It is at the end of the first line in post #1. No, it does not say AC, it does say 24 volts, though.

Ah that makes sense.
Note to self: 24v means 24vAC.

 

Ah that makes sense.
Note to self: 24v means 24vAC.

And all this time I thought my 9V batteries were DC. WOW! This opens up a whole new world of electronics for me.
Guess this one is also AC.

 

Not since June 30th has the TS been here.

The AC or DC question needs to be answered. For now I'm going on the assumption that a 24V (polarity unidentified) might just be 24VAC. I have several boards that are 24VAC in my scrap bin. HOWEVER, that doesn't mean that all 24 volt systems are AC.

Given the challenge of designing a circuit that will indicate properly when the fuse is blown I'd opt for the anti-parallel diode suggestion with the resistor. If the board is running on high current then a high resistance will prevent the board from seeing a dangerous current should something go wrong.

The circuit below will work for AC or DC. You didn't say what amperage the fuse is - which may be another key point of focus. For now I'll assume it's just a 10 amp fuse. At 24V (AC or DC) LED 1 will light ONLY if the fuse is blown. LED 2 will also only light if the fuse is blown. With the fuse being blown the 2.4KΩ resistor will not allow any more than 9mA of current pass through the circuit. Since it's normally protected by a 10 amp fuse, having 9mA still flowing will likely not cause any damage. But that's an assumption based on a lot of guesswork. With the numbers I'm ASSUMING you shouldn't see any more than 210mW of power. Yes, that's a bit of wattage, so you'll need at a minimum a 1/4 watt resistor. Me? I'd opt for a 1/2 watt resistor. More headroom means less problems.

 

And what's a blade at the end of his pcb?

My guess is that "blade" is a reference to a fuse. But it might reference a connector. It is interesting how the meanings of words can be important, isn't it??

and the circuit in post #23 will work for either AC or DC. The second LED solves the reverse voltage breakdown problem quite adequately.

 

IBM (and others) used to call their rack-and-stack servers "blades", but in the context of a pc board my thoughts go to a high-current contact, or the connector field on the back of a hot-swapable power supply.

ak

 

Personally, the term Blade? I take it to mean the male end of a quick disconnect connector such as these
https://www.amazon.com/Baomain-disc...lectrical/dp/B01G83SD06/ref=asc_df_B01G83SD06