[TechAssist] Re: Zenith flyback --FIXED
- From: Jorge Camboni <geo@xxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Thu, 17 Jul 2003 02:14:52 -0500
All power bi polar transistors should have a low ohms resistor
between base and emitter when operating part of the cycle at
cut-off. During the forward bias part of the waveform, the input
impedance is very low, in the range of fractions of ohms, so
a few ohms in paralell are virtually non existant. When it comes
to the reverse bias, it is a completely different story, the impedance
rises and the junction can go into avalanche condition, like a zener
diode but that kills the junction in the long run if you do not place
the resistor there, the transistor gain decreases gradually
until it dies, in this case as the beta decreases, the transistor
gets hotter and hotter (beta must be fairly high in order to
bring the transistor into saturation properly). So, wether
the resistor is inside or outside the transistor IT MUST BE THERE.
In the case of 1881 it ranges around 30 ohms.
best regards Jorge
At 03:17 p.m. 16/07/03 -0600, you wrote:
>I think a 2SD1881 should have a base-emitter resistance because it has a
>damper. (I always wondered if you can have a transistor with a damper
>but without base-emitter resisor). Note that a 2SD1882 and higher are
>in a different family without dampers. I once measured the base-emitter
>resistance of all the outputs I had in stock and found readings from 25
>to 70 ohms. I also found a 2 to 1 ratio of the resistances of the same
>transistor type but from different batches (or between "generic" and
>original) Does anyone know if this resistance make a difference in how
>hot the transistor will operate? I do not have a D1881 in stock but I
>just went thru a bag of D1880 and found resistances from 32 ohms to 47
>ohms with most of them at 40 ohms. John.
>
>
>
>Tri-County Tv wrote:
> > Jim,
> > I used a 2sd1881 and measured it before I installed it and it did not
> > show any resistance from base to emitter. It was my last one and the TV is
> > gone now, should a 2sd1881 have resistance from base to emitter? I know
> what
> > you are referring to as I also have seen many HOT that have about 50 ohms
> > from base to emitter. And at first I thought the original was ok , until I
> > checked it against my 2sd1881 which did not show any resistance.
> > Tom Berger
> > Tri-County TV
> > Robbinsville
> > North Carolina 28771
> > (tricountytv@xxxxxxxxxxxxx)
> > ----- Original Message -----
> > From: "Jim Myers" <jr.myers@xxxxxxxxxxx>
> > To: <techassist@xxxxxxxxxxxxx>
> > Sent: Wednesday, July 16, 2003 1:36 PM
> > Subject: [TechAssist] Re: Zenith flyback --FIXED
> >
> >
> >
> >>Tom, R-U sure? Most HO transistors have an internal base to emitter
> >
> > resistor
> >
> >>of about 45 ohms. This is a mistake we have all made at least once.
> >>**************************************************
> >>Jim Myers
> >>Since 1972
> >>Telrad Electronic Services Co.
> >>Fort Wayne, IN 46815
> >>*************************************************
> >>----- Original Message -----
> >>From: "Tri-County Tv" <tricountytv@xxxxxxxxxxxxx>
> >>To: <techassist@xxxxxxxxxxxxx>
> >>Sent: Wednesday, July 16, 2003 12:29 PM
> >>Subject: [TechAssist] Re: Zenith flyback --FIXED
> >>
> >>
> >>Jeff,
> >> Sorry it took a little while to get back to you, as I busy kicking
> >>myself in the AXX as you were completely right, and I should have known
> >>better. The H.O. Transistor has a base to emitter short of 45 ohms, when I
> >>checked it in circuit it read shorted but I took for granted it was just
> >>drive transformer secondary winding. But when you think about it
> >
> > logically,
> >
> >>it had to be the H.O.Transistor. Thanks Again , and to all who replied so
> >>quickly.
> >>Tom Berger
> >>Tri-County TV
> >>Robbinsville
> >>North Carolina 28771
> >>(tricountytv@xxxxxxxxxxxxx)
> >>----- Original Message -----
> >>From: "Shoreline Electronics" <jstielau@xxxxxxxx>
> >>To: <techassist@xxxxxxxxxxxxx>
> >>Sent: Wednesday, July 16, 2003 12:23 PM
> >>Subject: [TechAssist] Re: Zenith flyback --need sub info
> >>
> >>
> >>
> >>>Remove the output transistor completely: Fire up the set and check for
> >>
> >>good
> >>
> >>>base drive...that will confirm your H-drive question:
> >>>
> >>>Try another output transistor to be sure....it really sounds like it's
> >>>defective...since PS is not squealing once you unsolder the collector.
