Toshiba TV29C90 problem; Image fades to black...

used.....probably 6-7 year old t.v.

any ideas?


--
mhancock84
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"MikeC" <My_address@end.of.post> wrote in
news:HqBgh.10260$UC.9477@newsfe5-win.ntli.net:

Folks,

I'm not sure if this isn't a bit banale for this group, so please
direct me elsewhere if I'm in the wrong place.

My microwave oven has lasted quite a long time (it must be heading for
its 10th birthday). In the top of it, there is what appears to be a
mica window through which the UHF arrives. Intermittently (but
getting more frequently) it produces, on the magnetron side of this
window, what looks, smells and sounds like arcing - like a welding
set. The light comes through the mica window and lights up the inside
of the oven quite brightly. It arcs for two or three seconds then
stops, and may start again after 10 seconds. The problem has been
there, then disappeared for three weeks, but it's back at the moment.

I haven't taken it to bits yet, but can anybody tell me if they have
had the same experience, and whether it is even worth dismantling. If
it's the magnetron, how much do they cost? Ovens aren't very
expensive, so would it be worth repairing? It's quite a good one
(Matsui 170TC, if you know it), so it is worth more to me than a
bottom-of-the-range replacement.
Click to expand...
This is covered in Sam's FAQ:

http://www.repairfaq.org/sam/micfaq.htm#micarcaoc
 
"MikeC" <My_address@end.of.post> wrote in message
news:HqBgh.10260$UC.9477@newsfe5-win.ntli.net...
Folks,
Intermittently (but getting more frequently)
it produces, on the magnetron side of this window, what looks, smells and
sounds like arcing - like a welding set. The light comes through the mica
window and lights up the inside of the oven quite brightly. It arcs for
two or three seconds then stops, and may start again after 10 seconds.
The problem has been there, then disappeared for three weeks, but it's
back at the moment.

The inside of the plastic cover gets dirty over time. When there's enough
Click to expand...
gunk built up, arcing can and does occur. Remove, clean, replace.
 
eletlabs@gmail.com wrote:

I need a replacement crystal, but the MFG no longer helps on these
units. The Xtal is 122.6667MHz, HC49U package, but I have no idea what
the load capacitance of the circuit is. Is there an easy way to
measure this in circuit? All thoughts appreciated.

Thanks
Steve
Click to expand...
The obvious thing is to use an oscilator where the circuit capacitance
determines frequency, and make it with enough feedback that lossy
capacitance doesnt matter. Which leaves me wondering why you cant do
that? If you really need to. Is the new xtal malfunctioning?


NT
 
On Dec 15, 11:02 am, "MikeC" <My_addr...@end.of.post> wrote:
Folks,

I'm not sure if this isn't a bit banale for this group, so please direct me
elsewhere if I'm in the wrong place.

My microwave oven has lasted quite a long time (it must be heading for its
10th birthday). In the top of it, there is what appears to be a mica window
through which the UHF arrives. Intermittently (but getting more frequently)
it produces, on the magnetron side of this window, what looks, smells and
sounds like arcing - like a welding set. The light comes through the mica
window and lights up the inside of the oven quite brightly. It arcs for two
or three seconds then stops, and may start again after 10 seconds. The
problem has been there, then disappeared for three weeks, but it's back at
the moment.

I haven't taken it to bits yet, but can anybody tell me if they have had the
same experience, and whether it is even worth dismantling. If it's the
magnetron, how much do they cost? Ovens aren't very expensive, so would it
be worth repairing? It's quite a good one (Matsui 170TC, if you know it),
so it is worth more to me than a bottom-of-the-range replacement.

Incidentally, I started my carreer as a microwave engineer (S-band), though
I haven't been near that side of the business for a long time (in computer
storage now), but I'm aware of the consequences of running it with the
covers off, so please don't let that danger steer you to recommending a
replacement.

Many thanks,

MikeC
Click to expand...
I've seen this before, a couple of times on my Panasonic over-the-stove
model microwave oven, only not on the mica window. The arcing I've
seen always happens at the HV anode of the magnetron, and it it usually
fatal. Since the microwave cost more than 2 times the replacement cost
(even in today's dollars), I have the magnetron replaced (total cost
for part + labor around US$75) versus a new 1200Watt over-the-stove
model starting at US$199. The problem is the buildup of grease and
cooking aromatics in-and-around the magnetron. It usually arcs when
the humidity gets high (that's the variable factor you might be looking
for). If it happens to me again, I'll ask my repairman to put alot of
HV silicone around the anode terminal.

