June 2006

The buzzing is from the H-bridge that powers the IGBT’s. Half of the
fets are not getting a gate signal. The driver is not getting one of
it’s two gate signals. So I spent alot of time trying to buzz out the
board to find the pwm source for the H-bridge but could not. Anyone?

I’m glad I have a functional board now for reference. I can complete
my test fixture in minute detail. I’d like to duplicate the truck on
my bench so I can more completely test and characterize the board.
I’ve learned from rebuilding motor controls that just because
something spins a motor does not ensure that the various voltages and
pwm signals are at their nominal values. I’ve seen that a few times.
So I have a list of “test points” on my customers hardware that I go
thru and make sure are meeting spec. This took some time to figure
out. Our Dolphin boards need the same thing. I noticed that the pwm
firing the 300v supply chopper fet was 12v on one board and 10v on
another. Something is up. The board functions fine, but it strikes me
as trouble waiting to happen. A detailed test fixture makes looking at
these things much more thorough, accurate and repeatable, because
sometimes the tech gets tired 😉

Now where’s my celebration beer?


This is the prototype bridgeboard pcb that isolates the bridge rectifier from the Dolphin main pcb.

Here is the bridge board that helped save my Dolphin tonight!!


My Dolphin Main board is now officially working!! I figured out how to
rework the bridge circuitry with minimum trauma to the Dolphin PCB.
Now the bridge is located on the new prototype fuse board as seen in
the above link.

Can there even be better news? So I turn on the ignition key and
everything boots up. Stable and fine. So I decide to try plugging into
120vac for some charging. Everything boots up again and then

What was that? So After the 3rd verification that something was wrong
I turned off all of the lights and fired her up in pitch darkness. Ya
know how polished the aluminum Dolphin case is on the inside? It was
acting like a mirror and reflecting back to me some high frequency,
low amperage intermittent arcing from under the charger!!

So I guess the charger needs to come out. I’m wondering if this was
the demon that trashed my main board! I’ll find out soon.

Feeling like I’ve conquered a small army of gremlins, I tried to fire
up another board that had the same sort of damage. The board is
buzzing back at me when power is applied on the bench. All 4 of the
regulators and the chopper fet are working fine. The pwm to the
chopper fet is clean and pretty. Not sure where the buzzing is coming
from but it’s keeping the board from talking to the laptop.

I’m not much of a drinker and it’s time for a beer!

1 down, 3 to go.

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