Toshiba TV29C90 problem; Image fades to black...

[Malissa Baldwin]

On May 29, 12:44 pm, "p...@aol.com" <p...@aol.com> wrote:

On May 29, 1:38 pm, Malissa Baldwin <sitremaganais...@yahoo.com
wrote:

On May 29, 6:40 am, "Zebra" <t_perpet...@hotmail.com> wrote:

Dear All,

I have a malfunction Technics RS-TR555 Double Cassette Deck. It has soft
touch control buttons for controlling, auto reverse and independent motors.
Recently when I tried to check out my tapes before disposing them. It seems
that the logic goes wrong. For example, press "play" will forward your tape.
And after repeatedly pressing the buttons and you finally got it in the play
mode, the wrong wheel spin and the tape kept squeezing out.

Anyone got a hint on what to look for or where to find a schematic diagram?
Thanks.

Yes, you can find the schematic on Google, as always.

Now, the challenge to you, Ms. Malissa... would be to show us exactly
where this schematic resides (on google, of course)... can you?

Peter Wieck
Wyncote, PA

I'm not here to do you googling for you. If you post a question to
sci.electronics.repair without googling it first, then I will send a
complant to your ISP.

 

[Michael A. Terrell]

"pfjw@aol.com" wrote:

On May 29, 1:38 pm, Malissa Baldwin <sitremaganais...@yahoo.com
wrote:
On May 29, 6:40 am, "Zebra" <t_perpet...@hotmail.com> wrote:

Dear All,

I have a malfunction Technics RS-TR555 Double Cassette Deck. It has soft
touch control buttons for controlling, auto reverse and independent motors.
Recently when I tried to check out my tapes before disposing them. It seems
that the logic goes wrong. For example, press "play" will forward your tape.
And after repeatedly pressing the buttons and you finally got it in the play
mode, the wrong wheel spin and the tape kept squeezing out.

Anyone got a hint on what to look for or where to find a schematic diagram?
Thanks.

Yes, you can find the schematic on Google, as always.

Now, the challenge to you, Ms. Malissa... would be to show us exactly
where this schematic resides (on google, of course)... can you?

Peter Wieck
Wyncote, PA

Don't play with "Skippy", Peter.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[pfjw@aol.com]

Don't play with "Skippy", Peter.

Skippy had a sex-change? Yikes!

Well, I guess it was inevitable.

Peter Wieck
Wyncote, PA

 

[b]

On 29 mayo, 15:40, "Zebra" <t_perpet...@hotmail.com> wrote:

Dear All,

I have a malfunction Technics RS-TR555 Double Cassette Deck. It has soft
touch control buttons for controlling, auto reverse and independent motors.
Recently when I tried to check out my tapes before disposing them. It seems
that the logic goes wrong. For example, press "play" will forward your tape.
And after repeatedly pressing the buttons and you finally got it in the play
mode, the wrong wheel spin and the tape kept squeezing out.

Anyone got a hint on what to look for or where to find a schematic diagram?
Thanks.

you have some mechanical problem most likely perished belts or stiff
mechanism.
open it up and check the parts for old dried grease. relube.
see here - you might be lucky and fins some diagrams:

www.eserviceinfo.com

good luck. .B
..

 

[Arfa Daily]

"Zebra" <t_perpetuus@hotmail.com> wrote in message
news:465c2d57$1@127.0.0.1...

Dear All,

I have a malfunction Technics RS-TR555 Double Cassette Deck. It has soft
touch control buttons for controlling, auto reverse and independent
motors. Recently when I tried to check out my tapes before disposing them.
It seems that the logic goes wrong. For example, press "play" will forward
your tape. And after repeatedly pressing the buttons and you finally got
it in the play mode, the wrong wheel spin and the tape kept squeezing out.

Anyone got a hint on what to look for or where to find a schematic
diagram? Thanks.


Bad belts. Very very common on the Technics cassette mechs. Did one just

today with very similar symptoms. Usually the take up drive belts that go
very spongy. Originals that do this are often grey. Not especialy easy to
change.

Arfa

 

[Charles]

You have been reported for sending spam to sci.electronics.repair and
for impersonating a cartoon character.

Darned good impersonation, though!

 

[N Morrison]

On May 29, 2:35 pm, "Charles" <charlesschu...@comcast.net> wrote:

You have been reported for sending spam to sci.electronics.repair and
for impersonating a cartoon character.

