Sylvania 336mu
 

I powered up this chassis today new problem, I have a thin bright line acroos the screen no picture, I checked HV its there my voltages to tube are ok, Have I lost the deflection circuit?

Horizontal line means loss of vertical deflection and vise versa. Check the caps first.

The "vice versa" condition (vertical line) cannot occur in modern TV deflection systems. The only way a vertical line could ever appear on the screen would be in a very old TV (pre-war to about 1950), if the set used an RF high-voltage system; the flyback HV system, used in all TV sets from the '50s on, is set up so that if the horizontal sweep fails for any reason, the high voltage to the CRT 2nd anode goes with it.

You are correct, however, as to the vertical sweep. Failure of the tube or of any of the components in the vertical sweep stages will stop the vertical deflection, resulting in a horizontal white line across the width of the CRT screen. Turn the brightness all the way down to prevent burning the phosphors.

You are correct as far as TUBE sets go....but in a SOLID STATE deflection system...it IS possible to get a no horizontal condition WITH a vertical line DOWN the screen...for a short time--before the H-out transistor WILL blow, from unbalanced loading without the yoke.

Thanks that is what i thought, on the hunt again

In some tube sets it is possible if the horizontal yoke is disconected most need the yoke to tune the circuit to work properly, but some can still muster a line

I think i checked that but will look again, strange thing day before ok next day no raster.

sylvania deflection loss
 

I am giving you a update and hope i am replying correctly, This set is Sylvania 336m. I am supplying chassis with 117v line load is 2.56 amps.I have sound and a horizontal line across CRT, I checked the voltage on tube 12AU7 which if I read the print correctly is the oscillator section. Pin number 1 on the photofact shows 235v, on that pin I am reading 333v.Photofact shows pin number 6 at 135v, my reading on pin 6 is 113v. This is with line voltage at 117v which the photofact refers to when checking voltages. This chassis has been recapped and new electrolytics, I checked the electrolytics again and they show good. After I had recapped this set I had deflection and then is slowly went to horizontal line only. Thank you

Don't worry too much about voltages within 20% of correct (such as the pin 6 reading) those should be within tolerance.

Which stage is the 12AU7 in? A horizontal line on the screen is a symptom of Vertical deflection failure...So you should be scrutinizing the voltages and components in and around the the Vertical multivibrator/oscillator, output tubes.

Here is a quick test that can clear the vertical deflection transformer and yoke (the most rare/costly parts). If you have a variac disconnect the primary of the vertical output transformer, and connect it to the variac. With the set on slowly crank up the output voltage of the variac, and if that line expands vertically before you hit max output, then your yoke and output transformer are functional....If the line don't expand disconnect the vertical winding of the yoke connect it to the variac, and repeat.

Really....? On the surface I think it would work.... But I can't see going above
20V..... Anywhere near max output with only the unit's fuse could put
2 - 3 or more amps into it.... Cooking it for sure I would think....

Have you actually done this....?

At the 20V I would be looking for just a small deflection, not full screen.....

-------------

A higher voltage on the plate usually means the tube is turned off.... not working....

.

Not direct to the yoke, but the primary of the transformer should be able to take it since the output tube should create a few hundred volts AC across it. The goal is not to hit max variac output, but rather to get 1-2 thirds deflection to confirm the transformer and yoke work....Once decent deflection is obtained more voltage serves no purpose.

sylvania deflection loss
 

The 12AU7 I am referring to is the horz oc and horz discharge section, I had thought the voltage being 100v higher on that pin was causing a problem elsewhere in the set, I will check the vertical section next. I know the Vertical output tube pins read correct voltage.

Not to be insulting, But you have been intermixing Horiz, and Vertical
issues, or tv parts. Just to be clear, look at the picture, and tell
everyone which line type you are having.... Then lets go on from
then......

.

