Are these things I should consider bad - Page 8 - Videokarma.org TV - Video

TinCanAlley · #**106** 10-02-2013, 05:14 PM

Quote:

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 · #**107** 10-02-2013, 05:21 PM

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?

Username1 · #**108** 10-02-2013, 05:29 PM

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 · #**109** 10-02-2013, 05:46 PM

Quote:

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.

TinCanAlley · #**110** 10-02-2013, 05:52 PM

Quote:

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 · #**111** 10-02-2013, 06:20 PM

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 · #**112** 10-02-2013, 06:37 PM

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.

TinCanAlley · #**113** 10-02-2013, 06:42 PM

Quote:

Originally Posted by 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.

I'll check all the points of the 125V from the point it leaves the transformer to various points using both DMM and scope.

I've attached a pic of the power supply section.

Username1 · #**114** 10-02-2013, 06:53 PM

Well, that 16v is generated in the coupling transformer. So for that to be too high, all other stuff being good, the primary has to be getting too large a signal, and you have evidence of that. So the thing to do is try and figure that out....

Is the power supply too high?

or

is there something making the primary signal too high?

I am leaning towards double checking the power supply, that 125, and what else may be associated with it, be it larger or smaller sources that may be there.... Please post the power supply section when you get a chance, ( Isee it thanks ! ) and measure the different sources available....

And just in case the power supply is pumping out too much voltage, lets limit how long you keep the set on to just 10 minutes or so during each measurement period.

Be careful when measuring the power supply, if its regulated, you don't want to accidentally short anything that will fry anything in there....

Username1 · #**115** 10-02-2013, 07:10 PM

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

TinCanAlley · #**116** 10-02-2013, 07:24 PM

Quote:

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

I'll do these next. I've been going over the 125V sources and they all show up as 129V. The DMM and scope are in agreement there. I also checked the 125VAC and did the math. The DMM showed 128V and the scope had 126V after doing the calculation given me for RMS.

I'll let you know the voltages asked for.

jr_tech · #**117** 10-02-2013, 08:08 PM

Quote:

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

I have been looking at the schematic and scratching my head over that cap... what does it do? Is the transformer somehow set up to be a constant voltage device?

jr

TinCanAlley · #**118** 10-02-2013, 08:34 PM

Quote:

Originally Posted by Username1

If that 125v is too high, look at c248 in the power supply.... 3.5mfd off the 235v leg on the transformer....

128v at the diode there just before the filters and choke.

Also q212 voltage regulator.... Take a test of the 23v source on the scope, and dmm, that voltage should be spot on, and across that zener diode, should be 24v spot on....
good test for your dmm and scope for dc....

The voltage to and from the regulator (Q212) is correct. I get 23.4V and 24V. Each is only off by .2, but that's most likely my DMM. The scope also showed the proper divisions from baseline for DC.

I thought that 3.5uf canister wasn't soldered in, but it is. It's also 440V. What size resistor will I need to discharge it?

andy · #**119** 10-02-2013, 08:39 PM

...

TinCanAlley · #**120** 10-02-2013, 08:57 PM

Quote:

Originally Posted by Username1

128v at the diode there just before the filters and choke.

Okay, on the AC side of the diode I get 131VAC and on the other side I get 131VDC. According to the schematics, the Red-Blk is supposed to be 100VAC. So if I test directly to where the Red-Blk connects, I shouldn't seem much more than 100VAC, right?

Here's a pic of the red-blk connection and the 3.5uf 440V cap. If you think this cap needs to be checked, let me know. I'll have to unsolder one of the leads.