SB-104 Display problem: WWV and 20m

[Chris Iwata]

KE5ZB's suggestion to check the bandswitch and the associated wiring is the 
 key.
 
On the SB104 the 10Mhz digit is NOT part of the frequency counter  
circuitry.  It is hardwired to the bandswitch.  Heath used this scheme  to minimize 
parts on the counter board which never counts in the 10Mhz range. To  
illustrate, select the 29.5Mhz band.  Now tune to 30Mhz. The  display willl read 
29.0000Mhz.
 
There is one other possibility: The connections to IC156 are bad on the PC  
board. Cold solder joint, or bad contact in the IC socket?  KE5ZB is  
right, the IC sockets are poor quality. On my 104, I soldered most of the  ICs 
in, the rest I replaced with dual-wipe air-free sockets. 
 
73, Chris KL7DM   
 
 
In a message dated 11/6/2009 12:08:04 P.M. Pacific Standard Time,  
lhouseparker at LIVINGSTON.NET writes:

Alexander N. Gerli, Sr. wrote:
> My SB-104A has a little  problem: on the 20M and WWV bandswitch positions,
> the display reads,  get this, "34" then the correct kHz; on WWV, "35" then
> the correct  kHz. The rig's working fine otherwise.
> Of course, that "3" should be a  "1" in each case. Anyone have an idea 
what
> would be making this  happen? Only two bandswitch positions that do this, 
and
> the contacts  have all been cleaned and the boards reseated, etc.
> 73,  Sandy  AC1Y
 

For 20M  & WWV the band switch supplies a ground to connector
"C" on the display  board (10 MHZ), which then goes to pin one
on IC-156: check to verify that  ground is there when the band
switch is on those 2 positions. If a ground  were there for all
band switch positions the display segments for #1 would  always
be on, indicating either incorrect wiring to the band switch
or a  faulty switch. From your description that does not seem
to be the  case.

73
JF   KE5ZB



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