Burning Resistor.... No picture....

[mkoser]

Hello,

Well, I decided to get back to working on my Stewart Warner 9121A again today.

Dim bulb tested up to 50 watts, no problems.. jumped to 100 watts and PFFT a resistor in the audio section went off like a fourth or July display.

I figured I would have to do some work to audio section later, since I am out of resistors so I decided to try and get at least the video up and running..

Before, I had a raster, but no image.. just a bunch of lines... now after a full re-cap, I have nothing. No image, no raster, nothing... I do have high voltage. I can hear it.

My eyes hurt from staring at it. Boy, if I only knew where I went wrong... Looks like I've got some detective work to do..

thanks,

MK

[Eric H]

Mark, did you move the Ion trap on the neck of the CRT?
If it's positioned wrong you'll get no raster, make sure it's not flipped front to back either.

[mkoser]

Nah, I didn't remove it.

The tube mounts to the chassis. I didn't take anything off at all to replace the caps. Thought I would have less of a chance of breaking anything if I didn't remove the tube.

Matt K.

[Eric H]

Matt, sorry, I thought it was Mark for some reason.

In that case I would try to find out why that resistor burned, my guess would be a capacitor installed backwards or hooked to the wrong place.

I would try to fix that first, it's probably related to the lack of raster in some way.

[mkoser]

Yeah that's what I figured. I just went to the shop again to check them out... Nothing installed backwards... Have to check each one to make sure it is in the right location...

Thanks for the help,

Matt K.

PS. Since I don't trust myself, this is what I did before I began the recap...

Tried to photograph the polarity of each, and numbered each cap, according to the sams...

[ChrisW6ATV]

Did you have a raster after the resistor smoked, or only before?

Some sets (color ones, at least) take a DC voltage output from the audio-output circuit/tube, so such a setup could be part of your problem.

[Old1625]

Originally Posted by ChrisW6ATV

Did you have a raster after the resistor smoked, or only before?

Some sets (color ones, at least) take a DC voltage output from the audio-output circuit/tube, so such a setup could be part of your problem.

Yes, many set makers used the audio output tube as a voltage regulator, drawing about 150 volts off its cathode.

The burnt resistor needs to be replaced, and the cause of its demise determined, before carrying on in troubleshooting the missing raster. In some sets this cathode feed supplies the tuner, the pix IF chain and the video amplifier stages.

[mkoser]

Originally Posted by ChrisW6ATV

Did you have a raster after the resistor smoked, or only before?

Some sets (color ones, at least) take a DC voltage output from the audio-output circuit/tube, so such a setup could be part of your problem.

No,

I had raster before my recap, now after the recap, burning resistor, and no raster.

I thought I had possibly put a cap in backwards, I checked, then rechecked, then triple checked... They are all in the right way... So I'm thinking now that I shorted something someplace. I need to go down to the shop again with a brighter light and start looking.

I was looking at the schematic and it makes sense that if the audio section goes kaput, then that might take other things with it.

We'll see..

thanks for the help.

In one of my pictures above, you'll see a red err.... black resistor that is burned. I cut one leg of it off so i could power it up and try to meter some other areas.

MK

[mkoser]

Well I checked them AGAIN and found one cap that I put in backwards...doh!

it is a 4 stabilizing cap. I took it out and looked at it... it looked a litte more "round" than normal. I don't have an exact replacement, so I used a 4.7. I also replaced the burned decoupling resistor.

I powered it up... Same thing. No improvements. I wonder what else down the line I took out...

MK