Yes the clicking returned when I reconnected that rail.
I will go through what has happened so far.
Scope working but smell from power supply. Resolved by replacing faulty caps on primary side.
Then worked for several hours over several days. New fault. It would run for a few minutes then cycle on and off. Arcing noticed between C16 and cathode fixing of Cr24 due to leaked electrolyte. C16 replaced and board cleaned. No effect on cycling fault.
Replacement of all electrolytic and some tants started.
No improvement. When C19 replaced it would not start up. Clicking noticed and fan twitching st same time.
C30 31 replaced again and then no output at all from 15.5v rail. CR24 replaced. No improvement. Traced to broken link between caps and L4. Link restored and clicking fault resumed.
Low ESR caps ordered for C30 31 and 19.
A thought is that I could disconnect the crowbar again and see what happens to the voltage. I could either disconnect R63 and see whether the caps remain charged. Or I could use the new link to measure the current in the rail with no load, which should just be that through R63. I am very far from being an expert in this so comments on that would be welcome.
I could also just look for a new scope on eBay but that seems a bit defeatist!
I will go through what has happened so far.
Scope working but smell from power supply. Resolved by replacing faulty caps on primary side.
Then worked for several hours over several days. New fault. It would run for a few minutes then cycle on and off. Arcing noticed between C16 and cathode fixing of Cr24 due to leaked electrolyte. C16 replaced and board cleaned. No effect on cycling fault.
Replacement of all electrolytic and some tants started.
No improvement. When C19 replaced it would not start up. Clicking noticed and fan twitching st same time.
C30 31 replaced again and then no output at all from 15.5v rail. CR24 replaced. No improvement. Traced to broken link between caps and L4. Link restored and clicking fault resumed.
Low ESR caps ordered for C30 31 and 19.
A thought is that I could disconnect the crowbar again and see what happens to the voltage. I could either disconnect R63 and see whether the caps remain charged. Or I could use the new link to measure the current in the rail with no load, which should just be that through R63. I am very far from being an expert in this so comments on that would be welcome.
I could also just look for a new scope on eBay but that seems a bit defeatist!