Toshiba TV29C90 problem; Image fades to black...

[Michael Black]

"Ancient_Hacker" (grg2@comcast.net) writes:

The 1958 Fords had radios with 12 volt tubes and a 2-transistor power
amplifier. The transistors were 2N256's or thereabouts. If you looked
them up in the GE transistor manual, their high frequency cutoff was
like 4Kc ! Not Mhz or GHz, KHz!

That doesn't sound so great for audio use.

Transistors had to start somewhere. There was a famous article in
the amateur radio magazine "QST" where the author said something about
how transistors could never amount to much, and included something
about their not being able to work at radio frequencies. But it
wsa an early article.

IN retrospect, 4KC seems awful low, and even transistors suitable
for 455KHz IFs seem low, but at the time each increment must
have seemed a big step forward, because it was all so new.

Michael

 

[Sam Goldwasser]

Flyguy <Flyguy@bluesky.net> writes:

Sam Goldwasser wrote:
"ian field" <dai.ode@ntlworld.com> writes:


"Flyguy" <Flyguy@bluesky.net> wrote in message
news:XU86h.2749$bj1.1163@trndny05...

Homer J Simpson wrote:

mwpmorris@gmail.com> wrote in message
news:1162839588.995972.108850@h48g2000cwc.googlegroups.com...



Could I have been exposed to anything when the glass shattered inside
the set or when I powered the thing on with the glass shattered?


No.

Do they still use mercury to flash the getter in the CRT gun assembly? I'd
be a little worried about that possbility.

Do you have any technical info sources that show mercury was ever used in
getters?

I doubt it. Mercury is not that reactive. He's probably just thinking
of the shiny getter coating and associating it with mercury.

I got my vacuum technology mixed up. Mercury is used in some kinds of
vacuum pumps. Barium is the most used material for a vacuum tube getter.

Right. Older diffusion pumps used mercury. Newer ones use special low
vapor pressure oils. But both types are rather obsolete now.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

 

Yes i have looked for DC, and there isnt any.
Also there are 4 different relays, Front-Rear L&R None of them are
kicking in.


The fact that none of the relays is dropping in, is neither here nor
there - except to indicate that the problem is likely *not* related
to any particular relay driver. To avoid unncessary duplication, the
fault monitoring and switch on delay circuitry, will be a single
entity, monitoring all channels simultaneously, and acting on all
relay drivers simultaneously. Thus, any fault ( DC offset, over
current, over temp etc ) detected on *any* channel, will cause *all*
relay drivers to be inhibited. So, I would suggest that your problem
lies either with the fault monitoring circuitry itself, or the fact
that it is genuinely detecting a problem on one or more channels.

Arfa

Good point Afra

I think I've seen a couple bad 1 ohm resistors in the power supply cause
this. They're at the rear corner of the machine.

Mark Z.

Thanks mark.. Anything more specific on this 1 ohm resistor? location # perhaps?

i saw a few other posts of people complaning of the same problem, with no reply's of course, in other fourms on the web.
Ive put my Voltmeter on the outputs at the relay, i get 0.01 volts DC not enough to trip any protection circuit's.
thats why im seeking answers more like what mark has posted.
Known problems that ocassionally rear thier head.

I dont have the sony database of tips anymore cause I no longer subscribe, (i just dont do repairs like i used to)
but perhaps there is a sony bulliten on this issue?

 

[Ken G.]

Lets cut right to the way to fix this . First get the radio apart so you
can get to the capacitor connections .

Take a 25mfd at 15 volts or so , get the radio playing and touch that
capacitor across each one in the radio . If its bad te radio will
improve , replace the capacitor .
Another way would be to just replace all the capacitors ... probably 5
of them ?
This will eliminate any capacitor issues

If the radio still has the noise when cold . Get it so you can get to
the tops of the transistors and when cold & noisey touch a hot soldering
iron tip on each transistor top one at a time quickly to warm the part
up . If its a transistor this will find it .

 

[rogersk8ter]

N Cook wrote:

rogersk8ter <apengrg@yahoo.com> wrote in message
news:1163787537.011227.155270@m7g2000cwm.googlegroups.com...
Im trying to scope a TV signal. Where should I ground the probe's
ground? Over the common ground on the PCB board? Isn't that a floating
ground?

There seems to be 30V ac with reference to the scope ground when I use
a VOM to measure voltage. Will it blow or damage the scope? Anyway to
prevent sending live current down the scope ground and blowing it up?
Thanks.


The first thing you do is obtain an isolation transformer 110/110V or
240/240V that allows TV to float up or down relative to the scope ground.
Second you learn about the potential (in both senses) dangers associated
with TVs

--

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?

