how to repair using a schematic and DMM?

K

Kaycho

Guest
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?
 
"Kaycho" <tomtomtomtomtom@gmail.com> wrote in message
news:1123789474.989401.155960@g44g2000cwa.googlegroups.com...
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?
Click to expand...
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
 
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...


"Kaycho" <tomtomtomtomtom@gmail.com> wrote in message
news:1123789474.989401.155960@g44g2000cwa.googlegroups.com...
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?
Click to expand...
 
On 11 Aug 2005 12:44:35 -0700, "Kaycho" <tomtomtomtomtom@gmail.com>
wrote:

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?
Click to expand...
Heh.

Go to

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

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

Tom
 
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?
Click to expand...
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.
 
On Thu, 11 Aug 2005 17:05:25 -0500, Brinkley Hassebrock wrote:

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.
Click to expand...
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
 
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.
 
On Thu, 11 Aug 2005 17:05:25 -0500, "Brinkley Hassebrock"
<brink@isurf2.com> wrote:

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.
Click to expand...
---
That's putting it mildly. After "unpluging" it and being away from
it for over a year, I plugged it back in and turned it on and what
did I see? Janet Jackson's tit. Ugh! _Shockingly_ bad TV.

--
John Fields
Professional Circuit Designer
 
On Mon, 15 Aug 2005 10:38:50 -0700, Kaycho wrote:

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?
Click to expand...
Simple ones. :)

Cheers!
Rich
 
On 15 Aug 2005 10:38:50 -0700, "Kaycho" <tomtomtomtomtom@gmail.com>
wrote:

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.
Click to expand...
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?
Click to expand...
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.

>Thanks so much for the replies.
 
Kaycho wrote:
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.
Click to expand...
Ok. Essentially, all components "do something" in normal
operation. (There can be some components that "do something"
only in abnormal conditions.) Lashing a bunch of components
together in a particular way makes them "do something"
as a group. Perhaps they make an oscillator, or an amplifier,
or a regulator or a filter - whatever. Call that group a circuit,
and identify it by its function - eg "an amplifier circuit", "a
voltage regulator circuit" etc. You need to learn what each
component does. You need to learn what each circuit does.
Each circuit can be thought of as having input(s) and output(s)
and some circuits also need a power source.

Once you have an understanding of basic circuits, troubleshooting
consists of determining whether the input(s) is(are) correct and
whether the output(s) is(are) correct. When you find a circuit
that has correct input, but has incorrect output, you know
that either that circuit is bad, or the output is being improperly
influenced by the next circuit in line. To do this, you need
to know what a proper input is, and what a proper output is.
Once you know what input and output to expect, you can anwser
your own question about using a DMM to troubleshoot. This
assumes that you already know what your DMM is capable of.

Ed



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.
Click to expand...
 
On 20 Aug 2005 07:08:30 -0700, "redbelly" <redbelly98@yahoo.com>
wrote:

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

Rich Grise wrote:
Simple ones. :)

Simple AND SAFE ones!
Click to expand...
---
Not me; I was into the insides of radios when I was about 8 and
found out about AC mains and B+ early.

--
John Fields
Professional Circuit Designer
 
John Fields wrote:
Not me; I was into the insides of radios when I was about 8 and
found out about AC mains and B+ early.
Click to expand...

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
 
On Sun, 21 Aug 2005 00:24:29 GMT, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

John Fields wrote:

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.
Click to expand...
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
 
Kaycho wrote:
I'm curious what type of circuits did you guys learn on?

Rich Grise wrote:
Simple ones. :)
Click to expand...

"redbelly" <redbelly98@yahoo.com> wrote:
Simple AND SAFE ones!
Click to expand...
John Fields wrote:
Not me; I was into the insides of radios when I was about 8 and
found out about AC mains and B+ early.
Click to expand...
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.
 
On 21 Aug 2005 09:17:07 -0700, "redbelly" <redbelly98@yahoo.com>
wrote:

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

Rich Grise wrote:
Simple ones. :)


"redbelly" <redbelly98@yahoo.com> wrote:
Simple AND SAFE ones!


John Fields wrote:
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?
Click to expand...
---
Yup!
---

p.s. pardon my ignorance ... what is B+ ? TIA.
Click to expand...
---
The vacuum tube plate supply voltage.


--
John Fields
Professional Circuit Designer
 
John Fields wrote:
On 21 Aug 2005 09:17:07 -0700, "redbelly" <redbelly98@yahoo.com
wrote:

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

---
Yup!
---
Click to expand...
Ouch. I'd guess a lot of us have had that happen.

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

---
The vacuum tube plate supply voltage.
Click to expand...
Thank you.

Mark
 
John Fields wrote:
On 20 Aug 2005 07:08:30 -0700, "redbelly" <redbelly98@yahoo.com
wrote:


Kaycho wrote:

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

Rich Grise wrote:

Simple ones. :)

Simple AND SAFE ones!


---
Not me; I was into the insides of radios when I was about 8 and
found out about AC mains and B+ early.
Click to expand...
I feel your pain! :)

Ed
 
"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:Zz%Oe.4848$Ck2.2199@trndny04...
John Fields wrote:
On 20 Aug 2005 07:08:30 -0700, "redbelly" <redbelly98@yahoo.com
wrote:


Kaycho wrote:

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

Rich Grise wrote:

Simple ones. :)

Simple AND SAFE ones!


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


I feel your pain! :)

Ed
Click to expand...
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
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top