[TechAssist] Re: Mod RCA F32650----------Ch# ATC113 CA1
- From: "Joel Jacobs" <samurai@xxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Sun, 12 Jun 2005 14:12:21 -0400
No, the leading edge is turn off. It's the Left side of the HV pulse on the
scope. When the transistor is on it pulls the pin of the flyback to near
ground - you got B+ on the other end of the winding. When it turns off the
flyback pulse shoots up to ~1200V. Turn ON is really not visible, The end
of the HV pulse does not occur due to the transistor turning back on but
just because the flyback runs out of poop and the current reverses. the
damper diode keeps it from going negative. The output transistor turns on
later - about half way between the HV pulses.
Joel Jacobs
Ohio Consumer Electronics
Pickerington. Ohio
----- Original Message -----
From: <majorthom@xxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Saturday, June 11, 2005 5:13 PM
Subject: [TechAssist] Re: Mod RCA F32650----------Ch# ATC113 CA1
> Hi Joel,I thought the leading edge indicated turn-on time and the trailing
edge the turn off?No?
> The coll pulse seemed OK.Still looking for pulse width answer,tho.
> Best,Pete
>
>
> Joel Jacobs <samurai@xxxxxxxxxxxxxxxx> wrote:
> You want to look at the collector pulse, not the base. Set your scope to
> max v/div and use a 10x probe. You want to look where the flyback pulse
> starts. The corner of the waveform where the pulse goes from ~ground and
> starts upward to 1200v or so should be a very sharp transition. If it's
> rounded and not well defined then the transistor is turning off too slow.
> If it's turning off slow it will dissipate huge amounts of power during
> turnoff. That's usually why they run hot.
> Causes of slow turnoff are 1. insufficient base drive and 2. poorly
> matched transistor in a marginal design. Look for bad electrolytics in the
> drive circuit and if you don't find any try a different transistor. I'm
not
> afraid to use a substitute part as long as I can verify the collector
pulse
> is ok. I had allot of CTC187's that used a BU517 that ran scorching hot
for
> no apparent reason. Sub a 2SC5148 and they run cool.
>
> Joel Jacobs
> Ohio Consumer Electronics
> Pickerington, Ohio
>
> ----- Original Message -----
> From:
> To:
> Sent: Friday, June 10, 2005 5:23 PM
> Subject: [TechAssist] Mod RCA F32650----------Ch# ATC113 CA1
>
>
> > Got in w/ SMPS squeal,replaced HOT & fly.
> >
> > Tested and noticed a creeping temp of HOT.Did electrolytics around
> driver,L4401 resolder
> > After mucho time noticed the drive pulse to HOT base @ half-power points
> to be something like 10 usec.Can anyone refresh me[?] I've been all over
> NTSC sites -no help.
> >
> > My question is: What is pulse width in usec @ base of HOT in a sample
> television receiver?That would be @ 1/2 power point or .707 of peak
> > Regards[?]
> > Pete
> >
> > Peter Neal
> > Neal Electronics
> > 1905 E. Wm.Cannon
> > Austin,TX 78756
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
>
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> Peter Neal
> Neal Electronics
> 1905 E. Wm.Cannon
> Austin,TX 78756
>
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