Toshiba TV29C90 problem; Image fades to black...

[DaveC]

On Thu, 20 Nov 2003 9:20:32 -0800, DaveC wrote
(in message <0001HW.BBE237E000C60504F0080600@news.individual.net&gt:

By using a single, high-power FET one can reach equivalent results as a
multi-FET design.

Hmm... Better to say:

By using a single, high-power FET, one can reach equivalent *powers* as a
multi-FET design, but without the inherent distortions.
--
DaveC
me@privacy.net
This is an invalid return address
Please reply in the news group

 

[Walter Harley]

"DaveC" <me@privacy.net> wrote in message
news:0001HW.BBE237E000C60504F0080600@news.individual.net...

I would like to experiment with such a single-FET design, and since not
every
manufacturer makes high-power FETs in such a package, I thought I'd start
by
fiding out who makes such FETs. Then, ruling out those devices whose specs
are more appropriate for switching duties (rather than linear duties such
as
audio), etc. arrive at a short list of devices to start exploring more
closely.

Does that help clarify?

Of course this may all come to nothing more than intellectual curiosity.
But
that's what curiosity is for, isn't it, to be satisfied.

Aha! So, the problem is: "I would like to find a MOSFET that is appropriate
for a high-power class-A single-FET audio amplifier design. Said MOSFET
should be able to dissipate a lot of power."

Now, that's a nice clear problem statement, lacking only quantification of
"high power" and a particular schematic; and neither of those is especially
necessary, since the former can just be "how high can I get?" and the latter
is pretty obvious from the problem statement. (I'm assuming you're thinking
in terms of, e.g., the "Zen" amp.)

Group, any suggestions?

(Dave, if no one answers, you might want to re-post with a new subject line,
and with your new problem description.)

 

[Asimov]

"DaveC" bravely wrote to "All" (20 Nov 03 09:20:32)
--- on the heady topic of "Re: Who makes this MOSFET?"

Da> From: DaveC <me@privacy.net>

Da> Well said, Walter.

Da> I have come across the statement by some "single-FET" amplifier
Da> designers that when using paralleled output devices that because if
Da> their differences in turn-on characteristics there is some distortion
Da> introduced. This is a given, due to the manufacturing tolerance
Da> differences. (We won't argue about what magnitude this might be, and
Da> if it is at all audible.)
Da> By using a single, high-power FET one can reach equivalent results as
Da> a multi-FET design.

Da> I would like to experiment with such a single-FET design, and since
Da> not every manufacturer makes high-power FETs in such a package, I
Da> thought I'd start by fiding out who makes such FETs. Then, ruling out
Da> those devices whose specs are more appropriate for switching duties
Da> (rather than linear duties such as audio), etc. arrive at a short list
Da> of devices to start exploring more closely.

Da> Does that help clarify?

Actually some switching types are better suited to linear operation than
some linear devices but that's another topic altogether. Here is
something else to muddle the issue. Some power fets are not a single
device but are actually made up of an array of many fets all wired up on
the die in parallel. The theory is that the fets are virtually identical
and the best possible match that can be had. Some even mix in bipolar
devices to get the best of both types. There is a lot of choice out
there these days!

 

[Winfield Hill]

Walter Harley wrote...

DaveC wrote ...

I would like to experiment with such a single-FET design, and
since not every manufacturer makes high-power FETs in such a
package, I thought I'd start by fiding out who makes such FETs.
Then, ruling out those devices whose specs are more appropriate
for switching duties (rather than linear duties such as audio),
etc. arrive at a short list of devices to start exploring more
closely.

Aha! So, the problem is: "I would like to find a MOSFET that is
appropriate for a high-power class-A single-FET audio amplifier
design. Said MOSFET should be able to dissipate a lot of power."

Now, that's a nice clear problem statement, lacking ...

I have some comments. First, with the exception of Hitachi's
lateral MOSFETs, which feature a negative current tempco when
in the linear region, there are few features that make a FET
more suited for switching that linear use. For common D-MOS
power FETs the primary spec of interest is thermal resistance,
because that's what determines the maximum power dissipation.

