[?] Start-up fault on Panasonic TX32DTX40 (Euro9D chassis)

Hi,

Does anyone have any experience of any stock faults relating to the
Panasonic TX32DTX40 television (EURO9D) that they'd care to share?

I'm particularly interested in any power-supply related faults which
would explain a problem on switch-on where the TV attempts to start up
and then almost immediately shuts down again. I do have the full Service
Manual to hand.

Any help will be much appreciated.

TIA - Dave

David C.Chapman - Chartered Engineer. FIEE. )
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The message
from David Chapman contains these words:

Hi,

Does anyone have any experience of any stock faults relating to the
Panasonic TX32DTX40 television (EURO9D) that they'd care to share?

I'm particularly interested in any power-supply related faults which
would explain a problem on switch-on where the TV attempts to start up
and then almost immediately shuts down again. I do have the full Service
Manual to hand.

Any help will be much appreciated.

TIA - Dave

David C.Chapman - Chartered Engineer. FIEE. )
--------------------------------------------------------------------------
CHAPMAN ASSOCIATES is a Consultancy offering practical expertise and
design skills in the fields of counter-surveillance, electronic protection
and security. Visit our Web site at http://www.minda.co.uk
--------------------------------------------------------------------------

I don't have anything specific other than when our panasonic TV did
precisely the same thing, it turned out to be a dry joint on a high
wattage resistor according to the service engineer who fixed it by the
simple expedient of resoldering said joint.

Just check for dry joints on the high wattage resistors (I doubt
there'll be more than a couple of such candidates :-)

HTH

--
Regards, John.

Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.

Please do, and when you blow up the power supply because you stop the
protection circuit cutting in I'll let you have the address of a qualified
engineer.

If you have the service manual to hand why not check voltages.

"A little learning..."

--
Robert

The message
from "Rob" contains these words:

Please do, and when you blow up the power supply because you stop the
protection circuit cutting in I'll let you have the address of a qualified
engineer.

If you have the service manual to hand why not check voltages.

"A little learning..."

Quite, but I charitably assume that anyone who has gone out of their
way to lay their hands on an actual service manual is very probably
technically competent to make full and proper use of such. [1]

It was a policy of mine that, when buying an expensive piece of
electronics based kit, I'd immediately order a service manual from the
maker before it became obsolescent and almost impossible to get hold of.

The manual for my Akai GX630DB tape deck came in handy just a few years
back when I dug it out of storage in order to digitise my live
recordings only to find a capstain servo fault.

I didn't expect I'd actually end up using it to repair out and out
faults. I bought the manaul simply so I could repair _design_errors_ and
believe me there were some doozies. Having corrected such stupidities of
design (schoolboy howlers), as well as adding a few enhancements of my
own[2], the superb mechanics and glass crystal ferrite heads were
finally allowed to perform their intended function leaving even the best
quality tape as the limiting factor in the performance equation (just as
it should always be).

[1] I suppose, if getting a service manual is as easy as downloading a
PDF from the manufacturer's website, then you might have a point. :-(

[2] For the benefit of those interested in such things, here is a list
of my corrections and improvements:

I raised the +8dbm replay clipping limit to +18dbm (this defect had
been noted in a review when playing high level recordings made on high
output tape) by redesigning the output bias network in the playback
dolby decoding boards to include a capacitor and an extra two resistors
to maintain the signal gain but shift the bias level back to the
mid-point (indeed, I went as far as replacing the emitter follower load
resistors with constant current generators to further raise the clipping
level when faced with loads down to 3K ohms).

It seems Akai had decided they could get away without these components
and had severely compromised the output clipping level. It was quite
gratifying, a year or two later, to discover that I'd actually
're-invented' components that had existed in the original design as
published in an issue of the Wireless World magazine.

I later discovered that the record dolby boards also required the same
mod (except for substitution of the emitter resistor with a constant
current generator) in order to eliminate intermodulation distortion by
bass frequencies at quite modest levels ( a defect I had initially
assumed was due to a limitation of ferrite over mu metal record heads).

I added a crystal to the erase/bias oscillator circuit to eliminate the
frequency shifts that would occur due to selecting between stereo and
mono recording modes.

I added a 12 step attenuator to the recording amp (post VU and dolby
encoder) to permit tape sensitivity calibration. I also added a 12 step
bias level control and a 12 step 'treble control' also to permit
accurate and repeatable tape calibration adjustments. Such recording
calibration control is essential when using Dolby B noise reduction.

I modified the crude VU meter circuit to make use of op-amp driven
rectifiers to eliminate the non-linearity which, typically, results in
the -20db point coinciding with zero deflection on the meter (I had to
back the zero point below the -20db mark after this mod). This worked so
well that it would even show the warp frequency output from the record
deck not only on record but also on replay (This deck had a _very_ good
bass response :-)

After my experience with severely misaligned azimuth on an Akai D4000,
I figured out how to use triple play tape to determine absolute azimuth
alignment without having to put my trust in a prerecorded calibration
tape. It basically involved white noise from a mono source recorded 'in
stereo' and flipping the triple play tape over to replay from the back
surface mixing and the result back into mono.

A few iterations of azimuth adjustment later and I had an azimuth
setting I could trust a with a very high level of confidence. :-)

Of course, it's all rather academic now. There's no way I'd use
analogue tape as a recording medium now that digital recording to hard
disk can provide much better results.

Analogue tape recordings, even with professional equipment could suffer
IM products measured in tens of percent. Luckily, IM distortion is
better tolerated (by about an order of magnitude) than harmonic
distortion, so such high IM distortion in tape recordings wasn't
considered a serious defect.

