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LBRC
2008.10.25, 12:37 AM
I’ve seen three so far, all came with the same “but it was working” comment.

On the ASF CB the bare copper pads around the mounting post through-holes (via’s) are connected to circuit board ground (- Battery) and the right pad is just a hair’s width from the right FET. Too much solder and you’ve turned an H-Bridge into a Half-Bride amplifier for a lap or two that is, just long enough too heat all the FETs into glowing red hot circuit board run and pad toasters, smoken.

Bad
http://mini-zracer.com/forums/attachment.php?attachmentid=25747&stc=1&d=1224908961:mad:

Good
http://mini-zracer.com/forums/attachment.php?attachmentid=25748&stc=1&d=1224908961

One word:

mul•ti•me•ter [ mul tímmətər ] noun

Definition:

Instrument that measures electricity: an instrument that reads and measures the values of several different electrical parameters such as current, voltage, and resistance.

Preferably used before applying power and definitely before a test drive.

LED
2008.10.25, 08:09 AM
The most DANGEROUS thing for a circuit board you can do is going to measure resistance with a multimeter.
Simply becasue the multimeter is putting its own current on the board.

never ever measure resistance on electronic components, turn it on and measure the voltage instead.

LBRC
2008.10.25, 12:44 PM
Sorry dude but not, shudder to think of where you picked that up, it's not even an urban myth. The relatively low voltage/current levels put out by a multimeter for a resistance reading or continuity check will not damage the Mini-Z CB in any way. But turning power on with a short or incorrectly connected mosfet definitely will.

Discrete semiconductor devices like mosfets are susceptible to high voltages i.e. static but are highly tolerant of lower voltages, lol if they weren’t they'd never manage to operate.

dvsstrike
2008.10.25, 07:01 PM
lbrc how many fets are yyou putting on that asf board. 8 total? do you like running 8858 vs sp8m4. also have yo u tried the an113? but anyways that sucks about your board.

LBRC
2008.10.25, 08:58 PM
Don’t feel sorry for me the fried CB in the photo came with a pizza and beer bribe to see if I could salvage/repair it. It’s the third sent/brought to me with the same short to ground so I thought it would be good to post a warning about the potential problem. That and a good chance to take a close up photo with my new camera. I check for continuity and shorts before turning off the soldering station and calling a FET job done so almost never have problems with shorts and/or opens ;) do-overs don’t count.

Both the burnt and the good boards in the above photos have a single set of 8858’s stacked on the tope side set of stock 3010’s, popular trick quick, easy, no pad lifting risk, and works.

My overall favorite for the ASF CB is a single layer of 4 x 8858’s. The 8858’s and the SP8M4’s are very close, I prefer the 8858’s simply because of price and availability. Don’t really care for the so called AN0113’s from PN, aftermarket car companies don’t make mosfets all they do is buy cheep ones, handle them poorly i.e. questionable anti static program etc., scrape the labels off so you can’t see what they really are and find the true specks, then resell them to you at an inflated price. Used them on a friends 2x2 MR-02 at his request, they seemed ok but nothing special. If they were something special they’d leave the label on and provide you with a data sheet, otherwise someone might suspect that they are the same Chinese FETs that came on the Iwaver 02, lol also with the label scraped.

gnehcoel
2008.11.11, 12:19 AM
LBRC, when you mentioned that the FETs are short to Ground, is the entire board gone too? Or you just have to get new FETs ... I am planning to upgrade to new FETs (4562 or 8858). I just wonder if I can FRIED my entire ASF board?

Thanks.

LBRC
2008.11.11, 02:13 AM
Usually it’s just the FETs that get fried and an occasional pad that gets burnt/lifted. The above tasted board now works great with new FETs and one repaired run/pad.

gnehcoel
2008.11.11, 03:56 AM
thanks LBRC. When the FETs are fried ... do you always see a bubble on it? or if the forward is not working and only the reverse is ... do i need to swap out all the fets? I have seen different answers from different threads ... so I wanted to check with you.

