Not that knowledgeable on electrics but...

[Gerbert]

The thingies under the orange thingies (relays) are diodes no?
Am I correct that these should block the currrent on the side of the silver stripe?

 

[C.J]

 

[Gerbert]

Yeah I figured I'd ask a human being instead of the internet.
There are 5 or so on the board and all block current both ways...

 

[Sharny dubs]

Is the resistance infinite in both directions?

 

[sjt01]

The thingies under the orange thingies (relays) are diodes no?
Am I correct that these should block the currrent on the side of the silver stripe?

They are called flywheel diodes. They are there because when a relay turns off, the energy stored in the relay coil is dumped as a high voltage spike which can kill electronic component such as the 4069 hex inverter IC in the picture. The diode shorts out this "flywheel" energy, but forces the normal energising power through the relay coil

 

[e3120]

You can't just test them using resistance on a multimeter, as there's a voltage threshold before they 'open'. A lot of meters have a diode tester position.

 

[milkloss]

Zener diodes and they do as described above. The the high voltage spikes whizz around the circuit to dissipate them but trap the low 'working' voltage to do what it's supposed to.

 

[Gerbert]

You can't just test them using resistance on a multimeter, as there's a voltage threshold before they 'open'. A lot of meters have a diode tester position.

Ah thanks for that. I tested and the 3 above are all dickered it seems, letting it through both sides. However, can't it be that the current is finding another way through the board? Or is that illogical as it is parralel on the relais coil?

 

[milkloss]

Ah thanks for that. I tested and the 3 above are all dickered it seems, letting it through both sides. However, can't it be that the current is finding another way through the board? Or is that illogical as it is parralel on the relais coil?

they are parallel to the relay coil and so will read open whichever way you have the leads. You'll have to de solder on end to test correctly with a multimeter on the ohm setting.

 

[milkloss]

Oh, and there maybe two in the circuit as it helps close the relay quicker from memory. if you can break the circuit for that coil then both will test true.

 

[Gerbert]

There is a little more to it, I am afraid I fryed something.

 

[335d]

What does the board do and what is the fault? Why do you suspect the diodes? Is these a fuse blowing or something?

 

[Gerbert]

Ah sorry for the late reaction @335d , must've slipped my mind.
This is a voltage control/rpm sensing and switching board for a chipper. The voltage control is for the feeder roll speed and the other bit is the no-stress, as they call it. It switches the feed rolls to reverse for a little bit (like half a second) and then turns them off until the rps reaches a certain level and switches them back on again. I enquired on an electric diagram but instead I got the price for a new board, €623,50. I can live with that, but I would like the diagram anyway to make sure I didn't screw something up.
However, as the voltage control still works on the board I figured I might make something myself. I'd need an RPM monitoring device that gives a signal below a certain RPM and above some higher RPM (a bandwith). My eye came to something like this: https://www.amazon.co.uk/Extech-461960-Panel-Controller-Monitor/dp/B004WN5VIC
Does anyone have some experience with this?