Darned good impersonation, though!

_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ < / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/

 

[N Morrison]

On May 29, 2:35 pm, "Charles" <charlesschu...@comcast.net> wrote:

You have been reported for sending spam to sci.electronics.repair and
for impersonating a cartoon character.

Darned good impersonation, though!

_____ _ _
|_ _| | | | |
| | __ _ _ __ ___ | |__| | ___ _ __ ___ ___ _ __
| | / _` | '_ ` _ \ | __ |/ _ \| '_ ` _ \ / _ \ '__|
_| |_ | (_| | | | | | | | | | | (_) | | | | | | __/ |
|_____| \__,_|_| |_| |_| |_| |_|\___/|_| |_| |_|\___|_|
__ ____
/ _| | _ \
___ | |_ | |_) | ___ _ __ __ _
/ _ \| _| | _ < / _ \| '__/ _` |
| (_) | | | |_) | (_) | | | (_| |_
\___/|_| |____/ \___/|_| \__, (_)
__/ |
|___/

 

On May 29, 1:10 pm, "p...@aol.com" <p...@aol.com> wrote:

Don't play with "Skippy", Peter.

Skippy had a sex-change? Yikes!

Well, I guess it was inevitable.

Peter Wieck
Wyncote, PA

Addadicktome or Lopitoffuhme ?

GG

 

[Mark D. Zacharias]

Dave wrote:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:X3U6i.5973$C96.2887@newssvr23.news.prodigy.net...
Dave wrote:
"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:FMf6i.7530$4Y.6327@newssvr19.news.prodigy.net...

P.S.

At this point I'd say it's a virtual certainty that the outputs ARE
bad on that channel. Probably the only reason it's not just blowing
fuses is that one or both of the emitter resistors, R471/473 are
bad also.

Checked the outputs... they test OK on my transistor tester! No
leakage, both PNP and NPN had gain, although not anywhere near the
same amounts... I assumed they'd be "about the same"... anyway, the
outputs ARE NOT shorted and R471 and R473 DO NOT read open circuit
although I haven't pulled the resistors yet to test.

Started pulling transistors from the beginning of the signal path,
tested Q401 through Q413 so far, 5 more to go and they all test
okay, no shorted junctions and all show gain.

If it's a heat-related issue with a failing transistor, I'll never
find it. I don't think it is, because the DC bias on the outputs
shows up right away when the amp is powered on.

I'm out of ideas if the transistors all check out okay. I'm
inclined to blow $8 and replace all but the outputs, replace the
half-dozen smoked resistors, put it all back together and see what
happens. Dave

OK, well you're lucky then, the outputs are OK. Replace the bad
resistors, test the drivers and predrivers carefully, and test the
amp while monitoring the bias as measured across the emitter
resistors on a millivolts DC range of your DMM. A variac would be
most useful. Lacking that, one can pull the main fuse and substitute
a 100 watt light bulb which will limit current in the event of a
hard overload. If the lamp glows bright, all is not well. A light
glow after initial charging of the filter caps would be normal.

If the amp appears to be running OK, with no more than about 25
millivolts across the emitter resistor pair with no load, I would
recommend turning your attention to the bias diode D405 which looks
like it ought to have about 1.2 volts across it in normal operation.
If the diode opens up, the voltage across it will increase, maybe
slowly, maybe suddenly. If this happens, that would be proof the
diode is bad. You can compare the voltage to the one on the other
channel. They should be within a few millivolts of each other.

That was my next question to you... the varistor. How does one test
it? My understanding of varistors is that they are a high-value
resistor at low voltages, and a low-value resistor at higher
voltages. Kinda' like a zener. It's listed under diodes on the parts
list and its' schematic icon looks like a diode, which would indicate
polarity, no? Failing to find a datasheet or specs on this
particular part, I'll just check it against the one in the other
channel for resistance with no power. Maybe hook it up to 15V with a
series resistor and measure the voltage drop across it vs. the drop
with a 3V source? The "12" in the part number along with the
expected voltages across it (<2v) indicate a 12V transition point. Note to
self: keep an eye out for a variable DC power supply. If
this "diode" is bad, what would I replace it with?
I've got a device I made for TV troubleshooting, an isolation
transformer / series light bulb / GFI box, I'll use the series light
bulb to check things out.

