Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: TV Ears Splattering Across 20 Meters  (Read 7036 times)
AJ8MH
Member

Posts: 120


WWW

Ignore
« on: March 08, 2014, 10:27:33 AM »

My wife has two sets of TV Ears. The newer unit is splattering all across 20 meters when audio is applied from the converter box.  Both are way out of warranty.  Anyone else have this problem?  If so, did you fix it?

(The older unit would blow IR diodes all the time until I replaced all of them with diodes from Radio Shack.)
Logged
AJ8MH
Member

Posts: 120


WWW

Ignore
« Reply #1 on: March 09, 2014, 10:24:25 AM »

The problem is the high-speed CMOS logic phase-locked loop/VCO.  Somehow it modulates the infrared diode string.  I did find 5 pair of empty by-pass chip capacitor pads on the board, so I added two caps in critical spots, but no difference.  I placed a .001 on the pads at the input to the voltage regulator and another on the pads at the voltage input to the loop/VCO.

It's a TI chip (HC4046AM), and I looked it up on the web. The center freq is supposed to be 12 mhz with a max of 18 mhz.  There's a pot next to the chip, so I couldn't resist moving it.  I was able to slip the frequency outside of 20 meters (around 13.4 mhz center), but the pot is touchy, so it may not stay.  I may have to replace it.  I could still receive the IR signal with my wife's headset, but as I moved closer to 13 mhz the signal would drop out in the headset.

If this thing is supposed to be centered on 12 mhz, that would tell me the headset is off and TV Ears incorrectly adjusted the transmitter to match, and ended too high in frequency.  Hard to say since I couldn't find a schematic and tech manual for it.

If you have TV Ears and hear wideband FM modulation across the entire 20 meter band (sounds like S-9 splatter) you know what to do.  Send back if in warranty or take your chances with the pot.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!