Are these things I should consider bad

[Username1]

Good morning;

Ok, lets begin with your scope. It needs to be checked for some level of calibration. This can be done by you at home for a very little amount of money. You need to get a series of 9v batteries, hook them up to give you 18v, 56v, then check the voltages with a volt meter, write it down. Then use your scope, - lead to ground on scope, hit the + battery with your scope probe. If you have to make a circuit with a momentary contact switch and hook up your wires and watch your scope. You should be able to verify your scope is reading the proper voltage range this way.

You mentioned two spots where your voltages might not be correct. These need to be investigated. This is the way you will find this problem.

As an example, lets look at a audio amplifier, one with a pilot light on it. If you run it at some mid volume, the sound will be clear. If you turn it up to saturation, especially bass, it will distort, and in most cases the pilot light will begin to dim with the bass notes. Your jail bars are coming from something that is allowed to saturate, something in the horiz, output area, and it is ringing, and you see it everywhere in the tv, just like in the audio amplifier saturation blinking the pilot light. If your set were working correctly, this would be filtered out, but a spike it too large and showing up in places it should not. While the jail bars may show up in many places, it can only be fixed by removing it at the source, the horiz section of the tv.

In these sections in the pictures I am posting, you need to be sure all of the voltages, wave forms, are correct. There will be some clue, voltage wrong, wave shape wrong, open coil, changed resistor, something. Start with the Horiz driver, then go to horiz output, then flyback. Focus on the items in the three pictures I am uploading. If the voltages or wave shapes, sizes of wave shapes, p-p voltages are wrong, do not go on to the next stage. Check everything listed, voltages, wave shapes and sizes peak-to peak dc offset if its there. If the osc, driver section (left picture) has something not right, stay there until it is.... Do not go on to the center picture items.

Start with the left picture, then center, then right.

[TinCanAlley]

Originally Posted by Username1

Good morning;

Ok, lets begin with your scope. It needs to be checked for some level of calibration. This can be done by you at home for a very little amount of money. You need to get a series of 9v batteries, hook them up to give you 18v, 56v, then check the voltages with a volt meter, write it down. Then use your scope, - lead to ground on scope, hit the + battery with your scope probe. If you have to make a circuit with a momentary contact switch and hook up your wires and watch your scope. You should be able to verify your scope is reading the proper voltage range this way.

You mentioned two spots where your voltages might not be correct. These need to be investigated. This is the way you will find this problem.

As an example, lets look at a audio amplifier, one with a pilot light on it. If you run it at some mid volume, the sound will be clear. If you turn it up to saturation, especially bass, it will distort, and in most cases the pilot light will begin to dim with the bass notes. Your jail bars are coming from something that is allowed to saturate, something in the horiz, output area, and it is ringing, and you see it everywhere in the tv, just like in the audio amplifier saturation blinking the pilot light. If your set were working correctly, this would be filtered out, but a spike it too large and showing up in places it should not. While the jail bars may show up in many places, it can only be fixed by removing it at the source, the horiz section of the tv.

In these sections in the pictures I am posting, you need to be sure all of the voltages, wave forms, are correct. There will be some clue, voltage wrong, wave shape wrong, open coil, changed resistor, something. Start with the Horiz driver, then go to horiz output, then flyback. Focus on the items in the three pictures I am uploading. If the voltages or wave shapes, sizes of wave shapes, p-p voltages are wrong, do not go on to the next stage. Check everything listed, voltages, wave shapes and sizes peak-to peak dc offset if its there. If the osc, driver section (left picture) has something not right, stay there until it is.... Do not go on to the center picture items.

Start with the left picture, then center, then right.

The scope was professionally calibrated when I got it a couple of weeks ago. I know it reads the same voltage I get with my DMM.

Tomorrow I'll start on your list. I know it's not the horizontal driver as I replaced the module with a newer, NOS board and have the same problem. That module has the wave shaper, horizontal AFC, OSC and driver. The module isn't the source, but it could be affected by it.

