Well, I have been looking at this guy periodically. Still jot having any luck.
I replaced all electrolytics. This got all the LV power supplies to good values and ripples.
I was hunting a red herring on the horizontal, trigger, and vertical boards. I misunderstood why a waveform looked the way it did. I learned a lot about scopes exploring this, and am now pretty sure the problem is in the HV side, as I originally thought...
I replaced Q202, which I really thought was going to fix it, but the problem persists.
I checked the diodes, including the Zener ZD202, and they test OK. ZD202 seems to break down right at the 9.1V. However, when I put a meter on ZD202 in action I read close to 2kV on either side of it. I do not notice a difference. Should these two side of ZD202 read the same?
Of course I am reading this with an old Simpson 260 on the 5000V scale, which puts the reading way over to the left in the low accuracy area. I do not have a HV probe for any of my DMMs. So until I get one the Simpson is all I have. I also do not know how accurate it is on that scale. So it may not actually be right around 2kV. By the circuit design it should be about 1.6kV or less.
The only other thing I can think would be the three HV capacitors. These are all rated for just 1.6kV (apparently a known poor choice on Heath's part, and an issue if the circuit really is at 2kV). I get reasonable readings at the two diodes in the voltage multiplier circuit. And the display only fails at certain frequencies of input. At these frequency ranges the trigger is working, the blanking circuit on the LV side of the optocoupler IC is working, the horizontal and vertical deflection are all working.
Anyone know of a cheap source for these HV .1uF caps? Ideally 2kV. These guys seem pricey, and I hate to waste any more money of this thing, but it has become a bit of a Moby Dick obsession to get going.
I don't have any way to measure the HV side of the optocoupler. I need to get a HV probe for the scope.
I took C201 out and it measures OK.
All the resistors on the HV side read right near their ratings.
I am not sure what ZD202 is supposed to do, if someone could explain that this might help.
Any help would be very much appreciated.
Thanks.