THanks.:)

LBRC
2008.11.11, 05:26 AM
thanks LBRC. When the FETs are fried ... do you always see a bubble on it?Most of the time but not always.

... or if the forward is not working and only the reverse is Good indication of a bad FET (actually two on the ASF CB since in effect its a 2x2 just not physically stacked on top of each other), swap the motor wires and see if it now only goes forward.

... do i need to swap out all the fets?
That would be best, but if the car still goes in reverse that means that the reverse P an N channels on all 4 ASF mosfets are working. So the question that remains is; are both the forward P and N channels damaged? or just the forward P, or the forward N?

For example if you fried the FETs by running a motor that was too hot or having the pinion to spur gear mesh too tight then the chances are good that only the forward P channel would be blown because it handles the least current and like a fuse will blow before the N channel. In that case you could theoretically replace the two forward P channel FETs, get lucky and have a working CB.

However if you fried the FETs with a short then the chances of the other two FETs with the forward N channel surviving would not be good, or depending what and how your shorted them out the forward N channel could be bad and the forward P channel good.

Easier and safer to replace all 4 FETs on the ASF circuit board at the same time, avoiding all sorts of unpleasantness. Like the infinite loop of bad FETs scenario. It usually starts with one bad P-channel with a visible bubble so you replace that FET but unbeknownst to you that bad P caused the N to go bad in such a way that when you replace the N it blows the new P again, so you then replace the N but it’s too late as soon as you turned the car on it blue the P again, add infinitum. Drives people crazy they end up replacing all the FETs one or two at a time and then erroneously assume that the board must be bad.

gnehcoel
2008.11.11, 02:28 PM
THis is really great info. Thanks LBRC :)

dameetz
2008.11.14, 03:03 AM
LBRC which one will give a better performance the one with single 8858 stacked over 3010 or change to 8858 all together?

LBRC
2008.11.14, 04:10 PM
Replacing all 4 stock FETs with 8858’s (a few milliohms lower resistance and a ~1 amp better real world current handling due to better heat dissipation without the stacked FET), but it would take the princess who felt the pea under 20 mattresses to tell the difference.

I have tried and use CB’s/drive cars with both on a daily basis, the bottom line is that I like Christian’s single set of stacked 8858’s on top of the 4 stock ASF 3010's because it’s simpler, easier, has less risk of damaging pads, and honestly I can’t tell the difference unless I take off the body and CB cover to look.

Note: For high current applications like running an Atomic T2 in a lithium powered Mini-Z monster truck I would not use the (1+2stock)x(1=2stock) easy stack, in that case a true 3x3 of 8858's, 4562's, or SP8M4's would be advisable.

Old Crow
2009.06.26, 10:00 AM
I have tried and use CB’s/drive cars with both on a daily basis, the bottom line is that I like Christian’s single set of stacked 8858’s on top of the 4 stock ASF 3010's because it’s simpler, easier, has less risk of damaging pads, and honestly I can’t tell the difference unless I take off the body and CB cover to look.

Is this still your opinion? Because I can do that, just put fets on top of the stock ones. I'm looking for the most effective way to get a very similar(or same) result. I already ruined one ASF board trying to take off the stock ones, it's a risky job. The AM boards were much easier to do.

LBRC
2009.06.26, 03:02 PM
Absolutely! Low risk, commendable performance.

herman
2009.06.29, 01:45 AM
mul•ti•me•ter - Instrument that measures electricity: an instrument that reads and measures the values of several different electrical parameters such as current, voltage, and resistance.

Preferably used before applying power and definitely before a test drive.

warning newbie question coming up... how do you do this... i know there are two probes the red and black... where do you put them on the board? and what readings should you have to see if they are ok, or what readings should show if you have a short? do you have to put the probes on each leg?

pls. post pics as it would be a big help... thanks in advance :D