Horizontal Sweep Adjustment? - Page 2 - Videokarma.org TV - Video

zeno · #1 07-12-2015, 06:10 PM

Lets keep in mind what seems to be going on.
It seems when cold the pix has lots of lines.
This IS the hoz osc off freq. No question........
I assume as it warms there are less lines then the pix
comes in but is trying to float side to side & is very touchy.
First thing is to get the osc stable. Its probably a cap but
check all the resistors also. You can use freeze mist on the
caps. Just a little on one at a time. Too much can cause a
good cap to drift. After it warms back up move to the next cap.

After you get the osc stable if its still trying to move side to side
start checking around the diodes. Also there is a sample pulse
coming from the flyback to the phase ckt. Check that, resistors
are often stressed there.

If you can also post the hoz part of the schematic, a big help !

73 Zeno

Magnavox300 · #2 07-12-2015, 09:35 PM

Okay, I took a short video of the horizontal not locking in...

https://www.youtube.com/watch?v=7Gtz...ature=youtu.be

I also added the horizontal section of the schematic...

I have replaced all capacitors, less disc caps, and replaced most of the resistors, and left in those that measured correctly.

I believe the diodes are installed correctly, the cathodes, (banded ends), as common, both ends I soldered in the middle , where the middle leg of the dual diode was soldered in. Replaced the Horiz. Oscil. tube, a few times with different strong tubes. I also used Deoxit in the hor/hold pot.
Nothing seems to be working?

DaveWM · #3 07-13-2015, 07:17 AM

this is why a video is needed. Its not the AFC diodes at all. The horz osc freq is way off and no amount of sync signal will help. in other words this is not a "locking in" issue. Locking in implies a horz freq that is near the correct freq but not synced up to the video sync signals.

I would suggest you put back what ever you took out there just to reduce the number of variables.

DaveWM · #4 07-13-2015, 07:25 AM

Next would be did you try adj the horz osc coil. if its working this should change the freq (and number of lines to fewer until it can be momemtary lock anyway).

Did you confirm the values of parts that have been replaced so far. Did you replace the cap across the horz hold coil. Did you confirm the value of that cap, did you make sure the replacement cap that was used was good?

did you make and adjustments to the trimmer cap? any parts that have been replaced should be double checked to make sure you did not make a 10x error.

zeno · #5 07-13-2015, 08:41 AM

EXACTLY !!

If you try the hoz coil first clean the customer control R6b &
put it dead center. Put a flag (piece of tape) on your alignment
tool so you can count the turns & go back if need be.

73 Zeno

Quote:

Originally Posted by DaveWM

this is why a video is needed. Its not the AFC diodes at all. The horz osc freq is way off and no amount of sync signal will help. in other words this is not a "locking in" issue. Locking in implies a horz freq that is near the correct freq but not synced up to the video sync signals.

I would suggest you put back what ever you took out there just to reduce the number of variables.

Electronic M · #6 07-13-2015, 12:33 PM

If the osc. coil is soldered to the board check for cold or cracked joints at it's terminals, I've had troubles with board mounted coils developing bad joints and strange problems resulted.

DaveWM · #7 07-13-2015, 12:52 PM

other thing to check, the horz hold pot, make sure one side is not open. I like to use analog meters to check the action as well as the continuity of the end terminals. Analog meter movement is a better tool for evaluating the action, than a digital meter. confrim the voltage divider resistors that feed it as well. Dont forget to confirm ground connection of that pot as well.

old_coot88 · #8 07-13-2015, 03:15 PM

If the h.freq. coil has a hollow slug requiring a hex alignment tool ('diddle stick'), be sure the correct tool is used. Otherwise you'll fracture or split the slug making it impossible to turn.

Electronic M · #9 07-13-2015, 03:19 PM

Quote:

Originally Posted by old_coot88

If the h.freq. coil has a hollow slug requiring a hex alignment tool ('diddle stick'), be sure the correct tool is used. Otherwise you'll fracture or split the slug making it impossible to turn.

The correct tool is plastic. DON'T use a metal hex key on slugs EVER.

old_coot88 · #10 07-13-2015, 04:09 PM

Right you are. I shoulda mentioned the tool is plastic (nylon?).

DaveWM · #11 07-13-2015, 04:58 PM

hmmm if the sams says to clip a wire across the coil as part of the setup process, then I can presume its not really a horz freq adj as implied on the schematic, That plus the fact that it suddenly stopped working points away from the coil as an issue). a stabilizer is not the same as a freq adjustment coil.

You can try it but if you dont get instant changes the don't go tweeking. I really doubt its going to fix it.

Next up, was there any thing else that may have happened before it stopped working correctly? did you try to clean anything or do ANY other work or did you just turn it on and it stopped working?

I am presuming you already tried cleaning the pins of the sockets. The most likely error would seem to be in the feed back RC network OR the pot opening up somewhere.

Magnavox300 · #12 07-14-2015, 03:59 PM

Took another look at the chassis today, and found this very thin cloth wire just sitting on top of the Horizontal multi trimmer loose...
The other end is fixed into the board.

Is this thread supposed to be connected to the trimmer and possibly broke off???

DaveWM · #13 07-14-2015, 04:18 PM

no.

Did you check the horz pot connections and did you confirm continuity of the pot end terminals?

Magnavox300 · #14 07-14-2015, 08:31 PM

Quote:

Originally Posted by DaveWM

no.

I guess that thin wire is just excess? It looks as though that wire I showed a photo of, starts where it looks "broken", goes up, is glued to the PC board, then comes back down, and into a small hole of the PC board...

Quote:

Did you check the horz pot connections and did you confirm continuity of the pot end terminals?

Yes...
I tried both the Hold, and local distance... both had continuity.
The Hor.Hold Pot read 7.05 on the end terminals, and when I tested on the center wiper and turned the pot, it went from 0... up to 7.05 with my multimeter set at 20K resistance.
I think it's a 10K pot, but unfortunately, even though my sams schematic shows basically the same chassis layout, there are different values, and some caps and resistors are in different places than my set...

I wish I could find the exact schematic for my set, but after looking for a long time, this was the closest sams had...

DaveWM · #15 07-14-2015, 09:40 PM

just check the coil with ohm meter, should be 45 per sams 1 and 3 I assume 2 and 4 are not used. You can test in circuit. You can check voltages as well, its the plate supply so if its open you would have zero.

Try not to replace any more parts until you cover the easy stuff, like voltage checks and resistance checks (see the sams for pin resistance readings).

The biggest mistake that can be made is LOTS of parts getting replaced in a shot gun manner as a method of repair. It can make for a real tough dog.

Did you go back and double check all the values of the replaced parts looking for a 10x change? did you spray any cleaning agents (specifically near that trimmer cap)?