More screen anomalies

[TinCanAlley]

Originally Posted by old_tv_nut

Not sure what you mean by "saturating?" Do you mean the whole picture gets brighter? Does the bar pattern stay visible if you crank up the contrast AND turn down the brightness (to prevent "saturating")?

My suggestion is to try connecting known ground points directly to where they are supposed to go in case the connectors on the PC boards are still not making good contact even though you cleaned them. Also, you can try connecting different ground points on the PC board connectors to each other to see if that helps.

What is the maximum gain (volts/division) that your scope has? Depending on where in the circuit, you may need more gain than your scope provides to see this waveform, especially if you use a 10x probe.

Your scope needs to be synced to the horizontal sweep. If you cannot sync it independent of the probe input, it will be next to impossible to trace the waveform. You definitely then need a better scope. If the scope is locked to horizontal sweep and showing at least one complete sweep cycle, the jail bars will appear as a sine wave of decreasing amplitude from left to right, with about 10 or 12 cycles within one horizontal sweep (as you can count by looking at the TV screen). This decaying sine wave will be added on top of whatever normal waveform is at the place you are probing.

I have jumpers with alligator clips, would those be good for grounding? I can clip from ground to ground on the modules and then to a good chassis ground.

The scope has a X1, X10 and X100 setting and the probe has X1 and X10. I'm not sure what the maximum is, but I understand this one can handle all the way to the yoke and high voltage.

The scope can either sink with the probe, it's internal (using the AC line, I believe) and an external source (of which I don't have).

Where in the horizontal should I start? Should I start at the HOT and work my way back?

[old_tv_nut]

Originally Posted by TinCanAlley

I have jumpers with alligator clips, would those be good for grounding? I can clip from ground to ground on the modules and then to a good chassis ground...

Yes, these are exactly what you can do to experiment. Be cautious and make sure you don't connect to something besides ground. Turning the set off while setting up the connection is a good idea.

Regarding all the other questions about your scope, I see you are getting a good one to work with. When you have that, you will be able to use one channel/probe to sync the scope to horizontal and the other to look at various points for your problem.

If it is a ground problem, however, you may see the bars change when you hook up the probe ground leads to the chassis or circuit cards, the same as experimenting with clip leads. This could be either exasperating or fun, depending on how you want to think about it!

[TinCanAlley]

Originally Posted by old_tv_nut

Yes, these are exactly what you can do to experiment. Be cautious and make sure you don't connect to something besides ground. Turning the set off while setting up the connection is a good idea.

Regarding all the other questions about your scope, I see you are getting a good one to work with. When you have that, you will be able to use one channel/probe to sync the scope to horizontal and the other to look at various points for your problem.

If it is a ground problem, however, you may see the bars change when you hook up the probe ground leads to the chassis or circuit cards, the same as experimenting with clip leads. This could be either exasperating or fun, depending on how you want to think about it!

About now I'm wishing I had a test jig. This poor set has been on it's side and top so I can get to the underside for testing and repair.