You will find that older FET designs all have a lower thermal
resistance for a given current capability, because they had a
larger die area. But this really isn't relevant, because what
counts is die-size / thermal resistance vs. price. There are
some rather impressive low-cost high-power-handling MOSFETs
available nowadays, but you'll find that they aren't available
at reasonable high-power audio-amplifier power-supply voltage
ratings, i.e. 150 to 250V. That's because high-volume stuff
is concentrated in the automotive area, or in off-line motor
control, etc. For example consider the high-power FETs below:

part no. watts volts
-------- ---- ----
FQA170N06 375 60
IRFP2907 470 75
HUF75652 515 100
FDH44N50 750 500
STW47NM50 417 500

(FET thermal resistance ratings are inversely proportional to
the power rating in watts.) BTW, the power rating assumes a
25C case temperature, which of course is blatantly impossible.

All of these parts come in low-cost packages. The low-voltage
parts have too low a voltage rating, and the high-voltage parts
are too high. Well, maybe not; why does it matter if they have
an excessively-high voltage rating? Oops, if one digs deeper
and examines Ciss, you may have an answer.

Now, with respect to the SOT-227B parts. These do have a nice
low thermal resistance, but they cost $25 to $75 each, and are
very hard to get. Usually a high minimum order is required,
plus a long lead time for your expensive order.

A typical power rating for a SOT-227B part is 500 to 680 watts.
Not so attractive, compared to the lower-cost easier-to-get
parts listed above.

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Tony Williams]

In article <bpk2tn0cc@drn.newsguy.com>,
Winfield Hill <Winfield_member@newsguy.com> wrote:
[snip]

Now, with respect to the SOT-227B parts. These do have a nice
low thermal resistance, but they cost $25 to $75 each, and are
very hard to get. Usually a high minimum order is required,
plus a long lead time for your expensive order.

A typical power rating for a SOT-227B part is 500 to 680 watts.
Not so attractive, compared to the lower-cost easier-to-get
parts listed above.

As you know, I like the Thompson Isotop/SOT-227 package.

The isolation and the heavyweight connection bolts are both
already done for you. For 1-off or low volume jobs the simple
assembly can easily compensate for the higher purchase price.

And you can bolt a little pcb onto the lugs for close up
components (current shunts or surge suppressors, etc).

And maintenance in the field (by the customer) is relatively
uncomplicated, just a screwdriver operation. No need to
unsolder/resolder, and no worry about isolation being lost
by a careless tech.

And the nice hefty csa of the connecting lugs means that
you don't have to look out for that little ambush that
sometimes says (for Ipk) "Exceeds package capability".

Easy to get (in the UK) from Farnell or Radiospares.

--
Tony Williams.

 

[Winfield Hill]

Tony Williams wrote...

Winfield Hill wrote:

Now, with respect to the SOT-227B parts. These do have a nice
low thermal resistance, but they cost $25 to $75 each, and are
very hard to get. Usually a high minimum order is required,
plus a long lead time for your expensive order.

A typical power rating for a SOT-227B part is 500 to 680 watts.
Not so attractive, compared to the lower-cost easier-to-get
parts listed above. [ see below ]

As you know, I like the Thompson Isotop/SOT-227 package.

The isolation and the heavyweight connection bolts are both
already done for you. For 1-off or low volume jobs the simple
assembly can easily compensate for the higher purchase price.

Aha, I ignored the very important issue of case-to-heat-sink
thermal resistance. For a TO-247 package with a thin grease
layer (no insulator) this is about 0.24 C/W and dramatically
changes the actual-usage rating. The new calculated values
are below, using 175C junction temperature and 25C heat sink.

P = (Tj - Tc) / (R_theta-JC + R_theta-CS)

part no. watts volts real watts *
-------- ---- ---- ------------
FQA170N06 375 60 234
IRFP2907 470 75 268
HUF75652 515 100 283
FDH44N50 750 500 341
STW47NM50 417 500 232 (150C junction)

Now the TO-247 FETs look much less attractive compared to
SOT-227 parts. Yet if we were to redo the calculation with
0.5 C/W (or worse) insulators, then they'd really look like
wimps. The best FET above, a FDH44N50, rates only 214 watts
with a hypothetical 0.5 C/W insulator. This is only 1/3 to
1/4 of the capability of one of Tony's favorite parts.

