Not going to believe this, but I think it is finally working. Was going over the soldering and I happened to move the tweezers on a joint and it broke loose a bit. I reflowed and reassembled and just like that it seems to be working. Cap C423 was the culprit I think. I will let it run for the better part of tomorrow and check the voltages. I really appreciate everyone sticking with me through all the testing and suggestions. Will report back tomorrow after more testing but it looks promising.
Though, those components would not really explain why the VDU had the problem it did.I think C423 is in an unrelated part of the V deflection circuitry, and it could not explain why the EHT was 1.4 x too high.
At least there is a lesson here for you to learn.
This is the thing I have been trying to explain to you the whole way along, but you have been slow to pick up on it, and have kept tampering with unrelated parts of the VDU's circuitry.
When there is a fault, what you need to do is to disturb as little as possible. No removing and testing random components in other parts of the circuit.
Each time you manipulate and flex the pcb, if there is a fractured connection, elsewhere, it runs the risk that the VDU could suddenly start working again. This is not as good as it sounds and is not a "repair". It is impossible to find a fractured connection if it had re-connected.
You create an intermittent and latent problem this way. These always come back to haunt you, without exception.
The better situation is that the fault remains, and you can find it by gently probing with the scope. Identify exactly what the fault is, and correct it.
In a thorough World too, if you have really found the exact cause, such as a fractured solder join, then you should be able to re-create the exact same fault, by opening that connection, to convince yourself it was definitely the cause of the fault you were pursuing.
Interestingly, this notion was applied by Koch, in trying to identify the cause of infections, especially see point 3 of Koch's Postulates:
- The microorganism must be found in abundance in all organisms suffering from the disease but should not be found in healthy organisms.
- The microorganism must be isolated from a diseased organism and grown in pure culture.
- The cultured microorganism should cause disease when introduced into a healthy organism.
- The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.
So alas, I feel the real cause of the fault still resides in your VDU.
When the fault returns, which it most likely will, try not to interfere with pcb & components pulling out parts elsewhere and flexing the pcb.
Instead, set up a test situation with the scope and try to find the cause with as little manipulation to the pcb as possible. I think I know where the cause might be, we will wait and see.