How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

[Paul678]

There was the typical buffer boards problem on this one, so I replaced a shorted MOSFET on the Y-sustain board to get back a good Vscan of -190V,
and ordered the newer version of the LJ92-01203A/01202A buffer boards, and
the TV works now.

But there are 4 potentiometers on the Ysus board, that I had to adjust to get a decent picture, and I read somewhere that when you get a new Ysus, you have to adjust it using a 200MHz o'scope. It seems you can adjust these by eyeballing the screen, but if there is an official way to adjust it, I'd like to know about it. I couldn't find any info about this online.....

Thanks in advance.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

More info: I get a decent picture now, but there are "tracers" or
"ghosting" in red pixels. Anyone know what can cause this?

It's exactly the same problem here:

http://www.youtube.com/watch?v=eKeAxqtUnHY

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

The tracers or ghosting look exactly like this:

http://www.youtube.com/watch?v=eKeAxqtUnHY

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Ok, it looks like I have some sort of "non-extinguishing mal discharge" or "image sticking mal discharge" problem (page 21):




I believe it says to just replace the boards......Great!

Thanks for any advice....

[tom66]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

I have adjusted the timings before using just a 20 MHz oscilloscope.

The ghosting you show is possibly fixable. Random firing of red/green pixels usually means the main logic board needs replacing, or the firmware needs an update, which can only be done with an expensive programmer. But if you are getting trails, it means the Vsetup or Vsetdn timings are wrong.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Thanks for responding.

How do I adjust the Vsetup or Vsetdn timings?

I've already adjusted all the pots on the power supply. Nothing
worked, so I put them back to their original positions (I marked
them first).

I do have an older o'scope.

[tom66]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Thanks for responding.

How do I adjust the Vsetup or Vsetdn timings?

I've already adjusted all the pots on the power supply. Nothing
worked, so I put them back to their original positions (I marked
them first).

I do have an older o'scope.

Post a picture of the Y sustain board. I'll tell you where to test.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

I hope you can use this one:

http://www.google.com/imgres?um=1&hl...1t:429,r:2,s:0


Mine still has the support bar over it.....lol!

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Another angle:

http://www.google.com/imgres?um=1&hl...1t:429,r:1,s:0

[cadiman]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Once you start adjusting the y drive board it is alot like a rubics cube. You can really get sideways if you don`t watch what you do.

I would hook up a dvd player where you can still the picture. You will need bright scenes and dark scenes.

I have done these with a scope when possible and I have done these by eye.

You can set the beginning parameter voltages with a regular meter.

You should use a scope for v-set up and down of the waveform.

The samsung boards were a bit easier than the L/G boards to adjust and I was able to remove the speckles you talk about without a scope.

You need to take your time with this and it wouldn`t hurt to log your adjustments down on a notebook.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

You can set the beginning parameter voltages with a regular meter.
You should use a scope for v-set up and down of the waveform.

Ok, so where do I test and measure for the beginning parameter voltages?

I do have an older o'scope. Where do I probe for V-set up and down? What should the waveform look like?

[tom66]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Oh, this is a Samsung. Same idea though, but the timings are known as Yfr and Yrr.

Turn TV off.

Get out a 10x probe for your scope.

Attach the 10x probe to the resistor I've highlighted in RED. (VERY IMPORTANT! DO NOT USE A 1X PROBE!)



Set the scale to 10V/div or 20V/div.

Turn TV on and allow it to warm up for a minute.

Adjust the trigger until the waveform starts to look like this:



The important thing is the Vset ramp up, and the ramp down. Align the trace so you can see just this. This requires creative use of the trigger and hold-off features on an oscilloscope.

Next, get the service manual for your panel.

Adjust the upward ramp timing (black arrows) so it is the same as in the service manual.

Do the same for the downward ramp timing.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Ok, I'm not sure if you saw this on page 64:





Apparently, I need to set the screen all white, with a jumper on the
logic board, and also trigger from the logic board. A bit of a pain,
as the logic board is buried under the input panel, but oh well...

[tom66]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Ok, I'm not sure if you saw this on page 64:





Apparently, I need to set the screen all white, with a jumper on the
logic board, and also trigger from the logic board. A bit of a pain,
as the logic board is buried under the input panel, but oh well...

That's not usually necessary.

Just make sure there is something on the display, even if just snow from the tuner or a DVD player.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

If it's only 2 pots that adjust this, shouldn't I have
gotten closer than I have just eyeballing it?

Unless it's a SUPER hair-trigger adjustment.....

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

And I assume a x1 probe will load the circuit too much?

[tom66]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

And I assume a x1 probe will load the circuit too much?

No, an x1 probe will blow your oscilloscope up. You *MUST* use a x10. And your scope should be rated to 400V.

[Paul678]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Mine goes up to 600V, but yeah, that's a pretty big
signal there......ok, thanks much....

[tom66]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Mine goes up to 600V, but yeah, that's a pretty big
signal there......ok, thanks much....

The sustain drive is a -90V to +385V signal, and can provide several amps of current.

[cadiman]

Re: How to Adjust Ysus board (LJ92-01200A) from Magnavox 42MF231D/37????

Some plasma tvs have this feature in the menu if you can find it.
(panel wash or white screen)

I don`t remember it being on samsung only panasonic and some L/G sets had it.

thats why I use a dvd player.

Don`t forget the beginning voltage settings I refer to are the power supply and the z board. The service manual wants all the panel voltages set and the panel warm before setting the y drive board waveforms.

Thanks for the info and pictures for the samsung tom66!