Fan doesn't when 6pin cable between power supply and PA, is plugged in, however fan works when disconnected from PA board
The fan control receives two signals from the HCA2400 power amp module. Pin 4 is labelled POS+ and pin 5 is labelled POS-.
These two interact with T14,T15,T16,T17, and finally T7 which gates a -21 volt power to the fan.
From the schematic, it appears that if POS- is more positive than about 20 vollts negative the fan will be held off. It appears that the POS+ signal controls the speed and as it goes more positive, this would DECREASE the speed. Pots VR2 and VR3 are used to set these thresholds and I do not have setup instructions for those... I would be very careful about adjusting them without the procedure. . HOWEVER, first thing is to verify that you have -21 volts DC on pin 2 of the fan connector. With the HCA2400 disconnected, the POS- will drift to -21 volts and POS+ should drift to somewhere around -6 to -8 volts judging from the schematic.
Trying to trace these two signals on the HCA2400 is very difficult and the schematic does not show where they go... I did find that pin 5 does go to one of the thermistors on the heat sink labeled R2 and one side of R1 goes to pin 3 which is -12 volts by tracing an HCA2400 I have open. Pin 4 seems to go to the other side of R2 so then the R2 thermistor connects between POS+ and POS-.
The room temp (71F) resistance of R2 seems to be about 112 ohms and rises with increasing temp. It appears that R1 is involved with a signal sent to the power supply called OFF which probably shuts down the supply if the HCA2400 gets too hot... so R1 thermistor on the HCA2400 would have nothing to do with the fan... I can;t verify that R2 does more than connect to pins 4 and 5 of the connector... there may be biasing resistors on the HCA2400... I would find it odd that VR2 and VR3 would both be connected in series effectively with R2 thermistor... so I suspect there are additional biasing on the HCA2400 that one of the tweek pots conrols the ability to run and the other controls the speed above that... Please note that the resistance measurements of R2 are made on an HCA2400 that a hacker all but destroyed...
Nov 29, 2010 |
Behringer Europower Pmp5000 Powered Mixer...