|
|
Post by leonski on May 4, 2016 19:52:54 GMT -5
I have seen several threads lately in which changing fuses has been mentioned. One user was asking 'how to use my new DVM'. This guys is a PERFECT candidate for NOT opening the case. EVER.
IMO, if you don't KNOW how to use your DVM, you have NO BUSINESS cracking into the case and messing around. I just hope the guy At Least UNPLUGGED the amp for a while prior to going for it.
PS Capacitors hold a NASTY charge for an unknown amount of time. I've seen plenty of 'em with RESISTORS across the terminals to provide for self discharge when the power is removed. However, an OPEN resistor is as good as NO resistor. Learning how to safely discharge such caps or wait maybe even several HOURS is good, too.
IF Emotiva were to move the fuses to the Back Panel, that might help. It would cost a few pennies per amp, but save on service calls and shipping amps back and forth to simply install a new fuse. If it pops a 2nd fuse? Seek professional help.
Some other devices, (MICROWAVE OVENS) can be Deadly. Defeating the safeties and energizing the circuit can kill you. Stuff like Microwave Emissions will COOK you as well at that popcorn you love.
Safety First is NO accident.
|
|
klinemj
Emo VIPs 
Official Emofest Scribe
Posts: 15,086
|
Post by klinemj on May 4, 2016 20:02:13 GMT -5
So...I should unplug my gear and stick my tongue in the outlet quickly?
Confused...NOT!
Mark
|
|
|
|
Post by Jim on May 4, 2016 20:30:15 GMT -5
So...I should unplug my gear and stick my tongue in the outlet quickly? Confused...NOT! Mark I got bored with 9v batteries - instead of coffee, I just stick knives in my outlets each morning and hang on. Wait. Should I not do that? /off to point magnetron tubes at cats and squirrels. |
|
|
|
Post by rbk123 on May 4, 2016 20:47:05 GMT -5
|
|
|
|
Post by leonski on May 4, 2016 23:55:54 GMT -5
I'm glad everyone takes safety so seriously.
|
|
KeithL
Administrator 
Posts: 10,261
|
Post by KeithL on May 5, 2016 11:09:33 GMT -5
Technicians often use what's commonly known as a "suicide cord"... which is a line cord with a plug on one end and a pair of alligator clips on the other. You can simply attach one clip to each earlobe.... it's neat, and you don't have to worry about it falling off... So...I should unplug my gear and stick my tongue in the outlet quickly? Confused...NOT! Mark I got bored with 9v batteries - instead of coffee, I just stick knives in my outlets each morning and hang on. Wait. Should I not do that? /off to point magnetron tubes at cats and squirrels. |
|
|
|
Post by pedrocols on May 5, 2016 11:15:09 GMT -5
So.....I am very safe then because I do not own an Emotiva amp! In addition, I do not run the risk of taking anybody's suggestion to poke my nose inside an amp!  Please people Safety First!!! |
|
|
|
Post by leonski on May 5, 2016 11:31:48 GMT -5
Keith,
I WISH you had BEEN THERE maybe 35 years ago. I was working on an IMPLANTER. You have 2 main High Voltage power supplies. A fixed supply of about 20KV called the Extraction PS. And the OTHER supply which goes to up to 200KV and puts out some JUICE. Virtually ALL semiconductors you use in EMO amps have been thru such a machine from as few as 3 times to maybe 5 or 6 for complex integrated circuits.
Long / Short. (no pun intended) We were working OPEN BOX with the terminal box open. That's the INSIDE of the machine which is seperate from the REST of the machine by a large air gap and sits on long ceramic INSULATORS. When open for service you put the 'chicken stick' on it which is a long plastic stick with a metal HOOK connected to a copper braid which runs to GROUND. This is your 2nd safety. Usual practice is for a ground bar to come down as you open the outer doors and (1st safety) and yet a 3rd safety is the door switches which turn off stuff when you simply open certain doors. The Outer doors are lead-lined for soft x-ray purposes and weigh a ton. ALL safeties were off on the day of the incident.
We were having high voltage issues. So, me and my partner propped a FLUKE DVM up on top of the terminal with the high voltage probe connected to the point of interest. We could see the meter from where we stood, well outside the outer enclosure. Safe, right? NOT A CHANCE. When we kicked on the extraction all was OK. But when we went for the problem by turning ON the high voltage there was a HUGE flash of light and a BANG. The Meter was reduced to a Plastic / Carbon Wreck. Totally destroyed. OOOPS!