> >>>
> >>>==========================
> >>>Jeff Stielau
> >>>Shoreline Electronics Repair
> >>>344 East Main Street
> >>>Clinton,CT 06413
> >>>860-399-1861
> >>>860-664-3535 (fax)
> >>>jstielau@xxxxxxxx
> >>>==========================
> >>>"If you push something hard enough it will fall over."
> >>>Fudd's First Law of Opposition - Sir Sidney Fudd
> >>>
> >>>
> >>>----- Original Message -----
> >>>From: "Tri-County Tv" <tricountytv@xxxxxxxxxxxxx>
> >>>To: <techassist@xxxxxxxxxxxxx>
> >>>Sent: Wednesday, July 16, 2003 12:14 PM
> >>>Subject: [TechAssist] Re: Zenith flyback --need sub info
> >>>
> >>>
> >>>
> >>>>Jeff,
> >>>> I checked that and it's good.I did notice that there is no b+
> >>>
> >>>getting
> >>>
> >>>>to the driver transformer and I'm not sure if I should have voltage
> >>>
> >>there
> >>
> >>>>when you first plug it in.
> >>>>Tom Berger
> >>>>Tri-County TV
> >>>>Robbinsville
> >>>>North Carolina 28771
> >>>>(tricountytv@xxxxxxxxxxxxx)
> >>>>----- Original Message -----
> >>>>From: "Shoreline Electronics" <jstielau@xxxxxxxx>
> >>>>To: <techassist@xxxxxxxxxxxxx>
> >>>>Sent: Wednesday, July 16, 2003 12:02 PM
> >>>>Subject: [TechAssist] Re: Zenith flyback --need sub info
> >>>>
> >>>>
> >>>>
> >>>>>Your Horizontal Output is probably shorted.
> >>>>>
> >>>>>==========================
> >>>>>Jeff Stielau
> >>>>>Shoreline Electronics Repair
> >>>>>344 East Main Street
> >>>>>Clinton,CT 06413
> >>>>>860-399-1861
> >>>>>860-664-3535 (fax)
> >>>>>jstielau@xxxxxxxx
> >>>>>==========================
> >>>>>"If you push something hard enough it will fall over."
> >>>>>Fudd's First Law of Opposition - Sir Sidney Fudd
> >>>>>
> >>>>>
> >>>>>----- Original Message -----
> >>>>>From: "Tri-County Tv" <tricountytv@xxxxxxxxxxxxx>
> >>>>>To: <techassist@xxxxxxxxxxxxx>
> >>>>>Sent: Wednesday, July 16, 2003 11:19 AM
> >>>>>Subject: [TechAssist] Zenith flyback --need sub info
> >>>>>
> >>>>>
> >>>>>
> >>>>>>Hello,
> >>>>>> I got this zenith color TV model SS2761S , module 9-913
> >>>>>
> >>,and
> >>
> >>>>the
> >>>>
> >>>>>flyback had a slit in the side with stuff oozzing out , Flyback #
> >>>>
> >>>95-4203
> >>>
> >>>>,
> >>>>
> >>>>>when you look this # up on tritronics, it shows a 95-4203-REP for 17
> >>>>>dollars, so I ordered it, and installed it into the module and now ,
> >>>>
> >>>when
> >>>
> >>>>>you plug it in, the ps squeals, so I replaced all the usual ps
> >>>>
> >>>components,
> >>>
> >>>>>and same problem,also checked for shorts on secondary of fly and
> >>>>
> >>>>everything
> >>>>
> >>>>>looks ok, If I disconnect the collector of the HOT it stops
> >>>>
> > squealing
> >
> >>>and
> >>>
> >>>>ps
> >>>>
> >>>>>voltages return to normal, however I am not reading and B+ on any
> >>>>
> > legs
> >
> >>>of
> >>>
> >>>>>the driver transformer, I do not have the schematic and would
> >>>>
> > greatly
> >
> >>>>>appreciate if someone could upload one. Could this replacement fly
> >>>>
> > be
> >
> >>>the
> >>>
> >>>>>trouble? Has anyone had experience with this flyback?
> >>>>>
> >>>>>>Tom Berger
> >>>>>>Tri-County TV
> >>>>>>Robbinsville
> >>>>>>North Carolina 28771
> >>>>>>(tricountytv@xxxxxxxxxxxxx)
> >>>>>>
> >>>>>
> >
> ****************************************************************************
> >
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>
>--
>John Mielke
>Main TV
>Longmont,Co 80501
>303 776 6955
>303 776 0792 fax
>maintv@xxxxxxxxxxx
>
>
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Jorge Camboni, GY Electronics, Richardson, TX
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