Re: [ATM] My Mototrak V stopped working... what will I do?

["Christopher Dalla Piazza" <dalchri@hotmail.com>]

First, strike the report of 600V off the record.  I don't know what I was 
doing, but I can't reproduce it and now that I understand what an H bridge 
is, I don't think it was possible.

When I said I got it to work again, that meant it was driving the motor.  I 
trust it even less now that I found that it is driving the motor slow at the 
high power mode.  I also am baffled at the design if I am understanding it 
right.

So I replaced all four transistors at once and it is working ok at the low 
power mode.  At high power, it drives a little slow (perhaps some of the 
cycles aren't strong enough or are too noisy).  Using the fast correction 
just barely helps it to keep up, and slow correction just loses ground 
faster.

The transistors continue to emit an angry click that sounds for the life of 
me to be a short circuit, and from what I've found, I think that is the 
design.

Once I learned what an H bridge was, I examined the circuit and found the 
two DC parts of the circuit on either sides of the transistors.  They read 
100V DC.  If you use the low power setting, that drops to 60V.  I am 
uncertain if this DC voltage is chopped.

Now, what I found is that the two N channel transistors are triggered by a 
16 pin IC just as you said.  However, the P channel transistors appear to be 
tied directly into the positive side of the bridge using resistors.  If I 
understand right, does that not effectively make them both switched on, all 
the time?

So, although the N channel transistors alternately drain the circuit on 
either side of the bridge (I assume they are alternated by the IC), there is 
effectively a short circuit since both P-channel transistors are always 
transmitting the current.  Thus the current can both traverse the load from 
one side of the bridge to the other and also go directly through the same 
side of the bridge.  That would certainly explain the angry buzzing sound 
and the heat.

To some extent, I always remember the heat and the buzzing sound.  Perhaps I 
am just oversensitive to it now that I've delved deeper into the situation.  
Something is still definitely wrong with the high power setting now that was 
not broken before though.

Component wise, I guess the only thing left to replace that makes any sense 
would be the IC if I can find it.  Perhaps it is sending weak signals or 
eratic signals to the N channel transistors.

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