We were more careful with the NEXT meter and DID fix the darn thing.
I hope NOBODY here has to find out the hard way about electricity. I take my safety very seriously even measuring House Current or when working on a CAR.
|
|
KeithL
Administrator
Posts: 10,261
|
Post by KeithL on May 5, 2016 11:31:53 GMT -5
BUT SERIOUSLY FOLKS..... 
There are absolutely definitely voltages inside ANY line-powered piece of equipment that can quite literally KILL you.
(And, for that matter, you shouldn't go sticking fingers in live light sockets either.)
Even experienced electricians and engineers occasionally make fatal mistakes - and they don't always get a do-over.
And we should also mention that, even if you don't kill yourself, if you make modifications or sloppy repairs to something, you could also succeed in burning your house down the next time you plug it in.
Other than things like phones, and flashlights, which run on small batteries......
IF YOU DON'T KNOW EXACTLY WHAT YOU'RE DOING THEN DON'T DO IT !!!
Don't open things up and go messing around inside unless someone (who knows) instructs you to do so - or you know what you're doing.
And, if you're going to be changing board-mounted fuses, you should ALWAYS unplug the unit, and avoid touching other stuff nearby.
In many cases, it's sort of obvious when a fuse is blown (it's all black, or there's an obvious gap in the wire inside).
However, it's not uncommon for a blown fuse to look OK - because the gap is inside the cap where you can't see it - in which case you need to measure it to be sure.
To check a fuse with a DMM, you want to pull the fuse, then measure the resistance across it - on the "low ohms" scale.
Measuring a fuse while it's still in the clip MAY NOT give you a correct reading (it depends on the other circuitry).
This means that you usually want to lay the fuse on the table (NOT a metal table  ), then put one probe on each metal end cap.
Touching the probes with your fingers will affect the reading - but not significantly on the low ohms scale.
The resistance should be less than one ohm (you may measure an ohm or so due to the resistance of the probes with a cheap meter).
Many meters also have a "continuity" range - which you can also use - a fuse should be "continuous".
It will measure very high if it's blown (a fuse is either good or not).
(Note: AVOID old style "battery and bulb" or "flashlight" continuity testers with low-value fuses; some of them can actually blow the fuse you're trying to test.)
As far as poking around with a DMM, unless you know what to look for and where, even if you don't hurt yourself, you're unlikely to find out anything useful.
|
|
|
|
Post by leonski on May 5, 2016 11:34:32 GMT -5
And Pedrcols with his TUBE amps have that nice B+ power supply which can run up to maybe 500 to 600volts. Now THERE'S a nasty shock for 'ya.
|
|
KeithL
Administrator
Posts: 10,261
|
Post by KeithL on May 5, 2016 11:45:38 GMT -5
Ouch... well, at least it only cost you a meter. Too many people these days don't have enough respect for electricity. Keith, I WISH you had BEEN THERE maybe 35 years ago. I was working on an IMPLANTER. You have 2 main High Voltage power supplies. A fixed supply of about 20KV called the Extraction PS. And the OTHER supply which goes to up to 200KV and puts out some JUICE. Virtually ALL semiconductors you use in EMO amps have been thru such a machine from as few as 3 times to maybe 5 or 6 for complex integrated circuits. Long / Short. (no pun intended) We were working OPEN BOX with the terminal box open. That's the INSIDE of the machine which is seperate from the REST of the machine by a large air gap and sits on long ceramic INSULATORS. When open for service you put the 'chicken stick' on it which is a long plastic stick with a metal HOOK connected to a copper braid which runs to GROUND. This is your 2nd safety. Usual practice is for a ground bar to come down as you open the outer doors and (1st safety) and yet a 3rd safety is the door switches which turn off stuff when you simply open certain doors. The Outer doors are lead-lined for soft x-ray purposes and weigh a ton. ALL safeties were off on the day of the incident. We were having high voltage issues. So, me and my partner propped a FLUKE DVM up on top of the terminal with the high voltage probe connected to the point of interest. We could see the meter from where we stood, well outside the outer enclosure. Safe, right? NOT A CHANCE. When we kicked on the extraction all was OK. But when we went for the problem by turning ON the high voltage there was a HUGE flash of light and a BANG. The Meter was reduced to a Plastic / Carbon Wreck. Totally destroyed. OOOPS! We were more careful with the NEXT meter and DID fix the darn thing. I hope NOBODY here has to find out the hard way about electricity. I take my safety very seriously even measuring House Current or when working on a CAR. |
