Problems with Sanguinololu board

Hi,

I'm having problems with my MendelMax. I think I need help from someone who knows the internal workings of the Sanguinololu (1.3a).

Heating up my MendelMax 1.5 does not work. When I try to heat the extruder, the heatbed is heated also with about 10% of the current.
If I heat the heatbed, the extruder gets heated with 10% of the heatbed current, which makes the extruder quickly overheat.

The heating cables cannot be the source, they are separate.
I tried to replace the stock firmware (unknown Marlin) with a self built from Marlin git which did not help.
I tried to issue the heating commands manually using a simple serial terminal which produced the same results.

Changes to the original kit I made:
- I cut the 5V USB line, as suggested here: [reprap.org]
(this made the voltage regulators heat far less)
- I replaced the ATX power supply with an industry type 12V 30A.
- I screwed a single heatsink to both the (heating) drivers, so the heatsinks of them are electrically connected. Could this be the source of the problem?

There are some other problems, eg. if I print, it moves the Z-Axis up instead of feeding the PLA.
But I first want to fix one problem, then deal with the next, because I believe this is a software problem.
When I manually move the axes using pronterface, the axis' are correctly assigned.

Before I adjusted the axis' heating worked well... and I once(!) was able to print a test.
But since it's screwed up. I'm not sure which changes I applied before or after.

Thanks for any help,

Jan

Quote
JPT
- I screwed a single heatsink to both the (heating) drivers, so the heatsinks of them are electrically connected. Could this be the source of the problem?

That's a definitely bad, as this will short the output from the transistors, it shouldn't damage them though.

It is possible to get insulation washers, to put between the transistors and the hotend, but the easy solution is to just detach the hotend transistor from the heatsink (it shouldnt really get hot), and make sure it doesn't touch the heatsink. Use some tape, to isolate it.

But you really should isolate the transistor from the heatsink, to minimize the risk for shorting the output.

Quote
JPT
- I screwed a single heatsink to both the (heating) drivers, so the heatsinks of them are electrically connected. Could this be the source of the problem?

Yep. You just tied the outputs together by doing that.

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This helped!
Thank you very much.
Several months of trouble-shooting come to an end!