MIDI Time Piece - question

[Bissell, Harry]

If you can get some more information, I'd take an educated guess...
What is the DC voltage of the Power Supply Adapter, and what Current ( Volts
DC and Milliamps Out)
Can you tell what voltage the internal circuit runs at (a guess would be 5V)
but having that circiut from the resistor to the internal ckts run to a 7805
or similar regulator chip would make the voltage a for-sure. What voltage is
the first big capacitor that run goes to? (It must be higher than the
supply). With this info I could tell what value the resistor might have been
(at least safe enough so it won't blow up again) You might be right about
the purpose of the resistor in the circuit. When it is working, the power
dissapated in the part would normally be low. Is it a 1/4 watt resistor
size?  

Without that info, I'd guess that 20 ohms is too high a value. Try about 10
ohms to start, then measure the voltage across the part. Use Ohms law to
find the Current, and multiply by the voltage ot get watts.
Watts in your case should probably be less than .1 (assuming a .25W
resistor) Anything more than that is going to get the resistor real hot, and
the value should be made smaller.

If there is more internal damage, any resistor you put there will get hot.
Also, you could try a fuse (1/10A) or so in place of the resistor, to see if
there is any real bad damage you don't see yet.

Happy Hunting: Harry

> -----Original Message-----
> From:	WeAreAs1 at aol.com [SMTP:WeAreAs1 at aol.com]
> Sent:	Tuesday, February 02, 1999 5:35 AM
> To:	synth-diy at mailhost.bpa.nl
> Subject:	MIDI Time Piece - question
> 
> Hello DIY'ers -
> 
> I have acquired a MOTU MIDI Time Piece that has a small problem in the
> power
> input section.  There is a resistor which is in series with the DC input
> jack.
> This resistor has burned out (completely open), and it's not possible to
> tell
> what the value of the resistor was (it's kind of charred).  I'm guessing
> that
> the former owner tried powering it up with the wrong polarity power supply
> (although he wouldn't admit it...).  The unit has a 1N4002 diode across
> the
> power input and ground (with the anode going to ground).  This diode
> protects
> the unit from inadvertent reverse-polarity supplies, and the resistor is
> probably there to act as kind of a fuse, in the event that someone plugs
> in a
> backwards supply.  Obviously, the resistor has done its job, and valiantly
> given its life in service.  I'm fairly well convinced that replacing the
> resistor is all I will need do to bring the MTP back to life (I've seen
> this
> before in various other pieces - it's usually the diode or a similar
> resistor/fuse).
> 
> I'm hoping that someone on the list might have a MIDI Time Piece and be
> willing to look inside to find the value of the resistor for me.  It's in
> the
> corner of the board that is closest to the DC input jack and the two 1/4"
> SMPTE jacks.  It's labeled "R0", and judging by what's left of this one,
> it's
> probably 2.2 ohms or maybe 22 ohms.  It's located right next to the DC
> input
> jack, and there are no other resistors in this area.  Can anyone help?
> This
> is exactly the kind of question that is next to impossible to get answered
> by
> MOTU's, um, "product support" department.  Proprietary "stealth resistor"
> technology, you know.  Wouldn't want it falling into the wrong hands.
> 
> Please let me know if you can help me on this.  
> 
> Thanks,
> Michael Bacich
> 
> P.S. -  It's an original MIDI Time Piece, not a MIDI Time Piece II.