Re: Panasonic PV-8662 VCR, no power.

"Mark D. Zacharias" <spammenot@xxxxxxxxxxxx> wrote in message
news:cMHHe.217$646.75@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> David Farber wrote:
> > This Panasonic PV-8662 VCR came into the shop with a blown main fuse
> > and switching transistor, Q1001, shorted. I replaced both of those
> > components and this thing is still not showing any signs of life. The
> > switching power supply is not oscillating. I've looked over every
> > possible fault that I can think of. Is it possible that there is some
> > condition or fault with the uP that will shut down the oscillator?
>
> In addition to the possibility of a bad fusible resistor, as Sam
mentioned,
> I would also look at any control transistor near the main switcher (often
> designated Q2) and of course look for a shorted 18 volt zener and bad caps
> on the secondary side, and let's not forget a shorted recifier on the
> secondary will do this also.
>
> But then you probably already knew most of this, yes?
>
> Mark Z.
>
>

Hi Mark, Sam, and Jonathan,

Yes, I know all the weak points of these switching power supplies except for
the problem with this one. lol. This set is only a couple of years old and
unlike in the olden days (maybe more than a few years ago), these power
supplies are part of the main board. It's not a separate module. To service
it requires removal of the mechanism and main pc board. One of the nice
features about this set is that it has "commercial advance." Somehow it
knows where the commercials are and skips them during playback.

I did replace Q1001, 2SC4533, with an SK replacement. Though it is stamped
with the same number, I'm wondering if somehow it may not be up to specs.
There is a secondary transistor, 2SD2259, Q1002, which tests good. Looking
through the archives, somebody mentioned to replace it anyway even though it
tests good. I've checked all the other passive components and the ones that
looked questionable, I removed from the pc board just to make sure they were
good.

Here are the voltages I've measured:

Q1001: coll. 144V, base 0V, emitter 0V
Q1002: coll. 0.4V, base 0V, emitter 0V

I rang the switching transformer with Bob Parker's flyback tester. It tested
good. I'm not sure whether that tester was designed for a transformer like
that but it was an easy test.

Thanks for your replies.

--
David Farber
David Farber's Service Center
L.A., CA


.

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