Checking B+ Voltage

Kyrosfear

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Gentleman,
For you veterans, this post will be redundant and very basic. However, I think it will help some rookies out there because the topic of testing the B+ voltage is often spoke about as if everyone already knows how and where to do it. Even in the manuals, the lingo typically assumes you have some technical knowledge, so they simply tell you the location(s) and pins for testing. The problem is, this is often insufficient for someone nervous about testing circuits on a live high voltage monitor. Especially when you have never done anything close to this before, and are aware of the damage you can do to yourself or the monitor by making a mistake. When I was first learning to test B+ voltages, I had no idea how to do it, and this forum did not have a simple explanation for the process directed to someone that knew nothing about it. This is a detriment to those of us who are ignorant of these processes, and not the forum or its members. Nor did a Google search help, because the approach was the same. You could find chassis locations and voltage ranges, but not a step by step.

So, fellow newbies, keep this in mind when testing B+ voltages…..
You need a multimeter. Set it to VDC (I have been told set to 500v if you have it on there, but 200v will suffice). Place the black lead to a grounded source. This can be any heatsink on the chassis, or simply connect it to the chassis frame itself (preferred). Now you take the red lead, this is what you use to make contact with the location the manual specifies. Most of the monitors I personally work on are WG k7000s because most of my games happened to have those in them when I bought them (and they are extremely common). A good location to test on these chassis is "R301, which is the large ceramic resistor mounted to the side of the chassis" (member KevinMullins taught me this, thanks Kevin).

Ground the black lead, then place the tip of the red lead on one of the ends of this R301 resistor. There are two ends, one will give you a high reading of approximately 145v, but the other one, which is the important one, should read approximately 130v.

Although different monitors have different B+ testing locations, and usually multiple locations at that, the idea is the same and I hope this helps break it down a little more than you typically find with a search.

Kalamath's suggestion below is an excellent one. It is much safer because it saves you from having to put a hand near the danger zone.

The picture below was provided by Buffett on another thread. He provides a lot of suggestions regarding chassis repairs, and will even repair your K7000's if you cannot fix them yourself. Thank you Buffett.
 

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I like to use a jumper with alligator ends to clip to the B+ test spot, and my multimeter probe. This way I can clip on to it before powering up and not have my hand in harm's way. Also handy to do with the ground too, so you have both hands free to adjust B+ if necessary.
 
i want to make a video on how to do this someday but i do not have a camera to do it with.

here is a larger pic of the one above.

k7000bchart.png




if anybody needs their K7000 repaired please shoot me a PM.

Peace
Buffett
 
In addition to the test locations, what should be done if the voltage is off? I know on the U5000's and 20EZ's there are adjustment POT's, not sure on K7000, WG4900, and WG4600's as these are the monitors I deal with.
 
How bout a pic specifying how to check b+ on an Han polo 25"?

i do not work on theses chassis at all. ( they are the devil bobby boucher )
i usually trash the polo chassis and toss a K7000 on and change the yoke if needed on the tubes it's for the better.

In addition to the test locations, what should be done if the voltage is off? I know on the U5000's and 20EZ's there are adjustment POT's, not sure on K7000, WG4900, and WG4600's as these are the monitors I deal with.

if the VR is new and known to be working on theses chassis. and they are not in shutdown. it is usually resistors that are out of spec. that make the B+ off a tad.

i do not know which ones to check as i have never had a low or high B+ that was not a major part that i had to replace.
i guess i have just been real lucky with the chassis i have had.

if i find out i will let the world know so we know where to look.


Peace
Buffett
 
Old thread I know but Buffet said something that maybe answers my question...

if the VR is new and known to be working on theses chassis. and they are not in shutdown. it is usually resistors that are out of spec. that make the B+ off a tad.

Peace
Buffett

Ok so following on from that, I acquired a (currently non-working) 19" K7000 board. As you can see in the picture, someone soldered a regular carbon 1.8K Ohm resistor in parallel with R301. According to my parallel resistor calculator, that equals 196.04 Ohms; way off the 220 Ohms listed for R301 in the K7000 specs.

I once saw this done somewhere else on another 19" K7000 too. So CRT gurus... what's the deal here... Is it a bad hack or a legit mod? I have yet to hook the board up to the tube and add power so I can measure the resulting B+; maybe I shouldn't until I fix the resistor situation.

Edit: Measured the resistance in-circuit of the resistors combined and it came out to 196.7 Ohms. This also means that Ceramic R301 must be very close WG's specs of 220 Ohms. So this does seem pretty bad to me. If someone needed to lower R301's resistance that much, maybe this is indicative that the B+ voltage measured on the input side of R301 was already low? I.e. problems elsewhere I should look for.
 

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that is a well known factory mod on hundreds of chassis 19" and 25".

there is no explanation from wells why it was done.

it is another one of the 47 different revisions wells made to the K7000 to improve or fix an issue they had.

Peace
Buffett
 
that is a well known factory mod on hundreds of chassis 19" and 25".

there is no explanation from wells why it was done.

it is another one of the 47 different revisions wells made to the K7000 to improve or fix an issue they had.

Peace
Buffett

Wow, that is *good* info, cheers!
 
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