Toshiba TV29C90 problem; Image fades to black...

[Ancient_Hacker]

for the NPN, the MJE270 looks good-- same case and higher voltage. and
48 cents!

for the PNP try MJE172, a whopping 68 cents at digi-key.

Do check all the other transistors... there's usually a few more with
dead shorts, easily found by an ohmmeter.

And do power it up gradually and check the voltages along the way to
prevent another blowup.

 

[James Sweet]

Now, what I don't understand is what happened with my monitor. It looks
like when I plugged the video ground to the monitor, I was shorting the AC
power... busting the rectifier. Is it what you guys also think ?

That's exactly what you're doing. If you look at the schematic, "ground"
(the frame of the monitor) is connected directly to the negative output
of the bridge rectifier so by running it without an isolation
transformer you're creating a very dangerous situation where the entire
frame and any metal parts of the cabinet are floating at over 100V above
true ground. Many times the power supplies are not fully isolated, so
the video ground is also close to earth ground, if you connect it to the
monitor ground it's expected that you'll blow the rectifier in the
monitor and you may blow traces off the game board or damage the power
supply.

In short, get an isolation transformer for the monitor, they're cheap
(under 10 bucks from Bob Roberts) and are an absolutely essential safety
component. If you're unsure about anything relating to this, hire
someone who is, you or someone else using the game can be injured or
killed as well as a very real fire hazard if this is not done correctly.

 

[Just Another Theremin Fan]

Yes, there is a "DC Balance" preset and a "Bias" preset.
Oh, it all sounds too hard. Plan B beckons.

If you do carry on make sure you check the bias pot for
dead spots. If they go O/C they effectively switch the
OP transistors hard on - BANG!

You are either a brave man or an idiot trying to repair it!

 

[Jim Yanik]

Zak <duff@nomail.invalid> wrote in
news:Xns977263A612FB664A18E@66.250.146.159:

Can I buy something in the UK like a conducting "shim" to insert
between batteries and measure current?

Below are some details of what I mean.


===============================================

I want to measure the current provided by the battery when
something like a radio or walkman is used. The battery might be
anything from AAA to D and could be any type(alkaline, zinc-
carbon, rechargeable, etc).

----

I once made a "shim" out of a small thin piece of plastic which
was sandwiched by thin metal conductors on either side. A wire
was attached to each conductor and the two wires went a
multimeter.

The idea is to insert this "shim" between the cells. Then run the
appliance and measure the current you settings like volume, fast
forwards, band select, etc.

----

Can I buy something here in the UK like this "shim" to insert
between batteries and measure current? My "shim" was always bit
too thick and wan't durable.

Use a piece of .031 doublesided copperclad PCB stock;solder a wire to each
side for connecting to a DMM.
Sand the edges to make sure you don't have any shorts.

--
Jim Yanik
jyanik
at
kua.net

 

[Geo]

On 22 Feb 2006 04:01:40 -0800, chase_p_a@yahoo.co.uk wrote:

<snip>

I hoped that some cheap BD441/442 transistors might be sufficient for
me to find out if the rest of the circuit was OK. They are at least
rated for the voltage (73 volts rail-to-rail). But putting them, and
new 0.27R resistors, in the circuit and powering-up resulted in smoke.
I guess their characteristics (higher gain, lower current) are too
different, or there's something else wrong with the circuit. At least I
only blew up a few pence/cents worth of components.

Was it the new resistors that smoked?

Have your new transistors both gone short circuit or did you beat them to the
switch off?
I would try temporary insertion of much higher value resistors instead of the
0R27s e.g a couple of 1/2w 3k9. This should enable you to check through with a
DC meter (no signal) to see which of the drivers are dead.

Geo

 

[stickyfox@gmail.com]

I dunno.. you've kind of exhausted my repertoire of stepping motor
knowledge.

Is it perhaps a five-wire motor? If the two windings are tied together
at a center tap then your controller might be getting confused. Such a
motor would work if you only drive one winding, but when you drive
both, you'll be bypassing some windings.

suchi_84@yahoo.com wrote:

firstly,thanks for your response.i am not using pulse width modulation
for generating micro-stepping currents(that option in my drive stands
disabled...after your mail i tried enabling it and tried to run my
motor at maximum frequency of 40khz all the way down to 1.25khz...there
was no difference.same old story).could you think of any other
solutions to this problem.for ur info my stepper motor is of 0.16 amp
peak,5volt 1kg torque,1.8degree step angle,30mm diameter rating.
also another motor of 0.65 amp peak,24volt,1.8degree
step angle,80mm dia worked fine with the same drive(ofcourse with
different current settings).help me out on this please

 

[Dave Platt]

In article <Xns977263A612FB664A18E@66.250.146.159>,
Zak <duff@nomail.invalid> wrote:

Can I buy something in the UK like a conducting "shim" to insert
between batteries and measure current?

