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02-24-2011, 03:47 PM
| | | | Blown amp question
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So I loaned a PV 1200 power amp to my brother. He brings it back today saying that he smelled something burning when he hooked it up. Now one of the channels isn't working and the DDT light stays on. He is an idiot, but hey, that's what little brothers are for right.
Anyway I opened up the amp just out of curiosity to see if anything looked obviously fried. I found one tiny little resistor that looks fried. My question is this:
Is it likely that one burnt up resistor would render the entire channel inoperable? I don't know enough about electronics to test everything, but if this one resistor is the only thing wrong, seems like I could replace it myself and save the time and money involved with taking it to a shop.
Thoughts? |
02-24-2011, 04:35 PM
|  | Registered User | | Join Date: Aug 2007 Location: Toronto Ontario Canada | | Quote:
Originally Posted by Noose  Is it likely that one burnt up resistor would render the entire channel inoperable? I don't know enough about electronics to test everything, but if this one resistor is the only thing wrong, seems like I could replace it myself and save the time and money involved with taking it to a shop.
Thoughts? | Yes one burned up resistor could disable a channel. That said, the problem is more likely connected to whatever burned up said resistor. Sorry but it's tech time.
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Paul
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02-24-2011, 05:29 PM
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Originally Posted by BassmanPaul
Yes one burned up resistor could disable a channel. That said, the problem is more likely connected to whatever burned up said resistor. Sorry but it's tech time.
| From what he described (I wasn't there)he tried to run a line from both channels into one speaker. Essentially he went from the power amp output of channel A into the back of a speaker, then out from the speaker, back into the output of channel B. This is what caused the thing to blow.
I think it will be worth a shot to solder in a new resistor. There is one tech in this city and he stays backed up. Turnaround time in hi shop is a month at best. |
02-24-2011, 05:33 PM
|  | double parked
Endorsing Artist: Dark Horse strings | | Join Date: Oct 2009 Location: Verde Valley, AZ | | Quote:
Originally Posted by BassmanPaul Yes one burned up resistor could disable a channel. That said, the problem is more likely connected to whatever burned up said resistor. Sorry but it's tech time. | Yep. The only chance you'd have would be if that's the resistor in the L-C network on the channel output, and that's ALL that burned. Odds, I'd guess, of about 20:1 against. Sorry.
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Chuck
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02-24-2011, 05:59 PM
|  | I Know Nothing | | Join Date: Dec 2003 Location: Columbia River Gorge, WA. | | Quote:
Originally Posted by Noose I don't know enough about electronics to test everything, but if this one resistor is the only thing wrong, seems like I could replace it myself and save the time and money involved with taking it to a shop.
Thoughts? | To me it sounds like you will more likely make it worse and end up spending more than you would've just taking it to a tech in its present state. |
02-24-2011, 06:06 PM
| | | | What value burned resistor?
"Fix" it yourself, & next time it's liable to not only blow the amp, it'll burn down your house, too!
Tech time!
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02-24-2011, 06:17 PM
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Originally Posted by Passinwind
To me it sounds like you will more likely make it worse and end up spending more than you would've just taking it to a tech in its present state.
| Can't argue with you there. But how much damage can I do just soldering in a resistor in the same place? I'm smart enough to know that I need to use the right resistor and Im decent with a soldering iron. What can go wrong? |
02-24-2011, 06:20 PM
| | I Know Nothing | | Join Date: Dec 2003 Location: Columbia River Gorge, WA. | | Quote:
Originally Posted by Noose Can't argue with you there. But how much damage can I do just soldering in a resistor in the same place? I'm smart enough to know that I need to use the right resistor and Im decent with a soldering iron. What can go wrong? | Famous last words...  |
02-24-2011, 06:29 PM
|  | Hey, what does this knob do? | | Join Date: Sep 2008 Location: New Hampshire | | | This isn't your problem. It's your brother's problem. Tell HIM to get it fixed, and let HIM pay all the costs involved in getting it done. |
02-24-2011, 06:36 PM
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Originally Posted by craig.p This isn't your problem. It's your brother's problem. Tell HIM to get it fixed, and let HIM pay all the costs involved in getting it done. | Oh, he'll pay. But with sweat and tears. I have a back yard full of leaves and dog **** with his name all over it. He's 16 and a good kid. He had a brief moment of ignorance and admitted to it immediately. I can't fault him to much. |
02-24-2011, 06:39 PM
| | | | I bet the a majority of techs would just change the burnt part first - to see what happens...
