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Old 2004.02.14, 06:30 PM   #1
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Problem with glitching, reverse.

I replaced the foward fets on my friends Z today (MR01) and that went okay, and I thought I was done, but while screwing it back together all of a sudden it went into reverse, all on it's own. The power switch was off too! I took it back apart looking for a short in the wiring, or in my soldering job. I found some things that were suspect but played with them and it still has the problem, it's just intermittent now. Even when driving it, if you stop sometimes it will go into reverse on it's own. The steering also glitches pretty bad. The only thing I can think of is that maybe the reverse/steering FETS need to be replaced as well. What do you think? The reason I'm having to fix this in the first place is when he was changing the chassis to clear parts he pinched a wire and it shorted out and fried a forward fet, could it be it damaged something else as well?

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Old 2004.02.15, 11:18 PM   #2
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from what ive heard, theres really no such thing as a "forward" or "reverse" FET
the FETs work together

so if you only replaced one of the FETs, i would suggest replacing the other one too...
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Old 2004.02.16, 01:37 AM   #3
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Well, based on my experience with one of my OL's I'd disagree. An OL I bought used had forward, but no reverse or steering. I replaced only the set of fets that had the servo wires attached to them and then I had reverse and steering. Maybe there is a relationship between the two different sets of FETS, not sure what it would be. They are on far sides of the board from each other. Besides, when people talk about FET upgrades they only talk about replacing the one set that the servo wires are not connected to.

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Old 2004.02.22, 03:33 PM   #4
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davkin, pomme de terre is right, the FETs we use have two in one chip, one PNP and one NPN. Both FETs in the single chip are used in forward and reverse. I guess there are two because they're paralleled.

Look at this mod schematic for an external FET upgrade by neurokinetik, I think it illustrates it very well:

I suspect however what you say about the front FETs having to do also is right.

I'd make sure continuity on all the FETs is good, and check for shorts, just in case...
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