Fender Rumble V3 500 Head/AMP

[Groove 84]

I am working on a Fender Rumble V3 500 Head. What happens is when I plug my extension cabinets into the amp Parallel speaker outputs, the amp sounds like it's shorting. There is a very loud thumping sound coming through my speakers. It also smells like electronics are burning. I opened it up and see nothing that appears burnt or signs that it was even hot. I don't have much electronics troubleshooting experience so I thought perhaps the 125ASX2 power supply was shorting so I just purchased a new one. Tried the new power supply, same thing is happening. I have another V3 500 head that works and I plugged it in to the same cabinets with the same cables and it works fine. No issues.

So assuming that the brand new power supply/amp is good, what can I look at next? I want to buy a couple new boards but I cannot find them anywhere. Coming off the main power supply there is 120vac wiring that runs to another board. This board below. The problem only happens when I plug speakers into the main output jacks on the amp? I don't see any evidence of shorting or anything like that? Any ideas? If there is a board available I would appreciate a link.
This is when I hear the noise and smell burnt electronics, when I plug into the speaker output jacks..It says speaker jack breakaway.


Help!

[Jon Snell]

As you state, it is brand new.
Get it replaced for a new one.

There is not a lot to be done on these FM Class D amplifier modules; no service information for one and if faulty it is replaced not repaired.

[Groove 84]

Thanks for the reply, I appreciate it.

Any idea how or where I can get my hands on a new PCB as shown above in the post? A google search doesn't give me much.. Trying to find this board.

[g1]

Where did you buy the 125AX2 power amp module from?

[g1]

Coming off the main power supply there is 120vac wiring that runs to another board.

The power supply and power amp are the same module. (125AX2).
That connector (P104) that goes to the speaker jack board is not carrying 120VAC, it is carrying the power amp output.

[Jon Snell]

Thanks for the reply, I appreciate it.

Any idea how or where I can get my hands on a new PCB as shown above in the post? A google search doesn't give me much.. Trying to find this board.

PCBoards do not fail and are not stocked as a replacement item however, if faulty, under warranty, are available as an exchange item, through your Fender Service Centre.

[clintronics]

PCBoards do not fail and are not stocked as a replacement item however, if faulty, under warranty, are available as an exchange item, through your Fender Service Centre.

Im going to guess he's asking for a loaded PCB

[The Dude]

What are the impedances of your cabinets? Maybe you are dropping below the amp's rated output impedance. Also check for shorted speaker cables and/or cabinets.

[Groove 84]

I bought the power supply/amp from a site in China for $170.00. So what I am hearing is assuming the power supply is Good, since it is out of warranty, no replacement boards are available? Replacements are only available for warranty repair? If I take this to a electronics repair tech will they be able to test out the various components/boards or is it one of those deals, yup it's something in the board, not repairable?

[Groove 84]

The cabs I use are 8 ohms each. I use them in parallel. 4 ohms total. Remember though I have another Rumble 500 head that I plug into the same connectors/cables/cabinets and everything works perfectly. I have narrowed it down to this amp, when connected to speakers.

[Groove 84]

Can the power supply/amp that I just purchased be a piece of junk?

[glebert]

Loud thump and burning smell when speakers are hooked up soundsl ike there is DC on your speaker outputs. You can measure that with a volt meter. I would start with no speaker connected, then I would try a load resistor instead of a speaker (DC will ruin speakers), IIRC sometimes class D amps don't turn on if there is no speaker load.

The power module (125ASX2) is an ICEPOWER made by Bang and Olufsen. There are a couple of pins that tell you if the amp is in fault mode for overcurrent or temperature, but that is usually when the amp is not putting out anything.

Here is the datasheet. It has quite a bit of information about how it works.

FYI, I've done the same thing buying replacements for these boards and I haven't had problems. To me it seems odd that you would have two that have the same fault, but I'm not sure what would cause it to do this.

[Groove 84]

Really good information here. Thanks for the info on DC on the speakers. That is really interesting. The other fact is I have another Rumble V3500 that is identical, when I swap it out, it works great. Speakers, cables, all in order. Definitely only this amp has an issue.

[g1]

Try the newer power module you bought in your other amp.

[Groove 84]

That's a really good idea. I will try that later tonight. Thanks for the suggestion!!