Are these things I should consider bad
 

I've noticed a few things that I'm not sure about. I've posted pics.

The first is the damper on the HOT. The leads look like they've encountered a decent amount of heat. The leads are no longer silver. The same goes for the zener diode in the ABL circuit. All other diodes in the set have silver leads with no signs of discoloration.

The last one is a composite resistor in the ABL circuit. I don't know if this is a defect in manufacturing or if it's heat damage. Could be someone touched it with an iron.

Thanks.

Don't know aobut the resistor. If you know the correct value, you could measure it, or just replace it as a matter of course.

If those diodes have actual silvered leads, it is normal for them to tarnish over time. Any actual heat damage would likely cause a failure, so if working, leave well enough alone.

That's the thing. I don't know if they are good or not. With my limited knowledge, I've been able to find the ringing on the ABL. I've learned quite a bit lately from many here, but I can learn only so much via threads in a forum. That leaves me with the only thing I know, replacing components. Since I have no real training in electronics, I don't know if a zener diode in the circuit only works or doesn't work. Or if that diode could be semi-working and allowing the overshoot that is causing the ringing. I also am unsure how ringing and resistors relate or if they do at all.

I have the NOS zener and the resistors will be here on Saturday. I'm just going to replace them all and see if it helps.

You can rest assured that a damper diode either works or fails - there is no in-between. If it fails, the horizontal sweep doesn't work and you probably will blow a fuse. So, if your set is basically working and your complaint is those jail bars, it's not the damper diode. The zener, on the other hand, could fail open and the effect on operation might not be so obvious.


There are a couple of ways to check the Zener in operation. One is to measure the DC voltage across it and see if it is correct. This presumes that the Zener is conducting during normal circuit operation. But sometimes, a Zener is used in a circuit for over-voltage protection, and then it only conducts if there is a fault; in this case the voltage could be anything less than the specified value.

You can also check with a scope, but this is more complicated unless one end of the zener is grounded, because you have to check both ends and subtract one from the other to see if the voltage difference is constant and equal to the correct value.

This is where my lack of knowledge comes in. Take a look at the pics in this post:

http://videokarma.org/showpost.php?p...22&postcount=3

The schematic of the tripler with the brightness limiter and zener makes my head spin. If I'm reading it correctly, the zener is connected to the ground of the tripler and chassis ground. There's also a spark gap going across those two points. I can't seem to figure out how the zener gets its 7.5V for operation connected to two grounds. :no:

...

The Zener is not connected to two grounds, because the spark gap is an open circuit until the voltage gets very high and causes a spark. It is there probably to protect the Zener from being killed in case of a CRT arc.

I don't know if the Zener is supposed to be always regulating at 7.5 volts, or just limiting the voltage to 7.5 volts if it tries to go higher. You can find out by measuring the voltage from the top of the Zener to ground (or scoping the top) to see if it is 7.5 volts, or if it is less.

The problem was there before the recap. I didn't mention it because I figured it might have been a bad cap. That and whoever worked on it before messed up just about everything (pincushion, convergence, greyscale, etc.). It looked like crap, yet the person selling said it worked and looked great. It really wasn't until I started cleaning it up that I realized how bad the bar actually were.

I will put on the safety cover on the probe and let the plastic rest on the HOT to see if I can get a signal. I'll do the same for yoke and yoke wires.

Now the base of the HOT get the horizontal pulse from the horizontal board. I checked all those points on the horizontal board and they matched the waveforms given. The HOT's signal on the base has to go through the horizontal transformer. I haven't scoped the base of the HOT, so maybe that should be next. Maybe there's a problem with the transformer. The SM does show a waveform for the base of the HOT. It says it should be 7V.

Hang in here with me. Now isn't the 500ohm 7w resistor connected to the ground of the tripler? If so, then isn't the zener connect to that (ground) AND to the chassis point (ground).

I've attached a pic of the underside. I've circled the connections in question. In the left circle is the black wire which connects to the 500ohm resistor on the tripler ground, the white/green wire to the brightness limiter pot's T1, one leg of the zener and one leg of the spark gap. The right circle is a ground point (soldered to the chassis' top side) that contains the other leg of the zener and spark gap. I'm hoping you can understand why I see nothing but grounds and no voltage for the zener.

I can't tell much from the fuzzy picture, but I suspect that the "ground" terminal of the tripler is connected to ground only through the 500 ohm resistor and series zener diode as well as the pot and 10 ohm resistor.
Even if the 500 ohm resistor were connected *directly* to ground that would not short out the diode, as there can be a voltage drop across the resistor if current is passed through it. Do an ohms law calculation and you can determine how much current is needed to raise the voltage to the zener voltage.
jr

Here's a better picture. The red outline is the ground post for the diode and spark gap. The yellow outline is from the 500ohm resistor on tripler ground connection, other lead of the diode, other lead of the spark gap and terminal one of the brightness limiter pot. The wiper of the pot goes to base of ABL transistor and terminal two of the pot goes to ground. The green outlines are the spark gap and the diode.

The reason I'm going though all this that I am not an expert in electronics and am still learning. Until I can understand how all these connections can work when they all seem to go to ground and not one of them seems to have any connection to a power source. If I can understand where the voltage for the diode and transistor bias is coming from, it will help me greatly. Is there voltage on the ground terminal of the tripler?

Must be... the designer chose a 7 watt rating for the 500 ohm resistor... that would imply that something like 0.1 amp or more (DC or average pulse) is flowing through the resistor or else the designer would have chosen a lower rated (cheaper) part. The "ground" lead of the tripler must be at least 50 volts (DC or average of higher pulses) above ground for the 7 watt rating of the resistor to make sense. Without knowing the digram of the tripler or what it is connected to, the source of the voltage is not known... but for sure the "ground" terminal of the tripler is *not* at ground potential.

jr

So I can use my DMM to test for voltage at the resistor. I am doing my best to understand how all this works. Looking at the schematics I think I might understand how the zener is working. If the voltage coming off of the tripler (though the 500ohm 7w resistor) goes above 7.5V, it opens and sends the excess to ground? Does that sound right?

Yes, I think that you should be able to measure the voltage... it is likely a combination of DC and AC spikes, perhaps measure with both DC & AC scales. My Tek DMM 870 has a combination "AC+DC" range which is ideal, but I am not sure that many other meters have that function.

"Opens" is not the word that I would choose to describe the action of the Zener diode, it will *conduct* at its zener point and not allow the votage to rise above that point, unless its current ratings are exceeded, in which case it *will open* (burn out) and the voltage will likely go "sky high".
jr

What you called the "ground" of the tripler is not ground, it is just the low point and has some positive voltage on it due to being connected to ground through the other parts of the circuit, not directly to ground. If the Zener was connected on both ends to ground, it would indeed be doing nothing.