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

 

[Jim Yanik]

"rogersk8ter" <apengrg@yahoo.com> wrote in
news:1163822584.538024.30300@f16g2000cwb.googlegroups.com:

N Cook wrote:
rogersk8ter <apengrg@yahoo.com> wrote in message
news:1163787537.011227.155270@m7g2000cwm.googlegroups.com...
Im trying to scope a TV signal. Where should I ground the probe's
ground? Over the common ground on the PCB board? Isn't that a
floating ground?

There seems to be 30V ac with reference to the scope ground when I
use a VOM to measure voltage.

Don't forget DCV;the chassis can be as much as 170VDC difference from
earth ground for a 120VAC line supply.

Will it blow or damage the scope?
Anyway to prevent sending live current down the scope ground and
blowing it up? Thanks.


The first thing you do is obtain an isolation transformer 110/110V or
240/240V that allows TV to float up or down relative to the scope
ground. Second you learn about the potential (in both senses) dangers
associated with TVs

--

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?

It's a MUST. Repeat;a MUST.

TV chassis can be electrically hot WRT earth ground.
Just look at any switching power suppply schematic.
There's no ground,instead "common".

Hook your scope ground to it and you blow the TV and/or your scope,make
lots of sparks and smoke.

Or your scope case becomes electrically hot and you touch it and a real
ground,you get electrocuted.(that's why you don't use groundbusters.)

--
Jim Yanik
jyanik
at
kua.net

 

rogersk8ter wrote:
<snip>

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?

If you have to ask, it's MANDATORY - NO EXCEPTIONS !!!

GG

 

[N Cook]

Jim Yanik <jyanik@abuse.gov> wrote in message
news:Xns987EEFDF11FAjyanikkuanet@129.250.170.85...

"rogersk8ter" <apengrg@yahoo.com> wrote in
news:1163822584.538024.30300@f16g2000cwb.googlegroups.com:


N Cook wrote:
rogersk8ter <apengrg@yahoo.com> wrote in message
news:1163787537.011227.155270@m7g2000cwm.googlegroups.com...
Im trying to scope a TV signal. Where should I ground the probe's
ground? Over the common ground on the PCB board? Isn't that a
floating ground?

There seems to be 30V ac with reference to the scope ground when I
use a VOM to measure voltage.

Don't forget DCV;the chassis can be as much as 170VDC difference from
earth ground for a 120VAC line supply.


Will it blow or damage the scope?
Anyway to prevent sending live current down the scope ground and
blowing it up? Thanks.


The first thing you do is obtain an isolation transformer 110/110V or
240/240V that allows TV to float up or down relative to the scope
ground. Second you learn about the potential (in both senses) dangers
associated with TVs

--

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?


It's a MUST. Repeat;a MUST.

TV chassis can be electrically hot WRT earth ground.
Just look at any switching power suppply schematic.
There's no ground,instead "common".

Hook your scope ground to it and you blow the TV and/or your scope,make
lots of sparks and smoke.

Or your scope case becomes electrically hot and you touch it and a real
ground,you get electrocuted.(that's why you don't use groundbusters.)

--
Jim Yanik
jyanik
at
kua.net

Could you explain to a Limey what a groundbuster is and I'll add to this "2
nations divided by a common language" file

UK / USA Tool Terminology Translator
http://www.divdev.fsnet.co.uk/tool_terms.htm

 

[N Cook]

N Cook <diverse8@gazeta.pl> wrote in message
news:ejmfck$4fc$1@inews.gazeta.pl...

Jim Yanik <jyanik@abuse.gov> wrote in message
news:Xns987EEFDF11FAjyanikkuanet@129.250.170.85...
"rogersk8ter" <apengrg@yahoo.com> wrote in
news:1163822584.538024.30300@f16g2000cwb.googlegroups.com:


N Cook wrote:
rogersk8ter <apengrg@yahoo.com> wrote in message
news:1163787537.011227.155270@m7g2000cwm.googlegroups.com...
Im trying to scope a TV signal. Where should I ground the probe's
ground? Over the common ground on the PCB board? Isn't that a
floating ground?

There seems to be 30V ac with reference to the scope ground when I
use a VOM to measure voltage.

Don't forget DCV;the chassis can be as much as 170VDC difference from
earth ground for a 120VAC line supply.


Will it blow or damage the scope?
Anyway to prevent sending live current down the scope ground and
blowing it up? Thanks.


The first thing you do is obtain an isolation transformer 110/110V or
240/240V that allows TV to float up or down relative to the scope
ground. Second you learn about the potential (in both senses) dangers
associated with TVs

--

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?


