#16
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If you can, please post the vertical circuit section of the schematic . That will help us see possible causes of the problem. You have replaced all caps that are not micas or ceramic in the circuit which is good...But have you tested the vertical stage tubes, and the resistors in those stages? If not, then that is the first step to take in moving forward.
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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 |
#17
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sylvania deflection loss
Yes I checked the tubes and resistors that were out of tolerance replaced. I hope the attached file helps. I know its hard to diagnose something over a forum.The image cut off tube identification on right is 6L6GA tube on left is 12AU7
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#18
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sylvania deflection loss
this is the continuation of schematic from the vert osc transformer
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#19
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If you have confirmed the vert output stage transformers are ok, simply
by checking the resistance across the windings that are printed in the schematic, then it's possible the osc is just not running.... Don't forget the vert. yoke winding too... The timing cap and resistors with the red dots are pretty critical, you should be sure these parts are in good shape. New or at least checked, and you know they are good... and correct values. Do you have plate and screen voltages on the vert output tube...? Around 300V ??? Also the vert lin. control pot, and that r111 I think it is that goes to ground after the pot, please check it too.... .
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Yes you can call me "Squirrel boy" Last edited by Username1; 04-10-2015 at 10:25 AM. |
#20
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Yes I had over 300v on Vertical output tube will check again what you show. I know oscillator is not running I can not hear it.Thanks
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#21
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The vertical buzz is most often caused by the output transformer. I'd do the variac test on the output, then if it shows deflection go back to the oscillator.
If you're squeamish about the variac test, then here is another idea connect pin 2 of the 12AU7 to the non-grounded heater line through a large film cap (something like .047 to .47 should work) and see if you get any deflection. If you do it proves the output stages are working, if not then you need to work on the output stages first. Everything before (read left of) C87 should be ignored for now. That stuff is part of the synch separator, and you should have vertical oscillation and deflection even if C87 were to be cut out of the circuit.
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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 Last edited by Electronic M; 04-10-2015 at 12:03 PM. |
#22
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Thanks Tom I will do that, I checked everything Squirrel Boy suggested everything was to spec.I checked the deflection coil vertical and horz ohms were to spec.
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#23
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Tom, I did as you instructed jumping the pin 2 no deflection
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#24
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Okay that tells us that there is no functional signal path between the grid of the second stage of the 12AU7 osc tube and the yoke which is a problem...Since if we assume the oscillator is working (or is later made to work) in the current state of the circuit any osc. signal there is not able drive the yoke as it should.
Try pin 5 on the output (the grid). This test is supposed to be a signal injection/ substitution test. It uses 6.3V@60Hz from the heaters to approximate the oscillator drive signal (which is assumed to be absent). This signal injection may not yield much deflection, and it will not be synched or linear, but it should let you know if the output stage is working. If there is no deflection achieved from driving the grid of the output tube, then you will want to do the variac vertical output transformer drive test I outlined in a previous post since either the trouble is at the tube or in the transformer/yoke system if grid drive does not yield deflection. If you have ever trouble shoot a AA5 radio with no reception problems using a RF-AF generator, then you can think of this as the same basic idea only with different signal characteristics.
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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 Last edited by Electronic M; 04-10-2015 at 01:47 PM. |
#25
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Tom I found the problem, I kept looking at a resistor from the vertical output transformer that had been replaced in the past thinking it seemed small for the load 315v, Because my voltages were wrong in that area.I checked the photofact and sure enough it was supposed to be a 3300 ohm but a 330 ohm had been inserted, I replaced it and my deflection came back.When i got this set I never had a picture because CRT was bad.I have a replacement CRT but it has electrostatic deflection.
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Audiokarma |
#26
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Are you SURE the tube is bad? Likely it is just ASLEEP...after many decades of non-use. Unless it has gone to air--I would NOT give up on the tube yet. Give the fil. about 7.5 volts for maybe 10 mins...and see if that wakes it up some.
I have repeatedly stated and will continue to do so...at LEAST 2/3 of old CRT's I come across are at least uesable. This includes a 7JP4 tube, and a predicta 21" tube I recently acquired. It is not perfect....but IS useable. both emissions and cutoff are good--after a wake-up. lfe test does NOT hold long though...but that may improve after time.....and good 21" predicta tubes do NOT come along a dime-a-dozen. They are NOT makin 'em anymore--NOR rebuliding them either--AFAIK--so we MUST do our very best--to use the CRT'S we come across. |
#27
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I put this on my 465 for a day it barely raises the needle on emissions and when I found this set it had a brightener on the tube. I would love to have a new one for sure. The Magnavox tube I have has good emissions same voltage it is electrostatic deflection instead of magnetic.I am going to hang on to the old CRT for a while and hope some day it can be rebuilt somewhere.
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#28
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What tube # is it? I might have something here in somethg..
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#29
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Tube is 27RP4
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#30
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It has to be this resistor..... in the pic attached....
I almost included this one in my list to check because of your grid voltage on those two tubes..... But I didn't because my book made that timing cap just look more like a better starting point...... Sorry..... Sorry I was out for most of the afternoon..... Good to see you got it working ! ! .
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