Re: 556 problems

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Fucian-at-aol-dot-com>

In a message dated 2/9/02 9:40:36 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

<< Matt
 
 Need a schematic to help you.   8 volts out with a 14 V supply
 means something is seriously overloading the supply. May have
 a bad totem transistor, or bad/damaged 556.  Make
 sure your voltages are to the correct points on the 555/556.
 Direct power connections to certain points (discharge comes
 to mind) will detonate a 555.  It will catch fire.  Is anything
 running hot (if you can't hold your finger on it more then a
 second, its TOO HOT).  Also make sure to bypass each end
 of 555/556 with 1uF +0.1uF ceramic disk.  A soft power
 supply will cause ground bounce and can "confuse" the timer.
 
 Visually check board for workmanship and solder bridges,
 that may expalin where the power supply overloading is
 coming from.
 
 Regards
 Dave Sharpe, TCBOR
 Chestefield, VA. USA
  >>
Everything runs cool.No hot spots.Ive got several 556 timers and have tried 
replacing it.No help.Ive checked the board for solder bridges and still 
nothing.When you say bypass each end do you mean each unconnected pin?Does it 
have to be a ceramic?Wont a 1uf ceramic be very big?The transistors are good 
too.I used them right out from the solderless breadboard.

Its so strange that every time i transfer the circuit to a Radio Shack board, 
it goes nuts.Always 9 volts out.

As far as a circuit goes, MAXIM has a simple schematic for a 50%duty cycle.It 
uses only 2 parts.A timing cap and a pot for tuning.Im just doing this to 
both sides of a 556 timer and connecting the output of the staccato to the 
reset of the second timer.

I have had the 555's blow up before in the past.I dont know why.Probably cuz 
it was an unregulated input.Now im using a regulator and it stays nice and 
cool.

Again, maybe its Evil Radio Shack spirits!LOL!

Matt