Velodyne sub woofer blowing fuse...HELP!

[Fat Steve]

Looks like it hits the switch first, followed by the fuse. I could be wrong though.

 

[David Jayne]

Doesn't matter. If the cord is shorted the board will never see it, but your house will. This is electrical 101.

 

[CatSquare]

Shorted cord will blow the mains breaker the instant you plug it into the wall, ideally.
I'm certainly no electrical engineer, but I've gotten lucky finding blown components on things like this before - scored a sweet power amp someone was junking, all it needed was one of its bridge rectifier diodes replaced.
I've also gone down the rabbit hole chasing issues all around boards, only to find myself hopelessly lost, hours of work down the tube, and very very humble.
Sub electronics are the worst with all that potting and goop everywhere.

 

[agedhorse]

7You're welcome. I was an AV dork before I knew the difference between a guitar and a bass guitar, so I gotta rep for my Hi-Fi homies whenever I can.

Anyway, back to the board. Does any part of it smell weird? Any singe marks on the PCB? Those could be your first clue to finding the busted component. Failing that, you may want to check the power cord. If it has a short, then all bets are off.

I would recommend sound troubleshooting practices rather then guessing. The proper test equipment (and in the case of this amp a variac and current meter would be my first tool) should be used to identify WHY there is excessive current, then MEASURING voltages to determine where the currents are flowing (and their magnitude). Because this is a global feedback amp, a fault within one stage will always translate to the output stage as the global feedback tries to compensate.

This is one of my favorite mid power amp topologies, fairly easy to troubleshoot IF you understand the circuit.

Shorted power cord would blow your mains supply, not your amp fuse.

Correct, and it would make one heck of a spark when you plug it into the receptacle too

The pwr cord goes thru the fuse board first. See photo.

Doesn't matter, the power cord is on the line side of the fuse and a shorted power cord will not blow the amp's fuse. This is why the minimum power cord size is 18 gauge, this is to handle the line side of any fault without melting before the power circuit's branch breaker opens to clear the fault.

 

[cfsporn]

I would recommend sound troubleshooting practices rather then guessing. The proper test equipment (and in the case of this amp a variac and current meter would be my first tool) should be used to identify WHY there is excessive current, then MEASURING voltages to determine where the currents are flowing (and their magnitude). Because this is a global feedback amp, a fault within one stage will always translate to the output stage as the global feedback tries to compensate.

This is one of my favorite mid power amp topologies, fairly easy to troubleshoot IF you understand the circuit.



Correct, and it would make one heck of a spark when you plug it into the receptacle too



Doesn't matter, the power cord is on the line side of the fuse and a shorted power cord will not blow the amp's fuse. This is why the minimum power cord size is 18 gauge, this is to handle the line side of any fault without melting before the power circuit's branch breaker opens to clear the fault.

Oh thank Tesla someone who knows what he's talking about.

I'm going back to the sidelines to learn

In your opinion, what would a common point of failure be in this topology?

 

[nashvillebill]

First, construct a Dim Bulb Tester (Google it, it's easy). It will automatically limit the current going into your amp and let you troubleshoot without continuing to blow fuses.

Then, assuming the schematic posted is correct, methodically go from the mains input downward: Disconnect connector BC801. Plug the amp into the DBT, turn it on and see if the amp passes the DBT. Yes, then the transformer is OK and proceed. Disconnect V+ and V- and the 15V +/- rails. Again try the DBT. Passes, then your power supply is OK--your output transistors are likely shot. Check their emitter resistors and drivers as well.

 

[agedhorse]

Most common failures with these symptoms are output transistors, drivers, driver emitter resistors, bias transistor, VAS bias string, and a variety of other causes from mechanical issues.

Very important to be systematical and use proper troubleshooting (including measurement) logic.

 

[iceboxbass]

I would recommend sound troubleshooting practices rather then guessing. The proper test equipment (and in the case of this amp a variac and current meter would be my first tool) should be used to identify WHY there is excessive current, then MEASURING voltages to determine where the currents are flowing (and their magnitude). Because this is a global feedback amp, a fault within one stage will always translate to the output stage as the global feedback tries to compensate.