I'd look around for a scrap piece of the thinnest double-sided
PC-board copperclad that I could find. A few years ago I picked up a
few sheets of a very flexible double-sided copperclad - maybe .5 mm
thick - at a local surplus store. Quite useful stuff to have around.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[infamis]

Or any general info about how car radio CD players work (mechanically)?

 

[Just Another Theremin Fan]

I would try temporary insertion of much higher value resistors instead of the
0R27s e.g a couple of 1/2w 3k9.

AIR One other way to disable the O/P transistors while testing is to
simply
short both bases together.

 

[Ray L. Volts]

"infamis" <no.email@address.com> wrote in message
news:dmWKf.36155$H71.8616@newssvr13.news.prodigy.com...

I have a Clarion DXZ545MP car receiver. Recently it does not eject CDs. It
makes a repeated clicking sound as if the mechanism can't move & then
gives
up. I opened it up (past the point of no return even though I don't know
what
the hell I'm doing; I usually could just disassemble electronics & put 'em
back together and they magically start working again). The mechanism will
eject the CD if I press upwards on that whole gear array. I'm guessing the
sound is the gears slipping or something.

It's possible you have a warped rack gear. Does it get unusually warm
behind your dash (or wherever you have the unit mounted)? If it's under
warranty, put it back to together precisely and clean up any grease smears
you may have created (and/or fingerprints) so as not to invalidate the
warranty and return it. Of course, if you've damaged any tamper-resist
stickers or screwlock glue, you're SOL as far as warranty.

 

[infamis]

I have a Clarion DXZ545MP car receiver. Recently it does not eject CDs. It
makes a repeated clicking sound as if the mechanism can't move & then
gives
up. I opened it up (past the point of no return even though I don't know
what
the hell I'm doing; I usually could just disassemble electronics & put 'em
back together and they magically start working again). The mechanism will
eject the CD if I press upwards on that whole gear array. I'm guessing the
sound is the gears slipping or something.


It's possible you have a warped rack gear. Does it get unusually warm
behind your dash (or wherever you have the unit mounted)? If it's under
warranty, put it back to together precisely and clean up any grease smears
you may have created (and/or fingerprints) so as not to invalidate the
warranty and return it. Of course, if you've damaged any tamper-resist
stickers or screwlock glue, you're SOL as far as warranty.

Unusually warm? Not that I know of. I live in Chicago & it's Winter (past
couple days have been around 20 degrees Fahrenheit). Hell, I still don't get
any type of decent heat in my car!

It's far from under warranty; I bought it <used> 2 years ago. And I really had
nothing to lose (reason being is cause 1) out of warranty 2) nothing to stick
into the aux-in rca jacks and 3) radio sounds like crap & don't like it), so,
it's either try to fix it myself or just live without music [which I can't].

The thing is, I take it apart, and just see all these different parts. I don't
know what's supposed to do what. I do know that after I press the eject button
& stick a screw driver under the gears (the gears are like screwed to the
"ceiling" & covered by a plastic cover...so if I press up on that cover),
it'll eject the CD like it's supposed to.

I just haven't found any info on the net on how slot-type CD mechanisms load a
CD (which is the most common type in cars). If I could just find some
graphical representation of how a slot-loading CD mechanism looks, that'd be
really helpful.


