Re: Escaping smoke #ubitx

Jerry Gaffke

Not clear why this is happening, but:

The TDA2822M is rated for operation with a supply between 1.8v and 15v, which is an amazing range,
and suggests the output drivers are pretty low impedance.
Since we are running it at 12v (or more), which is near the top of its range, a shorted output could indeed be all it takes.
Specs and graphs in the datasheet stop at a 9v supply, it's only the spec for the supply voltage that 
suggests 15v might be ok.  

If you run the TDA2822M output to a stereo headphone jack with both ears getting sound,
then plugging in a mono jack will short the output to ground. 

If you wind up replacing the TDA2822M, you might lift pin 1 and insert a 4 or 8 ohm 1/2 watt resistor in series there as a precaution.

If really paranoid, perhaps add an 8 or 9v linear regulator (or string of diodes) to reduce Vcc into the TDA2822M.

I have no idea how R75 could have smoked, except maybe a catastrophic failure in the TDA2822M 
shorted that (normally) input pin to Vcc somehow.

How many have blown?   Maybe 2 or 3?  In all cases, is it possible the output got shorted?

Jerry, KE7ER

On Sat, Feb 24, 2018 at 04:54 pm, Bill KC5SB wrote:
Yep, one of the speaker leads could have been grounded - not sure.  Whatever happened, U1 came out on the short end of the stick.  Note to self - be careful with speaker leads.
Examination of the solder joints on the bottom of the board indicate no problems and quality workmanship.

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