mxr phase 90 hit with 18v power supply instead of 9v

alan brotz · August 07, 2011, 06:51:41 AM

What damage should i look for since the unit was accidentally plugged into an 18vdc supply? I would imagine that the op amps are fried..This is one of the newer units...model m-101 with only 2 ic's...an 8 pin and a 14 pin. Thanks for the help..Alan

selfpreservation · August 08, 2011, 08:05:21 AM

i dont know mate but most i think op amps have a pretty large voltage range usually 3 - 30v that ive seen

Circuitbenders · August 08, 2011, 11:34:37 AM

find the datasheets for the opamps and find out what the maximum supply voltage is. I'm guessing it'd be 18v or more but i wouldn't take it for granted that your PSU is actually supplying 18v unless its fairly expensive.

Next step would be to read this post by Gordonjcp which just happens to explain the workings of the Phase90 in intimate details http://www.circuitbenders.co.uk/forum/index.php/topic,1532.15.html

...... and then give him some positive karma!

alan brotz · August 10, 2011, 02:52:07 AM

Gentlemen, thanks so much for your suggestions....time to break out the meter and o'scope and find the culprit. I will report back as soon as it's fixed for your and others information. Thanks again...what a great website!!!

Gordonjcp · August 16, 2011, 01:34:38 PM

The opamps are just pennies. I'd replace them both, and I don't normally advocate just shotgun-replacing components ;-)

I also say you should never "re-cap" a piece of equipment unless you have hard evidence that the capacitors are faulty, but I'd be paying some attention to the behaviour of the decoupling caps across the supply. They're probably fine though.

alan brotz · August 17, 2011, 04:27:45 AM

Once again....thank you! Had some time this past weekend to do some testing and found the 4.7v zener diode shorted. I'll replace it and re-post...Loads of Karma to you all...Alan

Gordonjcp · September 12, 2011, 12:14:14 PM

That would do it, making a lovely mess of your "0V" rail ;-)