Oscilloscope

[13Willie]

I own a 100MHz scope but do not know how to use it to troubleshoot TV circuits, for instance how to use the probe. Where should ground go for instance. If I connect the ground on the probe to the ground of the TV the power trip, the 220V AC. Can I use the scope from the powersupply side to the tube. Can I for instance use it alone without a sweep generator. Do anyone know where I can get information on troubleshooting with just a scope. Can someone please help.

[i4004]

Re: Oscilloscope

ground
https://www.badcaps.net/forum/showth...ound#post60210

but practice on low voltage electronics first...tv has a great "bang" potential...heh..

oh yeah, tv has 2 grounds..one is hot(220v ground) and other is not.
when working on the hot side you must be especially carefull.
infact i suggest you do use scope on hot side only if you can't really do anything else with conventional troubleshooting methods...

how does it work?
well, in electric diagrams(usually found in service manuals) you have oscillograms which you compare to what you see on the scope, for particular point you're measuring.
if it's not the same, circuit is malfunctioning.

problem is the following: you can't expect scope to show you exactly what element is faulty. for example it can happen one elelemnt failure is making the whole circuit have wrong waveform, and touching any point in it shows wrong waveform, and in such cases scope is not very usefull at all.
ie you can't expect scope will magically isolate faulty element from the rest of the circuit.

post your particular issue here and we'll probbaly be able to tell you some basics of troubleshooting you'll be able to use later...
also, you can search the web for particular problems, but i think it's more fun if you reach conclucions yourself...

again, be very, very carefull with tvs...do anything you can think of to increase safety...isolation transformers(read the thread i linked above), rubber gloves, rubber sole shoes... anything and everything...

FIRST read this
http://www.repairfaq.org/sam/safety.htm

and THEN this
http://www.repairfaq.org/sam/tvfaq.htm

as repairing tv-set is such a piss-poor way to kill yourself...

[13Willie]

Re: Oscilloscope

Thanks very much, it is very helpful

[Krankshaft]

Re: Oscilloscope

An isolation transformer is a MUST don't even think of using a scope on a transformerless TV without one.

Here is what I use:

http://www.mcmelectronics.com/product/72-6670

Inexpensive comes in a nice box and worth its weight in gold.

As for which ground to use you usually use the ground in reference to the circuit you are measuring. If you are checking a horizontal waveform from the IC for example you would use the ICs ground.

Most scope probes have pretty short ground leads anyways so you'll need to clamp it nearby.

Scopes have limited use for TV repair unless you are comparing waveforms from a service manual to isolate circuit faults.

A high voltage probe is a nice addition too I only had to get zapped by a TVs HV once to realize the importance of this tool.

I use it to slowly discharge the anode cap. I hate pops and sparks from the screwdriver method .

Also fashion a shorting connector to attach between the CRT ground strap and the anode button since TVs just discharged can regain some of their HV (around 3,000-,5,000 volts when I measured) since they can store voltage deep in the glass.

Not as bad as the original charge but startling enough for me not to want it to happen again.

[Krankshaft]

Re: Oscilloscope

A wirewound resistor will discharge too solder wires onto the resistor and put alligator clips onto the ends alligator clip one end to a long flat head screwdriver and the other end to the ground strap.

The screwdriver will keep you away from the HV with a high enough resistance resistor you can reduce the chance of sparking rather than just shorting to ground.

[13Willie]

Re: Oscilloscope

This is great stuff thanks alot.