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I have built some months ago a Rostock Max v2 kit powered by a RAMBo v1.3L board.
It has been working flawlessly until I made a major electronics overhaul recently. Basically I changed to a 24V power supply and SSR for the Heated bed, but I am still feeding the Rambo at 12V using a 24V-12V Converter (Autek SB-44):

http://www.amazon.es/gp/product/B00MAZO ... ge_o09_s00" onclick="window.open(this.href);return false;

But now, every time I try to power on the board, the LCD screen lights on for a moment and then F3 fuse blows! I have checked all the Output connectors and there is no shortcuts there. I have also checked the Power Input Connector and it gives 12V between + and - in all the contacts.
I don't know what else to do. How can I be sure the board is killed before ordering a replacement???

Thanks for any help you may provide!

Ignacio

Could it be that the output voltage from the step-down fluctuates? That might be causing your fuse to blow.
I would try using the stock psu or one that I know it works fine.

Thanks Martin

It will be my next attempt. I will try to check with the original 12V PSU.

By the way, is there any way to avoid this fluctuation? Could you recommend another converter?

Best Regards

Ignacio

Changing F3 to a 10A type instead of the stock 5A would help?

Here's my recommendation:
Dont bother with that model converter or any converter that looks the same. Mine worked for ahwile and started randomly flickering - which screwed up the eeprom on my rambo. Use the stock power supply in conjunction with the 24v feeding the ssr > bed. Everything else, use the stock 12v power supply.

You can alleviate (Not eliminate) fluctuations using a bank of capacitors to smooth the power. If you have access to an oscilloscope (Not likely, I know), go ahead and look at the output wave-form. Use something as a dummy load. Add capacitors until your ripple goes away. This will likely result in you having a small brick of capacitors (Make sure that they are high-temperature ones, the others will die pretty quick) attached to that, which will make your Rambo take a while to power on and shut down. Remember that the capacitor time constant is resistance times capacitance, and that your rambo is likely going to have higher resistance than your dummy load, meaning it will have less ripple. Also remember than capacitors in parallel add, and in series reduces capacitance.

You could also just use 24V power (You will need to change the fans and heater in the hotend to accomodate that), and might need a higher amperage supply. If you want a converter still, and don't want to bother with capacitors to smooth it, ignore most of the cheap brick type ones. Find something that's DIN rail compatible. The will eliminate most (Not all) of the junk, and gives you better odds to succeed.

By flickering, I mean complete 12v power loss for a second or two, then it would turn on for a random duration and then off for a few seconds and then back on, early it was like after 20 minutes of printing it would shut off for enough to reset the board and then turn on again, but later it got worse and worse until it just kept on flicking on and off. Sometimes it would just be on, off, on, off over and over within seconds. It really was a headscratcher until I caught it with my multimeter attached to the 12v output. That converter is junk if you're going for something reliable. But hey, maybe I'm the only one that got a bad one?

I do not know how many amps the Autek can deliver but this one supplies 10 amp and is the one I use.

http://www.amazon.com/Nextrox-Converter ... c+to+12vdc

Here's a question for you then, since you had a meter on it. Did the power rise above 12V when it was on? If so, it may be that the internal capacitors are toast (I am assuming it's a SMPS unit, as a transformer doesn't work on DC). If not, either the pulses are too short for it to rise that high (Capacitor time constant), or that whatever is supposed to drive the switching is dying (Is it getting particularly warm, and is the PSU emitting actual 24Vs?).

Is it possible for you to attach an oscilloscope to the output? or have you already tossed it out? Is it a matter of not having an oscilloscope available? If that's the issue, perhaps a local college with an electrical department would be willing to help you look at it.

It's probably more expensive as far as your time spent troubleshooting it instead of ordering another one from china, but I personally enjoy a challenge and the learning experience (Plus finding the problem let's me help others and design in remedies for the future).