The voltage across the emitter resistors is adjustable with V403 and
is speced at 33mV. It's nearly impossible to achieve with a
single-turn 1K pot, but the working channel is close.

Dave

The bias diode is essentially two diodes in series. (Sometimes three,
actually). In this case two, looks like. A diode check function of a DMM
would be OK for a static check, and if it became necessary you could use the
DMM to help match a replacement pair of diodes to replace it with. However,
using regular diodes might not work as well in terms of correctly responding
to heat changes.
The proof is in the operation, and in this case that means the actual
voltage drop across the device in-circuit, while the amp is running. Bias
diodes opening up is uncommon but it does happen, and when it does,
catastrophe is the result.

In your case the resistors may have burned because of a momentary short at
the speaker wires, etc although this would ordinarily have destroyed the
output transistors as well.


Mark Z.

 

[Mark D. Zacharias]

Dave wrote:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:X3U6i.5973$C96.2887@newssvr23.news.prodigy.net...

If the amp appears to be running OK, with no more than about 25
millivolts across the emitter resistor pair with no load, I would
recommend turning your attention to the bias diode D405 which looks
like it ought to have about 1.2 volts across it in normal operation.
If the diode opens up, the voltage across it will increase, maybe
slowly, maybe suddenly. If this happens, that would be proof the
diode is bad. You can compare the voltage to the one on the other
channel. They should be within a few millivolts of each other.


Next question. If the diode/MOV D405 is shorted, am I ever going to
see the correct voltage across R471/R473?

Dave

If the diode shorts, I would expect to see nothing across the emitter
resistors. Some other amp designs would be the opposite, slamming full bias
if the diode shorts.

While we're on the subject, I recommend replacing the bias transistor Q417
no matter what. Just get the polarity right...

Mark Z.

 

[pfjw@aol.com]

On May 29, 11:53 pm, stratu...@yahoo.com wrote:

On May 29, 1:10 pm, "p...@aol.com" <p...@aol.com> wrote:
Don't play with "Skippy", Peter.

Skippy had a sex-change? Yikes!

Well, I guess it was inevitable.

Peter Wieck
Wyncote, PA

Addadicktome or Lopitoffuhme ?

GG

What a question! The former would be appropiate in either case in this
case. The latter would require microsurgery if even possible.

 

[Zebra]

I'll try opening it in a day or two to check out the belts. To my memory,
this cassette deck is a direct driven deck which at least consists of 2
motors on the main shaft on each side of the deck -- it still sounds like a
of high tech. 20+ years ago.


"Arfa Daily" <arfa.daily@ntlworld.com> źśźgŠóślĽóˇsťD:2H07i.5441$rW2.570@newsfe7-win.ntli.net...

"Zebra" <t_perpetuus@hotmail.com> wrote in message
news:465c2d57$1@127.0.0.1...
Dear All,

I have a malfunction Technics RS-TR555 Double Cassette Deck. It has soft
touch control buttons for controlling, auto reverse and independent
motors. Recently when I tried to check out my tapes before disposing
them. It seems that the logic goes wrong. For example, press "play" will
forward your tape. And after repeatedly pressing the buttons and you
finally got it in the play mode, the wrong wheel spin and the tape kept
squeezing out.

Anyone got a hint on what to look for or where to find a schematic
diagram? Thanks.


Bad belts. Very very common on the Technics cassette mechs. Did one just
today with very similar symptoms. Usually the take up drive belts that go
very spongy. Originals that do this are often grey. Not especialy easy to
change.

Arfa

 

[N Cook]

Zebra <t_perpetuus@hotmail.com> wrote in message
news:465d8198$1@127.0.0.1...

I'll try opening it in a day or two to check out the belts. To my memory,
this cassette deck is a direct driven deck which at least consists of 2
motors on the main shaft on each side of the deck -- it still sounds like
a
of high tech. 20+ years ago.


"Arfa Daily" <arfa.daily@ntlworld.com
źśźgŠóślĽóˇsťD:2H07i.5441$rW2.570@newsfe7-win.ntli.net...