|
|
|
Post by leonski on May 5, 2016 11:47:11 GMT -5
Thanks, Keith, for FINALLY chiming in on the side of Reason. The guy who was ASKING how to use a DVM gave me the Willies. I don't want to read about some guy having the last accident. And Yes, without a schematic and a knowledge base? Forget it. I'm a decent tech and I won't go inside ANY of my gear. I don't have the measurment equipment (a scope would be nice) or the schematics. About all I could do was:: 1. Check fuses. If I was the manufacturer, at least the MAIN power fuse would be back panel. Rail fuses? we can talk 2. Clean Volume Pot. Some contact cleaner LIGHTLY applied won't hurt anything. DON'T DROWN IT. 3. If I suspect a cold solder or IFFY output device, I MIGHT go to the can of Cold Stuff. Thermal Shocking stuff CAN help with a diagnosis. Again, I agree with Keith. if you DON'T KNOW…….than DON'T. As for a high current flashlight style or battery and bulb tester? JUNK. We had, prior to the advent of a decent DVM, a meter I STILL wish I had. The Simpson 260 VoltOhmist series was the BEST. It had a REAL meter (mirrored) and would provide enough voltage so we could check transistors. It almost took 3-hands, but using the ohm scale you could put one probe on one lead and the OTHER probe across the OTHER 2 leads which if the transistor was good, would turn it 'on'. Slide the probe tip OFF one of the 2-leads and the device would STAY gated ON. Indestructable meter, too. THEY STILL make 'em but they are $$$$$ for the casual home user. www.simpson260.com |
|
|
|
Post by Jim on May 5, 2016 11:52:02 GMT -5
Technicians often use what's commonly known as a "suicide cord"... which is a line cord with a plug on one end and a pair of alligator clips on the other. You can simply attach one clip to each earlobe.... it's neat, and you don't have to worry about it falling off... I got bored with 9v batteries - instead of coffee, I just stick knives in my outlets each morning and hang on. Wait. Should I not do that? /off to point magnetron tubes at cats and squirrels. Interesting. I've heard of a suicide cable before. Typically used for (improperly) backfeeding:  |
|
|
|
Post by Jim on May 5, 2016 11:53:25 GMT -5
I'm glad everyone takes safety so seriously. I take safety seriously, that's why I made an electric guitar: |
|
|
|
Post by Jim on May 5, 2016 11:55:40 GMT -5
Don't forget about ESD safety!
|
|
|
|
Post by monkumonku on May 5, 2016 12:31:53 GMT -5
Don't forget about ESD safety! I notice the main URL for this and that make your own guitar video is ELECTROBOOM.COM. Is that Boomzilla in those videos??? |
|
|
|
Post by pedrocols on May 5, 2016 13:10:52 GMT -5
And Pedrcols with his TUBE amps have that nice B+ power supply which can run up to maybe 500 to 600volts. Now THERE'S a nasty shock for 'ya. Precisely! I have measured the B+ when I turn on the amp and you are absolutely right! |
|
klinemj
Emo VIPs
Official Emofest Scribe
Posts: 15,086
|
Post by klinemj on May 5, 2016 13:57:59 GMT -5
Of course safety is important. But being safe with electrical things is not terribly hard. Following a few basic rules is all it takes.
Mark
|
|
|
|
Post by garbulky on May 5, 2016 14:50:08 GMT -5
So uh what's DVM? I assume it's not related to EDM and there's no Skrillex involved. I would like to know because I am standing here in my boxers. I've got no shoes but I grounded myself by getting in the bathtub. I plant to cool my emo amps by turning on the shower. After safely cooling it down then I shall get to work. (But seriously, what's DVM?  ) |
|
|
|
Post by rbk123 on May 5, 2016 15:26:15 GMT -5
Hey what a good looking crowd. I just flew in from Boston, and boy are my arms tired. Take my wife, please. You've been great, don't forget to tip your waiters.
|
|
), then put one probe on each metal end cap.
) 