Rumble 100 SMPS

[lowell]

Fender won't cough up the schematic for this newer model with an SMPS. Can someone send it to me? Amp came in supposedly smoking. Had some hum for me but worked. One of the main filters was bulging so i replaced it. It sparked upon powering up and now pulls too much current and blows my circuit breaker. (doesn't blow the pcb SMD fuse though). Thanks!

Also, the NTC thermistor is dead short in circuit with no power on. As I understand it, this should be a large resistance when the amp is off to suppress inrush current. If this was shorted could it cause the amp to draw too much current and REMAIN in an over current status?

[Jazz P Bass]

Fender will not release it.

All you get is the voltage pinout of the SMPS block diagram.

[lowell]

Gotcha. Thoughts on the NTC thermistor? Should it not be a short when cold? I don't believe there's anything in parallel to it. So they won't even release it to their authorized techs?

[lowell]

Ok so the switching MOSFET is dead short on all 3 pins. It's an 08N80C3. Other than drain current and D/S breakdown voltage, what specs do I need to meet if I were to sub. I don't have any of these in stock but do have a handful of MOSFETS in TO-220.

edit: nevermind, I don't even have any TO-220 N-channel enhancement types with a 80A rating. Will have to order.

[J M Fahey]

Junk it.
That´s what it was designed for.
Fender will not release the power amp or supply schematic for the very good reason that they have no clue themselves about it.

I don´t have Rumble 100 but 150 is a Fender designed **preamp** , tacked to a prebuilt, OEM Class D power amp and SMPS built by Ice Power , designed in Denmark but built by Terminator (not even human slaves)in automated Factories in China.

They can´t give you the schematic for the same reason they can´t give you the internal one inside, say, a TDA7294, it´s a part that you just replace when bad.

Enjoy the Terminator World:


Fender Rumble 150:
http://support.fender.com/schematics...atic_Rev-B.pdf

Ice Power module (might be the same, guess it´s the smallest they have):
http://www.icepower.bang-olufsen.com...ower50asx2.pdf
2x 50W or 1 x 170W

A full power amp and supply:


get used to it because all Fender Rumble, G&K, TC Electronics and eventually everybody else is starting to use these (or something very similar).

EDIT:they are available on EBay for U$99 , so seller pays them about U$70 and Fender must be paying around $50 each, by the container load.
How much does Fender charge a Service shop?

[lowell]

I think might be another one of those trends...

Transistors replacing tubes
Reverb in the 80s
SMPS now

Maybe eventually consumers will be educated on the matter and RUN from these bottom line products. I'm not saying they don't have a place in the market...but for anyone needing to depend on their gear professionally they have yet to prove themselves as reliable or "affordable" to repair.

All this said...the MOSFET is definitely shorted...I already replaced a bad filter cap...so can't hurt to toss a new MOSFET in and see what it does. I understand it's probable that more components than just the MOSFET may be bad.

[Jazz P Bass]

The inrush thermistor, if not measuring a lowish resistance, is probably bad.

I had one of these B&O modules on a Genz Benz bass amp that was bad.

One of the very few repairs that I refused.

[g1]

Like JM said, in the Rumble 150, the power amp and SMPS are a combined module and replaced as such.
Does the Rumble 100 have a separate power amp, or is it part of the SMPS module?

[J M Fahey]

Well, I don´t know the market value of that amplifier.
IF the owner can pay, say, $200, meaning $100 for the module and $100 to cover handling, 1 hour bench time and a little on the part itself, it still can be done.

Should have said $250 or 300 but I doubt the owner will go for it, but hey!! ,asking is free.

EDIT: a guy in Lowell (ring a bell ?) was selling these modules for U$81 ......

Bang Olufsen Icepower 50ASX2 BTL 1X170W Class D Amplifier | eBay

That said, it wouldn´t hurt trying a good MosFet there , you might get lucky.

[lowell]

Here's a pic

[nickb]

Fender won't cough up the schematic for this newer model with an SMPS. Can someone send it to me? Amp came in supposedly smoking. Had some hum for me but worked. One of the main filters was bulging so i replaced it. It sparked upon powering up and now pulls too much current and blows my circuit breaker. (doesn't blow the pcb SMD fuse though). Thanks!