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02-24-2011, 06:39 PM
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Originally Posted by Passinwind
Famous last words... | Yeah I know, but I'm honestly asking. What could go wrong? |
02-24-2011, 06:43 PM
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Originally Posted by JohnMCA72 What value burned resistor?
"Fix" it yourself, & next time it's liable to not only blow the amp, it'll burn down your house, too!
Tech time! | Not sure. Can't tell just by looking at it. Im gonna try to find a schematic before I do anything. |
02-24-2011, 06:46 PM
|  | amateur tube amp hoarder
Endorsing Artist: J Worrell Pickups / J Worrell Bass | | Join Date: May 2008 Location: Dayton OH | | | These threads make me sad because I still have a tubey guitar head at my old band's place. |
02-24-2011, 06:47 PM
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Originally Posted by seamonkey I bet the a majority of techs would just change the burnt part first - to see what happens... | That's what I was thinking. It's the only thing that appears to be damaged. Of course there could be something I don't see That is also damaged but I would think that things gonna get replaced regardless. |
02-24-2011, 11:00 PM
| | I Know Nothing | | Join Date: Dec 2003 Location: Columbia River Gorge, WA. | | Quote:
Originally Posted by Noose Yeah I know, but I'm honestly asking. What could go wrong? | If it's a fuse resistor, you could easily lose all the output devices on power-up. You could create a solder bridge and take out the whole power filtering section. You could make a hairline fracture in a circuit trace, with unknown consequences. I can think of dozens more possibilities, because I have seen them all in real life. If you prefer Russian Roulette, be my guest. |
02-24-2011, 11:02 PM
| | I Know Nothing | | Join Date: Dec 2003 Location: Columbia River Gorge, WA. | | Quote:
Originally Posted by seamonkey I bet the a majority of techs would just change the burnt part first - to see what happens... | If you use a Variac at first power up just doing that might be perfectly acceptable.
Last edited by Passinwind : 02-24-2011 at 11:07 PM.
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02-24-2011, 11:20 PM
| | Registered User | | Join Date: Apr 2007 Location: Finland (Northern Europe) | | | Hi.
Good luck.
If I was a gambling type, I'd say that You're just about to make a $50 repair into a $300 one.
There's good folks in this thread who probably have been in the same situation as You are at some point in their teens, and they're just trying to spare you the added expense. Me included obviously.
Most of them, me included again, have had several such devices on their benches, brought in by DIY "techs".
Just swapping (burnt/broken) parts is guessing, not repairing, and while guessing sometimes do work, IME uneducated guesses tend to have very poor success rate. In any field of life.
Regards
Sam |
02-24-2011, 11:30 PM
| | Registered User | | Join Date: Mar 2001 Location: Chicago and Virginia Beach VA | | | A "good" tech will check the surrounding circuitry to see if anything else is bad FIRST! Just swapping parts can lead to much more serious problems. These situations are one of the reasons I quit doing repairs and when I did I charged stiff rates, if somebody went in it before they brought it to me. Plus charged a diagnostic fee up front. Non Refundable! I now design and build tube amps . Much more enjoyable
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02-25-2011, 04:24 AM
| | Registered User | | Join Date: Oct 2009 Location: Mill Creek, WA | | | Secret Smoke dept...
As everyone knows, many solid state devices depend on secret smoke in order to work properly. If that smoke escapes it will never work again since the smoke mustbe inserted at the time of production.
Nowadays many components are smoke free. Which means that they can go bad without any external indications.
Seriously, you could have other trashed components that otherwise look fine.
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