It's a MUST. Repeat;a MUST.

TV chassis can be electrically hot WRT earth ground.
Just look at any switching power suppply schematic.
There's no ground,instead "common".

Hook your scope ground to it and you blow the TV and/or your scope,make
lots of sparks and smoke.

Or your scope case becomes electrically hot and you touch it and a real
ground,you get electrocuted.(that's why you don't use groundbusters.)

--
Jim Yanik
jyanik
at
kua.net

Could you explain to a Limey what a groundbuster is and I'll add to this
"2
nations divided by a common language" file

UK / USA Tool Terminology Translator
http://www.divdev.fsnet.co.uk/tool_terms.htm

I take it from Googling that a ground buster / groundbuster is an adaptor
that simply converts a 3 prong AC plug into a 2 prong.
In the UK they don't exist as such , the third earth/ground pin is needed to
open the safety sliding shrouds covering the powered sections of the socket.
"wall warts" for the UK always seem to have plastic earth/ground pins which
have to be there as dummies so you can physically plug into UK power
sockets.

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

 

[Jim Yanik]

"N Cook" <diverse8@gazeta.pl> wrote in
news:ejmif3$cjd$1@inews.gazeta.pl:

N Cook <diverse8@gazeta.pl> wrote in message
news:ejmfck$4fc$1@inews.gazeta.pl...
Jim Yanik <jyanik@abuse.gov> wrote in message
news:Xns987EEFDF11FAjyanikkuanet@129.250.170.85...
"rogersk8ter" <apengrg@yahoo.com> wrote in
news:1163822584.538024.30300@f16g2000cwb.googlegroups.com:


N Cook wrote:
rogersk8ter <apengrg@yahoo.com> wrote in message
news:1163787537.011227.155270@m7g2000cwm.googlegroups.com...
Im trying to scope a TV signal. Where should I ground the
probe's ground? Over the common ground on the PCB board? Isn't
that a floating ground?

There seems to be 30V ac with reference to the scope ground
when I use a VOM to measure voltage.

Don't forget DCV;the chassis can be as much as 170VDC difference
from earth ground for a 120VAC line supply.


Will it blow or damage the scope?
Anyway to prevent sending live current down the scope ground
and blowing it up? Thanks.


The first thing you do is obtain an isolation transformer
110/110V or 240/240V that allows TV to float up or down relative
to the scope ground. Second you learn about the potential (in
both senses) dangers associated with TVs

--

Can I just ground t to the TV chasis? Where the springs is? Or a
isolation transformer is a "must"?


It's a MUST. Repeat;a MUST.

TV chassis can be electrically hot WRT earth ground.
Just look at any switching power suppply schematic.
There's no ground,instead "common".

Hook your scope ground to it and you blow the TV and/or your
scope,make lots of sparks and smoke.

Or your scope case becomes electrically hot and you touch it and a
real ground,you get electrocuted.(that's why you don't use
groundbusters.)

--
Jim Yanik
jyanik
at
kua.net

Could you explain to a Limey what a groundbuster is and I'll add to
this
"2
nations divided by a common language" file

UK / USA Tool Terminology Translator
http://www.divdev.fsnet.co.uk/tool_terms.htm



I take it from Googling that a ground buster / groundbuster is an
adaptor that simply converts a 3 prong AC plug into a 2 prong.

Correct.

In the UK they don't exist as such , the third earth/ground pin is
needed to open the safety sliding shrouds covering the powered
sections of the socket. "wall warts" for the UK always seem to have
plastic earth/ground pins which have to be there as dummies so you can
physically plug into UK power sockets.

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

But one could still cut the ground WIRE either at the plug or inside the
scope to disable the ground(to "float the scope").
At least one scope offered a SWITCH to do this,others solder in diodes to
"isolate" the ground.Bad idea,as you have no idea if the diodes are always
functional and not shorted or open.

Tektronix used to offer a pamphlet about scope measurements and ground
safety.I used to include one with every scope I repaired that had the
ground pin cut off or otherwise disabled.It explained why various methods
of "floating" a scope are unsafe.
IIRC,TEK now has something similar on their website.

--
Jim Yanik
jyanik
at
kua.net

 

[Jim Land]

Jim Yanik <jyanik@abuse.gov> wrote in
news:Xns987F8172D2250jyanikkuanet@129.250.170.86:

Tektronix used to offer a pamphlet about scope measurements and ground
safety....It explained why various
methods of "floating" a scope are unsafe.

IIRC,TEK now has something similar on their website.

