Re: Amplifone HV

Joseph J. Welser wrote:
>
> Fellow vector posse,
>
> I just swapped an Amplifone back into my Quantum, and have made the
> determination that my HV transformer is bad (surprise, surprise.)
>
> The only reason why I post this is because of all the mention of
> the BLACK HV transformers being indestructable, and this is the kind we're
> talking about here....
>
Yep!!

> I have good +-24V. I measured the following voltages (rounded) on the
> BU406D (which I tested, and it looks good) B: -24V, E: -24V, C: +24V
>
> Now, having a Vbe of ~0 surprised me at first, but it seems that the
> BU406D has an internal resistor between the Base and Emitter. The other thing
> that sounds off warning bells is the 48V Vce. The BU406D was cool to the
> touch, and with 48V across that CE junction, I figured it should be at least
> warm (if there was any current flowing through it.)

well with a Vbe of 0V then the transistor would be turned off and
therefore no current
would flow through the ec junction. It is tricky to work on those
without a scope since
the base drive comes from an isolation transformer at 20KHz. Most of the
time the BU406D's
are bad if the flyback is bad. There is not an internal resistor in
them, only an internal
diode across the C and E. If it doesn't read like a normal transistor
(plus a reverse biased
diode across the C and E) then it is bad. If you look at the base
voltage on a scope you should have some 20KHz noise on there and even
some on the collector. With a voltmeter though you will get rail
voltages, especially if the flyback is bad.
  Your symptoms sound just like mine were, I replaced the flyback and
the BU406D. Works great now.
     good luck
       jess

-- 
Jess M. Askey                  Unofficial Atari Game Page
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