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#1
Old 12-29-2017, 05:01 PM
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What are the odds of killing myself trying to fix my amp?

Even if you unplug it the capacitors hold a charge. I was reading online that it can be very dangerous to work on them if the capacitors are not fully drained. I don't have a tube amp, I have a cheap piece of shit I found at a thrift store for $20. I don't want to risk death for this amp, it's a cheap piece of shit; even if I got it to power up again, it would still be a cheap piece of shit. But I'm also a cheap piece of shit, so I don't wanna just throw away $20. I saw some various ways of draining the capacitors, but I'm afraid to even open it up with out having a better idea of what I'm doing. Any suggestions?
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#2
Old 12-29-2017, 05:23 PM
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What's wrong with it; what's it doing/not doing?
#3
Old 12-29-2017, 05:42 PM
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(Warning! Don't kill yourself and blame me!) If this is your average solid-state amp, the danger is not very great. Old CRTs operated at much higher voltages and they could really kick you on your butt. I've worked on a lot of "piece of shit" amps and never really worried about discharging the caps. In fact, trying to discharge the caps when you don't know exactly what you're doing is more likely to cause other problems in the circuitry than protect you. Now, a NICE amp may surprise you when you poke around in it (as well as screwing up the circuitry).
#4
Old 12-29-2017, 05:44 PM
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Make and model would help a lot.
#5
Old 12-29-2017, 06:44 PM
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Quote:
Originally Posted by burpo the wonder mutt View Post
What's wrong with it; what's it doing/not doing?
It won't turn on, I think I blew a fuse, but maybe that's just wishful thinking - I can't solder for shit. It would turn on and have really crap/nonexistent base when I first got it. Then I started running it through a mixer from a piece of crap drum kit on the input and into headphones on the output. I'm a shitty drummer also, I'm not sure if that factors into the equation.
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#6
Old 12-29-2017, 06:52 PM
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Do not do this.
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#7
Old 12-29-2017, 07:01 PM
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Originally Posted by Mr. Nylock View Post
Even if you unplug it the capacitors hold a charge. I was reading online that it can be very dangerous to work on them if the capacitors are not fully drained. I don't have a tube amp, I have a cheap piece of shit I found at a thrift store for $20. I don't want to risk death for this amp, it's a cheap piece of shit; even if I got it to power up again, it would still be a cheap piece of shit. But I'm also a cheap piece of shit, so I don't wanna just throw away $20. I saw some various ways of draining the capacitors, but I'm afraid to even open it up with out having a better idea of what I'm doing. Any suggestions?
it depends where the capacitors are. if they're in the power supply section, they'll be somewhere around mains voltage (120V, assuming you're in North America.)

if they're in the audio section, they could be anywhere from 12-40 volts.

tube amps were the dangerous ones because they had plate voltages in the range of several hundred volts.
#8
Old 12-29-2017, 07:10 PM
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If it's solid state, then at the most you could have around 170 V on some caps. But they're likely discharged by now.

Unplug the amp. Then turn on the power switch and fiddle with all the knobs and other switches - doing this will very likely discharge the caps. After you take it apart, identify the power supply caps and discharge them for good measure.
#9
Old 12-29-2017, 07:32 PM
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you'd be hard pressed to be able to disconnect it from the power supply & start messing with it quickly enough to get any type of tingle, much less shocked.

test my advice by shorting something metal across it's leads, remember though - with the power disconnected to it.

did you see a spark? no.

did the metal you used to short the capacitor heat up? no.



there are surely capacitors that could get someone pretty good, i just don't think you'll find many with the capability to do anything in consumer electronics that have been unplugged, especially after a minute or so.

I've been lit up before with a 10mfd/120 volt cap for a fan motor that operating. I've been shocked several times over the years. that one would've killed me if i were older or in worse shape physically.
#10
Old 12-29-2017, 09:55 PM
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Fuses usually aren't soldered in, they fit in clips or sit in a holder with a screw-off cap.

