[Collins] KWM-380 Fix

[Heinz und Hannelore Breuer]

Hi Dave,

thanks for your report on your KWM-380.
I checked the manual and as already suspected the capacitor was one of
those pesky tantalum electrolytics which are known to go bad over the
time. Tantalums tend to short out when they fail. OTH an aluminium
electrolytic will probably dry out and lose its capacitance or get leaky
but hardly ever give a dead short. 

Happy new year to all.

73
Heinz DH2FA, KM5VT



David Knepper wrote:
> 
> Here are the details on my fix:
> 
> KWM-380 unlocked and started beeping.
> 
> Discovered that TP 1, 2, 3, on A5A1 did not have the correct voltages.
> These test points are not the same ones on A5A2 board to set the reference
> voltages for the synthesizer.  These are merely voltage reference test
> points that are clearly marked on the top side of the board.
> 
> I took an ohmmeter reading and, yes, there was almost a dead short at 100
> ohm resistor on A5A2.  The voltage buss from the 28 volt regulator next to
> the power supply board (this is the one that has the enclosed can)  goes to
> the frequency synthesizer variable referency frequency loop on synthesier
> board A5A2.
> 
> C-61 or a 4.7 mfd/30 volt yellow electrolytic was shorted.  This cap is on
> the input going to the 18 volt and 30 volt regulator circuitry.
> Now the 380 is back on the operating desk after a year of sitting in the
> corner.
> 
> File this one away somewhere if you own a KWM-380 and the synthesizer
> unlocks.  I trust that I explained this correctly.
> 
> Here I was thinking one of the chips but it turned out to be nothing more
> than a simple 10 cent capacitor!
> 
> Dave, W3ST
> Secretary to the Collins Radio Association
> Publisher of the Collins Journal
> www.collinsra.com