If your microwave is a cheap ($50 - $70) microwave, it's a throw-away.
If it is a $150+ high power fancy model, consider replacing the
magnetron.

good luck
Tom P.
 
meow2222@care2.com wrote in news:1166220763.581737.87000
@j72g2000cwa.googlegroups.com:

eletlabs@gmail.com wrote:

I need a replacement crystal, but the MFG no longer helps on these
units. The Xtal is 122.6667MHz, HC49U package, but I have no idea
what
the load capacitance of the circuit is. Is there an easy way to
measure this in circuit? All thoughts appreciated.

The obvious thing is to use an oscilator where the circuit capacitance
determines frequency, and make it with enough feedback that lossy
capacitance doesnt matter. Which leaves me wondering why you cant do
that? If you really need to. Is the new xtal malfunctioning?
Click to expand...
The OP needs to buy a replacement crystal, but the OEM no longer supplies
them. So he goes to any company that makes custom crystals, and the
first thing they ask is, how much circuit capcitance will be loading the
crystal? This is because this capacitance changes the crystal frequency,
and they want to grind the crystal so it will oscillate at the correct
frequency when it's in-circuit.
 
This is in existing equipment, built in the 80's. The old xtal is
shot, physically broken. In order to order a new xtal for it, they
need load capacitance specification.

Thanks for the reply.

Steve

On 15 Dec 2006 14:12:43 -0800, meow2222@care2.com wrote:

eletlabs@gmail.com wrote:

I need a replacement crystal, but the MFG no longer helps on these
units. The Xtal is 122.6667MHz, HC49U package, but I have no idea what
the load capacitance of the circuit is. Is there an easy way to
measure this in circuit? All thoughts appreciated.

Thanks
Steve

The obvious thing is to use an oscilator where the circuit capacitance
determines frequency, and make it with enough feedback that lossy
capacitance doesnt matter. Which leaves me wondering why you cant do
that? If you really need to. Is the new xtal malfunctioning?


NT
Click to expand...
 
I'll have to look at the schematic again, but IIRC it had an inductor
across the xtal. These circuits were designed in the late 70's, if
that helps.

On Fri, 15 Dec 2006 16:42:25 -0500, "Charles Schuler"
<charleschuler@comcast.net> wrote:

eletlabs@gmail.com> wrote in message
news:1166215936.618338.112050@80g2000cwy.googlegroups.com...
I need a replacement crystal, but the MFG no longer helps on these
units. The Xtal is 122.6667MHz, HC49U package, but I have no idea what
the load capacitance of the circuit is. Is there an easy way to
measure this in circuit? All thoughts appreciated.

Are there any 10 to 20 pF capacitors connected to the crystal in your
circuit?
Click to expand...
 
"Steve" <skamego@hotmaill.com> wrote in message
news:bv86o2l2k9hocckns28b54grtj2equcvsp@4ax.com...
I'll have to look at the schematic again, but IIRC it had an inductor
across the xtal. These circuits were designed in the late 70's, if
that helps.
Click to expand...
No, the design date does not help me.

Crystal resonators can be shifted in frequency with coils and/or capacitors.
Many times, a small ceramic trimmer capacitor is used to tweak the crystal
to the desired frequency.
 
Thanks for the replies. This circuit only uses trimmer caps for the
tuned amplifier (further down the circuit, not for the feedback loop),
and coils for the frequency adjustment. Had this unit used trimmer
caps, could you assume the load capacitance would be close to the
mid-range value of the trimmer cap, or is that a bad assumption?

I guess it just depends on the circuit.

Are there any general accepted values for xtals in terms of load
capacitance specifications?

Thanks again,
Steve

On Fri, 15 Dec 2006 18:00:02 -0500, "Charles Schuler"
<charleschuler@comcast.net> wrote:

"Steve" <skamego@hotmaill.com> wrote in message
news:bv86o2l2k9hocckns28b54grtj2equcvsp@4ax.com...
I'll have to look at the schematic again, but IIRC it had an inductor
across the xtal. These circuits were designed in the late 70's, if
that helps.