Like beowulff said, a brand name and model would be a big help.
#11
Old 12-29-2017, 10:11 PM
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^ Example: Fender Princeton, model #THX-1138. Model number found on a plate near the AC cord.

Last edited by burpo the wonder mutt; 12-29-2017 at 10:11 PM.
#12
Old 12-29-2017, 11:08 PM
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Originally Posted by burpo the wonder mutt View Post
Fuses usually aren't soldered in, they fit in clips or sit in a holder with a screw-off cap.

Like beowulff said, a brand name and model would be a big help.
I know that much, that's why I hope it's just a fuse and nothing else. My soldering skills are shit, probably get a bunch of cold solders and what not if I had to do a more involved repair. Sorry about the delay, but I'll get back to you with the model; I'm in bed now - if i start rustling around to much my wife might wake up and she'd be especially pissed since Aunt Flow is visiting this week.
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Last edited by Mr. Nylock; 12-29-2017 at 11:11 PM.
#13
Old 12-29-2017, 11:19 PM
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Quote:
Originally Posted by Mr. Nylock View Post
probably get a bunch of cold solders and what not if I had to do a more involved repair.
Heat the part, not the solder. Heating the solder is what often causes cold solder joints. Heat the part, let the solder flow onto it. That will make a much better solder joint.

Also, make sure the tip of your soldering iron is clean. Use a wet sponge to keep it clean. Tin your soldering iron (put a bit of solder on it) but don't put a big glob of solder on it.

Fuses generally don't just pop on their own. Even if you do find a bad fuse, there's a good chance you've got some other issue as well, like a bad tube or capacitors that are dried out and failing.

The crap/nonexistent bass makes me think bad capacitors or a bad ground (signal return) somewhere. You may have more than one problem here.
#14
Old 12-30-2017, 10:52 AM
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Quote:
Originally Posted by engineer_comp_geek View Post
Heat the part, not the solder. Heating the solder is what often causes cold solder joints. Heat the part, let the solder flow onto it.
I've always found this advice somewhat misleading.
When I solder, I feed the solder into the corner formed by the soldering iron tip and the part being soldered. Many times, the solder won't melt very easily until some of the flux coats the work. Pre-melting some solder helps with heat transfer.
#15
Old 12-30-2017, 11:29 AM
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Quote:
Originally Posted by burpo the wonder mutt View Post
Fuses usually aren't soldered in, they fit in clips or sit in a holder with a screw-off cap.

Like beowulff said, a brand name and model would be a big help.
It says T-Power on it, but other than that, I can't find any sort of model# on it; it's not in any of the places a model# usually would be. It's made in Korea, I don't know if that particular piece of information is useful, but it's all I got at the moment.

Quote:
Originally Posted by engineer_comp_geek View Post
Heat the part, not the solder. Heating the solder is what often causes cold solder joints. Heat the part, let the solder flow onto it. That will make a much better solder joint.

Also, make sure the tip of your soldering iron is clean. Use a wet sponge to keep it clean. Tin your soldering iron (put a bit of solder on it) but don't put a big glob of solder on it.

Fuses generally don't just pop on their own. Even if you do find a bad fuse, there's a good chance you've got some other issue as well, like a bad tube or capacitors that are dried out and failing.

The crap/nonexistent bass makes me think bad capacitors or a bad ground (signal return) somewhere. You may have more than one problem here.

I took it apart, I'm not dead yet. The fuse is busted and it looks like at least one of the capacitors is bad - it has some nefarious looking brown stuff on it. I was gonna just replace the fuse and see what happens, but then I was wondering if I should also replace the capacitor before powering on and testing.
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#16
Old 12-30-2017, 11:32 AM
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Bad caps are the #1 cause of power supply failures. Replace it.
#17
Old 12-30-2017, 12:31 PM
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Quote:
Originally Posted by mr horsepower View Post

test my advice by shorting something metal across it's leads, remember though - with the power disconnected to it.

