Damage from DC power supply?

Mike Wheeler · Post by **Mike Wheeler** » 20 Apr 2005 7:05 pm

John is right. I've been an practicing engineering tech for 37 years and I use the same procedure. It works.

edit: The key word is "analog" ohm meter. It provides enough current to bias the diode...most digitals don't.[This message was edited by Mike Wheeler on 20 April 2005 at 08:09 PM.]

John Daugherty · Post by **John Daugherty** » 21 Apr 2005 1:38 am

Mike,Thanks for verifying the info. We are here to help a fellow member fix his equipment,to the best of our ability. If anyone knows a better way,by all means jump in here. Criticism without a solution is worthless. Now,maybe,we can get back to work.
I want to add this: The "ohms" test WILL work "in-circuit" because a rectifier circuit cannot operate with a low resistance across a diode. If the diode has a low resistance component in parallel with it, it cannot function as a diode. Therefore any reading lower than 15 ohms in either direction indicates a defective diode.[This message was edited by John Daugherty on 21 April 2005 at 02:40 AM.]

Paul Osbty · Post by **Paul Osbty** » 21 Apr 2005 2:20 am

Silicon or Germanium?

As I said, "Use a Diode Check mode to check diodes." That is a valid response and far from "worthless". I would advise no other way nor will I elaborate.

To please you further, I will refrain from offering advice on this forum anymore.

It's too bad. I liked this place. I regularly went through the Electronics questions that had no responses and went out of my way to get people answers. I thought I was contributing to the forum, but I'll leave that to you guys.

Sorry, b0b.

LARRY COLE · Post by **LARRY COLE** » 21 Apr 2005 2:37 am

I once got my wall warts switched and had to replace the transistor and two diodes in the power supply circuit in a J L Cooper PPS-2 midi sync box. Now all of my power supplies have what unit they are for written in silver paint marker on all sides.

------------------
Playing For JESUS,LC. WILLIAMS U12,SHO-BUD PRO1,CARVIN TL60,GIBSON LES PAUL CUSTOM,YAMAHA L-10A ACOUSTIC,ROLAND JW-50 KEYBOARD,G&L AND BC RICH BASS'S

Robert Parent · Post by **Robert Parent** » 21 Apr 2005 4:02 am

1N4002 diodes are silicon.... One very seldom finds germanium diodes these days. When testing you need to have enough voltage in the test circuit to bias the silicon (~0.6 - 0.7volts) in the forward direction. As mentioned testing with a 1.5v circuit should work just fine. Majority current should flow in one direction but not the other.

John Daugherty · Post by **John Daugherty** » 21 Apr 2005 4:12 am

Paul, don't give it up. We want your help. Mark wants to know how to check those diodes and caps. He probably does not have a meter with the so-called "diode test". BTW, power supply diodes will be "silicon" diodes.

Mike Wheeler · Post by **Mike Wheeler** » 21 Apr 2005 4:39 am

Paul,

All input is valid. You obviously have substantial electronics knowledge, and that is valuable to others. Please continue to share it with the rest of us.

I don't believe anyone was intending to diminish your input. Just remember, this is a discussion based forum. As such, there will be various opinions and suggestions for solving any given problem or question. There are many paths to consider.

Thanks for your participation. I for one appreciate it.

Mark Herrick · Post by **Mark Herrick** » 21 Apr 2005 12:56 pm

Jeez, I didn't mean to start a fight...

The only meters I have are inexpensive digital units. No Rx1 scale.

I think I may just get a new Alesis power supply and try that. If it works, no damage. If it doesn't, then I'll go further.

I still don't know how to check the capacitors.

I know this doesn't help much but here's a link to a drawing of the area of the board near the power supply jack. The rectangular things are the diodes:

MidiVerb II