No, the design date does not help me.

Crystal resonators can be shifted in frequency with coils and/or capacitors.
Many times, a small ceramic trimmer capacitor is used to tweak the crystal
to the desired frequency.
Click to expand...
 
"Dani" <greeben@gmail.com> wrote in
news:1166202238.970293.197790@16g2000cwy.googlegroups.com:

Is there a parts availability law in Canada??


Parts Availability Laws

Can your item be repaired? If parts are required, are they available to
a servicer? In some states, the answer may be "no."

Does your state have a law governing the availability of parts?
Here are the states with such laws:

California:
7 years after date of manufacture for goods with a wholesale value of
$100 or more, 3 years for items valued at $50 to $99.99. This law
covers functional parts only.

Connecticut:
4 years after the date of final sale.

Indiana:
7 years after the date of final sale.

Rhode Island:
4 years after final sale.
Click to expand...


Tektronix does not follow any of the above states law on parts
availability,if those are truly law.

--
Jim Yanik
jyanik
at
kua.net
 
Steve wrote:
This is in existing equipment, built in the 80's. The old xtal is
shot, physically broken. In order to order a new xtal for it, they
need load capacitance specification.

Thanks for the reply.

Steve

On 15 Dec 2006 14:12:43 -0800, meow2222@care2.com wrote:

eletlabs@gmail.com wrote:

I need a replacement crystal, but the MFG no longer helps on these
units. The Xtal is 122.6667MHz, HC49U package, but I have no idea what
the load capacitance of the circuit is. Is there an easy way to
measure this in circuit? All thoughts appreciated.

Thanks
Steve

The obvious thing is to use an oscilator where the circuit capacitance
determines frequency, and make it with enough feedback that lossy
capacitance doesnt matter. Which leaves me wondering why you cant do
that? If you really need to. Is the new xtal malfunctioning?


NT
Click to expand...
the first thng will ask is it a series resonant or parallel resonant...

If it is series, you don't need to know the load C.

If it is parallel I'd order a crystal for 22 pF load. If it then runs
a little high, you could pad it down.
Mark
 
Steve wrote:

This is in existing equipment, built in the 80's. The old xtal is
shot, physically broken. In order to order a new xtal for it, they
need load capacitance specification.
Click to expand...
Why not go for a highish C value and add a trimmer. Adjust to correct
f.
Why not measure the circuit capacitance? You cant do it by looking at
part values because other cct elements have capacitances too in the pF
range.

So again, I dont understand where exactly youre having a problem with
this.


NT
 
Sorry if I was unclear. I was originally asking how to actually
measure the circuit capacitance. I have a handheld meter, however, it
runs at a fixed frequency, and when I hook it up to the circuit, it
measures negative capacitance, so I don't think it will work in this
instance.

Thanks again,
Steve

On 15 Dec 2006 17:52:30 -0800, meow2222@care2.com wrote:

Steve wrote:

This is in existing equipment, built in the 80's. The old xtal is
shot, physically broken. In order to order a new xtal for it, they
need load capacitance specification.

Why not go for a highish C value and add a trimmer. Adjust to correct
f.
Why not measure the circuit capacitance? You cant do it by looking at
part values because other cct elements have capacitances too in the pF
range.

So again, I dont understand where exactly youre having a problem with
this.


NT
Click to expand...
 
"mhancock84" <mhancock84.2iue5e@nospamplease.com> wrote in message
news:mhancock84.2iue5e@nospamplease.com...

used.....probably 6-7 year old t.v.
Click to expand...
OK. 'Just purchased' sounds like a warranty job!
 
Steve <skamego@hotmaill.com> wrote in
news:9sb6o21mhn7toflq120bc0c13p8a78jepr@4ax.com:

I have a handheld meter, however, when I hook it up to the circuit, it
measures negative capacitance.

This circuit uses coils for the frequency adjustment.
Click to expand...
This is getting interesting! How about if you scan the schematic and post
the oscillator circuit for us to see? (Somewhere on the web or in the
newsgroup alt.binaries.schematics.electronic)
 
I'll do that, but it'll be Monday before I get the schematic.

