[Kenwood] TS-940S Cooling Fan Problem

[Garey Barrell]

Walt -

I have been through this several times.  The problem is gummy or worn 
bearings in the fan motor.   The "locked rotor" current is too high, 
dropping the supply voltage (supplied through an 18k, 1W resistor) too 
low to start the motor.   The fan will start sometimes if you spin the 
blade to get it started.   The fan will start and run fine if the supply 
is stiff enough.   All Bill has to do is measure the voltage across the 
18k resistor and he will see about 22V.   The transistor will be 
saturated, and about a volt across the motor winding.   An 18V Zener 
across the resistor will allow the motor to start, and once it starts 
the voltage across the resistor will drop to about 12V, and about 9-10V 
across the motor.   But once the motor stops altogether, which it will, 
the transceiver WILL overheat, damaging AVR board parts first, and if 
you're unlucky, the PS pass transistor will short putting 40V across the 
final and driver transistors.   The fan motor will sound cheap then...

73, Garey - K4OAH
Chicago


Walt Breining wrote:

>Bill:
>I believe that your fan is OK.
>
>I cannot find a schematic on the 940s except in a manual that will take me 3
>hours to download on my 33.6 system from mods DK.  I may try to download it
>somewhere else next week.
>  
>