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HP 1707B Horizontal deflection issue

jdmaker

Mar 19, 2023
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I have a HP 1707B scope that has what first looked like a triggering or horizontal sweep issue. But, I found that even with the scope set to external horizontal input with no signal there is about 1/2 division of horizontal defection. Also, I do not see any voltage across the horizontal plates. Anyone know what could cause this issue?

Thanks
 

kellys_eye

Jun 25, 2010
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I do not see any voltage across the horizontal plates. Anyone know what could cause this issue?
Lack of horizontal drive...... ok, it's 'obvious' but we'd need a schematic to give you somewhere to start looking.
 

Delta Prime

Jul 29, 2020
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If memory serves push pull deflection amplifiers are used to manipulate the electron beam in low end CRT Oscilloscopes.
Without a schematic a reasonable educated guess could be made that all of the circuit stages in the horizontal amplifier, right, left plates or in the vertical amplifier, up, down plates, are almost identical as in, the inputs are 180 degrees out of phase , simply swap out the transistors from the left plate amplifier circuit to the right plate amplifier circuit. If the transistors you switched are good, then there will be no change in the deflection plate until you switch a bad transistor. Then the voltage difference at the plates should reverse.
Easy peasy lemon squeezy.
 

jdmaker

Mar 19, 2023
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Here are some picture to better explain the issue. The picture below is with a square wave applied to the scope. The vertical transitions are wide and blurry.
HP1707A_SQU.jpg

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The picture below shows the scope set to EXTERNAL HORIZONTAL INPUT with NO SIGNAL applied. There should just be a dot on the screen. But, I have a line about a half of division long. Something is causing horizontal defection and it's not from the defection plates. Under these conditions there is no voltage across the plates... like there should be with no input but yet there is still horizontal defection. What else can cause horizontal deflection?

HP1707B_Hor.jpg

Thanks!
 

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  • HP1707A_SQU.jpg
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jdmaker

Mar 19, 2023
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Ok, I just tried adjusting the FOCUS and ASTIGMATISM controls for like the fifth time and I was finally able to get a dot instead of the line on the screen. Don't know why it worked this time. Maybe "exercising" the pots clean them up.
 

73's de Edd

Aug 21, 2015
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Sir jdmaker . . . . .

Eeeeeeeeeew
. . . . . 'dat do be one old Hoooooolet Plastered . . . . . circa . . . . .early '70ish. . . . . . .BUT . . . I still have a 1740 and an even older 130 rack mount, that I still can use.

Looks like you need to check the incoming voltages at the VIOLET amd PINK blocked area mark ups and confirm if all are present and ok, then move to the 12 transistors and test their CBE voltages, as are given.
Lastly the individual testing of all of their junctions if no fault is already pin pointed by now.

SELECT TECHNO REFERENCING . . . . . . of most suspicioned area . . . . .



H.P. 1707B Scope Hoz Driver Board.png

ADDENDA . . . . . . . made just now, after having seen that you last added on 2 photos.
I see that you DO have hoz deflection, but with the shaky and blurry display and the lateral modulation of the phosphor dot with no sig in . . . . check the 60/120 ripple that might be piggy backing on one of your DC power supplies . . . . from deteriorated filters . . . that could cause it.
#2 . . . . . and THEN . . . . . . . . . your final, with the astigmatism and focus adjustments.

73's de Edd . . . . .

Two gold fish were moved from a pond into a new tank . One says, " How do you drive this thing? "


.
 
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Delta Prime

Jul 29, 2020
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Two gold fish were moved from a pond into a new tank . One says, " How do you drive this thing? "
1679286942373.jpg
Don't know why it worked this time. Maybe "exercising" the pots clean them up.
Something tells me you might not know how to read schematics. But that's okay but I am concerned about you perhaps trying to open up the oscilloscope. Have you ever dealt with high voltage before you know it's very dangerous I would consider taking it to a repair shop looks like an easy fix an inexpensive.
 
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