This is one of my favorite mid power amp topologies, fairly easy to troubleshoot IF you understand the circuit.



Correct, and it would make one heck of a spark when you plug it into the receptacle too



Doesn't matter, the power cord is on the line side of the fuse and a shorted power cord will not blow the amp's fuse. This is why the minimum power cord size is 18 gauge, this is to handle the line side of any fault without melting before the power circuit's branch breaker opens to clear the fault.

First, construct a Dim Bulb Tester (Google it, it's easy). It will automatically limit the current going into your amp and let you troubleshoot without continuing to blow fuses.

Then, assuming the schematic posted is correct, methodically go from the mains input downward: Disconnect connector BC801. Plug the amp into the DBT, turn it on and see if the amp passes the DBT. Yes, then the transformer is OK and proceed. Disconnect V+ and V- and the 15V +/- rails. Again try the DBT. Passes, then your power supply is OK--your output transistors are likely shot. Check their emitter resistors and drivers as well.

Most common failures with these symptoms are output transistors, drivers, driver emitter resistors, bias transistor, VAS bias string, and a variety of other causes from mechanical issues.

Very important to be systematical and use proper troubleshooting (including measurement) logic.

Thank very much gentlemen. Your help and pointing me in the right direction is much appreciated. I must confess...troubleshooting stereo electronics is slightly different than USAF aircraft electrical/electronic systems. Plus I've been away from all of that for almost 20 years now, but I still remember the basics etc...and I do have a multimeter and good soldering station. I will be writing down all that I check as it makes troubleshooting much easier so not to backtrack and second guess myself. Thanks again!

 

[agedhorse]

First step is to understand how the circuit works, then you can begin to appreciate how it can fail.

 

[Slevage]

Most common failures with these symptoms are output transistors, drivers, driver emitter resistors, bias transistor, VAS bias string, and a variety of other causes from mechanical issues.

Very important to be systematical and use proper troubleshooting (including measurement) logic.

I agree. There are trouble shooters and parts replacers----- two different skill sets.

 

[B-string]

Trouble shooting is a skill, parts changing is not skilled just WAGing (Wild A** Guess). Former is effective, the latter is expensive.

 

[Fishheadjoe]

Wouldn't it be cheaper to simply buy a new one? If I am correct, the Velodyn Sub is a bottom of the barrel sub that could be replaced for around $100? Taken into account the time you will be putting into this, I might be inclined to just dump it and get the 15!
Fishheadjoe

 

[Passinwind]

Thank very much gentlemen. Your help and pointing me in the right direction is much appreciated. I must confess...troubleshooting stereo electronics is slightly different than USAF aircraft electrical/electronic systems.

I was tasked with finding a replacement tech at one place I worked at many years ago. Someone with similar experience to yours came in and interviewed, but he was convinced that musical gear would be trivially easy to work on given his skill set. I eventually put him in front of a broken vintage tube amp piece with no schematic and explained that this was Job 101, and basically got a big earful of bluster and haranguing, but no useful input. He then flunked the Smoke On The Water test on guitar (aka "play anything"), and was shown the door as quickly as I could manage semi-politely. Hi-fi gear is a whole other thing in itself, something I had to learn the hard way. Paying dues on a one-off self repair job can turn into a deep rabbit hole pretty quickly, IME. Best of luck, however you proceed. Link Removed

 

[iceboxbass]

Wouldn't it be cheaper to simply buy a new one? If I am correct, the Velodyn Sub is a bottom of the barrel sub that could be replaced for around $100? Taken into account the time you will be putting into this, I might be inclined to just dump it and get the 15!
Fishheadjoe

Try adding more money...Impact 12 12" Powered Subwoofer by Velodyne This is the lowest price that's comparable to mine, then it goes up from there. I bought this as a shelf demo from Circuit City when they were still around, for $200 back in 2000.

