Re: Bulletproof your WG6100!

On Wed, 14 Jan 1998 15:53:04 -0700, Anders Knudsen
<Anders_Knudsen@btc.adaptec.com> wrote:

>
>>That's true!
>
>This *is* the best feature of the new LV PCB.

Considering in my experience, the number one killer of everything was the LV
design. What seems to happen is that during power on/off, one of the zener
diodes will explode and then take out the rest of the circuit.

If you look at one version of the schematic they have a good size capacitor
directly across the zener diodes No current protection what so ever. There's
enough current in that capacitor to take out the diode during a quick discharge.
Or it looked like if one channel of the power supply discharge/charged faster
than the other, the imbalance could cause havoc. Later they added a resistor in
series with the zener to keep it from dying, only to greatly reduce regulation
(and raising the output voltage from 25 to 27)

I've actually been staring at a zener when I turned off a perfectly working WG
and saw the arc shoot through the zener diode. Of course I was then stupid
enough to go "Huh?" and turn the thing back on! DoH! Many other things (that
were probably fine) smoked at that point.

>True. One thing that I had thought would help protect both the power pass
>transistors, and the deflection transistors, would be to add a TVS
>(transient voltage suppressor) accross the collector-emitter. This would
>clamp any voltage spikes. It is just a matter of soldering one directly
>across the ce of the transistor!

I like the idea, are the TVS's fast enough to protect the transistors?

-Zonn

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Received on Wed Jan 14 15:23:04 1998