[Collins] HF-380 tuning problem

[David Knepper]

Howard, here is what I posted to the Collins mail list on www.qth.net

I do hope that this solves your problem.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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
Publisher of the Collins Journal
Secretary to the Collins Radio Association
www.collinsra.com
Nets:  3805 Khz, Monday/Wednesdays 8 PM EDST
          14250 Khz Saturday, 12 Noon EDST

----- Original Message -----
From: "Howard Rock" <rocketman at beachlink.com>
To: "David Knepper" <cra at floodcity.net>
Sent: Tuesday, August 03, 2004 8:57 PM
Subject: Re: [Collins] HF-380 tuning problem


> Dear Dave
>   Thank you for the prompt reply. I do not receive the journal at this
time
> but I do want to subscribe.  I visited the website a few moments ago and
it
> looks like you are the contact to subscribe.  I will mail the dues to you
> tomorrow.   I have a Marine Electronic sales and service business in Nags
> Head, NC and work on TOO much equipment in the Summer and was hoping for a
> quick fix on the HF-380 and it looks like you are the answer.
> Howard
> ----- Original Message -----
> From: "David Knepper" <cra at floodcity.net>
> To: "Howard Rock" <rocketman at beachlink.com>
> Sent: Tuesday, August 03, 2004 6:32 PM
> Subject: Re: [Collins] HF-380 tuning problem
>
>
> > I had a similar problem and it was a tantalum capacitor on the voltage
> buss
> > going to the synthesizer circuit.  I wrote about this in an early spring
> > issue of the Collins Journal.  I assume that you do not get the Collins
> > Journal, which is the official publication of the CRA.
> >
> >
> > Dave, W3ST
> > Publisher of the Collins Journal
> > Secretary to the Collins Radio Association
> > www.collinsra.com
> > ----- Original Message -----
> > From: "Howard Rock" <rocketman at beachlink.com>
> > To: <Collins at mailman.qth.net>
> > Sent: Tuesday, August 03, 2004 7:30 PM
> > Subject: [Collins] HF-380 tuning problem
> >
> >
> >   I have a HF-380 that over the weekend it developed a problem in that
the
> > tuning will only go up in freq no matter which way the tuning knob is
> turned
> > or where the resolution push buttons are pushed.  Before I breakout the
> > diagram and dig around does anyone have a clue what the problem may be.
> > Perhaps one of the tandalum caps in the VCO PCB or something like that??
> > Any help would be appreciated.  Thanks!!
> > WA4UBZ
> > Howard Rock
> > rocketman at beachlink.com
> > ______________________________________________________________
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>