[TinCanAlley]

I do have a question, though. On the schematics for the H. Sweep it says that point is T5 and is 63.7V. However, the waveform shown for that point says it's 120VPP. How is that? How can you get a 120V PP with a driving voltage of 63.7V?

This is the point I had a 160V PP. That will be my first recheck tomorrow morning. Today is a complete mess and no time for the poor set.

[N2IXK]

Originally Posted by TinCanAlley

I do have a question, though. On the schematics for the H. Sweep it says that point is T5 and is 63.7V. However, the waveform shown for that point says it's 120VPP. How is that? How can you get a 120V PP with a driving voltage of 63.7V?.

The 63.7V is the DC voltage you should read if you measure that point with a DMM. The 120 Vpp is the amplitude of the AC waveform present.

The waveform looks to be roughly 50% duty cycle (pretty close to a square wave), and if it oscillates from 0 to 120V peak, the average voltage would be around 50% of 120V, or somewhere around 60V. 63.7 sounds like a perfectly reasonable reading to expect on a DC voltmeter.

Did you ever sit through that scope training course? Real basic stuff like this really needs to be understood before you can really hope to be able to repair a TV except by sheer luck...

[Username1]

The test point may contain information that can be interpeted 2 different ways. With a scope, you will see the entire wave, peak to peak. Your volt meter depending on design will read whatever it is designed to read, some will read and store peak, some will read average, and most will read some type of R.M.S. this is a area under the curve calculus derived average voltage. The schematic often details how all readings are taken, and in some cases even details the type and model instrument used, (or equiv.) is often written. Your RMS voltage will depend on the quality of your meter, and the old expensive ones did say what frequency you can use it and expect a certain level of accuracy. I don't know what new ones say in the instructions...

It is important to be sure your test equipment is reading correctly, or you will be chasing something that does not exist. A calibrated ebay piece of equipment means squat unless you do a little checking to be sure it really is what it is....

If tp5 is not reading correctly, your problem may be right there, everything very near that point needs to be checked.

Funny thing about man made stuff.... Sometimes one model of something all have the same problem. So don't overlook something just because you got a replacement somewhere.... Go by what good troubleshooting skills are taking you towards.

[TinCanAlley]

Originally Posted by N2IXK

The 63.7V is the DC voltage you should read if you measure that point with a DMM. The 120 Vpp is the amplitude of the AC waveform present.

The waveform looks to be roughly 50% duty cycle (pretty close to a square wave), and if it oscillates from 0 to 120V peak, the average voltage would be around 50% of 120V, or somewhere around 60V. 63.7 sounds like a perfectly reasonable reading to expect on a DC voltmeter.

Did you ever sit through that scope training course? Real basic stuff like this really needs to be understood before you can really hope to be able to repair a TV except by sheer luck...

Yep, I watched it. I was pretty much on the right track and just needed a few visual instructions to understand the rest. I can now do all the basics and am learning more each day.

[TinCanAlley]

Originally Posted by Username1

The test point may contain information that can be interpeted 2 different ways. With a scope, you will see the entire wave, peak to peak. Your volt meter depending on design will read whatever it is designed to read, some will read and store peak, some will read average, and most will read some type of R.M.S. this is a area under the curve calculus derived average voltage. The schematic often details how all readings are taken, and in some cases even details the type and model instrument used, (or equiv.) is often written. Your RMS voltage will depend on the quality of your meter, and the old expensive ones did say what frequency you can use it and expect a certain level of accuracy. I don't know what new ones say in the instructions...

It is important to be sure your test equipment is reading correctly, or you will be chasing something that does not exist. A calibrated ebay piece of equipment means squat unless you do a little checking to be sure it really is what it is....

If tp5 is not reading correctly, your problem may be right there, everything very near that point needs to be checked.

Funny thing about man made stuff.... Sometimes one model of something all have the same problem. So don't overlook something just because you got a replacement somewhere.... Go by what good troubleshooting skills are taking you towards.

