how to repair using a schematic and DMM?

[Kaycho]

I would like to know how to troubleshoot circuits using a schematic
(with voltages) and a DMM/VOM. Specifically I'm working on transistors
in a TV. Should i take measurements with the tv plugged in? Can I
make in-circuit tests or do i have to desolder things?

 

[Tom Biasi]

I would like to know how to troubleshoot circuits using a schematic
(with voltages) and a DMM/VOM. Specifically I'm working on transistors
in a TV. Should i take measurements with the tv plugged in? Can I
make in-circuit tests or do i have to desolder things?

You need more than a schematic and a DMM.
You need some basic training. Don't be in a hurry to jump in and fix
something.
Before you can fix something you need to know how it works and what is
happening to make it not work. The fixing part is easy most of the time.
When you troubleshoot you are looking for a reason the unit doesn't perform
as it is supposed to.
TV's are very complicated and require more test equipment than a schematic
and a DMM. They are also very dangerous.
Regards,
Tom

 

[Alan Adrian]

Hehe... if this is not a troll post.... you are about to get a bit of a
suprise...

I'll try to put this mildly...... TV's have very dangerous voltages in them
and are not the place to learn how to troubleshoot. People die from messing
about inside TV's...

Al...

 

[Tom MacIntyre]

I would like to know how to troubleshoot circuits using a schematic
(with voltages) and a DMM/VOM. Specifically I'm working on transistors
in a TV. Should i take measurements with the tv plugged in? Can I
make in-circuit tests or do i have to desolder things?

Heh.

Go to

http://repairfaq.ece.drexel.edu/

and select the icon for the table of contents...then start reading.

Tom

 

[Brinkley Hassebrock]

I would like to know how to troubleshoot circuits using a schematic
(with voltages) and a DMM/VOM. Specifically I'm working on transistors
in a TV. Should i take measurements with the tv plugged in? Can I
make in-circuit tests or do i have to desolder things?

I grew up in my dad's tv repair shop.
Most tv repairmen are starving these days.
Reason: Television sets are disposable.
It takes more time to repair one than it takes to earn enough money to buy
one by raking leaves.

The warning about high voltages can't be stressed enough.

You can even be shocked months after the set had been unpluged if you get on
the wrong spot.

 

[Rich Grise]

I grew up in my dad's tv repair shop.
Most tv repairmen are starving these days.
Reason: Television sets are disposable.
It takes more time to repair one than it takes to earn enough money to buy
one by raking leaves.

The warning about high voltages can't be stressed enough.

You can even be shocked months after the set had been unpluged if you get on
the wrong spot.

This is true _EVEN THOUGH YOU'VE DISCHARGED IT!_ The tube is a big
Leyden jar. I've discharged them (fat clip lead to ground, small
screwdriver under the cap), and then later, drew another arc - the
glass itself holds a charge.

And I also concur with the others - unless you already know how
a TV works, and how to troubleshoot, it's not worth it, unless you
want to call it "home schooling".

Good Luck!
Rich

 

[Kaycho]

I generally know how tv works; I've read a few books. I've also read
Sam Goldwasser's site.

Thanks for the caution.

The problems I'm facing are with defective components that i think can
be tested with only a DMM. I just need some pointers on
troubleshhoting them. I suppose I can simply replace the component I
suspect is at fault based on deductive reasoning of how the tv works
and which component failure will cause a certain tv problem, but I'd
rather have some test to back up/confirm this suspicion.

I'm curious what type of circuits did you guys learn on?

Thanks so much for the replies.

 

[John Fields]

I grew up in my dad's tv repair shop.
Most tv repairmen are starving these days.
Reason: Television sets are disposable.
It takes more time to repair one than it takes to earn enough money to buy
one by raking leaves.

The warning about high voltages can't be stressed enough.

You can even be shocked months after the set had been unpluged if you get on
the wrong spot.

 

[Rich Grise]

I generally know how tv works; I've read a few books. I've also read
Sam Goldwasser's site.

Thanks for the caution.

The problems I'm facing are with defective components that i think can
be tested with only a DMM. I just need some pointers on
troubleshhoting them. I suppose I can simply replace the component I
suspect is at fault based on deductive reasoning of how the tv works
and which component failure will cause a certain tv problem, but I'd
rather have some test to back up/confirm this suspicion.

I'm curious what type of circuits did you guys learn on?

Simple ones.

