URGENT (to me!) MARCO - my 24v power supply just dropped to

[NickWL]

A few minutes before this my power meter (ammeter) died. This has now happened twice.
Partway through a job the whole DSP system just stopped - front panel lights went out.
A quick measurement showed that the 24-volt supply had dropped to near-zero and at first I blamed the power supply.
Took it out and tested it and it was OK. Started disconnecting things and eventually found that the voltage regulator (2405CS) supplying the power meter (ammeter) was the culprit. It was quite badly melted around the input voltage end (pin 1).
I imagine there is some connection between this and the dead ammeter - but I have no idea what!
Can you help please?

[Tech_Marco]

Extremely odd! The 2405 is 'rock' and it hardly failed. If it melt, seems some short circuit somewhere may caused it.
Double check your connection

Marco

[NickWL]

Marco - is it possible that some stray 23,000 volts could be responsible?
When my first ammeter died there was much burning between the anode and cathode pins on the back of the ammeter. I think the connector had come loose and had shorted.
I'm not familiar with very high voltages - could they stray and damage stuff if a connection in their circuit was 'less than perfect'?
Nick

[Tech_Marco]

If you connected to the negative side of the PSU and the tube, it won't happened. It seems to me that you connected it to the Positive terminal instead. If so, it will well cook the meter and will damge the isolator. That's why I suggested folks to uae the 2405 as a protection guard or you may damge theDSP card


Marco

[NickWL]

No, Marco, it was not a wrong-way-round connection. Remember, it had all been working perfectly well - with correct readings on the meter - until it suddenly stopped halfway through a job.
And I've ALWAYS used a 2405 isolator!

I don't know if you've seen the photo of the ammeter connector that I sent to your sales department, but there is heavy burning between the two HV pins on this. I wonder if the connection INSIDE the meter had failed and 23000v was arcing across these two pins and thus producing unexpected high voltages elsewhere in the system?

Nick

[Tech_Marco]

Nick

If you connected it to the negative, there is no 23,000V or whatever high voltage appear on the meter. It works if you connected it to the Positive but it will blew the meter. And it was lucky you have isolator installed otherwise it will blew the whole things.

I never seem anything like that the connector melt like that. If it was not reverse the Positive/Negative, I couldn't see any other possible way could happen

I may do an experiment see if I could duplicate your case

Marco