CurtPalme.com Home Theater Forum

[cmjohnson]

Lately I've seen a surprising number of people who are asking for assistance in performing technical operations on their
CRT projectors. I find this to be kind of alarming because, to be quite direct about it, the high voltages present in CRT projectors make them absolutely, positively, no place for an electronics novice to be poking around in!

If you have to ask how to set a volt-ohmmeter, or need help testing a transistor or diode or reading a resistor color code,
or don't know Ohm's Law or Thevenin's Theorem, you really should refer all servicing tasks to someone who has some
formal training in electronics.

This is for your own safety.

Your CRT projector is more powerful than the largest commercial grade bug zapper, and YOU are the bug, if you make
a mistake. If there's a serious problem and you get your pink little body between a leaking anode cap and ground, the projector will smite thee, send you to your final reward, and never even hiccup. It will KILL you. DEAD. Say hi to Saint Peter for me.

Even things that don't seem important, ARE. There are ground straps bonded to the conductive paint that is applied to the back
of every CRT. Those straps have to be connected to ground. I've pulled those straps off just to find out what happens, under safe conditions, and what happens is that the bell of the CRT picks up a heck of a voltage charge on it in a matter of seconds. Discharge it to ground and it'll pull an arc about a quarter inch long, which implies a voltage of around 5000 volts.
And that's nothing compared to the roughly 35,000 volts going into the anode from the high voltage power supply.


On the neck card, there's a G2 line, which can range upwards of six hundred volts. It'll bite you, HARD. It COULD kill you,
if you weren't lucky.

The horizontal deflection yoke can carry up to 1500 volts AC on it, at frequencies up to 180 KHz depending on model and scan rate selected. While you won't really get SHOCKED by that, you'll get an RF burn instead, one that feels like being jabbed with a hot soldering iron. Been there, done that, maybe I can still find the scar if I look hard enoug for it.



There are hazards and high voltages all over your projector. It's no place for a neophyte to be screwing around.

And you can damage the projector if you don't know what you're doing, too. Interrupt the deflection circuits and bang, spot burns in your tubes, spot burns that will be there forever. Instant ruined tubes, no fun at all.

I want us all to have fun, be safe, and enjoy a great picture. Being safe means in part, knowing your limits and leaving the repairs that are beyond your skill level for those who are equipped to handle them.

Don't think digital projectors are necessarily any safer, either. Their lamps strike at high voltages and their power supplies are quite robust enough to throw you around, too.

I know a few former TV technicians from back in the day when every TV had a picture tube and a flyback transformer in it.
The few techs who got across the flyback transformer USUALLY ended up hurt so badly by it that you can literally say they were never quite right again. I know of technicians who were KILLED by a TV's flyback transformer. Our CRT projectors generate roughly the same anode voltage as the tech killer TVs. Between 35 and 40K.

If you are not AFRAID of messing around in your projector, or at least are not HIGHLY respectful of the dangers, you really SHOULD be. Complacency will make you the bug, and your PJ is the bug zapper. Get too confident and anybody can predict the eventual outcome.

Get some electronic education before you start messing around and trying to fix your machine. Seriously. Because I want you to survive the attempt, and be successful at it. With some education this can be made to happen, and SAFELY, most importantly of all.


It comes down to that one thing: SAFETY. Ignorance makes you unsafe. Education makes you safer.

[larryp]

Many are forced to look into repairing their sets themselves because finding anyone to work on them is very hard.
Great advice

[cmjohnson]

So get a handbook that'll teach you basic electronics. They're not that hard to come by.

[tanwn1]

Couldn't agree more, most of the faults are not as simple as replacing a diode, resistor, transistor etc. What is the exact root cause? Been there done that too. Short of replacing the board, there's not really much you can do unless you are qualified to do it.

[barcodude]

wasn't this the place to learn this?? it's not that i'm going to kill myself because i'm putting my finger in a place it shouln't be.
green hoarns got to start some were. Any how good advice

[Francisco]

Sometimes I get the feeling that people see a crt projector as my first electronic playing box. There are dangers about a crt projector and it can kill you in two ways. 1) it'll fry you, 2) it'll fall on your head when you didn't hung it right.

[cmjohnson]

NO, this is not the place to learn basic electronics!

