Fender Stage 160 amp problem

[F100390]

I have a fender stage 160 I bought brand new about 8 or so years ago. It's had problems in the past where the capacitors would get loose, causing the amp to start buzzing and then stop working here and there. I've fixed this problem before a few times by re-soldering the connections and it's set. This time, my brother was messing with it and the capacitor broke off. I went to the local electronics store and bought two new ones and replaced the broken one and then the other one, for good measure. The first time I got everything hooked up, I was able to play for a few minutes, then the fuse blew. I took it apart and checked everything, it all seems well, but the fuse keeps blowing right away now. I'm wondering if anyone has a wiring schematic for this amp, though I took pictures of the wires and am "pretty" sure that it's all good, I'd like a schematic just in case, unless it sounds like it's something else.

I'm gonna keep looking at it and trying to figure it out, any help/suggestions would be appreciated.

Thanks,

Tyler

[Enzo]

It never blew fuses until you changed the cap. Experience says that something about your work was wrong. My first guess would be that one of the filter caps is in backwards. Look carefully, one for plus and one for minus, so check.

When an amp is breaking parger parts like caps away from their solder or breaking their wire leads, you need to anshor them to the board. SOlder them down tight, leave as little wiggle room as possible. Then run glob of silicone rubber around the part, or use hot melt glue. If it is a can cap standing up on t he board, run the stuff around the bottom. If it is an axial leaded cap laying on its side, glob it under either side. This wil hold teh patr in place and keep it from shaking around.

[F100390]

I'll recheck all my work........... I'm wondering if I have a wire or two mixed up too, but all I have to reference is the pictures I took, which ended up not being as good as I had hoped...............I should have check 'em before I started tearing it all apart....

I noticed you're from Michigan, I just moved out to California from Ann Arbor.

Anyway, I really appreciate your input especially being so fast!! I'd like to get this fixed!

[F100390]

I put both old capacitors back in and it has the same problem, when I turn it on, the fuse blows immediatly. I have 1 fuse left, so I have one more shot tonight to get it fixed till tomorrow. So, I'm not sure what it means if I put the old caps back in and it still has the same problem........ I'm thinking a wire, but I'm sure they're right. There are no cross solderd terminals or anything, I'm pretty stumped.

[Enzo]

My concern here is the orientation of the caps. Looking from the front of the amp, the two filters are right in front of the power transistors. The one on the left has its positive lead away from you and the one onteh right has the positive side facing you. Is that how they are in your amp?

Now even if it is now correct, whatever happened could have damaged some parts.

So start with the power transistors - powr OFF. Measure for short between center and right leg of each one. SHould NOT be shorted.

Just to the right of them are the four main rectifiers - check them for shorted.

FLip the board over and measure for shorted across each of those large caps. Even if they themselves are not shorted, a solder blob somewhere could still be shorting across them. Inspect everything within 3" of anyplace you soldered looking for a solder splash or blob shorting two traces together.

Over closer to the fuse is a row of four smaller rectifiers - for the low voltage suplies. Check them for shorts as well.

Until you have it not blowing fuses, disconnect the speaker wires and tape them so they don't touch anything. If the amp is spitting out DC, then that wull help keep it from blowing more fuses.

[F100390]

Ok, so the caps were on right and I brought my multimeter up and started testing stuff. I'm not the most knowledgeable when it comes to the electronics, but I've been looking up how to test stuff. So far, both the old and the new caps are good. I tested the transistors, they tested good. A big problem that I'm not sure if I'm screwing up or if it's a real problem, there are 4 resistors in a row that are supposed to be 2,200,000,000 ohms...... has 2 red bands, a gray/silver band then a gold band. They all read 0.2 ohms. They are R114-R117, Also, R106 has a similar problem, it reads .03 ohms. So, I'm not sure what that means........... and I'm not sure what would cause the resisitors to go bad........... like I said, I'm not that smart with this stuff, so I'm not sure what to think of it. I've tested a lot of the other resistors and they match up with the bands they have.

Thanks for the suggestions so far!!!!

[F100390]

Also, I found another resistor that is "bad". They are all gray resisitors. There are 6 of them, and they are all testing bad. I'm not sure if that means anything, them being gray and all.