"Zebra" <t_perpetuus@hotmail.com> wrote in message
news:465c2d57$1@127.0.0.1...
Dear All,

I have a malfunction Technics RS-TR555 Double Cassette Deck. It has
soft
touch control buttons for controlling, auto reverse and independent
motors. Recently when I tried to check out my tapes before disposing
them. It seems that the logic goes wrong. For example, press "play"
will
forward your tape. And after repeatedly pressing the buttons and you
finally got it in the play mode, the wrong wheel spin and the tape kept
squeezing out.

Anyone got a hint on what to look for or where to find a schematic
diagram? Thanks.


Bad belts. Very very common on the Technics cassette mechs. Did one just
today with very similar symptoms. Usually the take up drive belts that
go
very spongy. Originals that do this are often grey. Not especialy easy
to
change.

Arfa

Before disassembly mark between parts with felt tip pen and take some photos
as some of these mechanisms can be devillish complicated, just to change
belts

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Dave]

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:Q%d7i.6286$C96.4135@newssvr23.news.prodigy.net...

Dave wrote:
The bias diode is essentially two diodes in series. (Sometimes three,
actually). In this case two, looks like. A diode check function of a DMM
would be OK for a static check, and if it became necessary you could use
the DMM to help match a replacement pair of diodes to replace it with.
However, using regular diodes might not work as well in terms of correctly
responding to heat changes.
The proof is in the operation, and in this case that means the actual
voltage drop across the device in-circuit, while the amp is running. Bias
diodes opening up is uncommon but it does happen, and when it does,
catastrophe is the result.

In your case the resistors may have burned because of a momentary short at
the speaker wires, etc although this would ordinarily have destroyed the
output transistors as well.

If the bias diode is two diodes in series, why does the parts list call it a
varistor? It's a funky-looking thing that looks like one of those
connectors you put at the end of a wire to connect it to a screw. Don't
think I'd likely find another one. It's physically screwed to the heatsink
the outputs use.

Has technology evolved so that a momentary crossing of speaker wires could
not destroy expensive output transistors? You see all sorts amps with
"protection" circuits in them nowadays and lots of amp module IC's which
boast both thermal and overcurrent resettable protection...

I measured D405 vs D406 in circuit with no power applied and the value,
although useless quantitatively, was the same for both channels. I'll check
it in operation when I get all the resistors replaced (and Q417).

Bonus for me: the one transistor used in that amp which I've got in stock
is 2SC945, which matches Q417 the bias transistor. I like BD Enterprises
which you directed me to, they seem to stock all sorts of transistors nobody
else does, or their search facility immediately suggests an alternative if
they don't have the original.

Dave

 

[Smitty Two]

In article <J%f7i.62157$V75.33167@edtnps89>,
"Dave" <dspear99ca@yahoo.delete.com> wrote:

Has technology evolved so that a momentary crossing of speaker wires could
not destroy expensive output transistors?

It hasn't as much to do with technological evolution as it has to do
with intelligent design. Hasn't there always been good stuff and bad
stuff? A good design would allow you to hard wire the speaker leads
together and go fishing.

 

[Dave]

"Smitty Two" <prestwhich@earthlink.net> wrote in message
newsrestwhich-3F50C4.08391130052007@news.phx.highwinds-media.com...

In article <J%f7i.62157$V75.33167@edtnps89>,
"Dave" <dspear99ca@yahoo.delete.com> wrote:



Has technology evolved so that a momentary crossing of speaker wires
could
not destroy expensive output transistors?

It hasn't as much to do with technological evolution as it has to do
with intelligent design. Hasn't there always been good stuff and bad
stuff? A good design would allow you to hard wire the speaker leads
together and go fishing.

Yes but for the same money, wouldn't you rather have a cool-looking volume
knob that glows blue in the dark or a built-in function to make it sound
like Britney is playing in a gothic cathedral than a protection-oriented
design? Sadly it appears most people would.

 

[Mark D. Zacharias]

Smitty Two wrote:

In article <J%f7i.62157$V75.33167@edtnps89>,
"Dave" <dspear99ca@yahoo.delete.com> wrote:



Has technology evolved so that a momentary crossing of speaker wires
could not destroy expensive output transistors?

It hasn't as much to do with technological evolution as it has to do
with intelligent design. Hasn't there always been good stuff and bad
stuff? A good design would allow you to hard wire the speaker leads
together and go fishing.

