Mustang II amp no power

[faulkner1953]

I have a Mustang II amp that I picked up. It does nothing when I turn it on. No lights, no pop , no sound, no action at all. I'm not finding a fuse anywhere. The switch seems to be good. I would suspect the problem would be on the power board somewhere, maybe the transformer. Anyone know where I could get a new board for this? Or how to go about troubleshooting it? If I can't find a new board, or isolate and replace the problem components, I may have to convert this cabinet to a tube amp, but I would rather fix it if possible at a reasonable expense. Thanks for any suggestions.

[joecool85]

The fuse is probably PCB mounted so you would need to take the amp apart to get to it.  I'd start your search there.  Be sure to have it unplugged while doing this.

[faulkner1953]

There is no fuse that I have found anywhere in this amp, board mounted or otherwise. I'm looking for a glass fuse, and it's nowhere to be seen. Is there something else that is used nowadays? Surely they have something for circuit protection.

[joecool85]

There is no fuse that I have found anywhere in this amp, board mounted or otherwise. I'm looking for a glass fuse, and it's nowhere to be seen. Is there something else that is used nowadays? Surely they have something for circuit protection.

It has to be *somewhere*.  Does this amp have it in the power socket?  Unplug the power chord and see if it's "in" the socket.

[J M Fahey]

Agree.
IEC ("computer type") connectors often have a small "tray" below which slides away to show a small fuse.
It's "kid proof" so you'll need a small screwdriver to pry it open.
Or follow power wires inside, through the switch and into the power transformer, *somewhere* there must be *something*.
Worst case: some transformers have an *internal* fuse; if that one blows you are in trouble.

[teemuk]

That one, as far as I know, will just have a regular IEC connector without the internal fuse holder. I don't know all the tidbits of regulations in various countries but I doubt things could be passed on without a fuse these days and I don't know if the regulations would pass on a fuse integrated to transformer as the sole fusing means.

Anyway, sometimes fuses may look more or less like any other soldered-in component so you may not neccessarily find a glass fuse in a fuse holder or something similar. You may on the other find eg. a SMT fuse which will resemble pretty much any other SMT component, so it doesn't really jump out as being a fuse in an instant. Anyway, I'm pretty sure there should be something...

Even without locating the fuse you should be able to quite easily test if the power supply (which I believe is of switch-mode -type in those things) is giving up anything. After that you should pretty easily find out whether its internal rectifier works and provides the HT for the switchers. If not, THEN it could be something as simple as a fuse issue.

BUT I've seen plenty of that SMPS stuff failing in the regulator control circuit. That will still keep the rectifier going, does not burn the fuse or blow any components, it just stops the switching from working and effectively you're left with a dead power supply. It may not be an easy fix so if you can deduce the power supply being dead and the fault being in something else but the fuse or failed rectifier circuit then likely easiest repair might be ordering a replacement board from Fender.

[faulkner1953]

I did find the fuse on the board, a T3.15al. It's good. I knew there had to be a fuse somewhere! Obviously, I'm no expert in these matters. I wouldn't know what to check next. I haven't found a place to obtain parts for these, they are probably too expensive anyway. I would replace the power supply board if it wasn't too expensive.

[teemuk]

Obviously, I'm no expert in these matters. I wouldn't know what to check next.

You fitted a replacement fuse. Does it work now?

Have you even tested the board yet? For all this time have you actually even verified the problem lies within the power supply board?

Have you contacted Fender and asked for a schematic/service manual? Are you familiar with working on high voltage live circuits that are not isolated from mains with transformer and that can hold the high voltage charge for days after powering off? That's what a SMPS will be.
Do you know how a SMPS works? Obvioulsy if you do, then you should have at least handful of ideas of what to test next.

Point is, are you sure your skill levels are up to fixing that thing? With luck one can sometimes encounter cheap and easy fixes like refitting replacement fuses or fixing one component that is obviously failed and then have everything else work like charm after that. But at least to me this thing already seems to have exceeded that level and you should just bite the bullet and either pay someone to fixing the thing or accept that it will remain broken forever.

[joecool85]

You fitted a replacement fuse. Does it work now?

He didn't, he said he checked it and it was fine.  Not sure how he checked it though.