[Enzo]

"Bad" doesn't tell me anything. SHorted, open, wrong value? WHich? ANd it helps to know which resistors they are, R#???

R114-117 are 0.22 ohm resistors. Learn your color code. red-red is 22, but silver as a multiplier means divide by 100. Then teh gold stripe means 5% like on any resistor. The four of them are in parallel, which means they add up to 0.05 ohms. This should measure on your meter like a piece of wire - essentially zero ohms. You cannot measure 0,05 ohms unless you have a lab quality meter.

R106 is a 10 ohm resistor, but it is in parallel with L1, which is an inductor, in other words a coil of wire. SO it will also read as a short circuit of essentially zero ohms. But at least you are thorough.

Oh wait, are the 6 bad ones R94, 95, 98, 99, 102, 103? And they measure shorted? Those are 0.47 ohms each - half an ohm. Your meter will see them as almost shorted. Those rectangular cement resistors are either open or they are OK most always. If they check as shorted, then they are OK.

How about those rectifier diodes? D54, 55, 56, 57.

[Enzo]

And look down under the board from the end. ANything hiding under there that could touch the chassis? Something like an untrimmed component lead wire, a piece of hardware, something.

[F100390]

Hey, I've been working quite a bit to test more stuff, I'm a repo agent and I've been working a ton the past few days, I'll check all that stuff this weekend and I'll let you know what I find!!!

Thanks for all the help so far, Also I was wondering if there was a good way to test the power supply......

[Enzo]

Have you measured those four large rectifiers for shorted? Have you measured across the two filter caps for shorted? That is how I check the power supply.

When you took it apart the first time, did you remove the wires from the transformer to get at the board? if so, any chance the wires are on the wrong terminals?

When a SS amp like this blows fuses, it is most likely shorted output transistors, after that shirted rectifiers, after that shorted filters, after that mechanical shorts, and beyond that pretty weird.

[F100390]

Ok, I checked the rectifiers, two of them short to ground on the power input side and two short to ground on the output side. On the caps, the only the negative on one shorts to ground, then only the positive of the other shorts to ground, being in series, that's how it's supposed to be, right?

I took all the wires off of the thing...... I took pictures to reference, but the pictures sucked. I believe I got em all on right, but that dosnt prove anything.

Is there a way to check the transformer too?

I'm pretty lost, I kinda feel like it's a misplaced wire, since there's no solder globs and it seems it's all testing alright.

[F100390]

Oh, also, is Flux conductive? I didnt really clean the board after I soldered. There wasn't a bunch on there, but I just cleaned it off, havn't put it back together yet though. I figured I wait while it's apart to test all the stuff I can.

[F100390]

I hooked up the wires like on the schematic, put it all back together and it turns on for a split second buzzes for that second and shuts off........

[Enzo]

Don't think of the caps in series, they are just drawn one over the other. One has the negative to ground because it filters the positive. The other has its positive to ground because it filters the negative. Series implies current flowing through both together. SO it sounds OK, but not for the series reason.

Putting your readings together, it sounds like none of the rectifiers is shorted. The way to check them though is to put the ohm meter directly across the diode, not to ground. Due to the way they stick them in the board, you usually have to do this from the under side.

Ignore the flux.

OK, the wires should be this way, check them.

Right by the main filter caps is a push-on terminal that takes the yellow wire. Should have P2 Yellow printed on the board next to it.

Just to the right of the four large rectifiers are two push-ons P1 and P3 which each get a red wire. Says red next to them on the board.

Further to the right, closer to the fuse are four smaller diodes in a row. D61,D59,D58,D60 - might as well make sure they are not shorted either while at it - and immediately to the right of them are three push-ons P4, P5, P6. The remaining transformer wires go there. Brown in the middle on P5, and the other two get blue wires. Note that it has BLU, BRN, BLU printed next to them.

That is the secondary side, now the primary. There is a row of push-ons to the right of the fuse, that's where they go.

From the transformer, the black wire to P10 and the white wire to P11.

From the power switch, the black wire to P7 and the white wire to P8.