Fender Rumble 40 Power PCB capacitors blown

[iamthesteve]

I totally get this, but, some people buy puzzles to relax in their free time, I like solving things. I personally enjoy learning now things work, and fix them if I can. It's quite a rush if I can figure it out.

Hi, I just joined to reply to this thread.
In my case, there's nothing relaxing about this puzzle... but having this amp apart eats away at me in the back of my brain...

My initial problem was that the power supply showed no signs of life past the AC input section.
I ordered some parts that I thought were possible suspects and replaced them.
After replacing the PWM controller, it now blows the fuse, which I take as progress.
I ordered some replacement power MOSFETS, but the existing one measures the same (as the new) out of the circuit so I left it in.
I also replaced the little 4-pin optocoupler which didn't make a difference.

I agree that this circuit isn't worth spending time on. Just wanted to subscribe to this thread in case anyone learns more.
I spent a couple hours yesterday scouring the internet for a suitable replacement switching power supply, but came up empty.

The closest search string I came up with was:
switching supply pcb "28v" "dual output" "open frame"

As you all know from the schematic, we just need +/- 28V and a 5VDC output.
If we could just find a +/- 28VDC supply we could easily add a little 5V supply and fit it in there.

Edit: I should have added that the output connector is disconnected.
Also, I did not have the problem of the OP, as mentioned. No initial signs of life past the AC input section. Good fuse initially.

 

[KevinInPMtn]

I just opbainted a Rumble 40 with a similar issue. Initally, I noticed that C319 on the PSU had experienced a violent death. I found this thread while searching for a replacement power supply. After reading this thread I noticed that I also have a blown C400 on the power amp board.

I don't know if it helps the OP or if they are even working on their amp still. And, since I got this amp as a non-working unit, I can't say that these two cap exploded at the same instant.

Where are people getting the schematics that are attached to this thread?

This is likely to become a speaker cab for me but it there if an easy solution has been found, I be interested in that too.

 

[iamthesteve]

Rumble 40 V3 Schematics-Diagrams - Google Search

Good luck.

 

[KevinInPMtn]

ah,, sometimes I overlook the simple solution and expect things to be more complicated than they are.

I will try some 50V caps in place of the 35s and see what happens. If they blow again or it fails in some other way I may give the Hotone Thunder a try.

 

[KevinInPMtn]

I replaced the blown caps and the partners to the blown caps with 50V version. When I power up I get a flash on my overdrive light and the power light turns on then fades out. After it fades out the cycle repeats. But if I swith the OD to the opposite position then both the OD light and power light fade together. Maybe this is useless info but I guess it can't hurt to add it.

I got a response from Fender that told me to have one of their service centers look at it. I will give them a call tomorrow but I suspect that will say what was said early in this thread - not worth the repair. But the phone call will be free.

 

[Misiektr83]

Hello I would like to refresh topic. I measured the voltages out from power pcb . However they are not constance , meaning oscylating from 27 to 34 v , it is normal ?? I measured it without the resistance . When I connecting the amp pcb then the voltages drops even more. It possible that tda7249 making the shorts??