[faulkner1953]

I checked it with my meter for continuity. And no, i'm not qualified to work on these types of circuits. I know almost nothing. From what I gather, fender does not give out schematics, or sell parts for this new of a product. I'm not about to spend money to take it to a service facility. If I can't fix it, (and I'm pretty sure I can't) I'll probably sell the whole of the electronics boards in this amp on ebay, and keep the cabinet for a project.

[Minion]

Well ,if even the lights don"t come on when powered up and the fuse is good then it to me seems that it could be a bad power transformer .....

[teemuk]

It could be several things, the said power board under suspect or just as well a broken power cable, power wire, switch, connector, etc. or any other imaginable thing that would cause the described symptoms. Truth is, we'll never know for sure unless things are measured and tested.

So while nothing has been really done, except for verifying that fuse was ok, things still remain more or less at mere guessing stage. There's not much point in being hasty to point fingers to a specific fault or component, or start buying replacement boards, etc. If you want to fix things by playing guessing game then be my guest, but in the end it might end up costing more than just paying for pro to fix the thing. If it's an amp with SMPS you most likely may need a connection to Fender's service dept. and knowledge of part numbers to even be able to order right replacement parts from them.

These things can be tested more or less easily (eg. test whether the power supply board even receives AC power, test if the board outputs a set of DC voltages or not, test if the rectifier + filter pre switching devices works (assuming the power supply is SMPS), search datasheets of the switching logic IC and verify voltages based on datasheet's application circuit, and so on). Even without an actual schematic one can get quite far with troubleshooting. With a handful of proper tests the faulty circuit section should be quite easy to at least locate. It might be something entirely different than what we're even expecting it to be but in the end actions by OP are needed to verify it.

It also doesn't hurt to at least drop an email to Fender and ask if they could provide service information. What do you loose in that?

But if all this is over someone's head its over his head. I'm not the one who is going to start writing long troubleshooting guides and tips for an amp I barely even know - especially when its such that likely contains quite lethal circuitry such as SMPS, non-isolated from mains, working at high voltages and capable of storing HT charge for days. I've been shocked by non-live SMPS circuits a few times and I don't urge many people to touch that stuff unless they really know what they are doing. Not to mention, sometimes fixing them is downright impossible without custom parts ordered straight from the manufacturer.

[faulkner1953]

I see the points that you are making. A man's got to know his limitations! I can understand a tube circuit, just barely at this point. I'm new at that, too. I am aware of the stored voltage potential in capacitors. I picked up this amp knowing that it was broken, hoping it was something simple, like a blown fuse. Also with a plan B of maybe putting a tube amp in the cabinet. It's quite shallow, and it's interior is pretty full with the 12" speaker. I still feel that I can get a chassis in there, and will most likely just discard the electronics. It's a shame, but I don't want to pay more than it's worth to fix what's there. I don't need it, it's only a project to fool with.

[joecool85]

I see the points that you are making. A man's got to know his limitations! I can understand a tube circuit, just barely at this point. I'm new at that, too. I am aware of the stored voltage potential in capacitors. I picked up this amp knowing that it was broken, hoping it was something simple, like a blown fuse. Also with a plan B of maybe putting a tube amp in the cabinet. It's quite shallow, and it's interior is pretty full with the 12" speaker. I still feel that I can get a chassis in there, and will most likely just discard the electronics. It's a shame, but I don't want to pay more than it's worth to fix what's there. I don't need it, it's only a project to fool with.

If you are going to discard the electronics, let me know.  I'd be interested in having them.  Not much money right now with the baby on the way, but I might be able to come up with shipping at least - better than the dumpster right?

[teemuk]

I still feel that I can get a chassis in there, and will most likely just discard the electronics. It's a shame, but I don't want to pay more than it's worth to fix what's there. I don't need it, it's only a project to fool with.

Pretty much what I figured already, recycling it is then.  

Anyway, I suggest you don't throw away the internal electronics, boards and stuff. You may regret it later, especially if you after few years from now find out that your skills have improved to a level that the project of fixing that thing doesn't sound impossible no longer, generate a special interest to what stuff actually was inside it besides a (possibly) broken power board, or simply find someone who fixes it for fun (basicallyfor free or extremely cheaply), or anything in that manner. ...Or just sell it to joecool85, very likely a damn good home for such project. Basically anything's better than the dumbster.