Supply voltage / error mystery

[Chris Shields]

Hey everyone, first post.

I have a DLP projector which flashed the error code for "fan error". The service manual recommended checking each fan's connector on one of the PCBs to see if it's returning an error signal (higher than 0.7V on pin 1 of each connector). Sure enough, one of the connectors (G19), still plugged in, read 1.06V; all the others read close to 0V. I then removed the connector and the error message persisted, and I realized the pin associated with the fan's connector (now disconnected) still read 1.06V.

So the problem is coming from somewhere other than the fan.

Here is the connector on the schematic. I can't see where that 1.06V should be coming from at all, or what to do next:

**broken link removed**

Any ideas? Thanks, Chris

PS. Out of curiosity, Pin 3 is connected to "FAN3V" on the schematic, which i'm assuming means a 3V supply. Why is it labeled +7.4-12V on the connector label? The pin reads 10.1V.

 

[JimB]

So the problem is coming from somewhere other than the fan.

Actually, no.
The problem is the fan.
When the fan is operating normally, it will pull the voltage at pin 1 down to zero.
You can check this out by connecting pin 1 to pin 2, and this will make your Fan_Error alarm go away.

JimB

 

[Chris Shields]

Yes, thank you! Much appreciated!!

 

[Tony Stewart]

Fan speed is regulated by the voltage on pin 3, hence "FAN3V"

A broken fan crimp wire can also explain open circuit bias voltage of >1V on pin 1.