Re: {Collins} KWM-380 Control Card - Low Pass Filtrer Repair - Need Advice Disconnect PA?

No tants on the Low Pass board - all silver micas.  I have 14.5vdc from PA
to the Coupler (as expected) and from Coupler to the A2A1 low pass card
(E7).  It goes dead somewhere on the 14v bus on the A2A1 card that should
feed all the relays.  I just found out that 4 of the 10 relays are getting
14vdc (2 LPF pairs) but the other 6 are not.  So the 14v bus must either be
split into a few parallel buses or are daisy-chained ... which I cannot
believe Collins would ever do.  Jim WA9X has been generously helping me and
told me how to work on the board, disconnecting PA coax and HV is fine but
the 14dc originates on the PA board so the ribbon between PA and Coupler
needs to stay connected.  I am trying to trace out as much as possible
before removing the A2A1 board from the mounting plate and checking the
traces on the back of the PCB.  This is all relatively low current paths so
hard to believe I scorched a pcb trace but ??


-----Original Message-----
From: Scott Kerr [mailto:skerr@xxxxxxxxxxxxxxx] 
Sent: Thursday, August 8, 2019 11:19 AM
To: Jerry O. Stern <jsternmd@xxxxxxx>
Subject: Re: {Collins} KWM-380 Control Card - Low Pass Filtrer Repair - Need
Advice Disconnect PA?

I bet it is a shorted tantalum on the line. Look at the line and see if it a
dead to ground or close to it. They can be relaxed with small electrolytics
but increase the voltage rating to about 30v for a 14v line. 


Scott Kerr skerr@xxxxxxxxxxxxxxx

> On Aug 8, 2019, at 9:10 AM, Jerry O. Stern via Collins
<collins@listservecom> wrote:
> I have isolated my No-Receive/No-Transmit problem to a loss of 14v on 
> the ribbon connector going to my Low-Pass A3 board, however there is 
> 14v on most of the ribbon pins going to the A1 filter board.  The 
> voltages on the various pins going to A1 change when I cross the 
> filter frequency boundaries.  So at least parts of the controller card and
A1 are working.
> I want to pull the entire low pass filter card and disconnect my PA 
> (for
> safety) and measure the voltages and logic from the controller card to 
> the
> A1 and A3 LP filter circuits.  I am slowly learning more and more 
> about the
> KWM-380 but there are so many subtle things I don't want to create new 
> problems by in advertently placing the radio into a bad configuration.
> Also, I don't want to accidentally put the radio in TX while poking 
> around, so can I run the radio with the PA section high voltage 
> disconnected and the Input and Output coaxes from PA to Coupler 
> disconnected but leaving all ribbons connected?
> 73 Jerry NY2KW
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