Also, the NTC thermistor is dead short in circuit with no power on. As I understand it, this should be a large resistance when the amp is off to suppress inrush current. If this was shorted could it cause the amp to draw too much current and REMAIN in an over current status?

I think having the cap on flying leads like that is a bad idea. It adds inductance in series with the transformer which in turn will lead to unclamped spikes that will take out the MOSFET. Put the correct cap on the board. Replace the NTC and the MOSFET.

Worst case this looks like a fairly simple flyback converter with a singe-chip integrated amplifier. You should be able to trace it out.

If the transformer is bad, you're out of luck (I nearly said something else).

I would not be surprised to learn that Fender don't know much about this board. They probably drew up a paper spec and some Far East company did all the engineering and put the Fender name on the silk screen. I've met some of these people - they're not stupid. Sad times for Western engineering.

[Jazz P Bass]

What is under the heatsink clamp?

It looks like two TDAXXXX ic's.

[J M Fahey]

LOWELLLLLLL !!!!!!!!
You should have posted this earlier
You send us in wild chases trying to figure out what´s inside

Ok, I wasted time imagining it was a downgraded Rumble 150 , which does use a 100/150W ICE module, then when I read about the presumed 2 x TDA729x I thought : it´s an upgraded Rumble 75 but with an SMPS instead of a conventional supply:


clearly designed by a non-MI Engineer : absolute waste of resources: 2 x TDA7294 (capable of up to 100W RMS each) needlessly bridged, fed from less efficient +/-25V , while a single one fed +/-30/35V would have accomplished the same.

Of course, that might be fully explained by

I would not be surprised to learn that Fender don't know much about this board. They probably drew up a paper spec and some Far East company did all the engineering and put the Fender name on the silk screen. I've met some of these people - they're not stupid. Sad times for Western engineering.

I also met these people.

You go to some big Expo (think NAAMM or Frankfurt or ExpoMúsica in Brazil) and in the main floor or central area you have the HUGE Fender/Marshall/Yamaha/you-name-it stands but if you walk around, in the far corners you´ll find small unadorned booths sporting a few unscrutable Chinese, dressed in Engineer uniforms (formal pants, short sleeve white shirts, pens in the shirt pocket, a fancy calculator hanging from the belt) who speak broken English ... and who represent OEM factories, large and small, which can churn out whatever you want for peanuts.
Your design ... or theirs.

More and more often I see MI amp schematics, many late Marshalls for example, and think: this was NOT designed by an MI guy, no way.

Back to lowell´s problem:
that is definitely NOT an ICE amp and supply, in fact I think in horror about the unshielded SMPS radiating trash all over the place.

Might have 2 x TDA7294 under that clamp (looooweeeellllll !!!!!!!! , please look and teeeeellllllll!!!!!! ) but that huge toroid (pair?) between chipamp and speaker out pads stinks of some Class D thingie.

And those toroid doughnuts, a heavy component *glued* on edge on a PCB, just waiting for slight rough handling (amp falling on its front/back or carelessly dumped on stage or pickup truck bed or some road bumps) to fly fee and tear wires and pads ...

Puzzled look on Chinese/Indian/Malaysian/Indonesian Engineer face: "but who would subject his computer to such abuse? ........"

[lowell]

Welp... the thing still ain't powering on after replacing the mosfet. Also replaced that filter with a radial lead snap in. I do see this startup resistor is toast. Now, a fried startup resistor points to a fried PWM IC. Correct? Or not? I can't read the value because it is obscured. The 2nd two of 3 digits are 02. So it reads ?02. It's R324 towards the right.

Here's a pic. Please give me some feedback...I may or may not go any further with it. Will also report back on the output IC.

[nickb]

Your best bet now is to look up the datasheet & app notes if ness for the pwm chip. There is usually a reference design and equally often that is what you will find on the board. You will probably need to to trace out at least enough to see how it compares. Once you know the circuit you can figure out the resistance.