Are these things I should consider bad

[TinCanAlley]

Okay, so how do I go about checking my scope for proper AC voltage calibration? I just tested another point that is supposed to be 170VPP. With the scope on 50V/Div I get almost 4.5 divisions. That's almost 225VPP. I checked with my DMM and it reads as 130VAC. I check the one next to it that was supposed to be 20VPP and it showed as 25VPP. The DMM had it as 16.9VAC. I'm pretty sure my DMM isn't showing the exact voltage (everyone keeps writing about RMS and such).

I need to know if there's something wrong with my scope. If so I need to return it to be fixed.

Thanks!

[andy]

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[TinCanAlley]

Originally Posted by andy

The first thing to do is to check the calibrator output on the front of the scope. You should see a perfect square wave with the amplitude specified. If the top and bottom is curved, then adjust the probe (this applies to X10 mode only).

Comparing things to the Sams folder is a bad way to check your scope for accuracy. Sams often have mistakes, many of the circuits in the TV (which isn't working properly) have wide tolerances, and your 465 probably has 10 times the bandwidth as the one Sams used (meaning high frequency signals, and fast pulses will appear larger on your scope).

Yes, the calibrator is 1V and with the probe in 1x and .5V/Div I get a perfect square wave. I then put the probe in 10x and 50m/Div and get another perfect square wave.

See my other post where the 125VAC shows up as 325V on the scope.

[Username1]

Who makes your dmm, where did you get it, and how much$.

The pins at the horiz board, tp5 is 123, next one down is 124, and bottom is 6. The schematic you posted is not that clear, and gets worse when I blow it up, so If you check the voltages at each one of these points, are they correct, higher, lower?
You need to post "posted" value as in (sams) and actual, (what you read), How DMM Scope.

How about the wave form at the base of the HOT? is it good?

The diode, and cap in the collector circuit closest to the HOT on the schematic? they good?

Does the schematic detail the meter used ? for sams voltage readings?

[TinCanAlley]

Originally Posted by Username1

Who makes your dmm, where did you get it, and how much$.

The pins at the horiz board, tp5 is 123, next one down is 124, and bottom is 6. The schematic you posted is not that clear, and gets worse when I blow it up, so If you check the voltages at each one of these points, are they correct, higher, lower?
You need to post "posted" value as in (sams) and actual, (what you read), How DMM Scope.

How about the wave form at the base of the HOT? is it good?

The diode, and cap in the collector circuit closest to the HOT on the schematic? they good?

Does the schematic detail the meter used ? for sams voltage readings?

My DMM is a Craftsman and is about 13 yrs old. (See pic)

I will check those other points and post their voltage and the Sams voltages.

I was told that the diode on the HOT had to be good since the HOT would be dead if it wasn't. As for the capacitor, I didn't test. Can I use an ESR meter to test it? I believe if I pull the hot, I should be able to test that capacitor without disconnected a leg an it should be pretty much isolated at that point.

I will put the set on her side and remove the bottom to get the waveform of the base of the HOT.

[Username1]

Hopefully, this step is completed already..... Remember the scope videos we talked about looking at earlier.

[TinCanAlley]

Originally Posted by Username1

Hopefully, this step is completed already..... Remember the scope videos we talked about looking at earlier.

Yes, I've sat though hours of videos including the 2hr+ training. I truly believe I'm doing the settings correctly.

How about I do the horizontal sweep again and when the 170VPP waveform comes up I take a picture of the entire front of the scope so all the settings can be seen?

[Username1]

Your camera will adjust to the brightest items, so set the trace very dim, and the graticule very dim as well. You can set the sweep to display one or two cycles of the pulse, just turn the knob to what you want. Set the vert volts/div. so you get close to a full screen, it will be easier to read that way..... you know 3 to 4 divisions is more accurate than say 3/4's of a cm..... or 3/4's division...

[TinCanAlley]

Originally Posted by Username1

Your camera will adjust to the brightest items, so set the trace very dim, and the graticule very dim as well. You can set the sweep to display one or two cycles of the pulse, just turn the knob to what you want. Set the vert volts/div. so you get close to a full screen, it will be easier to read that way..... you know 3 to 4 divisions is more accurate than say 3/4's of a cm..... or 3/4's division...

Okay, let's see how this goes. Here's a pic of what Sams has for T5 and what I got on the scope w/full face of scope so you can verify settings. If something isn't clear in the pic, let me know and I'll fill you in.

EDIT: Added a third pic as you can't read the face without the flash lighting it up.

[Username1]

ok, so its about 3.5 divisions, which v/div are you using? what does it work out to be...?

just under 175v if you are using 10x probe?

[TinCanAlley]

Originally Posted by Username1

ok, so its about 3.5 divisions, which v/div are you using? what does it work out to be...?

just under 175v if you are using 10x probe?

That is correct.

[Username1]

Lets try something a little different....

Measure that same spot using d.c.
1. put the scope on gnd. using that 3 position switch input for channel 2
2. move the display trace to a lower line on the grid, using the position knob.
3. turn the 3 position knob to dc, then measure the 125v source, see that it reads 125.
4. check tp5 again, see if it saturates at what the 125v source is...

[TinCanAlley]

Originally Posted by Username1

Lets try something a little different....

Measure that same spot using d.c.
1. put the scope on gnd. using that 3 position switch input for channel 2
2. move the display trace to a lower line on the grid, using the position knob.
3. turn the 3 position knob to dc, then measure the 125v source, see that it reads 125.
4. check tp5 again, see if it saturates at what the 125v source is...

I followed each step and got the attached pics. The DC of the 125V source (B2) reads just under 140VDC (with my DMM I get 130VDC). When I then check the DC of T5, I get 175V. This is with the same v/div as the previous test (50V/Div).

[Username1]

At this point, I am going to assume your 125v source may be 140V.
You are also seem to be having different readings on your two pieces of test equipment. You will have to figure out how you want to deal with that.

I would check through the low voltage power supply where the 125v comes from, and check through the voltages listed there, there should be 4 or 5 low supply spots you can test, Use both your dmm, and the scope on DC, see which one you are more willing to trust. If that 125v is way off, then your HV may be using too much power and creating that ring just because the voltage is too high....

If you can, please post the power supply circuit, lets see if its a doubler with a possible bad part making too much voltage.....

I'm sorry to be casting doubt on your test equipment, but I have been there before, it may seem to be a stupid step, but we have to follow the evidence we have to find the real problem.

[TinCanAlley]

Here's my results with the base of the HOT. I'm attaching the Sams waveform (not very clear) and mine. I had my scope set on 2V/div and as you can see it filled the display. It's about 16V. The Sams has it as 7V.