This is the place to discuss CRT projectors, and if they need service, you refer service to a qualified serviceman,
and if you've made a study of electronics, it MIGHT be you. If not, there are a few people here who can provide
those repair services for you.


I'm not telling anybody that the CRT projector is a sacred thing, never to be touched for any maintenance or repair purposes unless you have a Ph.D in electrical engineering and have been baptized in ethylene glycol and glycerine so as to have the gift of clarity of vision, or that you need to have been knighted by the grandson of Hiram Percy Maxwell or anything like that.

I AM telling you that the projector is NO place to start your personal Electronics 101 learning experience!

In order to have a good chance of being able to understand any given system in the projector well enough to be able to diagnose a failure and SUCCESSFULLY repair it, you need to have at least THIS coursework under your belt, and understand it well enough to get a passing grade in all of it:

Lesson 1 Fundamentals of Electricity

Lesson 2 Voltage and Current

Lesson 3 Power Supplies and Simple Circuits

Lesson 4 Resistor Circuits and Ohms Law

Lesson 5 Resistor Networks

Lesson 6 Capacitor Circuits

Lesson 7 Fundamentals of Magnetism

Lesson 8 Inductor Circuits

Lesson 9 Building Electronic Circuits

Lesson 10 Introduction to Semiconductor Devices

Lesson 11 Electronics Applied: Transformers

Lesson 12 Electronics Applied: Basic Communication Circuits

Lesson 12 Vacuum Tube principles (Cathode Ray Tubes)

And more.


And you need to have logical troubleshooting skills. Know how to isolate faults. To the board level at least, to the component level if you want to put the extra time into it.


The beauty of it is that all the coursework can be found online, and if you know where to look, for free.


To really learn it you need practical experience with, at the least, a handful of components and an experimenter's kit, so you
can construct circuits and see them operate for yourself, and understand the function of every part in the circuit.

None of this is difficult. It's a bunch of easy steps. If you want to fix your own projector, your odds of being both successful and surviving the experience are exponentially improved by getting the education needed.

If you still think that you can do a component level repair inside your projector but you can't tell me what resistor value is needed
to limit current to 50 milliamps in a 110 volt DC supply circuit, and tell me what wattage rating that resistor needs to be as well, then you need to stop and acknowledge the fact that you do not have the basic knowledge that is absolutely NECESSARY to be able to successfully repair electronics.

And you WILL need much more knowledge than that required just to size a resistor.

[racerxnet]

Buy a CRT projector for little or nothing. Spend 1000.00 or more to service it. Great advice, but I see where the other half of the problem lies. We just don't have the disposable income as when we were younger. No sense in griping about our economic situation. It won't fix the projector.

MAK

[cmjohnson]

Getting the education you need doesn't have to cost more than a few dollars for tools.

I say that again: A basic electronics education can be FREE. With this in mind, you have no excuses to fall back on.


My point is ENTIRELY about one thing only: SAFETY. NOT GETTING KILLED BY YOUR PROJECTOR.

If you are unwilling to learn basic electronics, don't even pop the covers off your projector for any repair related purposes.

If you just know where the high voltage areas are and you are careful around them, you can do all routine maintenance on
them without any electronics knowledge. NO PROBLEM.

It's when you decide to start trying to fix a failed circuit that you will need to know more.

[barcodude]

it's all about finding a cheap crt learning some basics in the hope you can own a high end one in the future and no harm in discussing some basics and if you die in the proces so be it than it whas my time to go anyway

[racerxnet]

[cmjohnson]

That's "yoke", not "yolk". Eggs got nothing to do with it!

Moving the magnetics, adjusting flare, astig, focus, etc., can all be done safetly by anybody who just knows where the high voltage danger areas are. I'm not saying that you shouldn't be doing those things.

[racerxnet]

[larryp]

Every crt owner should move in next to Curt!

[cmjohnson]

Curt would move away to an undisclosed location! He's already pulling 100 hour weeks.

Which should be no problem, that leaves 68 hours a week for him to answer your emails, answer nature's call, take a shower as needed, etc.

Right?

Just remember, I'm not trying to discourage you from working on your own projector. I'm only trying to get you to be realistic about your skill level because that thing can kill you if you are not aware of the hazards.