Thanks I miss read

sylvania deflection loss
 

ok the Vertical section tube 12AU7 which is vert osc and vert disch pin 1 photofact shows 160v I read 112v. Pin 2 on photofact shows -74v, I read -12v. Now the vert osc side of tube 12AU7 pin 6 of photofact shows 05v I read 155v on pin 6. Pin 7 on photofact shows -74v I read -12v on pin 7

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.

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

sylvania deflection loss
 

this is the continuation of schematic from the vert osc transformer

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....

.

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

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.

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.

Tom, I did as you instructed jumping the pin 2 no deflection

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.

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.

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.

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.

What tube # is it? I might have something here in somethg..

Tube is 27RP4

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 ! !

.

Thanks for help, I have to make adjustments to video and its pretty messed up great sound. Can not get picture to focus enough to see it clearly

Contrast
 

I have got the picture on a test CRT, seems the picture not very bright.Have I got used to new LCD tv's and forgot how much dimmer pictures were on old B&W tv?

I don't have a feel for the relative brightness, but the max available brightness depends on the amount of HV you have and the CRT emission capabilities (ie how good the CRT tests), and how well the circuits driving the neck are working (and position of the ion trap if present). On most sets made after 1952 you should be able to watch the set in a sun lit room (pix may not be optimal in this case) as long as the sun is not directly shining or reflecting onto the screen....Less brightness than that indicates significant miss-adjustment, wear, or correctable defects.

It looks like you have very weak contrast. Is the contrast control maxed and have you adjusted the AGC control properly?

I have the contrast turned way down, it washes out the pic if I go higher. The AGC pot does not seem to be working because when I adjust it I see no difference,

If you crank the AGC from min to max you should go from blank raster to weak contrast to strong contrast to wildly excessive contrast/loss of synch to negative video and or useless chaos on screen. If you don't have that then the AGC circuit is not properly functioning.

More contrast should not wash out the picture, less should. More should make the darks darker relative to the brights areas. The brightness control should normally be able to washout the image when maxed out.

Have you ever put that test CRT you're using through a proper CRT test using a CRT tester? If it is in bad shape it could be contributing to things.

Hi !

Before going into any further guessing about a possible cause of your problem.....
I think we should clarify what you are seeing..... You say you have the
contrast turned way down, (to the left) but to turn it up, washes out the
picture.... To me washing out the picture means almost no contrast, as if
the picture were almost all gray, no sharp black and white....

This action is almost the exact opposite of what we expect when turning
either the contrast knob to the right (up) or turning the AGC knob up.....

Turning either of those knobs should produce an almost "overloaded"
picture, too much light for the bright areas, and too much dark for the
dark areas.....

When you turn the contrast "up" would you still say that the picture gets
even less contrast...?

.

What I am seeing is if I turn contrast up (making it brighter) it washes out picture.If I darken it (less bright) I can see it clearer. The AGC does not seem to effect picture adjusting to right or left. The test CRT was supposed to be new old stock and I tested it and it showed good emission. I do think the AGC circuit my not be functioning properly very little response from adjustment on back of chassis.

Ok, well the AGC is a kind of Automatic signal amplifier adjustment, so with
no response from that control, you most likely have - or possibly have some
signal loss along the IF section..... But before we go there, what is the quality
of the sound....? Good full tone, loud, or is it also kind of washed out, and
have some noise in it.....?

First, you should leave the set on, and locate the tubes in the tuner, and IF section
and first, second Video IF and wiggle these tubes in their sockets, tap with a wood
stick the circuit board, or chassis near these tubes, and look for any noise, or
jumping in the picture..... Possibly a momentary better picture....

.

You sure you don't have the brightness and contrast controls mixed up?

Contrast should not change the average brightness.

I could of done that, I am using sound control pot to make it brighter which washes out most of pic i can still see it but very dim so I turn brightness all the way down. Contrast adjustment helps a little.Definitely AGC not responding I can turn it all the way right or left just get a little flicker at end of travel of pot. I have very good sound quality. Possible AGC
pot is bad it feels like it has no resistance when turned.