Yep, here it is:

http://www.tek.com/Measurement/cgi-bin/framed.pl?
Document=/Measurement/App_Notes/Technical_Briefs/tds3000-
float/eng/limitations.html&FrameSet=oscilloscopes

Quoting from the web page,

"Floating" a ground referenced oscilloscope is the technique of defeating
the oscilloscope's protective grounding system - disconnecting "signal
common" from earth, either by defeating the grounding system or using an
isolation transformer. This allows accessible parts of the instrument
such as chassis, cabinet, and connectors to assume the potential of the
probe ground lead connection point. This is dangerous, not only from the
standpoint of elevated voltages present on the oscilloscope (a shock
hazard to the operator), but also due to cumulative stresses on the
oscilloscope's power transformer insulation. This stress may not cause
immediate failure, but may lead to future dangerous failures (a shock and
fire hazard), even after returning the oscilloscope to properly grounded
operation!

Not only is floating a ground-referenced oscilloscope dangerous, but the
measurements are often inaccurate. This results from the total
capacitance of the oscilloscope chassis being directly connected to the
circuit under test at the point where the common lead is connected.

WARNING

Never attempt to defeat the protective grounding system of your
oscilloscope by using an isolation transformer or disconnecting the
ground connector on the power plug. Failure to follow safety warnings can
result in serious injury or loss of life.

 

[Mark D. Zacharias]

I think I've seen a couple bad 1 ohm resistors in the power supply
cause
this. They're at the rear corner of the machine.

Mark Z.

R804, R805 in the rear corner pf the machine, the side where the power cord
comes in, as I recall. The board is called the "DC" board.

You may mail me directly at:

mzacharias@labolgcbs.net

and reverse the domain name.


Mark Z.

 

[Charlie East]

Sample, If you want the whole thing, you have to order it.
I found a site that has a lot of manuals and schematics to download, the
charge 20 bucks a year, but unlimited downloads, The Schematic page

"Doug" <dougq@shaw.ca> wrote in message
news:HKV5h.298962$1T2.93221@pd7urf2no...

In looking for service info for a couple of my tv's I came across this
site. When I looked at the sample info for E:Fact it did not appear to
be complete.

Any one care to comment.
Thanks

Doug Quance

TV's are chassis CTC177 and XS2050

 

meow2222@care2.com wrote:

wrongaddress@att.net wrote:
meow2222@care2.com wrote:
wrongaddress@att.net wrote:

Would you guess the solution is a silicon transistor? or just adjust
the bias on the existing germanium transistor?

neither, increase the stage gain. That probably means higher collector
R or similar. You may then need to adj the bias a little.

Or with an old radio like that it might just be biased way wrong, where
gain is down. Meter it and see where Vce sits when not oscillating.

The collector appears to drive the oscillator coil and mixer coil in
series (no collector R other than maybe decoupling). There is a emitter
resistor of 2K with a drop of 0.35 volts. I figure the oscillator stage
is running at 0.35/2000 = 175 miroamps. I added a 3K resistor in
parallel with the 2K so the current is increased to 0.35/1200 = 292
microamps. This brings up the gain about 3dB, but the radio still fails
at low temperature in the refrigerator. At low temperature there is
only noise and no signal. I tried this with a more modern radio using
silicon transistors and it works well an 40 degrees or so. So, I'm
almost convinced the problem is the germanium transistors.

Will continue to investigate.

-Bill

This is just illogical. What is Vce when not oscillating, and whats psu
v? Posing the osc cct would give more opportunities for upping or
stabilising the gain.


NT

Vce is about the same as the battery voltage. I haven't traced it all
out but most of the voltage is dropped across the oscillator
transistor. As I said, reducing the emitter resistor increased the
current and gain about 3dB or more. It now works fairly well outdoors
on warm days. But there is still too much internal noise. The noise is
not from the antenna, and must be coming from the oscillator or IF
stages. I suspect the germanium transistors.

I'll take it apart again Monday and try and figure out the bias scheme
for the oscillator.

-Bill

 

[Kirk S.]

Might get flamed, however...

I've got an RH8524 set with the same basic boardset (PTV300). I would check
the screen/focus voltage as described in the troubleshooting section of the
manual. My experience with this set is that if the HV fails, the whole set
goes into shutdown which shuts down the audio as well. I suppose you could
also have a bad HV splitter. I had this exact same situation occur on my
set with a bad screen/focus connection at the flyback. Does the flyback HV
exit from the top (gray flyback) or the side at a 45 degree angle (white)?

Send me your e-mail and I'll try to make some scans from the troubleshooting
section of the service manual. I believe one of the tests is to remove the
CRT board from each CRT and try it again. You have to remove the front
speaker grill and drop the convergence board down to easily reach the CRT
boards. I believe there is a release button on the right rear side that
allows the trim piece above the grill to come loose. After that, simply
remove the speaker grill, then the inner screws to drop the convergence
board down. Many times, there is a wiring diagram on the back of the set.

