how to repair using a schematic and DMM?

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

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.

Heh.

Go to

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

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...

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.

Simple ones. :-)

Cheers! Rich

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.

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.

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

Simple AND SAFE ones!

Mark

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.

"redbelly" wrote:

John Fields wrote:

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.

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

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

Thank you.

Mark

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!

1. 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.

2. 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

I feel your pain! :-)

Ed