.
Don't do this. You may damage the capacitor. (and definitely the screwdriver you're shorting it with)

Proper practice is to put a 10-Ohm wirewound resistor of several watts rating across the capacitor for a second or two. Thus the current is limited.
#18
Old 12-30-2017, 01:34 PM
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Quote:
Originally Posted by beowulff View Post
Bad caps are the #1 cause of power supply failures. Replace it.
IANAE; many (many) years ago I was fiddling with capacitors and a 9-volt battery. I'd connected the capacitor a few times, then I accidentally shorted it with my finger and got a strong shock. But - this was capacitors in the size of a 35mm film can give or take. This or bigger is what you'd find in tube equipment and really old PC's.

Today, unless you bought a 400-watt amp, you'll be fine. unplug it, let it sit for a minute, then try the short trick with a screwdriver you wouldn't be sad to lose. (I had a friend who tried to fix an electrical outlet - it left a small semicircular hole in his knife blade while he removed insulation, because the electricity in the house was backward, the neutral as the live, so the breaker didn't kill the power. That's 120V, lotsa watts) Anything smaller around than your thumb, you are more likely to get a nasty shock unless you give it a minute to drain. Bad capacitor - probably no charge anyway.

There was a problem with capacitors about the early 2000's. Someone in Taiwan sold a huge number of electrolytic capacitors containing a faulty fluid (allegedly someone else sabotaging an attempt at industrial espionage by feeding the wrong list of ingredients for the electrolyte). So any seriously bulging or leaking electrolytes could be a problem.

Also as a hobbyist friend of mine found many years ago trying to fix an early computer of mine (adding memory) - there are soldering irons and there are soldering irons. the ones for heavy duty work may be too powerful, dump too much heat and damage more advanced electronics. My friend had the traces lifting off the circuit board of my Commodore Pet while trying to add memory. Fortunately, he was careful after that and it actually worked. Watch that you are not overheating the board and components when trying to solder. (or unsolder, to remove the bad capacitor).

Last edited by md2000; 12-30-2017 at 01:35 PM.
#19
Old 12-30-2017, 02:52 PM
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Quote:
Originally Posted by Mr. Nylock View Post
I took it apart, I'm not dead yet.
Well that's good, and always preferable to the alternative.

Quote:
Originally Posted by Mr. Nylock View Post
The fuse is busted and it looks like at least one of the capacitors is bad - it has some nefarious looking brown stuff on it.
It's hard to tell without looking at it, but I suspect the brown stuff used to be inside of it. Definitely replace the cap.

There is probably a rectifier bridge or possibly some discrete diodes in the power supply as well. As beowulff said the cap is your most likely point of failure, but it may have taken out the rectifier when it went, or possibly the rectifier went first. You can check the rectifier with a multimeter as long as your meter has a diode check function.
#20
Old 12-30-2017, 07:21 PM
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Originally Posted by engineer_comp_geek View Post
Well that's good, and always preferable to the alternative.



It's hard to tell without looking at it, but I suspect the brown stuff used to be inside of it. Definitely replace the cap.

There is probably a rectifier bridge or possibly some discrete diodes in the power supply as well. As beowulff said the cap is your most likely point of failure, but it may have taken out the rectifier when it went, or possibly the rectifier went first. You can check the rectifier with a multimeter as long as your meter has a diode check function.
I put it back together and I'm still alive. I changed the fuse and it powers on now, but it sounds the same as before I had the problem with it not powering on - which is acceptable to a degree but with terrible bass. I mostly just use it with headphones, so I'll see how that all works tomorrow.

Oddly enough, my multimeter was stolen a few months ago. Noone just stole the multimeter in case you're wondering, it was in a bag that someone stole out of my car. I used to bring it to work in case the work issued piece of crap failed me in the field. I haven't found any at thrift stores yet, and pawn shops only ever seem to have super high end ones. Moral of the story is never get an expensive looking bag.
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#21
Old 12-31-2017, 12:16 AM
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This thread makes me wonder whether many messages about electricity sum up to "better to be safe than sorry".