* Note for novice engineers: we can rarely assume 25C heat-
sink temperatures in real life. Not only is the heat sink
going to get hot in operation, but the FET contact point will
be even hotter due to internal thermal resistance in the heat
sink. For example, a 60C heat-sink surface might be seen in
a well-designed aggressively-used system. This reduces the
FDH44N50 rating to 164 watts. Furthermore, most engineers
will NOT design for operation of a power MOSFET continuously
at it's full rated junction temperature. If we use Tj = 150C,
then the FDH44N50 rating drops to only 128 watts.

128 watts is a realistic maximum operating power dissipation
for this FET, which carries a data-sheet rating of 750 watts!
Those insulators can be real performance killers! :&gt

And you can bolt a little pcb onto the lugs for close up
components (current shunts or surge suppressors, etc).

And maintenance in the field (by the customer) is relatively
uncomplicated, just a screwdriver operation. No need to
unsolder/resolder, and no worry about isolation being lost
by a careless tech.

And the nice hefty csa of the connecting lugs means that
you don't have to look out for that little ambush that
sometimes says (for Ipk) "Exceeds package capability".

Easy to get (in the UK) from Farnell or Radiospares.

OKEY DOKEY!

Thanks,
- Win

whill_at_picovolt-dot-com

 

[Dave Moore]

Got a new flyback from Union and installed it.
Everything seemed ok, but I noticed that the HV
regulator seemed not to be working.

The problem turned out to be a shorted 820pf
capacitor on the HV splitter voltage sensing circuit
that is mounted on on the splitter itself.

Thanks for all the tips folks
--DM--


"Dave Moore" <novalves@N0$pamdatasync.com> wrote in message
news:boabbr$mt4$1@news.datasync.com...

I just fixed an early Family 1 version PTV for a
friend of mine. What a nightmare, fixed SMPS,
replaced 7 bad xstrs and numerous weak caps
in convergence power section, repaired no video,
and no sound problem ( TV from hell,thought
all was ok, then the dang thing just quit working.

After defeating/bypassing a number of the shutdown
circuits I got it to run for about 5 seconds. Just long
enough to notice that the HOT was getting hot.

So, I figured that the flyback was probably bad.
Out of desperation to verify this, I took a flyback
off of a 169 chassi for a 31" TV.

Ok, here's where it gets interesting. After studying
the situation a bit, I determined that the black wire
for the PTV flyback and the same black wire for
the 31" TV are not the same. On the PTV, this black
wire is the other end of the CRT anode winding,
and not the focus tap like it is on the flyback for
the 31" set.

So, I put the 31" flyback in the PTV, only I didn't
connect the black wire to the HV regulator board.

Instead I cut
the ground traces going to one of the pins on the
flyback which I had determined was the other end
of the HV anode winding for this 31" flyback and
soldered my own "black wire" to this pin and connected
it to the HV regulator board.

Well, the PTV came up and worked beautifully. All PS
voltages measured within specs and the HV measured 28K.
a little low I think but the picture looked fine. Well, I ran it
for about 8 hours and started to work on adjusting the
convergence. While I was working on the convergence, the set
went *POP* and shut off and immediately came back on.
Then about 5 minutes later it did the same. Then after that.
it never did this again for about 3 hours.

After I finished the convergence I shut her down and told my
friend that he could give it a go if he wanted to, but I didn't
really trust it. Sure enough, when he came to get it, we
turned it on, it came up and went *POP*,, for good this time.

Ok, I am about to order a new flyback from MCM for $29.
I just stumbled on a thread in the freelists group where some
techs are discussing some problems with the replacement parts
for this set. Also I found an article by JURB in the SER
Google archives about this same issue.

So, 2 questions,,, anyone have any suggestions about why
2 flybacks crapped out when everything seemed to be ok?
I realize that the 31" flyback may simply not have HV diodes in
it sufficient to handle the beam current in the PTV, but I really
have some doubts as to whether this was the reason that the
origional flyback checked out.

2'nd question,, anyone had any problems using the sub part
232191 from MCM ?

