[TenTec] TT 1220 problem

[Bill Miner]

Brian,

I agree with Jerry K0CQ.  This is most likely a bad (open or high ESR)
aluminum electrolytic capacitor.  The type of noise you describe could
be from the Microcontroller or the BA618 display driver as well as the
PLL circuit. I would look at C-44,C-48, C-42, C-41, C-87, etc.  Perhaps
you could tack solder a known good cap across these one at a time and
see if the problem goes away.
Have you installed the "optional" C-86 4700 ufd filter cap? This may
help also.

I have built several of these kits and they have all worked great.  The
receiver has exceptional sensitivity.

Good luck. Please let us know what you find.

73,
Bill - K6WLM 

Brian Haren wrote:
> 
> Hello All!
> 
> I have a 1220 2-meter kit that has an 'issue' I hope someone can help me with...
> 
> The kit was built by a local ham with a lot of kit-building experience and was recently received back from TT where they replaced a few switching diodes, checked functionality and gave it a clean bill of health.  I bought it from the original owner and a good friend.  According to him it has less than 2 hours operating time on it.
> 
> The radio emits a constant low-level high pitched whine.  It's not a 60 hz 'hum', it's much higher frequency whine.  It can be heard by receiving stations behind my audio and I also pick it up through the radio speaker while receiving other stations.  I ran a number of tests today, to include turning off all appliances, lights and power supplies in the house and running the radio from a battery.  The whine persists.  The interesting thing is that other stations report the whine fades during long transmissions, but always returns after unkeying and beginning another transmission.  One local ham stated that it sounded like some of the capacitors had not yet formed and might well go away with time.  I'm not so sure.
> 
> Does anyone have experience with this radio and perhaps have experienced the same problem?  I'd love to get this problem solved without having to return it to TT.  Thanks in advance!
> 
> Brian
> W8BYH
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