As a 14yr old, I used to regularly unscrew the frame of the microwave and probe the parts. Never removed anything because I stripped many screws especially the one securing the magnetron.

Being the idiot I was, I tried to discharge it with a kitchen table knife that gave me a nasty shock. The pain was amplified by the fact that it was plugged in, Pain stayed for several minutes in the muscles of both arms.

I don't know which Doper said it, but most electrical appliances around the house doesn't contain enough current to kill.
#22
Old 12-31-2017, 12:41 AM
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Originally Posted by rastafarian View Post
I don't know which Doper said it, but most electrical appliances around the house doesn't contain enough current to kill.
Seriously, you were lucky. Very lucky. You rolled the dice on dying that day.

Microwaves also contain a power supply that can turn you into a raisin when powered up. They can kill you so dead that no amount of CPR will get you back.

Anyone who says "most electrical appliances around the house doesn't contain enough current to kill" is clueless. They don't realise that they are spouting scientific gobbledygook. The sentence is meaningless.
#23
Old 12-31-2017, 12:47 AM
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Originally Posted by Mr. Nylock View Post
It says T-Power on it, but other than that, I can't find any sort of model# on it; it's not in any of the places a model# usually would be.
T-Power is odd. I wonder if it is a Tripath based chip amp? They are ubiquitous simple and better then you might imagine class-D amplifiers. Usually they run from an external power supply, but some are made with an internal simple switcher.

I would say that unless you have a schematic and some minimal clue how to read the schematic you have only a mediocre chance of fixing it. But, no doubt, any electrolytic capacitor with the schmoo leaking out is going to need replacing. Such a failure could indeed be responsible for very poor bass, but there are a great many things that could be wrong.

Last edited by Francis Vaughan; 12-31-2017 at 12:48 AM.
#24
Old 12-31-2017, 04:26 AM
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Originally Posted by rastafarian View Post
I don't know which Doper said it, but most electrical appliances around the house doesn't contain enough current to kill.
Either you misunderstood what someone said, or they were wrong.

Most appliances don't contain enough current to RELIABLY kill you. Most contain enough current to POSSIBLY kill you.

Electricity typically tends to kill you in one of two ways.

At low current levels, electricity can screw up your heartbeat and throw your heart into fibrillation. Your heart has kind of a funny design in that the fibrillation state is stable. Get it into fibrillation and it will tend to stay in fibrillation unless something acts on it to take it out of fibrillation (like someone zaps your heart with a defibrillator).

It doesn't take much current to throw your heart into fibrillation. Most safety standards are built around 5 mA (0.005 amps) being the "safe" level. Anything above that is dangerous. 6 mA obviously isn't going to be too likely to screw up your heart, but as the current increases, so does the risk. Once you are up around 50 to 100 mA, you're well up into the danger zone.

The thing is, this type of shock is very hit and miss. Your heart is significantly more likely to get thrown out of whack at certain times in its rhythm than others, so it's very random. You might take a 50 mA shock across your heart and go into fibrillation and die. You might take a shock at double that current and your heart might not be bothered by it at all. It's very random. But anything above 5 mA is dangerous, and 5 mA is a very tiny amount of current.

One funny thing that happens is that at first, the risk of death increases with the current. But then the risk decreases significantly. The reason for this is that at higher current levels, instead of the heart going into fibrillation, it is more likely for all of the heart muscles to just clamp. At that point, your heart isn't pumping blood, so if no one removes the source of the current, you're toast. But if the current is removed, the heart will generally start beating in a normal rhythm again.

If you continue to increase the current though, the fatality rate once again starts to climb. This is because you start getting into the second way that electricity kills you. It literally cooks you to death. Current flowing through anything that isn't a superconductor generates heat. One demonstration that they used to do on science shows was they'd stick a nail in either end of a hot dog. Then they would attach each nail to one of the wires from an electrical cord, and plug in the other end of the cord into an outlet. Kids, don't try this at home. We tend to call electrical cords with exposed wires on the ends "suicide cords", for a good reason. But if you do this, you'll cook the hot dog pretty darn quickly.