 

[iceboxbass]

I was tasked with finding a replacement tech at one place I worked at many years ago. Someone with similar experience to yours came in and interviewed, but he was convinced that musical gear would be trivially easy to work on given his skill set. I eventually put him in front of a broken vintage tube amp piece with no schematic and explained that this was Job 101, and basically got a big earful of bluster and haranguing, but no useful input. He then flunked the Smoke On The Water test on guitar (aka "play anything"), and was shown the door as quickly as I could manage semi-politely. Hi-fi gear is a whole other thing in itself, something I had to learn the hard way. Paying dues on a one-off self repair job can turn into a deep rabbit hole pretty quickly, IME. Best of luck, however you proceed. Link Removed

Yeah I totally agree with what you're saying. Comparing Apple to Oranges. I'm the type that wants to know what's wrong, is it fixable without breaking the bank. Also, I'm now retired and have some time on my hands between working on other projects. After Christmas I'll probably be buying a 15" sub anyways but I still want to solve this mystery of the fuse blowing on the ct120.
When I was taking Electronics course in HS my main project was taking a TV out of a dump, troubleshooting and putting it back into working condition. That was in 10th grade. I've completed other electronic projects during and after my USAF stint. One thing that I learned in life is to use your networks to learn if others have encountered the same problems as yours. It makes troubleshooting less time consuming, less expensive and just smarter. Asking for advice or help doesn't mean that you're not knowledgeable or over your head. Of course techs who work on home electronics day in and day out for 10,20,30+ years as their livelihood are going to be much more skilled at this hands down. Me, I'm considered a hobbiest at this that has background in electrical and electronics but of a different sort. I know my limitations and I'd NEVER consider bogarting my way into a job like you described an individual did with you. At this point in time I have nothing to lose or invested and as I said before, I'm a very curious sort and I want to know why something isn't working and what caused it. And perhaps I CAN fix it. That's all. Thank you for your advise and best wishes. Cheers.

 

[Passinwind]

Yeah I totally agree with what you're saying. Comparing Apple to Oranges. I'm the type that wants to know what's wrong, is it fixable without breaking the bank. Also, I'm now retired and have some time on my hands between working on other projects. After Christmas I'll probably be buying a 15" sub anyways but I still want to solve this mystery of the fuse blowing on the ct120.
When I was taking Electronics course in HS my main project was taking a TV out of a dump, troubleshooting and putting it back into working condition. That was in 10th grade. I've completed other electronic projects during and after my USAF stint. One thing that I learned in life is to use your networks to learn if others have encountered the same problems as yours. It makes troubleshooting less time consuming, less expensive and just smarter. Asking for advice or help doesn't mean that you're not knowledgeable or over your head. Of course techs who work on home electronics day in and day out for 10,20,30+ years as their livelihood are going to be much more skilled at this hands down. Me, I'm considered a hobbiest at this that has background in electrical and electronics but of a different sort. I know my limitations and I'd NEVER consider bogarting my way into a job like you described an individual did with you. At this point in time I have nothing to lose or invested and as I said before, I'm a very curious sort and I want to know why something isn't working and what caused it. And perhaps I CAN fix it. That's all. Thank you for your advise and best wishes. Cheers.

Cool, and I totally dig where you're coming from. When I started DIY building in earnest a few years ago I leaned heavily on the network I've built up over the years, and often still have to do reality checks to make sure I'm not just burning Franklins. As you say, there are plenty of other worthy motivations besides cost and time effectiveness though.

 

[iceboxbass]

Cool, and I totally dig where you're coming from. When I started DIY building in earnest a few years ago I leaned heavily on the network I've built up over the years, and often still have to do reality checks to make sure I'm not just burning Franklins. As you say, there are plenty of other worthy motivations besides cost and time effectiveness though.

Amen & Right on!

 

[wcriley]

...He then flunked the Smoke On The Water test on guitar (aka "play anything")...

I might be able to pass that test...just don't ask me to identify any of those firecracker-looking things on the circuit board.

 

[Passinwind]

I might be able to pass that test...just don't ask me to identify any of those firecracker-looking things on the circuit board.

Here's your Cliff's Notes tutorial:

 

[B-string]

I might be able to pass that test...just don't ask me to identify any of those firecracker-looking things on the circuit board.

Those are the magic smoke containers.