Background on my problem:
1. I use my MP3 player 99% of time, plugged into the aux-in of the car radio.
2. Recently had to send the MP3 player back cause of a hard drive failure.
3. So now I'm stuck with the CD player & radio.
4. I load a CD in, play it, but when I hit eject, it makes clicking noises &
doesn't eject. It tries about 3 or 4 times to eject, then gives up with an
error "Error 2" (which in the manual means the CD mechanism is stuck &
cannot be ejected)
5. So now, no CD.
6. I have no antenna on my car, so radio sounds like crap.
7. Now, nothing; I can either take loss trying to fix it myself & failing, or
just not doing anything. I'm an EE major...that is, once I get accepted to my
school of choice, so I know a little about electronics, but recent days have
made me realize I don't know anything

 

[Ken Weitzel]

infamis wrote:

I have a Clarion DXZ545MP car receiver. Recently it does not eject CDs. It
makes a repeated clicking sound as if the mechanism can't move & then
gives
up. I opened it up (past the point of no return even though I don't know
what
the hell I'm doing; I usually could just disassemble electronics & put 'em
back together and they magically start working again). The mechanism will
eject the CD if I press upwards on that whole gear array. I'm guessing the
sound is the gears slipping or something.


It's possible you have a warped rack gear. Does it get unusually warm
behind your dash (or wherever you have the unit mounted)? If it's under
warranty, put it back to together precisely and clean up any grease smears
you may have created (and/or fingerprints) so as not to invalidate the
warranty and return it. Of course, if you've damaged any tamper-resist
stickers or screwlock glue, you're SOL as far as warranty.


Unusually warm? Not that I know of. I live in Chicago & it's Winter (past
couple days have been around 20 degrees Fahrenheit). Hell, I still don't get
any type of decent heat in my car!

It's far from under warranty; I bought it <used> 2 years ago. And I really had
nothing to lose (reason being is cause 1) out of warranty 2) nothing to stick
into the aux-in rca jacks and 3) radio sounds like crap & don't like it), so,
it's either try to fix it myself or just live without music [which I can't].

The thing is, I take it apart, and just see all these different parts. I don't
know what's supposed to do what. I do know that after I press the eject button
& stick a screw driver under the gears (the gears are like screwed to the
"ceiling" & covered by a plastic cover...so if I press up on that cover),
it'll eject the CD like it's supposed to.

I just haven't found any info on the net on how slot-type CD mechanisms load a
CD (which is the most common type in cars). If I could just find some
graphical representation of how a slot-loading CD mechanism looks, that'd be
really helpful.


Background on my problem:
1. I use my MP3 player 99% of time, plugged into the aux-in of the car radio.
2. Recently had to send the MP3 player back cause of a hard drive failure.
3. So now I'm stuck with the CD player & radio.
4. I load a CD in, play it, but when I hit eject, it makes clicking noises &
doesn't eject. It tries about 3 or 4 times to eject, then gives up with an
error "Error 2" (which in the manual means the CD mechanism is stuck &
cannot be ejected)
5. So now, no CD.
6. I have no antenna on my car, so radio sounds like crap.
7. Now, nothing; I can either take loss trying to fix it myself & failing, or
just not doing anything. I'm an EE major...that is, once I get accepted to my
school of choice, so I know a little about electronics, but recent days have
made me realize I don't know anything

Hi...

If you think you don't know anything, then at least you're not
a teenager, eh?

Dunno how helpful it may be, but a few years ago I had a CD stuck
in a GM cd player. 'twas a burned one, with a stuck on label.
The edge of the label lifted and separated just enough that it
caught on the edge, and no eject.

Discovered the prob by lifting the flap with a pencil, and peeking
inside with a flashlight. Once seen it was easily fixed just by
pushing the edge of the label down again with a jewellers screwdriver
while it was ejecting.

Take care.

Ken

 

In light of people's responses, I looked again at the circuit and could
see that it does all look rather fragile. Although I am an electronic
engineer by education, I don't have all the test gear (Variac etc.) and
stocks of components that I used to. So I have decided to take the
coward's way out and replace the power amp by a ready-made module. I've
been able to find one of the right rating that works with the same
mains transformer as the amp already has, keeping the cost and
modifications to a minimum.

I just wanted to thank everyone for their help and excellent
suggestions. I'll be better informed for my next project, certainly.

 

[Ron(UK)]

chase_p_a@yahoo.co.uk wrote:

In light of people's responses, I looked again at the circuit and could
see that it does all look rather fragile. Although I am an electronic
engineer by education, I don't have all the test gear (Variac etc.) and
stocks of components that I used to. So I have decided to take the
coward's way out and replace the power amp by a ready-made module. I've
been able to find one of the right rating that works with the same
mains transformer as the amp already has, keeping the cost and
modifications to a minimum.

I just wanted to thank everyone for their help and excellent
suggestions. I'll be better informed for my next project, certainly.

