

As your board has overheated, there is a strong possibility that the pads & tracks will lift and that part of the board will be ruined. If that is the case you can re-build that part of the circuit by hand and encapsulate in epoxy to have an ugly but fully functional board.

Dave

Edited 1 time(s). Last edit at 08/31/2016 07:53AM by dmould.

As Dave says.

The track that is most likely to be burned is the one on the top surface at the edge of the board that joins the VIN+ and Bed Heater+ terminals together. You can bypass it by linking those two terminal block pins together on the underside of the board using a piece of thick copper wire.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'll also add that you should check your bed wiring carefully - if it is shorted you will blow the replacement FET as soon as you activate the bed. I suspect that one terminal of the bed was shorted to the metal heat-spreader - make sure you have fitted that plate the correct way around so that its cut-out clears the bed terminals.

Dave

Thanks Chaps,

Exactly the gen I was seeking - parts ordered & winging their way.

As I said I think the problem was finger trouble when I was fixing the clips: I've done it dozens of times but must have been clumsy or wore through the insulation. I've already taken the bed off & checked it under power - no problems with it or the wiring.

I'd only just given the bed a run at higher temperature in order to use ABS filament. I couldn't get the bed above 98c - well below the target. Either it shut down without reaching the temperature within 150 seconds or just plodded along at 98c; I've already written an amended line in the config file as recommended.

Any recommendations about using relays or additional fuses, although I've now ordered 20 TR1 (pack of 20) I'd still rather blow a fuse than an electronic part.

regards
Richard

The usual cause of the bed heating being too weak is that the power supply voltage is too low. Have you measured the output of the power supply?

If your machine is an Ormerod 2 then you can adjust the voltage pot at one end of the PSU terminal block to turn up the voltage a little.

If you have an Ormerod 1 then replacing the cheap ATX PSU by a good one will help somewhat (I used a Corsair CX430M for a while, but it's probably obsolete by now). Or you can replace it by a Chinese LED power supply with a voltage adjustment pot, and a printed enclosure.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I use a Chinese 30A LED PSU adjusted to give 14V at the terminals, and that allows the bed to reach 110 deg within 5 minutes or so. The original PSU was delivering under 11V at the bed heater, and barely reached 100 deg after 30 minutes. As far as I am aware there is no time limit for the bed heater to reach temperature. I did not change anything on the Ormerod when increasing the voltage, but if you want to play safe you can put 3 or 4 diodes in series with the hotend fan to drop its voltage back to 12V - though mine has run happily on 14V for well over a year of very frequent use. The hotend will also heat more quickly, and you may need to tweak the PID values, though in my case the heating profile is not bad enough to need to change. Make sure the wires you use from PSU to Ormerod are thick enough to take the current without any significant voltage drop.

e.g. [www.amazon.co.uk] - though cheaper units are available on eBay (but you take your chances with safety conformance)

Dave

Edited 1 time(s). Last edit at 09/01/2016 07:16AM by dmould.