rackmount mod safety

[famous beagle]

Hey everyone,

I've worked on tube guitar amps before, and I know there's a shock hazzard with those and you need to discharge the caps before working on it, even with it unplugged from the wall.

But I've never worked on a rackmount processor, and I was wondering if the same problem exists. I want to modify my old DOD R-825 compressor by replacing the op amps in it. Is it safe to poke around in there once it's been unplugged, or do I need to do anything beforehand?

Thanks

 

[Lt. Bob]

nah, make sure it's unplugged and that'll do it ..... you don't have anything storing the large amounts of juice that tube amp power supplies have in those big caps. Heck ...... lots of rack mounts use wall wart power supplies and that's where the danger would lie anyway although those little power supplies aren't gonna store enough electricity to amount to much.

 

[famous beagle]

nah, make sure it's unplugged and that'll do it ..... you don't have anything storing the large amounts of juice that tube amp power supplies have in those big caps. Heck ...... lots of rack mounts use wall wart power supplies and that's where the danger would lie anyway although those little power supplies aren't gonna store enough electricity to amount to much.

Ok, thanks! That's what I figured, but I didn't want to take any chances.

 

[Chili]

But you do want to be careful with electrostatic discharge. Especially if the humidity is low. Make sure you're well grounded when touching components, don't work on the carpet, etc, etc.

 

[antichef]

Yeah, I'd be dead by now if there was significant danger. If the unit has an internal power supply, then it has filter caps, and these might have enough juice to be painful, but the trick is to stay away from them, and that's usually pretty easy.

On the subject of safety-for-the-device-itself, it's worth determining whether you're working with a multi-layer circuit board before you start yanking the old opamps. I pretty much bricked my Digital MPA, because it has a two layer circuit board, and when I pulled the old (unsocketed) opamps, I hosed up a bunch of traces without even noticing. I eventually got it working again, but it really sucked.

Of course, if your opamps are socketed, then this is not an issue at all.

 

[dgatwood]

Yeah, I'd be dead by now if there was significant danger. If the unit has an internal power supply, then it has filter caps, and these might have enough juice to be painful, but the trick is to stay away from them, and that's usually pretty easy.

Even with filter caps in the power supply, unless you're dealing with a switching supply, the filter caps are attached to the DC rails, so the device itself provides enough load to drain them very rapidly---usually in a fraction of a second. It is, however, a good idea to switch the device on with the device unplugged. That way, even if the power switch is on the DC side instead of the AC side (bad design), the filter caps still get discharged.

On the subject of safety-for-the-device-itself, it's worth determining whether you're working with a multi-layer circuit board before you start yanking the old opamps. I pretty much bricked my Digital MPA, because it has a two layer circuit board, and when I pulled the old (unsocketed) opamps, I hosed up a bunch of traces without even noticing. I eventually got it working again, but it really sucked.

That's also a good reason to follow the first rule of junk parts: cut the leads, then unsolder them one at a time.

 

[famous beagle]

Yeah, I'd be dead by now if there was significant danger. If the unit has an internal power supply, then it has filter caps, and these might have enough juice to be painful, but the trick is to stay away from them, and that's usually pretty easy.

On the subject of safety-for-the-device-itself, it's worth determining whether you're working with a multi-layer circuit board before you start yanking the old opamps. I pretty much bricked my Digital MPA, because it has a two layer circuit board, and when I pulled the old (unsocketed) opamps, I hosed up a bunch of traces without even noticing. I eventually got it working again, but it really sucked.

Of course, if your opamps are socketed, then this is not an issue at all.

Thanks for the help y'all. Luckily, these op amps are socketed.