Thanks for the reply! The voltage seems to be at 5v, I tried the old wiring and it still doesn't work so I suppose the issue is with the board
Five volt, then you measure the logic signal from the processor so the transistor is fried!
There's a contact between collector and base, but emitter (to ground) is fried..
As I see you have a good instrument, -you've electronic experience.
The transistor can be bought from RS component or any good source for electronics in your country.
I'll guess you have the wiring for your main PCB as well?
Here's the web for RS Component international, just search your country and go:
PS. You'll need to check your wiring thoroughly, as there might be some issues that caused this to happen.
You may try to test your fan circuit J14 by installing the connector "led light" into J14, then try to start the fan using the advanced menu, if led light up and can be controlled your fan circuit is ok.
The use of a digital scope in such a circuit is ok, but can sometimes mislead us. I ask this because the 5 V peak to peak might also be measured if you measure with ground as reference.
If this is true, your circuit might be ok.
This is just a practical way of testing this fan output, BUT do not try to use the light output (J15) for testing the fan's as there might be a fault in your fan wiring that might fry the other (the led) transistor as well.
TorgeirEdited by Torgeir
Thanks, I will try it!
I am just measuring between the 2 pins on the plug (and I might have shorted them when I am poking around), I think that should read 24v?
As your scope reference is floating at +24 V DC and your scope read an "AC" signal you will only see the pulse peak signal input to the base of T1 that's receive PWM pulses at max 5 V peak from the microprocessor.
This is indicating that the transistor T1 BC817 is not working, when it is working there should be a 24 V peak PWM signal here.
BC817 is a very small transistor..
I did the test with the LED, and it acts a bit weird and is a lot dimmer than normal, which is in line with the 5v measurement.
I ordered a bunch of BC817 and they just arrived, and after making a bit of a mess on the board and some burnt flux later, I desoldered the transistor and soldered the new transistor.
Did the LED test again, and it works! The light would turn off at 10%, which I guess is in the software, but the brightness is normal.
Then I go back the check the wiring of the 2 fans, the socket of the fan plug each only have one wire connected. When I first started troubleshooting I didn't pay too much attention to this, but now that I know the 2 fans are supposed to be in series, but they are not connected.
There's a whole wire missing! How could this ever work?!
Upon closer inspection, the 2 sockets were directly soldered together. I must have broken it when I replace the heater wire, and fried the transistor when I poke around with the scope. I soldered them back together and secured them together with some tapes so this doesn't happen again.
If I paid more attention to the sockets, I would have saved a lot of trouble. I hope this mistake will help someone troubleshoot in the future.
Those wires will break after (normally) a long service life, actually the same thing "might" be the reason why your heater failed.
It is possible to fry the "driver" transistor if the two wires yellow and green come in contact, or if the current through this circuit become to high. However, you measured the output of the two connectors going to the fans.
If the voltage on your "scope" is 24 V DC between the top and bottom of the pulse your wiring seems to be ok. What is the voltage measured here, kind of hard to see on your scope.
However, normally we would measure this voltage when the fans are connected, cause an open circuit "may" have a little high resistance that would not be detected when measuring in open circuit. This might be caused by loose crimped contact etc.
Here is the actual circuit that's controlled by PH4, a PWM (pulse width modulated (controlled)) from the micro processor.
Here is the circuit with T1 a NPN transistor BC817, that's possible to change if fried.
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