RE: BU406D (was Wintron install: Does this look right?)

From: Dan Rasmussen <sscanf_at_yahoo.com>
Date: Wed Oct 24 2001 - 13:53:49 EDT

Bret,

Thanks for the clarification. This is helpful. I was
getting -33 (as I recall) from pin 3 of the 7924 and I was
getting +21.6 (as I recall) from pin 3 of the 7824.

I'll check the other pins. By the way, I find taking these
measurements difficult due to the fact that my tools are
limited. My DMM probes are pretty standard fare and sort
of "large" for this particular job. I sometimes wonder
what damage can be done if I slip. Keep in mind I was
taking these measurements with the bu406d removed (If HV is
running, I am not touching that board).

Thanks.

Dan R.
--- Bret Pehrson <bret@infowest.com> wrote:
> Just to clarify on reg voltages:
>
> These regulators take in +30 and -30 to output +24 and
> -24. The input
> voltages come pre-filtered from the deflection board.
> Although spec is
> +30/-30, I typically see +33/-33.
>
> To test input voltages on the HV, check pin 1 of the 7824
> (VR1) and pin 2 of
> the 7924 (VR2). If your 7924 tests real low or 0,
> check/replace the wire
> jumper W1 on the deflection board.
>
> To test output voltages on the HV, check pin 3 of the
> 7824 and pin 3 of the
> 7924. Spec is +24/-24.
>
> > -----Original Message-----
> > From: owner-vectorlist@synthcom.com
> > [mailto:owner-vectorlist@synthcom.com]On Behalf Of Dan
> Rasmussen
> > Sent: Wednesday, October 24, 2001 6:16 AM
> > To: vectorlist@synthcom.com
> > Subject: VECTOR: BU406D (was Wintron install: Does this
> look right?)
> >
> >
> > Hey,
> >
> > I'm following up to my own post.... I found the
> following
> > on the archives (after my sig), seems applicable. I'm
> just
> > not sure if that 21.6V on the 7824 is too low and I
> have
> > other problems besides (possibly) the bu406d.
> >
> > In summary, the posting below states, even though a
> bu406d
> > may test good, it may not be good and that the best way
> to
> > check is to first get good readings from the 7824/7924
> and
> > then, if the HV still seems to be dead (as mine seems
> to
> > be), try replacing the bu406d.
> >
> > My main question is this: is the -33 V from the 7924
> and
> > the 21.6V on the 7824 too far out of range for me to
> > consider them good?
> >
> > If it makes sense to try a known good bu406d now, can
> > anyone around here (Boston area) help me with a BU406D
> > (Joel!!!)... My 9YO son's birthday party is Saturday
> and
> > I'm trying to get it back up for it. If someone can
> lend
> > me one, I'll replace it as soon as I can get a hold of
> a
> > new one.
> >
> > Thanks.
> >
> > Dan Rasmussen
> >
> > From: jwelser@ccwf.cc.utexas.edu
> > Date: Tue Oct 21 1997 - 13:40:05 CDT
> >
> > On Tue, 21 Oct 1997, Joel Rosenzweig wrote:
> >
> > > How have you all gone about testing the BU406D?
> >
> > The BU406D is a wierd one. There shouldn't be a diode
> drop
> > from C -> B, or from C -> E (I think I got that
> right...the
> > case where the diode across C and E is reverse biased
> > should be infinite impedance, of course, is what I'm
> > saying.)
> >
> > Even on good BU406D's, the B -> E and E -> B will show
> low
> > impedance, because there is an internal resistor (in
> > addition to the diode) from B <-> E
> >
> > The way I fixed a bunch of HV units: Test the BU406D.
> If it
> > tests bad, throw it out (obviously) if it tests good,
> > you're still not out of the woods yet, because I had a
> > couple that caused no HV, even though they tested good.
> >
> > > When yours have failed, do they open up, or short, or
> ???
> >
> >
> > Short from C <-> E just like most other transistors...
> >
> > > I have three more Amplifone HV units that I'm trying
> to
> > repair. I
> > > suspect the HV transformer in all cases, but I'd like
> to
> > know how to
> > > tell if the BU406D is at fault or not.
> >
> > No HV, heater, etc. Same symptoms as the bad HV
> > transformer, shorted regulators, etc.
> >
> > > One last thing .. I have 4 HV boards in total, all
> with
> > red Hv
> > > transformers. One of the HV units actually works. (I
> > know, a rare
> > > breed) Similar to what Clay mapped out with a DMM for
> the
> > Wells Gardner
> > > HV transformer, I performed similar type measurements
> on
> > the Amplifone
> > > HV transformer units. Every last one of them
> (including
> > the working
> > > one) had the same measurements. Yet, only one of them
> > actually works.
> > > The ohm test seemed pretty logical to me, and it
> sounded
> > like it would
> > > be a surefire way to detect an open or shorted
> winding
> > ... but
> > > apparently, that's not the whole story. If the
> windings
> > appear to be
> > > good, what else is wrong with these transformers? The
> > BU406D's that I
> > > can't test? :-) :-) :-)
> >
> > I measured the same on good and bad Penn-Tran/Wintron
> HV
> > units. I think what sometimes happens is that the
> > insulation between turns breaks down, and the effect is
> > that the transformer has fewer windings, so the HV
> drops.
> > >From the schematic of the HV unit from Wintron, it
> looks
> > like there is a diode IN the HV transformer, so maybe
> that
> > breaks down too, but I'd guess you could test for that
> > <shrug>
> >
> > > I have not removed the HV transformers and swapped
> them
> > into the known
> > > good HV board, but I have checked every component
> except
> > for the BU406D
> > > and MC1, whatever that is?? Aside from that, these
> units
> > have basically
> > > been rebuilt! Any ideas?
> >
> > I just repaired a half-dozen of these boards, and the
> most
> > common failures are the 7824 and 7924 regulators (The
> 7924s
> > failed in all but one instance) If you're getting good
> +/-
> > 24V, then try the BU406D. I found a bunch of creative
> > replacements that previous techs had done (but all
> > incorrect) for the BU406D, so check to make sure that
> the
> > transistor that's there is actually a BU406D. If you've
> got
> > those cheesy brown jumpers (W1, etc) on the board,
> check
> > them out, because they DO open up. If you're not
> getting
> > +/- 24V (or the +/- 30V input to the board) check the
> brown
> > jumpers on the deflection board. I had this happen in 1
> > case.
> >
> > Joe
> >
> >
> >
> > =====
> > ------ replies to sscanf@yahoo.com ------
> >
> > Anything that appears after this sentence is inserted
> by
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> >
> > __________________________________________________
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> >
>
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Received on Wed Oct 24 11:05:20 2001

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