how to avoid getting shocked

[aragorn723]

Hi,

I have a large solid-state amp - an Inter-m R500.  It came with handles installed, but a few years ago, a friend removed them for me.  I would like to put them back on, but one has a transformer directly behind it.  Is there a way to measure the voltage in the amp to determine if it's safe to reach in and work?  (This would be at my own risk).  After that, the usual safety measures apply-wearing rubber-soled shoes, only one hand in the amp at a time, etc.  Any help would be appreciated.  Thanks,

Dave

[Paul Joppa]

Add to your safety measures Number One: Unplug the damn thing!

Yes, a 500-w amp will have a minimum of +/-100v power supply rails, more in real life. Anything over 24v or 40v is too much according to the Authorities in different countries. Hopefully they will drain after it is unplugged, but hopefully is not an adequate protection! You'll have to find some safe way to monitor the power supply if you are to have confidence.

[aragorn723]

Paul,

Yes, agreed, unplugging goes without saying    What if I disconnect the IEC plug on the back, then clip lead each of the terminals to a multimeter?  (guessing that should be on an AC setting).  Or, leave the power plug in the amp, and connect the hot plug to the + on the meter, and common to the -.  Good?

Dave

[Paul Birkeland]

There are giant filter capacitors in 500W solid state amps.  Usually they are sticking up with screw terminals, measure the DC voltage across them.

[aragorn723]

Hi Paul,

Just found a pic of the inside.

http://i56.tinypic.com/2mi19ty.jpg

Looks like there's no easy way to get to the leads of the big caps; the bottom and sides of the chassis are one piece.  Any ideas?

Dave

[2wo]

The 2 big black caps is the area of possible danger. They are a fair distance from the transformer. I think that if you unplug the amp and let it sit for a few days, then just use care and keep your hand away from that part of the board and the rectifier...John 

[Grainger49]

I'm with John, there are only two big caps well away from the front of the chassis.  The handles should be installed with no fear of shock.  If you want put a wash cloth, dry of course, over the back board were the caps, fuses and diodes are.  If you touch that you know not to rest your hand on it.

[mcandmar]

Looks safe to me, as above just leave it unplugged for a while before taking it apart.

Found you a copy of the service manual -> http://62.49.91.212/interm/audiosm1/R-150_300_500.pdf

[aragorn723]

What about if I touch the transformer?  There's a shield on the top, but touching it is almost unavoidable because of where the handle screws will go.  Is having the amp unplugged for a full day enough time?  Thanks,

Dave

[Grainger49]

If it is unplugged the transformer will have no voltage on it.  The capacitors are the only things that store a charge.  So you are pretty safe.

[aragorn723]

Thanks!

[aragorn723]

Got 3 of 4 screws in.  There is a screw deep in one side in the pic below, can't seem to get that one in, even with a right angle screw driver.  Any suggestions?

Dave

[Grainger49]

Does the bottom of the chassis come off?  Would it help to remove the two slide on lugs on the power switch.  If not, you might need to unmount the power transformer.

How did your friend remove the handles?

[aragorn723]

It was quite a few years ago, but he didn't take anything apart.  Maybe it was just a regular straight-shafted screwdriver, but I can't remember.  It looks like there are some screws on the bottom that hold in the faceplate, so maybe if those come off and there is enough slack in the cables going to the front board, I can work it that way.

Dave

[Paul Birkeland]

Go to the hardware store and get a hex head screw to replace that one, then use a ratcheting box end wrench to snug it in.

-PB