Resistences on Pololu connector pins

Hi there,

I am having some trouble with my Z axis (RAMPS 1.4). Sometimes it refuses to work (completely random occasions).

Before that, I had trouble with my X axis as well. This was "solved" simply moving the X-axis Pololu to the second extruder): http://forums.reprap.org/read.php?160,151290,154247#msg-154247

But now, it looks like that this Z-axis problem may be somewhat related to the X-axis one: performing resistance tests around the board, I discovered that the EN and the MSx pins of the X driver position in the RAMPS have a resistance of about 13 Ohms between them, meanwhile, at the same pins in all the other drivers' positions the resistance is about 10kOhms... Regarding the Z-axis, between the DIR and STEP pins I read a resistance of about 87 kOhms, while on all the others the circuit is open.

Apparently there is no (visible) problem with the soldering in both places, however, as those are the conectors' pins, perhaps they are somehow shorted through behind (that is almost impossible to see without desoldering the entire connector, due to the connector's plastic), or even inside the connector itself... any guesses? Should I desolder the connector or there is another possible origin for this issue?

Edited 1 time(s). Last edit at 09/16/2012 01:28PM by Algol.

Ok, I desoldered the entire connector of the X, Y and Z drivers (for the next version, the connectors could be splitted on three 8 pin connectors... it was not easy to desolder this 24 pins one - I shall thank PACE a lot!).

The resistance between the Z-axis DIR and STEP points are completely open now, so basically the problem was originated on the connector.

But on the X-axis, the problem remains: i keep reading between 13 and 15 Ohms between the EN and MS1 points (still didn't resoldered the connector, so the connector is not to blame here). Perhaps the problem is on the X-axis' R18 (as suggested by wolfmanjm @ the IRC), which is reading the same value (13-15 Ohms) - basically, it looks like that this SMD resistance is shorted...

Today, a friend and I dessoldered the R18 SMD resistance from the X-axis region of the RAMPS PCB. The multimeter reads ~10kOhms directly on the resistance, so we just cleaned the board and soldered it back. Now it reads about 10kOhms, just like in all other axis. Probably there was solder between the resistance and the PCB shorting the connection... [UltiMachine, where is your quality control?]

Now I will solder the connector back and plug the Pololus... hopefully, RAMPS will work.

All the axis are working fine now. Hopefully there will be no other significant problems further ahead...

Lessons learnt:

- Be very carefull when soldering the connectors that came with the RAMPS' UltiMachine: internally, they leave an open space between the plastic and the board, thus if some solder passes through the PCB holes and fills this small gap it will short two pins (and you will never see it, unless you dessolder the entire thing). So, make yourself a favor and perform a continuity test after soldering the connector.

- UltiMachine quality control is not flawless (or perhaps I am very unlucky to receive a board with an SMD resistance with solder between itself and the board, closing the connection).

Cheers!

Oh, btw, thanks to wolfmanjm, os1r1s and Tom_itx from the #reprap IRC channel!