As a matter of interest, which module did you use?

Ron(UK)

--
Lune Valley Audio
Public address system
Hire, Sales, Repairs
www.lunevalleyaudio.com

 

http://www.velleman.be/ot/en/product/view/?id=360356

(The description of a "200W" amplifier is marketing BS. It's actually a
70-100W amp, ideal for the Rick which was originally 75W).

 

[Matti Adolfsen]

Just Another Theremin Fan wrote:

I would try temporary insertion of much higher value resistors instead of the
0R27s e.g a couple of 1/2w 3k9.

AIR One other way to disable the O/P transistors while testing is to
simply
short both bases together.

This seems to be a quite modern VINTAGE transistor amp, as the schematic

says "1977". A complementary symmetrical emitter-follower darlington
circuit as output stage, input stages are quite modern-looking as well
(differential pair, current generators etc...).

leaving the output transistors disconnected allows you to apply power to
the circuit to make DC-measurements.

Using a light bulb in series with the mains supply has saved many output
transistors when testing amplifiers. Even if the DC readings seem OK,
there might sometimes be HF oscillation which can burn the transistors.
Btw, check the R/C network in parallel with the speaker...

Replacing the output stage with a power module is a bad idea: all kinds
of modifications drop the value of the amp and make it a "do-it-yourself
electrical equipment". Repair the amp with proper components, and you'll
be happy with the results.

Btw, a vintage transistor amp in my opinion has germanium output
devices, both transistors are PNP, power supply is single-sided and
negative, speaker is connected to the circuit via a big electrolytic
capacitor, and there is a transformer between the driver stage and output...

Matti

 

[pboavida]

Robert L. Milton, Sr. Wrote:

I am trying to find a component part number or a schematic for a Blower
Control Board for a 1989 BMW with a 535i engine. The board has the
number
275 526. L 06 stamped on it, and the Control Assembly has the name BEHR
and
the numbers 90 . 947 . 00 . 842, E 3264/11 and 1 388 629 . 2 stamped
on it.
There are four (4) blower motor settings on the control switch and only
one
(1) works...High Speed! Anyone that can let me know where to find the
replacement FET transistors on the board would be of tremendous help.
The
four (4) FET's are all the same. I have looked at the transistors under
a
magnifying glass and can find no numbers stamped on them. I do not know
if
they are made by an European Manufacturer or not. I also do not know
whether
the FET's or N or P type or MOSFET's, etc. Any help as to the source of
this
information would be very appreciated.
Thanks!

The FET is a type N 60V 14A - BUZ 71S3 but you can replace for the
regular BUZ 71 (the diference is instead of 60V is 50V)

The IC is a LN2903 - Dual differential comparator -
http://www.fairchildsemi.com/ds/LM%2FLM393.pdf


--
pboavida

 

[Just Another Theremin Fan]

chase_p_a@yahoo.co.uk wrote:

(The description of a "200W" amplifier is marketing BS. It's actually a
70-100W amp, ideal for the Rick which was originally 75W).

It all depends on how you measure the power doesn't it? Are we talking
of
power input, RMS output or peak music power?

In the days of the amp' mentioned manufacturers (and sellers) could
juggle with these figures all day long to come out with ridiculous
figures and an ignoramus customer would
often be shown the ac power input which due to the sheer inefficiencies
of the day
could be 3 times the RMS output figure. Peak music power could be
quoted as 3 times this again! Fun eh?

 

[Ron(UK)]

chase_p_a@yahoo.co.uk wrote:

http://www.velleman.be/ot/en/product/view/?id=360356

(The description of a "200W" amplifier is marketing BS. It's actually a
70-100W amp, ideal for the Rick which was originally 75W).

Hmm CPC dont seem to stock them, I wonder how they stand up to abuse.
I much regret the discontinuation of the Maplin 150watt Mosfet Amp which
was perfect for resurecting old 70`s H=H and Carlsbro amps. I must have
built well over 50 of those kits.

Ron(UK)

--
Lune Valley Audio
Public address system
Hire, Sales, Repairs
www.lunevalleyaudio.com

 

[Ancient_Hacker]

How do you know the FETs are bad? Did they explode?

FETs tend to fail shorted, so the more likely symptom of a bad FET
would be that the fan runs at nearly top speed on all settings.

I'd go check out the on-line junkyards if you can lower yourself to do
so.