This is how the electric chair kills you. It literally cooks you to death. This is not so hit or miss. Very few people survive the electric chair, and those that do only do so because something in the chair failed to work properly. A perfectly functioning electric chair is 100 percent fatal.

Most household appliances don't have enough current in them to reliably cook you to death, but most do have more than enough current to potentially screw up your heartbeat.

5 mA is barely a tingle. Your symptoms indicate a significantly higher shock level. You were well into the potentially fatal shock range.

One thing about electricity and the human body is that it's not a simple linear resistor. A common (if oversimplified) model of the human body is often a resistor in series with both a resistor and a capacitor in parallel with each other. The thing is, the values of those components change based on the applied voltage. Low voltages, like 24 volts and below, won't usually overcome the resistance of your skin, and it's almost impossible to get any measurable current flowing. Once you get into the 50 volt range or so, then it starts getting dangerous. Anything that plugs into an outlet has a lot higher than 50 volts in it, and therefore can easily inject a potentially fatal amount of current into your body. At low voltages (below 24 volts), your body acts like a resistor with many megs of resistance. At higher voltages, like household AC voltage levels and above, that effective resistance value of your body drops down into the thousands of ohms range, and you get a significantly higher amount of current flowing.

Since people don't tend to have CRT type televisions any more, a microwave oven is probably the most dangerous appliance in their house to tinker with. The high voltage output that powers the magnetron is typically somewhere between 1,000 and 3,000 volts, and it has more than enough current sourcing capability to totally whack out your heartbeat.

I wouldn't say it's a miracle that you are alive, because a lot of people have been shocked by microwave power supplies and haven't been killed. It's not anywhere near as reliable at killing someone as the electric chair is. On the other hand, while you think what you did was perfectly safe, you're wrong. The chance of death was definitely not zero, not by a long shot.

If you are going to tinker with something, tinker with something that is battery powered. It's awfully hard to kill yourself with anything operating below 12 volts.
#25
Old 12-31-2017, 04:35 AM
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Originally Posted by Mr. Nylock View Post
It says T-Power on it, but other than that, I can't find any sort of model# on it;
T-Power is a brand name. It should have a model number on it somewhere. Typical T-Power model numbers are things like TP-125 or TPB-500F.
#26
Old 12-31-2017, 06:50 AM
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Originally Posted by rastafarian View Post
This thread makes me wonder whether many messages about electricity sum up to "better to be safe than sorry".
...
Good observation.

IMO/IME there are 3 kinds of posters in electricity threads:

The kind who know they know what they're doing.
The kind who know they don't know what they're doing.
The kind who don't know they don't know what they're doing.

The folks in the middle group ask the questions. The folks in the middle group are also the ones who answer with "Stay away. Better safe than sorry." Usually with some half-truth/half-BS details thrown in to muddy the waters.

The folks in the first group make two kinds of answers: "Here's the risks and here's how to mitigate them." and, depending on the Q, "If you have to ask this particular Q, you're probably biting off more than you can chew."

The folks in the third group post answers like "What me, worry?" Plus some total BS details. And never think to post questions at all.


Almost every curious kid has spent time in group 3. Usually with a few memorable shocks to show for it. Whether they graduate to groups 2 or 1 or withdraw to group 4 (dead and buried) is down to luck. Me? I was lucky.

Last edited by LSLGuy; 12-31-2017 at 06:54 AM.
#27
Old 01-01-2018, 08:36 PM
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Originally Posted by burpo the wonder mutt View Post
Fuses usually aren't soldered in, they fit in clips or sit in a holder with a screw-off cap.
I do see quite a lot of cheap portable items with soldered in fuses now.

Originally, fuses were replaceable in repairable items. Now, they are replaceable in disposable items when it's cheaper/easier to install them that way.
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