Thanks
=^^=DM

 

[Ben]

"Tony Williams" <tonyw@ledelec.demon.co.uk> schreef in bericht
news:4c5554de6btonyw@ledelec.demon.co.uk...

In article <bpk2tn0cc@drn.newsguy.com>,
Winfield Hill <Winfield_member@newsguy.com> wrote:
[snip]
Now, with respect to the SOT-227B parts. These do have a nice
low thermal resistance, but they cost $25 to $75 each, and are
very hard to get. Usually a high minimum order is required,
plus a long lead time for your expensive order.

A typical power rating for a SOT-227B part is 500 to 680 watts.
Not so attractive, compared to the lower-cost easier-to-get
parts listed above.

As you know, I like the Thompson Isotop/SOT-227 package.

The isolation and the heavyweight connection bolts are both
already done for you. For 1-off or low volume jobs the simple
assembly can easily compensate for the higher purchase price.

And you can bolt a little pcb onto the lugs for close up
components (current shunts or surge suppressors, etc).

And maintenance in the field (by the customer) is relatively
uncomplicated, just a screwdriver operation. No need to
unsolder/resolder, and no worry about isolation being lost
by a careless tech.

And the nice hefty csa of the connecting lugs means that
you don't have to look out for that little ambush that
sometimes says (for Ipk) "Exceeds package capability".

Easy to get (in the UK) from Farnell or Radiospares.

--
Tony Williams.

 

[Winfield Hill]

Ben wrote...

... You were saying?

Thanks,
- Win

whill_at_picovolt-dot-com

 

[BFriedl]

GO FRY's!! I live in AZ, but was in San Diego this summer and saw their
ad in the paper and grand opening and such. I guess they had just opened
or sometyhing. We have 2 Fry's in Phoenix, with 2 more on the way. I
work for them and love to go in there in a white shirt and tie or to shop.

scopes, and other things I've forgot. They even have some Philmore
parts--I don't recall seeing that name on a parts rack since the
1960s. It's been a long time since I've found this kind of stuff
stocked nearby.

Brian
A good majority of the stuff we carry is NTE. We can also special order

some parts, as long as it is in the system.

--
BFriedl
A+ Certified Technician
AIM: UACybercat
** Bear Down Arizona! **
******* Go Cats! *******

 

[bobinphx]

If you work for them, tell them to stock the parts more often, I did an
informal survey, with a store person right there with me and found that in
any given section ( physical rack unit) there was about 20% of it empty.....

Bob in phx.

 

[Bill Jeffrey]

bobinphx wrote:

If you work for them, tell them to stock the parts more often, I did an
informal survey, with a store person right there with me and found that in
any given section ( physical rack unit) there was about 20% of it empty.....

Bob in phx.


Right on, Bob -

In the two Phoenix area stores, I actually found the semicondiuctor
section to be better stocked than the others. Check out switches, for
example, or relays or pilot lights. The out-of-stock rate approaches
50% for all of those. Didn't check basic stuff like resistors and caps.
It appeared that Small Appliances was pretty good, though, so if I had
come in for a can opener or a toaster oven, I'd be all set.

If they build two more stores but don't improve the stock situation,
ain't no one gonna be happy - including them, when the stores underperform.

Bill Jeffrey

--
Remove NOSPAM from my address before e-mailing a reply.
Outgoing mail is automatically scanned by Norton Anti-Virus.

 

[TV Fixer1]

Yeah, well I'm an ex-convict myself, having done County, State and Federal time
25 years ago before I wised up and went straight. Most of the people I met in
prison belonged there. Permanently.

 

[RonKZ650]

Have a Emerson TC2555D that has INSF . Width . Have no schmetic . Set was
DEAD . Replaced Q401 , STR30110 , C435 ,R521 , R507 , Solder R473 , R474

Some brands of STR30110 ICs do not work. For some odd reason, the output
voltage (pin 4 of the STR30110) is supposed to be 130v instead of the expected
110v. A bad new STR30110 will read 110v on pin 4 and cause low width. If this
is the case either try another brand, or try a STR30125, or 30130. Check
voltage on pin 4 to verify you are around 130v. Also make sure you used the
right value for R507 47 ohm.
Ron

 

[John Del]

Subject: Srt 25 sylvania or funai - how to get into service mode?
From: "IanV" newsgroups@smiggy.com
Date: 12/4/03 3:02 PM Pacific Standard Time
Message-id: <_1Pzb.12813$465.2143267@newsfep2-win.server.ntli.net

Can someone please let me know how to get into the service mode on a srt 25
sylvania or funai tv?

