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

I've always tested w/ the components (BU406D) in place. Just use care, and
you shouldn't have a problem w/ HV (remember, it comes out of the HVT to the
second anode on the CRT). From what I understand, the voltage regulators
need a load to regulate properly.

As for testing -- don't try your luck w/ trying to connect to the actual
pin/leg of the reg. Test from the solder-side of the board, and use a
*trace* that goes to the pin you are testing -- it is a lot easier and
safer, even w/ std probes. See what I'm saying?

> -----Original Message-----
> From: owner-vectorlist@synthcom.com
> [mailto:owner-vectorlist@synthcom.com]On Behalf Of Dan Rasmussen
> Sent: Wednesday, October 24, 2001 10:54 AM
> To: vectorlist@synthcom.com
> Subject: RE: VECTOR: BU406D (was Wintron install: Does this look right?)
>
>
>
> 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
> > >
> > >
> > >
> > > =====
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> >
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Received on Wed Oct 24 12:04:41 2001