[Heathkit] SB-303, SB-301 LMO instability

Tue Jan 21 16:28:08 EST 2014

Glen's article was just the ticket for the tube LMO - I sprayed deoxit on the capacitor wiper and now it is as smooth as silk and without warble.

I then tackled the  SS LMO in my SB-303, which exhibited the same symptoms.  I should NOT have removed the LMO from the chassis.  It turned out that the only removable access cover (on the bottom) does not expose the variable capacitor.  There are two large holes under the piece of aluminum sticky tape topside which is exposed by removing the RTTY board, and the hole to the left allows one to easily spray deoxit right into the capacitor wiper surface.  Reassembly demonstrated that the warble in this one was now gone, too.

Unfortunately, somewhere along the line, the LMO's "bandspread" got messed up, and the LMO now tunes from 5.46 through 4.97 over the 5 MHz mechanical range, instead of the usual 5.51 to 4.98 . I cannot obtain the lowest 100 KHz calibrator signal or Extra CW portion on any band.  I was careful to not touch any of the other adjustments exposed when I removed and replaced the bottom cover.  The calibration points cumulatively "walk wide" by 4-6 KHz for each 100 KHz segment

I am now seeking instructions or tips needed to align the SS LMO.  I wonder if excessive deoxit could have caused a problem? 

All help and suggestions are greatly appreciated.

Jack  W3RU

> Message: 4
> Date: Tue, 21 Jan 2014 03:26:20 +0000
> From: jack m <oldvette at hotmail.com>
> To: "heathkit at mailman.qth.net" <heathkit at mailman.qth.net>
> Subject: [Heathkit] SB-303, SB-301 LMO instability
> Message-ID: <COL126-W44D54771E02F9E510696E6DEA40 at phx.gbl>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Is anyone aware of the cause for instability and "squirrel-iness" in Heath SB LMO's?  The symptom can be described as severe frequency wandering while cranking the dial, which returns to rock-solid, on-frequency stability when you are done tuning.  It is really annoying!  I don't want to open it up until I hear back from someone else.
>  
> Thanks  Jack
>  		 	   		  
> 
> ------------------------------
> 
> Message: 5
> Date: Tue, 21 Jan 2014 08:18:36 -0800 (PST)
> From: Glen Zook <gzook at yahoo.com>
> To: jack m <oldvette at hotmail.com>,	"heathkit at mailman.qth.net"
> 	<heathkit at mailman.qth.net>
> Subject: Re: [Heathkit] SB-303, SB-301 LMO instability
> Message-ID:
> 	<1390321116.92811.YahooMailNeo at web142301.mail.bf1.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
> 
> Very common problem! ?
> 
> The following link gives a solution to the problem:
> 
> http://k9sth.com/uploads/LMO_rebuild-1.pdf
> 
> ?
> Glen, K9STH
> 
> 
> Website:  http://k9sth.com
> 
> 
> 
> On Tuesday, January 21, 2014 2:12 AM, jack m <oldvette at hotmail.com> wrote:
>  
> Is anyone aware of the cause for instability and "squirrel-iness" in Heath SB LMO's?? The symptom can be described as severe frequency wandering while cranking the dial, which returns to rock-solid, on-frequency stability when you are done tuning.? It is really annoying!? I don't want to open it up until I hear back from someone else.
> 
> Thanks? Jack
> ??? ???  ??? ?  ??? ??? ? 
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> ------------------------------
> 
> Message: 6
> Date: Tue, 21 Jan 2014 10:41:48 -0600
> From: "Gary H. Harmon, Jr." <gharmon at idworld.net>
> To: "Heathkit-Radios " <Heathkit-Radios at egroups.com>,	"Heathkit1 "
> 	<heath at puck.nether.net>,	"Heathkit2 " <heathkit at mailman.qth.net>,
> 	"Heathkit3 LIST" <heathkit at yahoogroups.com>
> Subject: [Heathkit] WANTED
> Message-ID:
> 	<[email protected]>
> Content-Type: text/plain;	charset="us-ascii"
> 
> IP-28 power supply
> 
> GR-43A transistorized receiver
> 
>  
> 
> Vr,
> 
>  
> 
> Gary H. Harmon, Jr. - K5JWK
> 
> 6003 Archwood
> 
> San Antonio, TX 78239-1504
> 
> 210.657.1549h / 210.884.6926c/t
> 
>  
> 
> "Retirement means every day is a Saturday except Sunday"
> 
> http://www.grissomroadcoc.org
> 
>  
> 
>  
> 
> 
> 
> ------------------------------
> 
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> End of Heathkit Digest, Vol 120, Issue 12
> *****************************************