Why?

John Del
Wolcott, CT

"I'm just trying to get into heaven, I'm not running for Jesus!"
Homer Simpson

(remove S for email reply)

 

[mrocus]

Backdoor.IRC.Bot
This is a virus.

Backdoor.IRC.Bot is a detection for a group of Backdoor Trojan Horses that
uses the IRC channels to launch Denial of Service (DoS) attacks, and that
allows a hacker to control a victim's computer.

It is possible that the functions of the files may change. The information
discussed in this writeup is based on the samples that Security Response has
reviewed.

Note: Virus definitions containing an updated signature for Backdoor.IRC.Bot
were released on October 27, 2003 to account for the discovery of a minor
variant.


Also Known As: BackDoor-BBB [McAfee], BKDR_FOLLA.A [Trend]

Type: Trojan Horse
Infection Length: varies



Systems Affected: Windows 2000, Windows 95, Windows 98, Windows Me, Windows
NT, Windows Server 2003, Windows XP
Systems Not Affected: DOS, Linux, Macintosh, OS/2, UNIX

1:20 PM 14/12/2003

"underground" <underground@hotmail.com> wrote in message
news:GcCBb.12137$655.818302@news4.srv.hcvlny.cv.net...

Britney Spears nude
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[Jerry G.]

Citrus PunchFirst of all, never send full HTML, and especialy with graphics
on these newsgroups.

Your VCR may have a power supply fault to start with. Without detailed
references to voltages from the power supply to start with, this would be
difficult to guess at.

You may have a warn head, or you may be lucky, and it is a bit dirty. The
alignment should not be off, unless you messed with it. When changing the
head, you would have to do the guide alignment. You would need a scope,
calibration tape, and most likely the service manual.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Manzur Yazdani" <farmanz@hotmail.com> wrote in message
news:brkt6g$de9$1@news01.intel.com...


Hi folks,
I am new to this forum and have 2 specific problems I am hoping to get your
expert help with. I have 2 of these combo units.
One of them turns on fine, but after a while turns back off automatically.
Am I correct in assuming that its the VCR portion that is making it do so?
Could it be that the roller guides (supply or take-up) are stuck and that is
what is making the power turn off? Or is it the reel sensors?
The 2nd unit DVD works fine, and the vcr loads fine and plays fine except
that the picutre looks like a dirty head for some cassettes and some will
play just fine with crystal clear picture. Tracking has no effect. Is this a
misaligned head, and if so, how do I fix this?
Thanks in advance for your help.
Manzur.

 

[Ken G.]

The tapes that dont work are probably recorded at slow speed . A couple
heads being dirty could cause that ... clean the heads .

Otherwise these are cheap junk products that probably need replacing
even though relatively new due to cheap non repair construction . the
parts & boards would out cost a new one

 

[feklar (was feklar@rock.c]

On Tue, 16 Dec 2003 06:30:47 GMT, " Stephen Cowell"
<scowell@sbcglobal.net> wrote:

"feklar (was feklar@rock.com)" <ptaakhangsat@sbcglobal.net> wrote in message
news:3fde7279.9903140@news.dallas.sbcglobal.net...


...

I want to modify my wireless microphone transmitter to better serve as
a guitar transmitter. The signal getting from the guitar to the
transmitter is weak.

You need a high-to-low transformer, or a
buffer amplifier, in between your guitar and
the wireless unit. It is designed for low-
impedance, whereas guitars are high-imp.
I won't confuse you with balanced-unbalanced
right now... just get a mic transformer at
Rat Shak and put it in between. It's pretty
obvious where to connect the high/low.
__
Steve
.


I take it you mean this one:

http://tinyurl.com/zfmm

1,000-ohm center-tapped primary, 8-ohm secondary.

