Soldering a Broken TV

[[email protected]]

I started having trouble with my TV after it was moved in a U-Haul from
San Francisco to Seattle. I managed to locate a faulty solder joint on
the board. Applying pressure to the joint with a strip of wood fixes
the problem.

My problem is this: I am very experienced with electronics and
soldering, but I have little experience when it comes to high voltage.
I need to fix the solder joint but I have no hardware to properly
discharge any high voltage capacitors in the TV. I don't think this is
a problem as the faulty solder joint is attached to what appears to be
a FET. However, it could also be a triac, which could mean that it's
attached to a HV part of the circuit. I don't want to stick my head in
there to find out exactly what it is. Would you advise fixing the
solder joint without first discharging the TV?

Thanks in advance!

 

[Michael Black]

I started having trouble with my TV after it was moved in a U-Haul from
San Francisco to Seattle. I managed to locate a faulty solder joint on
the board. Applying pressure to the joint with a strip of wood fixes
the problem.

My problem is this: I am very experienced with electronics and
soldering, but I have little experience when it comes to high voltage.
I need to fix the solder joint but I have no hardware to properly
discharge any high voltage capacitors in the TV. I don't think this is
a problem as the faulty solder joint is attached to what appears to be
a FET. However, it could also be a triac, which could mean that it's
attached to a HV part of the circuit. I don't want to stick my head in
there to find out exactly what it is. Would you advise fixing the
solder joint without first discharging the TV?

Thanks in advance!

Huh?

You're "very experienced in electronics and soldering" yet you don't
know whether something is an FET or a triac?

Michael

 

[Homer J Simpson]

I started having trouble with my TV after it was moved in a U-Haul from
San Francisco to Seattle. I managed to locate a faulty solder joint on
the board. Applying pressure to the joint with a strip of wood fixes
the problem.

Fix it that way. You don't have the skill set to do more.

 

[Clyde Crashcup ..........................]

I started having trouble with my TV after it was moved in a U-Haul from
San Francisco to Seattle. I managed to locate a faulty solder joint on
the board. Applying pressure to the joint with a strip of wood fixes
the problem.

My problem is this: I am very experienced with electronics and
soldering, but I have little experience when it comes to high voltage.
I need to fix the solder joint but I have no hardware to properly
discharge any high voltage capacitors in the TV. I don't think this is
a problem as the faulty solder joint is attached to what appears to be
a FET. However, it could also be a triac, which could mean that it's
attached to a HV part of the circuit. I don't want to stick my head in
there to find out exactly what it is. Would you advise fixing the
solder joint without first discharging the TV?

Thanks in advance!

Just lay some steel wool or tinsel around where you will be working and
it will short out any voltage.

--

You are living somebody else's dream. The whole world, laws
and way of life; not your dream.


Clyde Crashcup

 

[[email protected]]

Huh?

You're "very experienced in electronics and soldering" yet you don't
know whether something is an FET or a triac?

Michael

I don't want to stick my head in between the high-voltage electronics
and the CRT to see it more closely.

 

[Ken G.]

You dont need to discharge anything to do some soldering . The charge is
held up under that big suction cup on the picture tube . Simply turn the
set off and wait a few minutes for the filter capacitors to discharge by
themselves , turn the board over then solder .
In some cases when you walk up to a tv and touch metal parts you may get
a static zap just like you do from the car door or door knob in your
house .

 

[CJT]

You dont need to discharge anything to do some soldering . The charge is
held up under that big suction cup on the picture tube . Simply turn the
set off and wait a few minutes for the filter capacitors to discharge by
themselves , turn the board over then solder .
In some cases when you walk up to a tv and touch metal parts you may get
a static zap just like you do from the car door or door knob in your
house .

That "big suction cup" has a wire extending from it to the HV section.
Touching any bare section of that wire (although there shouldn't be
any), or of the parts in the HV section to which it's attached, can
give you a big surprise.

The picture tube itself holds the charge.

 

[CJT]

Just lay some steel wool or tinsel around where you will be working and
it will short out any voltage.

That sounds like a recipe for problems later, when bits of steel wool
left behind cause further shorts. Besides, putting steel wool on a
board containing capacitors that aren't fully discharged already can
discharge them through inappropriate paths.

 

[Sam Goldwasser]

Just lay some steel wool or tinsel around where you will be working and
it will short out any voltage.

Responses like this are not constructive and downright dangerous.

Simply leave the TV off overnight. That should discharge any capacitors
that would affect soldering on the mainboard. The only possible remaining
charge may be on the CRT anode but that only goes to the flyback and you
should not need to disconnect it. And, that will almost certainly be
discharged by then in any case.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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Important: Anything sent to the email address in the message header above is
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[Sam Goldwasser]

That "big suction cup" has a wire extending from it to the HV section.
Touching any bare section of that wire (although there shouldn't be
any), or of the parts in the HV section to which it's attached, can
give you a big surprise.

