Will this burnt out amp survive?

[mitpatterson]

So a buddy of mine asked me to try and fix this amp, it works... just cuts out every so often..... I think i know why.... 

Obviously the big inductor got too hot and burnt the coating and some of the board. Some of the caps are bulging as well. So given that it *sorta* works now do you think recapping it will make it work fully? or will something need done about that inductor?

This amp "retails" for about $700 new yet they used mostly 85C caps and one hung low at that("Sam young" and "Sanwha").

So any advice on it working or not? if it needs more than caps? Any other advice/feedback?

[Bertho]

So a buddy of mine asked me to try and fix this amp, it works... just cuts out every so often..... I think i know why.... 

Obviously the big inductor got too hot and burnt the coating and some of the board. Some of the caps are bulging as well. So given that it *sorta* works now do you think recapping it will make it work fully? or will something need done about that inductor?

This amp "retails" for about $700 new yet they used mostly 85C caps and one hung low at that("Sam young" and "Sanwha").

So any advice on it working or not? if it needs more than caps? Any other advice/feedback?

The current state is a fire-disaster waiting to happen.

You can replace all the caps with good ones, that should be easy. Also, scorched resistors may need replacing.

The inductor is goner and there are two possibilities: 1) replace with a new one, or 2) rewind the inductor. This is probably a custom inductor, so you probably need to rewind it manually and hope that the core and plastic has not taken too much damage. Removing the burned windings is a tricky business, you need to count correctly. You also need to find the correct gauge wire for rewinding, although that should be the easiest part.

[grumpydoc]

Go for it. Yes that inductor needs replacing.

Photos could do with a little work, though. Even if you have only your camera-phone could you try to make sure that they are in focus without motion blur and are presented at a suitable resolution.

[mitpatterson]

Also, a note if someone can tell me if this means something special, the 2 big ones in the middle are bulging slightly on the top so i want to replace them, they are labeled as "63WV 3300uf" what is the WV? I expected them to be labeled just as V. Is it same?

[ve7xen]

Also, a note if someone can tell me if this means something special, the 2 big ones in the middle are bulging slightly on the top so i want to replace them, they are labeled as "63WV 3300uf" what is the WV? I expected them to be labeled just as V. Is it same?

"Working Voltage." It's the same.

[mitpatterson]

Also, a note if someone can tell me if this means something special, the 2 big ones in the middle are bulging slightly on the top so i want to replace them, they are labeled as "63WV 3300uf" what is the WV? I expected them to be labeled just as V. Is it same?

"Working Voltage." It's the same.

Thanks

Ok, next probably stupid question is how do I determine if the Inductor is actually bad or just looks bad(due to the enamel and glue burning)? and if its determined the inductor is bad how I go about finding a replacement? I don't have an LCR meter(and even if I did if the inductor was bad I don't know if measuring it would help). I did stick my multimeter on it and found there was about 1/2 an ohm of resistance(which given than an indutor really is just a coil of wire is probably about right)

[vk6zgo]

In your pictures there is another inductor which looks very similar.
If it is the same,you may be able to compare them.

Remove both,wire a capacitor in parallel with the good one,feed it with a square wave,& look for the ringing at the top of the waveshape with an Oscilloscope.

Determine the frequency of the ringing--calculate the inductance.
Count the number of rings & their amplitudes

Try the faulty choke:

If the ringing frequency is the same,the inductance is the same.
If there are the same number of rings,& their amplitudes are similar,the "Q" is about the same.

[mitpatterson]

In your pictures there is another inductor which looks very similar.
If it is the same,you may be able to compare them.

Remove both,wire a capacitor in parallel with the good one,feed it with a square wave,& look for the ringing at the top of the waveshape with an Oscilloscope.

Determine the frequency of the ringing--calculate the inductance.
Count the number of rings & their amplitudes

Try the faulty choke:

If the ringing frequency is the same,the inductance is the same.
If there are the same number of rings,& their amplitudes are similar,the "Q" is about the same.

Now if only i had more tools lol... right now an iron and a meter is about all i got

[peter.mitchell]

These are pretty terrible; http://www.ebay.com/itm/190884536018 But are probably also the cheapest inductance meter.

[madsci]

Judging by the not so simple filtering near the speaker terminals, this must be a class D amp of some sort.

Hmm....I've seen this type of issue in The Mad Scientist's Lair before; I'm getting flashbacks of that stupid JBL PowerBass PB12 and its class D amp with an output filter blown to hell.

Check the modulator output, repair as necessary. Mine had a bit of an issue with the modulator.

Use suitable caps in the output filter. General purpose caps won't hold up for long under the ripple encountered. Treat it like an SMPS.

Refer to this application note for a Class D primer: http://www.irf.com/technical-info/appnotes/an-1071.pdf

[mitpatterson]

Ok so i have a BOM for the caps. I checked the resistor closest to the burnt inductor and its within spec based upon its color codes. The question I mainly have at this point is the current inductor still good? or just cosmetic damage? I pulled off the "good" inductor as well. Given the only thing i really have to test with is my multimeter I measured the resistance of each and they are both about .4-.5 Ohms which for a coil of wire sounds reasonable(no breaks in the wire etc). Any other testing I can do with only a meter and some spare parts? and if it needs replaced how can I find a replacement again given my limited tool set.

[mitpatterson]

Judging by the not so simple filtering near the speaker terminals, this must be a class D amp of some sort.

Hmm....I've seen this type of issue in The Mad Scientist's Lair before; I'm getting flashbacks of that stupid JBL PowerBass PB12 and its class D amp with an output filter blown to hell.

Check the modulator output, repair as necessary. Mine had a bit of an issue with the modulator.

Use suitable caps in the output filter. General purpose caps won't hold up for long under the ripple encountered. Treat it like an SMPS.

Refer to this application note for a Class D primer: http://www.irf.com/technical-info/appnotes/an-1071.pdf

No clue the class amp but it is a JBL BPx500..... so hope that doesn't create any more flashbacks.... And color me stupid but how does one check the modulator output? is that something one would need a scope for?(and if so i don't have one... but yes its on my wish list)

Edit: and regards to your comment about not using general purpose caps what does one use? in the specs that i'm inputting into digikey(cap value, voltage rating and lead spacing and such) It only pulls up General Purpose and Automotive grade/rated.

[grumpydoc]

You might find the service manual useful! http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/ServiceManual/bpx500.1%20sm.pdf

[mitpatterson]

You might find the service manual useful! http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/ServiceManual/bpx500.1%20sm.pdf

Thanks. My google Fu must have been weak the day I went looking as I only found like user guides.

[mitpatterson]

You might find the service manual useful! http://www.jbl.com/resources/Brands/jbl/Products/ProductRelatedDocuments/en-US/ServiceManual/bpx500.1%20sm.pdf

Thanks. My google Fu must have been weak the day I went looking as I only found like user guides.

Now if only the "CL-1600E" MFG part number got any good hits on google to actual specs....

[mamalala]

Is there a specific reason to upload images in that size, just to have them full of blur?

Greetings,

Chris