#1
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Zenith 852-120 HV probe repair
Forget it. I no longer have the probe anyway, and I'm not going to fight with anyone, especially with hotheads who have offended me repeatedly and without cause.
There are only two people who help me regularly anyway, and I don't need the board to contact them. Last edited by Jon A.; 09-22-2017 at 03:44 PM. |
#2
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Shouldn't be any problem using 1W metal oxides. Couple of questions - Did you suspect the probe of reading high, or low?
In your schematic, you show a shunt across the paralleled 30K and 33K resistors. Is that shunt supposed to be there? |
#3
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I was just about to say... that shunt would negate the 2 resistors on the far right. In fact... why are they in parallel? Wouldn't that be like... (33+30)/2 = 31.5kohm? Oddly specific value. You sure your schematic is right?
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#4
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...
Last edited by Jon A.; 09-20-2017 at 02:56 AM. |
#5
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Your math is wrong (should be ~15.7K). Two resistors in parallel are Req=(R1*R2)/(R1+R2) Three or more are Req=1/( (1/R1) + (1/R2) + ... + (1/Rn) )
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
#6
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Last edited by Jon A.; 09-20-2017 at 02:57 AM. |
#7
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Only if they are both rhe same value.
jr |
#8
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Last edited by Jon A.; 09-20-2017 at 02:56 AM. |
#9
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The equation simply says that 1/R = 1/R1 + 1/R2 and to continue adding them up for as many resistors (n means number of resistors) as you have in parallel, that's all that ....+ stuff in the mathematical series means. Do you have a calculator that inverts?
My guess is that the shunt and the two resistors across it are to be used in calibration and can be clipped out if necessary by the calibrator if the calibration pot does not have adequate range. Why do you think the meter reads low, have you measured a known voltage standard? jr |
#10
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The only reason I can think of for the shunt is that maybe this assembly was also used in another probe model where the shunt was replaced with a switch to change the meter full scale reading.
BTW, your schematic does not show the huge resistor that is in the probe body. |
Audiokarma |
#11
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Another thing, the 2.2M is apparently only a current-limiting safety provision and does not affect calibration.
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#12
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It was 1 am dude, cut me some slack.
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#13
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Last edited by Jon A.; 09-20-2017 at 02:57 AM. |
#14
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Quote:
jr |
#15
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I've seen videos made by Doug in which his meter measured accurately. Mine wouldn't even register on a tripler focus tap. Only saying this because the mods ignored my delete request which doesn't surprise me or help my opinion of them. It's not what you know but who you know.
Nothing like having a know-it-all bully around to pick apart my efforts. Now, can the patronizing attitude and go back to tube town. Last edited by Jon A.; 09-20-2017 at 03:58 PM. |
Audiokarma |
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