Rambo death, layer height and calibration

[senake]

Hello all,

I have had my Rostock for some time now and recently recalibrated it to try and improve the print quality. Following the recalibration, I set it going on an overnight job - after watching it put the base layers down.

When I took a look in the morning, the print had stopped midway and the printer was completely dead. The switched mode PSU did not power up - even after changing the fuse in the plug and disconnecting it from the Rambo. All three fuses on the Rambo had gone. I have since replaced the PSU with a slightly upgraded (40A 12V rail - http://tinyurl.com/MyNewRostockPSU) version and replaced the fuses. The Rambo is still completely dead and it appears that the power rails are shorted out somewhere - the PSU cuts out (indicated by the cooling fan stopping) when it is plugged into the Rambo.

Can anyone tell me:

(1) How the Rambo could have been damaged to this extent - when protected by the three fuses? Could this have occurred as a result of the end effector colliding with a print and stopping the motors moving - or - the hot bed drawing too much current? I have ordered a new Rambo, but don't want this to recur again if possible.

(2) If there are any circumstances where the layer thickness as calculated by Slicr could be too small - so that the hot end starts colliding withe the print? If so, how can this be cured? Is it a setting in Repetier or the Arduino sketch?

(3) If there are any recalibration steps that I have missed which could improve my print quality - so far I have:
(a) re-squared the towers
(b) adjusted the belt tensions
(c) reset the end stops screws and centre point in the Arduino sketch

(4) The effect of having the hot bed temperature slightly higher (60 degrees instead of 55 degrees) on a PLA print? Currently, my print seems to be stuck - through the blue tape - onto the borosilicate glass bed. Rather than risk breaking the glass, I'm going to wait until the replacement Rambo arrives and warm up the bed then...

Img - The problem with being UK based - a temporary fast blow fuse hack whilst waiting for little fuses from Mouser

Thanks


Senake

[Eric]

It's hard to think of scenarios that would blow all three fuses at once. That's a real puzzler. When you remove the Rambo from the printer, look on both sides for any visible damage. An internal short on the board could present as a burned or bulging area.

[Polygonhell]

Make sure you're New PSU will actually supply 12V without a load on the 5V line, a lot will not and some just shut off when you try to draw a load off the 12v line.

If you have an old optical drive lying around, plug it into the PSU, and see if it still just shuts off when attached to the board.
As to what would blow all 3 fuses, it's unlikely to be anything on the board itself, there are literally 3 completely independent circuits on the board, my guess would be a power spike from the PSU, but I've never seen a PSU fail like that.

As to the motors getting stopped, they would draw no more than the rated current! which wouldn't damage the board, and IME on a rostock what happens is the motors eat the belt rather than stopping.

[JohnStack]

My money is on a power-spike with spreading the odds a bit with overheating.

I'm refusing to take chances now. Fan directed at the board, high end switched PSU, and it sits away from the printer. Lastly, a decent surge supressor. (I always have them...)

[senake]

Hi All,

A bit of an update...

Having received the very expensive "little fuses" from Mouser, I plugged them into the Rambo and switched on the power - ALL of the Rambo fuses blew again, but the PSU still works fine.

I have removed the Rambo and checked for damage, but there isn't anything obvious. The last print seems to be firmly adhered to the borosilicate glass disc - even through the blue tape - which could have been because I set the hot end temperature 5 degrees too high for PLA after printing with ABS. I checked the resistance at the Rambo connection blocks - for the heated bed it was 1.2 ohm at room temperature and for the hot end it was 10 ohms.

Can anyone think of anything that I should check prior to fitting a new Rambo - to minimise the risk of damaging it?

Any thoughts would be very much appreciated.


Thanks



Senake

[Polygonhell]

There is little if anything that would blow all the fuse, maybe a direct short from the 12V line to ground, if the ground planes aren't distinct.
If it were me, I'd unplug everything from the board, start with just 5V supplied, and then plug things back in one at a time (turning off the power at each step) until the problem arrises, my guess would be the bed or the hotend, the Hotend resistance should be closer to 3 Ohms than 10, it's two 6 ohm resistors in parallel if it's wired correctly. The resistance you want to measure is the thermistor at room temperature, if the resistor is shorted to the thermistor somewhere, it doesn't affect the resistance of the circuit much, it does on the thermistor side.