The scope was calibrated by Teletek using N.I.S.T. standards and certified by them. I have a certificate of calibration. I also get a free calibration within one year, but they're up north and I don't know how practical it would be shipping to and from.

Okay, so how about this. I have tested it on DC and it reads correctly. For AC, can I check an outlet? I have a meter that plugs into the outlet and shows the voltage. It has an outlet to plug things in and measure wattage, etc. Can I use the scope to see if it reads the same AC voltage as the meter? Would also be interesting to see how noisy the AC line is.

[jr_tech]

Originally Posted by TinCanAlley

Can I use the scope to see if it reads the same AC voltage as the meter? Would also be interesting to see how noisy the AC line is.

I would *NOT* try that...I believe that the scope chassis and therefore the probe "ground" clip are indeed connected to earth ground through the power cord... if you happen to connect the probe ground clip to the "hot" side of the line sparks will fly !

jr

[dtvmcdonald]

As to AC line voltage: if its a two-channel scope, you get two identical probes
and use one of them on the hot side, one on the cold (not ground wire) and
use the difference setting. You don't attach the ground lead of either probe
to anything ... the scope case is connected to the power line ground already.

[Username1]

You really need to be careful anytime you connect any plug in test equipment to ground on anything you are working on. You should always use a battery volt meter and check ground on test equipment to ground on your test subject item, If there is a wiring inconsistency either in your bench items, or house wiring, you will see 120v across the two grounds, if you then connect them, yes you will have your own semi-private fireworks show.

[TinCanAlley]

Okay, there seems to be an issue with the "Trig view" button. When I measure AC in the 50V / Div setting, it covers 7 divisions. I know that's not correct. So when I push the "Trig View" I get the proper waveform and the right number of divisions (2 1/2 divisions). That same button, if you pull it, is the bandwidth limiter. If I play with the button, it eventually shows the proper waveform height. If I touch it again, it gives the expanded waveform again. It's like it's dropping from 50V/div to the next lower setting.

It could be a dirty contact in the switch. I'm going to contact the company I got it from to see if it's okay to give it a shot of Deoxit. If I can't get it going I'm going to have to send it back for repair.

[TinCanAlley]

Originally Posted by Username1

You really need to be careful anytime you connect any plug in test equipment to ground on anything you are working on. You should always use a battery volt meter and check ground on test equipment to ground on your test subject item, If there is a wiring inconsistency either in your bench items, or house wiring, you will see 120v across the two grounds, if you then connect them, yes you will have your own semi-private fireworks show.

So I should put the meter between the ground of the chassis and ground of the probe and look for voltage? If I see voltage I should reverse the plug to see if it makes it better? How much is acceptable?

[andy]

...

[TinCanAlley]

Originally Posted by andy

Actually, that is correct. The wall outlet is supposed to be about 120v RMS. You're looking at peak to peak voltage on the scope. Divide the p-p voltage by 2 to get peak voltage (350v p-p is 175v peak). Divide the peak voltage by the square root of 2 to get RMS (123.7v RMS in your case).

Also, you need to know that most AC volt meters are designed to read AC voltages as RMS, but that it only works for a pure sine wave like the AC power line. For anything else (like a square wave), it will be wrong unless it's a "true RMS" meter.

Well then I feel better. Now I need to get back into the set to recheck the horizontal sweep as the PP I got put it at 160V and the Sams says it should be 120V. Since the board is driven by the 125V B+, I don't see how it could be putting out a 160V waveform.

Fun stuff, fun stuff.

[TinCanAlley]

Originally Posted by jr_tech

I would *NOT* try that...I believe that the scope chassis and therefore the probe "ground" clip are indeed connected to earth ground through the power cord... if you happen to connect the probe ground clip to the "hot" side of the line sparks will fly !

jr

I was just going to touch the tip of the probe to the hot side and leave the ground clip disconnected.