So, I take and wire the 8 ohm secondary to the guitar side, and the
1000 ohm primary to the mic jack on the transmitter?

That halfway makes sense considering the average 8 ohm or so
resistance of a guitar pickup... or did you mean the other way
around?

Say a strat single coil measures at 6 ohms. Is that the impedance
value?

What are the average impedance values for pickups and microphones,
just out of curiosity?

The transmitter accepts a mini mono plug, it doesn't expect a balanced
mic input, just an el cheapo mic input. I haven't checked it yet but
it would not surprise me if the input jack was putting out a small
current for a condenser mic. If it is, I wonder if there is any
danger to my pickups? Seems to work fine the way it is, with the
exception of the low input signal problem.

If it is putting out voltage and current to power a condenser mic,
what voltage measurement would I expect to find across the mic input?

TIA

ptaakhangsat@sbcglobal.net
subtract where I hang at to unmunge

feklar's guitar playing:
http://www.angelfire.com/empire2/kahless
This will always take you to my ftp server if its up.

The Amazing and Mysterious Powers of Mexican Females.
Chapter 1: Levitation and Summoning.
http://www.angelfire.com/empire2/ptaak/images/mexwench.jpg

 

[Stephen Cowell]

"feklar (was feklar@rock.com)" <ptaakhangsat@sbcglobal.net> wrote in message
news:3fdec7d4.31756961@news.dallas.sbcglobal.net...

On Tue, 16 Dec 2003 06:30:47 GMT, " Stephen Cowell"
scowell@sbcglobal.net> wrote:


"feklar (was feklar@rock.com)" <ptaakhangsat@sbcglobal.net> wrote in
message
news:3fde7279.9903140@news.dallas.sbcglobal.net...


...

I want to modify my wireless microphone transmitter to better serve as
a guitar transmitter. The signal getting from the guitar to the
transmitter is weak.

You need a high-to-low transformer, or a
buffer amplifier, in between your guitar and
the wireless unit. It is designed for low-
impedance, whereas guitars are high-imp.
I won't confuse you with balanced-unbalanced
right now... just get a mic transformer at
Rat Shak and put it in between. It's pretty
obvious where to connect the high/low.
__
Steve
.


I take it you mean this one:

http://tinyurl.com/zfmm

1,000-ohm center-tapped primary, 8-ohm secondary.

So, I take and wire the 8 ohm secondary to the guitar side, and the
1000 ohm primary to the mic jack on the transmitter?

Exactly, perfectly wrong... strike that and reverse it.
The guitar connects to high impedance i.e. 1K primary.
The low-imp secondary connects to the unit side.

That halfway makes sense considering the average 8 ohm or so
resistance of a guitar pickup... or did you mean the other way
around?

A guitar pickup that measures 8 ohms is a speaker,
not a guitar pickup. We're talking impedance here,
anyway, not DC resistance. You don't get impedance
by using an ohmmeter... takes a special instrument to
measure it. The more wire, the bigger the difference
between DC resistance and impedance... speakers
track pretty closely (ie measure 6 for 8ohm imp)...
pickups are an order of magnitude different, at least.

Say a strat single coil measures at 6 ohms. Is that the impedance
value?

No... it should measure lots more, IIRC, more like 8Kohms
for DCR.

What are the average impedance values for pickups and microphones,
just out of curiosity?

Pickups are up in the tens of Kohms... mics are
normally 600ohm (there are high-imp mics, just
not common in the PA world).

The transmitter accepts a mini mono plug, it doesn't expect a balanced
mic input, just an el cheapo mic input. I haven't checked it yet but
it would not surprise me if the input jack was putting out a small
current for a condenser mic. If it is, I wonder if there is any
danger to my pickups? Seems to work fine the way it is, with the
exception of the low input signal problem.

If this is so, you need to install a blocking cap so
the DC doesn't interfere with the transformer
(DC will saturate a transformer core). You can
use a 1uF ceramic in series with the lead to the
transmitter.

If it is putting out voltage and current to power a condenser mic,
what voltage measurement would I expect to find across the mic input?

It takes about 1.5VDC to power an electret
condenser, IIRC.
__
Steve
..