Another curious limitation of analogue tape was the fact that a square
wave, although sounding like a square wave would look nothing like such
when fed to an oscilloscope display. Digital recordings preserve phase
relationships between the harmonics of such waveforms and, therefore,
preserve the origional waveshape when viewed on an oscilloscope.

It was just lucky that these shortcomings in analogue tape recording
technology didn't cause aural distress otherwise it would have been
still-born. Even so, these are all very good technological reasons for
making 'direct cut' acetates for analogue vinyl pressings.

Although I won't be making any further serious recordings onto analogue
tape, I've still got a lot of existing tape recordings that I'd like to
digitise over the coming years. I won't be chucking the service manual
away any time soon. :-)

--
Regards, John.

Please remove the "ohggcyht" before replying.
The address has been munged to reject Spam-bots.

"David Chapman" wrote in message
...
Hi,

Does anyone have any experience of any stock faults relating to the
Panasonic TX32DTX40 television (EURO9D) that they'd care to share?

I'm particularly interested in any power-supply related faults which
would explain a problem on switch-on where the TV attempts to start up
and then almost immediately shuts down again. I do have the full Service
Manual to hand.

I assume you mean that it actually switches itself off, and not that it goes
into standby, waiting to be switched on with the remote, as that may be
normal operation.

No, it couldn't be that simple...

--
Max Demian

In article , Max Demian
writes
"David Chapman" wrote in message
...
Hi,

Does anyone have any experience of any stock faults relating to the
Panasonic TX32DTX40 television (EURO9D) that they'd care to share?

I'm particularly interested in any power-supply related faults which
would explain a problem on switch-on where the TV attempts to start up
and then almost immediately shuts down again. I do have the full Service
Manual to hand.

Just to update readers of this NG, I've now opened up the TV and, with
the aid of the service Manual, discovered that the Horizontal Output
transistor was dead short E-B-C.

That certainly explains why the TV wouldn't start up since the
switched-mode PSU was shutting itself off because of the excessive
current that was being drawn.

That LOP transistor must be worked VERY hard, since its breakdown
voltage is 1,700 volts (!) and its maximum collector current is 20 AMPS.

That's quite a move on from the OC71 transistors that I cut my teeth
on MANY years ago.

ATB - Dave

David C.Chapman - Chartered Engineer. FIEE. )
--------------------------------------------------------------------------
CHAPMAN ASSOCIATES is a Consultancy offering practical expertise and
design skills in the fields of counter-surveillance, electronic protection
and security. Visit our Web site at http://www.minda.co.uk
--------------------------------------------------------------------------

David Chapman wrote:
Just to update readers of this NG, I've now opened up the TV and, with
the aid of the service Manual, discovered that the Horizontal Output
transistor was dead short E-B-C.

That certainly explains why the TV wouldn't start up since the
switched-mode PSU was shutting itself off because of the excessive
current that was being drawn.

That LOP transistor must be worked VERY hard, since its breakdown
voltage is 1,700 volts (!) and its maximum collector current is 20 AMPS.

If that has happened then there's a strong probability that its driver
and pre-driver have also been taken out by the event. Don't try powering
the replaced part until you've checked them out.

That's quite a move on from the OC71 transistors that I cut my teeth
on MANY years ago.

It certainly is! Remember those ally tweezers that were intended to act
as a heatsink for the lead up to the body of the device whilst solder it
to the board? Never used them myself and never killed a device either!


--
Graham W http://www.gcw.org.uk/ PGM-FI page updated, Graphics Tutorial
WIMBORNE http://www.wessex-astro.org.uk/ Wessex Astro Society's Website
Dorset UK Info, Meeting Dates, Sites & Maps
Change 'news' to 'sewn' in my Reply address to avoid my spam filter.

On Wed, 18 Oct 2006 18:04:47 +0100, "Graham W"
wrote:

Remember those ally tweezers that were intended to act
as a heatsink for the lead up to the body of the device whilst solder it
to the board? Never used them myself and never killed a device either!

Likewise. Clearly the notion of heat damage by soldering was just a
superstition. It makes me wonder how many other bits of advice have
been generated the same way.

Rod.

Roderick Stewart wrote:
On Wed, 18 Oct 2006 18:04:47 +0100, "Graham W"
wrote:

Remember those ally tweezers that were intended to act
as a heatsink for the lead up to the body of the device whilst
solder it to the board? Never used them myself and never killed a
device either!

Likewise. Clearly the notion of heat damage by soldering was just a
superstition. It makes me wonder how many other bits of advice have
been generated the same way.

I used one of those diligently when I was building projects as a kid. I was
convinced that failure to do so would bring instant death to my transistors.
It was quite a shock when I discovered, years later, that entire circuit
boards were being routinely dunked in molten solder.

...and what about the 50Hz mains hum that was picked up by an
amplifying OC71 if some of its black paint got scraped off? The first
time I experienced that problem on a battery-powered amplifier it took
me a while to find the cause.
The OC71 made quite a good photo-transistor (for its time) and was a
lot cheaper than the OCP71.

Ahhhh! Nostalgia - it 'aint what it used to be ;-)

- Dave


David C.Chapman - Chartered Engineer. FIEE. )
--------------------------------------------------------------------------
CHAPMAN ASSOCIATES is a Consultancy offering practical expertise and
design skills in the fields of counter-surveillance, electronic protection
and security. Visit our Web site at http://www.minda.co.uk
--------------------------------------------------------------------------