Do not attempt to take voltage readings on this set while live even with an
isolation transformer. I use jumpers to connect the meter where I want it
AFTER unplugging the set. I know enough to know I don't know enough...
There are a number of basic readings you can make on the power supply with
it off to determine if the problem is there or on the deflection board.
I'll look for the troubleshooting section of my manual.

Better safe than sorry... Sometimes you don't even get a first chance with
line voltage!

Kirk S.
"Bill S." <NoSpam@OnMe.com> wrote in message
news:MPG.1fc26aad4ba283cf989693@news-server.woh.rr.com...

In article <jpgolf14.2h4qbo@diybanter.com>,
jpgolf14.2h4qbo@diybanter.com says...
Hi, I have an old 46" Magnavox TV model RH8520 AK08. The video just
stopped working the other day. Audio still works fine. It turns on
and off ok. Does anyone have any ideas what might be causing this?
Maybe the light source?

These sets have CRT's. Most likely the high voltage has quit, and
there are numerous possible reasons. Bad flyback transformer,
focus bleeder breakdown, cracked solder joints, protection circuit
shutdown from over voltage, over current, loss of vertical scan...

You need a tech familiar with the set and armed with schematics.
Learning curve is very steep for anyone not familiar.

 

[TorbenGB]

On Nov 20, 1:51 pm, "Dani" <gree...@gmail.com> wrote:

RCA Model # DRC 500 DVD changer. Works fine, but when you press the
eject
button, a red "lock" appears in the display.

The "eject" is driven by a motor connected via a rubber band to the
tray mechanism. I have seen a couple of cases where the rubber band
became old, slack, or broken. Replacing the rubber band solved these
cases.

Could you diagnose your case some more?
- Do you get the "lock" icon immediately, or can you hear the eject
motor whirring unsuccessfully for a moment first?

 

[Jumpster Jiver]

Sarah wrote:

Hello, can anyone help with what to do if certain DVDs don't play on my
Dell Inspiron 640m laptop. VCDs and some DVDs ok. Thanks! Sarah

First check that you have the latest drivers, and reinstall if necessary.
However... chances are the drive is bad. If you are able to
disassemble it you can try cleaning the lens, but your best bet is to
replace the drive.
You can buy any brand drive - it doesn't have to be dell brand.

 

[Andrew Rossmann]

[This followup was posted to sci.electronics.repair and a copy was sent
to the cited author.]

In article <1164027085.269095.136090@e3g2000cwe.googlegroups.com>,
greeben@gmail.com says...

RCA Model # DRC 500 DVD changer. Works fine, but when you press the
eject
button, a red "lock" appears in the display. Nothing on the RCA
warranty site.
What's the trick to resetting this problem? I have tried holding down
the eject
(either on the remote or the player) for several seconds? Thanks, Dani.

According to the manual for several RCA DVD players:
Press and hold the STOP key on the DVD player and press and hold the
ON/OFF button on the remote (make sure to aim at the display). Keep
holding them down for at least 2 seconds.

From another model:
To lock/unlock, press SETUP 0 0 0 8 3

--
If there is a no_junk in my address, please REMOVE it before replying!
All junk mail senders will be prosecuted to the fullest extent of the
law!!
http://home.att.net/~andyross

 

[dantecl@gmail.com]

check the region code for the DVD, and try using PowerDVD as software.

Sarah wrote:

Hello, can anyone help with what to do if certain DVDs don't play on my
Dell Inspiron 640m laptop. VCDs and some DVDs ok. Thanks! Sarah

 

[bz]

Jumpster Jiver <me@no.spam.today> wrote in news:45620E6A.3020902
@no.spam.today:

Sarah wrote:
Hello, can anyone help with what to do if certain DVDs don't play on my
Dell Inspiron 640m laptop. VCDs and some DVDs ok. Thanks! Sarah


First check that you have the latest drivers, and reinstall if necessary.
However... chances are the drive is bad. If you are able to
disassemble it you can try cleaning the lens, but your best bet is to
replace the drive.
You can buy any brand drive - it doesn't have to be dell brand.

I think you missed the fact that it is a laptop computer.

1) She doesn't need to disassemble in order to clean the lense.
2) It is unlikely that another brand drive will fit. It is even unlikely
that the drive from another model dell will fit.
She COULD get an external drive.
She could check with dell for price of a replacement drive
She could look for a junker of the same model and hope the cd drive is
good.






--
bz 73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.

bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap