Blown Xylotex control... Repair or replace with a Geckodrive?

[adatesman]

Well, it looks like my trusty 4 axis Xylotex gave up the ghost last night. My guess is a chip made its way into the X axis stepper plug and shorted out the drive chip, as everything else checks out ok. Unfortunately the blown chip means the board won't power up (sends the power supply into overcurrent protection), so I'm stuck either replacing it or going with something different. I've heard that Geckodrives give somewhat better performance due to their higher voltage output, and given that a G540 runs only 50% more than the replacement Xylotex drive board I'm kinda tempted.

Any thoughts?

On a side note, Xylotex support was very quick (around an hour) with a response to an email asking about repair options. Unfortunately they don't repair, but only replace since it costs them more to repair than to make a new one. They did send me a link to Digikey for the chip I'd need, so most likely I'll be giving that a try before doing anything else. It's only $10, so no reason not to. If it works, great. If not then I have more than enough justification for SWMBO for the Geckodrive upgrade...

Oh, and it's for a Taig mill with 269oz-in steppers, if it makes a difference.

-aric.

[macona]

I just messed around with one of the G540's last weeks and it seems pretty nice. I would ditch the Xylotex. They were marginal to begin with.

[Evan]

The only problem with the Xylotex board is the lack of proper heat sinking. I tossed the original heat sinks and scraped off the useless themal tape and put on proper heat sinks. I run the boards with fan cooling with the current turned to max and never any sort of problems. There isn't an actual fixed limit on the current the chip can handle in the data sheet. It all depends on the junction temperature up to the point where the chip traces act like a fuse. That's a lot higher than the specified current rating and as long as it is kept cool it isn't an issue. Anything that has thermal tape holding on a heat sink must be changed for a real heat sink. Tests show that thermal tape is almost as bad as no heatsink on very small chips. The Xylotex boards use the Allegro controller chip which is a very good chip but it still must be kept cool or it will eventually fail.

This is how I set them up. I used the individual boards they used to sell. In use there is a computer fan mounted on top of the heat sinks that blows down into the center of them.

[sansbury]

The G540 is a great unit... breakout board and a 0-10V spindle control built in too. The axis modules are also individually replaceable so if you do manage to blow one you don't have to replace the whole thing.

[adatesman]

Thanks Guys. Looking over the specs I'm completely sold on the Gecko unit, but aside from this I've had no problems with the Xylotex board and it just doesn't seem right to not try and replace the blown chip given that it's only $10 from Digikey. That said, I have low expectations for the results of my first attempt at surface mount soldering so will likely give it a single try and if it doesn't work right off the bat go with the Gecko.

Oh, and thanks for the tip, Evan. If I do get it to work again I'll definitely upgrade the heat sinks as I was unimpressed with how well the stock ones worked with the thermal tape.

Thanks!

-aric.

[Evan]

To remove the old chip use a big hot iron like 80 watts and apply it to the center of the top of the chip while holding the ends of the chip with long nose needle nose pliers. It should loosen in a second or two at which point lift it off. If necessary then use fine copper solder wick to clean up any bridging but don't clean off all the solder, just remove any lumps or bridges. Then reflux the board pads with some liquid flux. The flux is most important as that is what prevents bridging when you resolder.

Place the new chip in position and apply good downward pressure with a wood stick. Solder pins 7 and 21 on each side center to hold the chip down so it doesn't lift on one end . Use a very fine tipped iron of about 20 watts. Flux the iron tip for every pin, apply solder to the tip of the iron and shake it off. You shouldn't need to apply more solder to the part or board, the film of solder on the iron, the board and the chip pins should be enough. Do the corners next and then work around the chip like tightening head bolts. The key is to use a hot enough iron to complete the heat transfer very quickly. The chip is designed to take molten solder temperatures for up to ten seconds. Wait at least 30 seconds between soldering each pin to allow the chip to cool.

Inspect with a 10 power glass to see that there are no bridges and that every pin is reflowed to the board. If you find a bridge suck it off with some wick, then if necessary reflux the iron and pin and resolder without adding solder.

[adatesman]

Heat the chip to get it off? D'oh! Why didn't I think of that!

I ended up simply cutting each pin where it enters the chip with a small blade and then removing them one by one. It worked ok, but was a bit of a PITA.

Thanks for the tips on soldering on the replacement, BTW. Digikey shipped it yesterday, so hopefully it'll be here by the weekend.

[adatesman]

Well, no luck whatsoever getting the replacement chip soldered on; I simply don't have the time, patience or correct equipment to do it. Looks like it's a Geckodrive upgrade for me.

On a side note, it looks like the Xylotex board might still work once the blown chip is removed (the power LED stays lit and nothing smokes or gets hot) so perhaps it'll be useful for a lathe conversion or router/plasma table down the road.

Thanks for the help, Guys.

-aric.

[macona]

What is the part number of the chip?

It should still work for the other axis when the chip is removed.

[adatesman]

Word direct from Jeff@Xylotex is that the chip is a A3977SED, although that part is pretty much out of stock everywhere. He said to use a A3977KEDT instead, but for obvious reasons (read: my inability to get it mounted) I can't comment on whether it would actually work or not. Digikey has the latter listed for ~$9.21, which worked out to ~$14 shipped. At that point it was well worth giving it a try, but having tried it I'd suggest not going that route without the proper equipment (read: my very nice temp-controlled solder station was no match for doing a 44 pin SMT mount chip 1/3 the size of a postage stamp).

-a.