[TechAssist] Re: Horizontal output overheating.
- From: Joe Batchelor <jbc@xxxxxxxxxxxxxx>
- To: techassist@xxxxxxxxxxxxx
- Date: Tue, 17 Dec 2002 08:26:32 -0600
In a linear circuit there is a problem with thermal run away.
When the transistor gets hot the resistance is less.
A horizontal output should be full ON or full OFF. The transistor
resistance is very low when full ON so does not get hot. The problem
is in the transistion period. The drive signal is critical.
Sony had a modification to use a higher power transistor, but the
base drive resistor needed to be changed. The D1881 can take more drive
than the D1880 and is a higher power transistor.
Two transitors in parallel needs some negative feed back because they
are not matched. If running high power, the resistance of the emitter wire
may be enough.
Joe Batchelor CET TX-80
12/16/02 9:27:41 PM, Al Gutz <alg@xxxxxxxxxxx> wrote:
>
>Paralleling transistors is not a problem, if one starts to conduct more
>it gets hotter and its effective resistance increases causing the other
>cooler transistor which has a lower effective resistance to pickup more
>of the load. A point of balance is reached. I have worked on high power
>broadcast applications where you may have many transistors or mosfets in
>parallel. When you are looking for outputs of up to 50 Kwatts you don't
>do it with one transistor. This aside I don't know if I would do it with
>a HOT. You can safely sub these provided you pay attention to switching
>times and transition times, max CE volts, Max BE volts and total Pout.
>If you sub and keep transition/switch times the same its no problem to
>increase the Imax ans Pout. ei 2SD1879, 1880, 1881 all have same specs
>except for Imax and Pout.
>
>Al G
>Al's TV-Electronics
>Pembroke Ont.
>Canada
>
>Gary McCartney wrote:
>>
>> I always read that using two semiconductors in parallel will cause the
>> one of them to hog all the current, unless you install a small current
>> limiting resistor (perhaps 0.01 ohm or there abouts) in the paths of the
>> 2 emitters. Has anyone else heard of this?
>>
>> Gary McCartney
>>
>> McCartney Electronics
>> 7134 Fife Rd, RR 7
>> Guelph Ontario Canada N1H 6J4
>> Fax: (519)821-1530
>> email: gary (at) number63.ca
>>
>> teltek2 wrote:
>> >
>> > I agree...using 2 will put you into price range of OEM.
>> >
>> > Fix the fault..install OEM part, ship it. Done.
>> >
>> > -Ed-
>> > Tel-Tek Electronics
>> > Ontario-Canada
>> >
>> > teltek2@xxxxxxxxxxxx
>> > ----- Original Message -----
>> > From: <HSWAD@xxxxxxx>
>> > To: <techassist@xxxxxxxxxxxxx>
>> > Sent: Monday, December 16, 2002 9:09 AM
>> > Subject: [TechAssist] Re: Horizontal output overheating.
>> >
>> > > Wouldn't it be about the same price to replace with the correct part?
>> > > Modifications put you in a responsible position . Hollis Bates, field
>> > > engineer-retired In a message dated 12/16/02
>> > > 5:13:25
>> > AM
>> > > Eastern Standard Time, villyboor@xxxxxxxxx writes:
>> > >
>> > >
>> > > > Subj:[TechAssist] Re: Horizontal output overheating.
>> > > > Date:12/16/02 5:13:25 AM Eastern Standard Time
>> > > > From:<A HREF="mailto:villyboor@xxxxxxxxx";>villyboor@xxxxxxxxx</A>
>> > > > Reply-to:<A
>> > HREF="mailto:techassist@xxxxxxxxxxxxx";>techassist@xxxxxxxxxxxxx</A>
>> > > > To:<A
>> > HREF="mailto:techassist@xxxxxxxxxxxxx";>techassist@xxxxxxxxxxxxx</A>, <A
>> > HREF="mailto:techassist@xxxxxxxxxxxxx";>techassist@xxxxxxxxxxxxx</A>
>> > > > Sent from the Internet
>> > > >
>> > > >
>> > > >
>> > > >
>> > > > Villy Boor
>> > > > Boorelec Durban
>> > > > --
>> > > > Perhaps I am a wee bit off the topic but I have been finding many TVs
>> > > > with troubles after the horizontal output has been changed. What I find
>> > is
>> > > > if you get the expensive manufacturers transistor all is well, the
>> > generic
>> > > > fails. My tip here is use 2, parallel them up and there is no need to
>> > > > increase heat sinks as there will be less heat, the input inpedance
>> > drops
>> > > > so it is more stable, as yet after 2 years on sets where no faults were
>> > > > found and the transistor failed, I have had no returns. Your comments
>> > > > welcomed, Villy.
>> > > > On Sun, 15 Dec 2002 08:13:25
>> > > > Paul Medvetz wrote:
>> > > > >We have a Sony KV-32S35 , Set came in dead with shorted horiz.out,
>> > > > reg.Q601 and Q602, Replaced Q601,Q602, Q502, VDR601,R607,C502.Set now
>> > plays
>> > > > but Q601,Q602, get very hot just after three minutes,This set was in
>> > shop
>> > > > two months ago for shorted flyback and horiz.out transistor.Don't want
>> > to
>> > > > leave it on any longer I know it will short again,Also I did go over
>> > > > connections in horiz. thanks in advance for any help.
>> > > > >
>> > > > >Paul Medvetz
>> > > > >TV- Service-CO.
>> > > > >Hazleton,Pa. 18202
>> > > > >paulcho@xxxxxxxx
>> > > > >
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