Cheers!
Rich

 

[Kitchen Man]

I generally know how tv works; I've read a few books. I've also read
Sam Goldwasser's site.

Thanks for the caution.

The problems I'm facing are with defective components that i think can
be tested with only a DMM. I just need some pointers on
troubleshhoting them. I suppose I can simply replace the component I
suspect is at fault based on deductive reasoning of how the tv works
and which component failure will cause a certain tv problem, but I'd
rather have some test to back up/confirm this suspicion.

My experience with television is that there is no point trying to use
deductive reasoning - the damn things work on magic. Better luck
might be had finding an old tape player or stereo receiver that's
crapped out. I tracked down a bad part in a home stereo power amp
once, with only a dmm and no schematic, and I once found a bad chip in
a tuner by using freeze-spray. But at the time I did that, I'd had
quite a bit of job experience with troubleshooting circuitry.

I'm curious what type of circuits did you guys learn on?

Well, I learned electronics on the AN/APG-109 RADAR set. Ten months
of training and a couple years of OJT and I was ready to go. Thirty
years later I'm still learning.

 

[redbelly]

Simple ones.

Simple AND SAFE ones!

Mark

 

[John Fields]

Simple AND SAFE ones!

 

[Michael A. Terrell]

Not me; I was into the insides of radios when I was about 8 and
found out about AC mains and B+ early.

Good for you! I built a radio from a kit at 8, and was working part
time in a TV shop at 13. This shows that not everyone was stupid or
lazy as kids, when we were kids.

--
Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.

Michael A. Terrell
Central Florida

 

[Tom MacIntyre]

Good for you! I built a radio from a kit at 8, and was working part
time in a TV shop at 13. This shows that not everyone was stupid or
lazy as kids, when we were kids.

I built a foxhole radio (razor blade, pencil lead, safety pin, etc)
when I was 9, and again when I was 13. The second one I used until my
parents bought me a multi-band radio for a high school graduation
present.

I was always interested in electronics. It wasn't until my teens,
though, that my late 50's Fender Super guitar amplifier taught me
about how a filter capacitor can retain a charge, when I touched one
of the connectors on the Standby switch.

Tom

 

[redbelly]

Not me; I was into the insides of radios when I was about 8 and
found out about AC mains and B+ early.

John, let me know if I'm reading too much into this: is
"finding out" about AC mains a euphemism for getting
shocked?

Mark

p.s. pardon my ignorance ... what is B+ ? TIA.

 

[John Fields]

John, let me know if I'm reading too much into this: is
"finding out" about AC mains a euphemism for getting
shocked?

 

[redbelly]

On 21 Aug 2005 09:17:07 -0700, "redbelly" <[email protected]>
wrote:

Ouch. I'd guess a lot of us have had that happen.

Thank you.

Mark

 

[ehsjr]

I feel your pain!

Ed

 

[clf]

I feel your pain!

Ed

Some of my own "electrofying" adventures....

1. When I was old enough to be able to unscrew a lightbulb from a nearby
table lamp, and understand that the "knob" had to be turned to get it to
come on - I did just that - only I replaced the bulb with my finger.
Ahhhhh - the rush. I've been shocked many times since. Usually it is still
about 1x a month. Some not so bad, others - OUCH! The worst ones were as bad
as some "RF" burns I've gotten. Those can tend to hurt too!

2. I was working on a Heathkit Transmitter. I needed to take a voltage
reading inside and I just couldn't get the probe in place due to a small
wire that kept getting in the way. I'm thinking the ole familiar electronics
safety rule - "KEEP ONE HAND OUT"..... but dummy me, I ignored it and as I
was putting my hand in to hold the wire, kept thinking "you're going to get
lit up" and damned if I didn't. That sucker hurt. I didn't get the voltage
reading either, so the pain was for nothing. I turned the thing off til my
arm stopped paining - went back - rigged something up inside to the point I
needed and then placed the probe on. I waited til the set warmed up to
stabilize the reading to make sure it was correct.

3. Was working on an old Tube Type CB once, sitting on a "Cement" porch -
bare foot. Set hadn't been plugged in for a while. I still got a tingle.
Though I was a bit shocked (pardon the pun) - I reasoned that there must
have been enough voltage stored yet to do that. So, I guess I wasn't too
awfully surprised considering it all.

So, I always tell people I have an "electrofying" personality!

Just some of my adventures in "diverted" electricity. I try NOT to get
shocked, but we all know - S*&t happens.

clf