Sorry. From a technical standpoint, that is an idiotic statement, one that
has been made before, and disproven time and again. People like to make
statements like "This amp will drive a nail!" etc but it simply isn't true.
It is the nature of bipolar transistors, in fact any semiconductor, that
they cannot carry current much beyond their rating for more than a
split-second. The instantaneous current demanded by a short-circuit will
destroy ANY semiconductor output device unless that device is being so
limited that it cannot produce music, which is dynamic in nature. Any
protection circuit is there simply to protect the speakers from an amp
failure, and to protect the amp only if the overload isn't too severe. This
presumes that the sensing circuit will sense a large (but not TOO large)
current surge prior to total failure. Any circuit which would really protect
the amp from a short circuit would also protect it from the music.


Mark Z.

 

[Mark D. Zacharias]

Dave wrote:

"Mark D. Zacharias" <spammenot@nonsense.net> wrote in message
news:Q%d7i.6286$C96.4135@newssvr23.news.prodigy.net...
Dave wrote:
The bias diode is essentially two diodes in series. (Sometimes three,
actually). In this case two, looks like. A diode check function of a
DMM would be OK for a static check, and if it became necessary you
could use the DMM to help match a replacement pair of diodes to
replace it with. However, using regular diodes might not work as
well in terms of correctly responding to heat changes.
The proof is in the operation, and in this case that means the actual
voltage drop across the device in-circuit, while the amp is running.
Bias diodes opening up is uncommon but it does happen, and when it
does, catastrophe is the result.

In your case the resistors may have burned because of a momentary
short at the speaker wires, etc although this would ordinarily have
destroyed the output transistors as well.


If the bias diode is two diodes in series, why does the parts list
call it a varistor? It's a funky-looking thing that looks like one
of those connectors you put at the end of a wire to connect it to a
screw. Don't think I'd likely find another one. It's physically
screwed to the heatsink the outputs use.

Has technology evolved so that a momentary crossing of speaker wires
could not destroy expensive output transistors? You see all sorts
amps with "protection" circuits in them nowadays and lots of amp
module IC's which boast both thermal and overcurrent resettable
protection...
I measured D405 vs D406 in circuit with no power applied and the
value, although useless quantitatively, was the same for both
channels. I'll check it in operation when I get all the resistors
replaced (and Q417).
Bonus for me: the one transistor used in that amp which I've got in
stock is 2SC945, which matches Q417 the bias transistor. I like BD
Enterprises which you directed me to, they seem to stock all sorts of
transistors nobody else does, or their search facility immediately
suggests an alternative if they don't have the original.

Dave

I was going by the schematic, and had not seen the physical mounting. Of
course the best choice to replace the "diode" would be to order it from
Harmon. I would be comfortable using diodes out of my tool box if necessary
though, using the diode check function of a DMM to help match the voltage
drop of the original (from the other channel, that is).

As I state in another post, output transistors cannot be fully protected
from shorts without also protecting them from the music.


Mark Z.

 

[Smitty Two]

In article <2Lo7i.6745$5j1.1214@newssvr21.news.prodigy.net>,
"Mark D. Zacharias" <spammenot@nonsense.net> wrote:

Smitty Two wrote:
In article <J%f7i.62157$V75.33167@edtnps89>,
"Dave" <dspear99ca@yahoo.delete.com> wrote:



Has technology evolved so that a momentary crossing of speaker wires
could not destroy expensive output transistors?

It hasn't as much to do with technological evolution as it has to do
with intelligent design. Hasn't there always been good stuff and bad
stuff? A good design would allow you to hard wire the speaker leads
together and go fishing.

Sorry. From a technical standpoint, that is an idiotic statement, one that
has been made before, and disproven time and again. People like to make
statements like "This amp will drive a nail!" etc but it simply isn't true.
It is the nature of bipolar transistors, in fact any semiconductor, that
they cannot carry current much beyond their rating for more than a
split-second. The instantaneous current demanded by a short-circuit will
destroy ANY semiconductor output device unless that device is being so
limited that it cannot produce music, which is dynamic in nature. Any
protection circuit is there simply to protect the speakers from an amp
failure, and to protect the amp only if the overload isn't too severe. This
presumes that the sensing circuit will sense a large (but not TOO large)
current surge prior to total failure. Any circuit which would really protect
the amp from a short circuit would also protect it from the music.


Mark Z.

I stand corrected. Maybe my ignorance is the reason I'm still listening
to tubes.