Dead RAMPS v1.4

[Garth Kidd]

Damn. 

I wanted different stepper connectors on my RAMPS 1.4, so desoldered the male headers and soldered the new ones on. I also removed the male headers for the thermistor connection and replaced them with female headers. 

Now the board won't work. I plug the thermistor into the headers, but it's not detected. Worse: if I plug any stepper motor driver in anywhere on the board, it won't boot. That certainly wasn't the case before I did my work. I've tested with multiple positions and multiple drivers. 

One potential additional screw-up: the capacitor at F2 was poorly soldered, and guaranteed to break a lead if it wiggled. It did break. I re-soldered it and checked connectivity, but figure I should disclose everything I did in case it helps. 

Any ideas? I'm not that up to speed on electronics, but I can drive a multimeter. Any tips on figuring out where I missed a layer on a two layer connection, broke a lead, or shorted something? 

 – Garth

[David Lyon]

first before you unsolder everything, check the circuit-breaker on
your power board.

On 4/27/12, Garth Kidd <ga...@garthk.com> wrote:
> Damn.
>
> I wanted different stepper connectors on my RAMPS

> 1.4<http://reprap.org/wiki/RAMPS_1.4>,

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[Garth Kidd]

F2 is a fuse, not a cap. Connectivity between its pads is solid. 

I've checked the connections between the 1A/1B/2A/2B headers for the drivers and the matching pins for the stepper motors, and they're fine. There's also no bridging between adjacent pins, and nothing is shorted to either the Arduino ground or the 12V ground. 

There's also no connectivity from the thermistors on JP7 to the ground pins, which worries me because the schematics show that all odd pins should ground. They do seem to connect to the other side of the capacitors (the side without the black line), though, so perhaps the local ground is working fine. 

Checking the black line side (+?), though: I have solid connectivity for all but the thermistor I need. So, maybe I've stuffed up that one joint.

I still have no idea why the board is failing to boot if I plug in any drivers. 

 – Garth

[Garth Kidd]

Power's OK: the board boots from USB power with no drivers plugged in, and the 12V supply from the PC power supply nearby is fine. 

[Garth Kidd]

Taking the board off the Arduino…

The joint looks clean. I can connect through the header to the far side of the board, so the header itself is OK. Still no connectivity from pin 1 on JP7 to the - side of C5, though. There's a tiny amount, but it goes up — much like if there were a capacitor in the way. My multimeter reckons it's about 16.4uF from pin 1 to C5, but C5 itself measures at 10uF and its neighbours at 20uF. 

This is well beyond my ability to nut out. Any ideas how I can save $80 by avoiding having to buy a new RAMPS v1.4 kit? 

 – Garth

[Andrew]

This is an interesting read...

 

http://www.globalspec.com/FeaturedProducts/Detail/micromo/Thermoplastic_Rapid_Prototyping_Machine/180947/1

 

[Garth Kidd]

Ok, took JP7 off to fix my pin 1 problem, only to make new problems by destroying the pads: http://forums.reprap.org/read.php?219,130452

Any ideas? 

[Brett]

Hi Garth,

I can't really see sufficient detail around there, but here's some
pointers.

First, is it actually that bad? Any chance you can take a more
detailed close up?

The pads rely on the plating from the bottom pad to the top pad. That
implies a good solder joint with solder that wets well up to the top-
side of the board, assuming there is also some plating in the via/
header hole. How reliable do you think that might have been before
you did your desoldering? Was there much sign of solder on the
topside?

The pads only have four incoming copper runs from the pour that leads
from the pad on the cap to the pad on the header. The solder mask
prevents the solder flowing over that gap and bridging it better.
Perhaps carefully clearing away some soldermask and tinning the link
between the pad and the surrounding pour will help.

When you put the headers back in, make sure you use a heap of extra
flux, and a heap of solder to let it flow back through the board. I
don't know what that header plugs into but if you have the chance to
raise the header off the board (ie it doesn't need to be flush with
the arduino headers) and you want some more reassurance that the
joints are good, you can leave it sticking a millimetre or so proud
and check that the solder flows through.

hope that helps

[Garth Kidd]

Thanks, Brett!

I've lifted the pads for THERM0 and THERM1, destroying the paths from header to capacitor and header to Arduino pin — and, of course, from capacitor to pin. 

I think my best option is to rebuild the thermistors circuit with three 10µF caps and three 4.7k resistors on some strip-board, with a strip of cable to the data pins and some conveniently nearby GND and VCC pins on AUX-4. 

What I'll have to deal with then is that I've blown some/all of my Pololu drivers by inserting them back to front. Is there a quick way to test these using just a multimeter? If not, I can hack a test circuit together. 

If I don't have enough spare Pololu drivers around to replace my bricks, resurrecting this board will cost another $50. At that price, perhaps I'll be better off throwing the board out, buying a Printrboard, and selling my Arduino Mega 2560. 

 – Garth