Thanks for all the replies everyone.

Steve

On Sat, 16 Dec 2006 05:43:13 -0000, Jim Land
<RrrrFfffTttt(NO)@(SPAM)hotmail.com> wrote:

Steve <skamego@hotmaill.com> wrote in
news:9sb6o21mhn7toflq120bc0c13p8a78jepr@4ax.com:

I have a handheld meter, however, when I hook it up to the circuit, it
measures negative capacitance.

This circuit uses coils for the frequency adjustment.

This is getting interesting! How about if you scan the schematic and post
the oscillator circuit for us to see? (Somewhere on the web or in the
newsgroup alt.binaries.schematics.electronic)
Click to expand...
 
In case anyone reads this, I traced the circuit back as best as I
could. This unit has two HV power supplies, positive and negative.
The balance is adjusted using the Balance adjust pot. The front fan
grill is isolated and used as a sensor. The grill is connected to an
amplifier, which is fed into a window comparator. VR2 and VR3 adjust
the limits of the window comparator, VR2 is high limit, VR3 is low
limit. The comparator drives the balance alarm LED. I didn't look
into the cleaning LED section, I got tired of reverse-engineering it.

The test jack on the back is a mini-din type jack. Pin 1 is the high
limit signal of the comparator, pin 2 is the amplified grill voltage,
pin 3 is the low limit, and pin 4 is gnd. Pin 5 & 6 are N.C.

Due to there being no monitored output of the cleaning alarm, I assume
with the unit clean you adjust the pot until the light just goes off.

I adjusted balance for appx 0VDC, and set the limits for -.25 &
+.25VDC. No idea if this is right, but without any info, it seems
like my best bet.

Also, the pins on the power jack are as follows (when looking into the
jack with the pins at the top)

The left two pins are -15VDC, middle two gnd, and right two +15VDC

Hope this helps someone, and don't take all of this info for fact, I
could quite possibly be wrong.

Steve
 
Does the standby indicator glow?
The chameleon power l.e.d. reports the state of the unit.

"solid green: The projector is plugged in, or the projector has been
turned on and the
software has initialized. The projector has been turned off and the
fans have stopped.

blinking green: The Power button has been pressed and the software is
initializing, or the
projector is powering down and the fans are running to cool the lamp.

blinking red: A fan or lamp failure has occurred. Make sure the vents
aren't blocked. Turn off the projector and wait one minute, then turn
the projector on again. If the projector
has been working for 2000 hours or more, replace the lamp and reset the
lamp timer by pressing Volume +, then Volume -.

solid red: An unidentifiable error: please contact Technical Support."

Which of the above four modes does the l.e.d. report?
Jango
 
"Steve" <skamego@hotmaill.com> wrote in message
news:4in6o25t3g78hjrrvrv43a7a3iu5b50mec@4ax.com...
Sorry if I was unclear. I was originally asking how to actually
measure the circuit capacitance. I have a handheld meter, however, it
runs at a fixed frequency, and when I hook it up to the circuit, it
measures negative capacitance, so I don't think it will work in this
instance.

Thanks again,
Steve

On 15 Dec 2006 17:52:30 -0800, meow2222@care2.com wrote:

Steve wrote:

This is in existing equipment, built in the 80's. The old xtal is
shot, physically broken. In order to order a new xtal for it, they
need load capacitance specification.

Why not go for a highish C value and add a trimmer. Adjust to correct
f.
Why not measure the circuit capacitance? You cant do it by looking at
part values because other cct elements have capacitances too in the pF
range.

So again, I dont understand where exactly youre having a problem with
this.


NT
Click to expand...
May be right off the wall, but many items back in those days had crystals
specified at 30pf parallel resonance. I have had occasions where I have had
to have a xtal custom cut, and have not known the specs, and the xtal
cutting company has just asked me to send in a copy of the schematic with my
order, along with the make and model number of the equipment. It's amazing
what they have archived away in dusty filing cabinets, or what they can
deduce about a crystal from a schematic. With the experience that they have
in these matters, they might even be able to work out specs from the broken
xtal.

Arfa
 
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