The picture tube itself holds the charge.

In nearly all CRT TVs and monitors less tha 30 years old, it goes directly
into the flyback and bare sections would be extermely unlikely.

--- 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.

 

[Homer J Simpson]

In nearly all CRT TVs and monitors less tha 30 years old, it goes directly
into the flyback and bare sections would be extermely unlikely.

Unless the ground to the outside of the kine is disconnected. Not a good
thing to touch if you are standing on the ledge of a second floor window.

 

[James Sweet]

I started having trouble with my TV after it was moved in a U-Haul from
San Francisco to Seattle. I managed to locate a faulty solder joint on
the board. Applying pressure to the joint with a strip of wood fixes
the problem.

My problem is this: I am very experienced with electronics and
soldering, but I have little experience when it comes to high voltage.
I need to fix the solder joint but I have no hardware to properly
discharge any high voltage capacitors in the TV. I don't think this is
a problem as the faulty solder joint is attached to what appears to be
a FET. However, it could also be a triac, which could mean that it's
attached to a HV part of the circuit. I don't want to stick my head in
there to find out exactly what it is. Would you advise fixing the
solder joint without first discharging the TV?

Thanks in advance!

Just get in there and solder it, if the set has been unplugged for a few
days there's no risk.

 

[Sam Goldwasser]

Unless the ground to the outside of the kine is disconnected. Not a good
thing to touch if you are standing on the ledge of a second floor window.

I'm not sure I'd want to test it out this way, but in principle, if the
ground only were disconnected after the set was turned off, there would
be no voltage between it and ground.

--- 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.

 

[Homer J Simpson]

I'm not sure I'd want to test it out this way, but in principle, if the
ground only were disconnected after the set was turned off, there would
be no voltage between it and ground.

True, but when it is run that way and you just turned it off to twist the
yoke . . . . .

 

[[email protected]]

I think a lot of the reponses so far have been attempts at humour.
Possibly because you say youre very experienced yet dont know how to
discharge a psu cap or the tube eht. No, you cant rely on them to self
discharge over a day or so. Since youre experienced, figure it out.


NT

 

[Homer J Simpson]

I think a lot of the reponses so far have been attempts at humour.
Possibly because you say youre very experienced yet dont know how to
discharge a psu cap or the tube eht. No, you cant rely on them to self
discharge over a day or so. Since youre experienced, figure it out.

He made his skill level clear and the best advice for him is to not try.

Applying pressure to the joint with a strip of wood fixes
the problem.

Fix it that way. You don't have the skill set to do more.

 

[Sam Goldwasser]

True, but when it is run that way and you just turned it off to twist the
yoke . . . . .

HeHeHe... If it's run with the CRT ground disconnected, that's a different
story.

--- 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
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[bz]

[email protected] wrote in

I think a lot of the reponses so far have been attempts at humour.
Possibly because you say youre very experienced yet dont know how to
discharge a psu cap or the tube eht. No, you cant rely on them to self
discharge over a day or so. Since youre experienced, figure it out.

Go to the library. Get an older copy of the Radio Amateur's Handbook. It
should show you how to make a tool consisting of a wire, a wooden dowel, and
a resistor, that can be used to safely discharge high voltage capacitors.

These devices were called 'crowbars' because that is what they essentially
were, a crowbar with a heavy wire that connected it to ground.

The operator would turn off the power, hang the crowbar on the high voltage
line, grounding it, and work on the equipment, secure and safe. IF someone
accidently turned on the power without removing the crowbar, it would blow
fuses.

Nowdays, a circuit that shorts the output of a power supply to ground in case
of overvoltage output of the supply is called a 'crowbar' circuit, for
reasons that should now be clear.





--
bz 73 de N5BZ k

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

[email protected] remove ch100-5 to avoid spam trap

 

[Michael A. Terrell]

Go to the library. Get an older copy of the Radio Amateur's Handbook. It
should show you how to make a tool consisting of a wire, a wooden dowel, and
a resistor, that can be used to safely discharge high voltage capacitors.

These devices were called 'crowbars' because that is what they essentially
were, a crowbar with a heavy wire that connected it to ground.

You are describing a "Shorting Stick" which is a safe way to discharge
a HV power supply to service the equipment. It was also used in
broadcast transmitters, in case the safety interlocks failed. A crowbar
is not current limited, it is a fail safe shutdown circuit, and you can
expect damage if it is triggered.

The operator would turn off the power, hang the crowbar on the high voltage
line, grounding it, and work on the equipment, secure and safe. IF someone
accidently turned on the power without removing the crowbar, it would blow
fuses.

Nowdays, a circuit that shorts the output of a power supply to ground in case
of overvoltage output of the supply is called a 'crowbar' circuit, for
reasons that should now be clear.

--
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

 

[[email protected]]

Fix it that way. You don't have the skill set to do more.

discharging CRT skill easily learnt

NT