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Hybrid guitar amplifier help!

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doctormario777

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Hi all, I'm new to this forum, but from what I can tell I like it already!

I've got a fender performer 650 hybrid amplifier at home in Maryland, but I'm stationed out in colorado. The amp is just something I use when I come home on leave, but this time I haven't been able to use it much at all. At first, the input jack malfunctioned and had to be replaced. Done, no hassle there. So after repairing the amp I sat down and played it for about 10 minutes and all of the sudden it just turned off and won't come back on. I opened up the amp and noticed a blown fuse, so I replaced said fuse and expected everything to be fine. Instead, immediately after turning on the power the new fuse blew.

At this point I'm not too sure what is wrong with the amp, possibly a bad transformer? Any insight or suggestions would be helpful, and thanks in advance!
 
if that's one of the amps with a tube input stage and SS outputs, you most likely have shorted output devices, did the fuse go off like a flashbulb? if you didn't see it go, is it blackened inside or the glass have a silvery coating on it? that's usually an output device. if it looks like the fuse went slowly (you can see the ends of the wires in the fuse and they just look like the melted apart a little bit), then something less obvious is wrong with it.
 
I was able to watch a the replacement fuses blow after the initial problem, and yes, they did blow like a flash bulb. The amp itself is a little different from the hybrid amps today, instead of a SS output stage, only the distortion channel uses the tube... however, the fuse blows on both channels.
 
the outputs are solid state, the tube (most likely a 12AX7 or ECC83) is the preamp tube for the distortion channel. the output stage on that amp is a large flat pack IC (an LM3886 on an aluminum heat sink) and most likely that's what is shorted. input stage components when blown rarely cause enough current draw to take out the line fuse, but will burn out regulator IC's or current limiting resistors. when i mention the large flat pack IC, i'm not talking about the DSP chip which has about 150 pins, but the large chip with a staggered row of pins on one edge. it's mounted on a heat sink. the speaker wires go to the board the amp chip is on. the best way to test it is to measure with an ohmmeter and with the speaker disconnected, from the speaker wires to the DC rails that supply the chip, it should be 10k or higher. if it's shorted enough to flash the fuse it's likely to be a dead short. there may also read a dead short between the rails. LM3886 chips tend to get holes blown in them when they short, so the failure may be an obvious one upon visual inspection. if you remove the clip holding the chip to the heat sink, you can see the whole face of the chip.
 
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Is this the pack IC? I recently changed a 9 pin input jack on this amp... could it be possible that maybe I crossed some solder over between two of the pins?
 

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ok, your amp has output transistors not a chip... i was thinking of a different amp.... one or both of your output transistors is most likely shorted to cause the fuse to flash. if you check from the center pin to the right hand pin (collector to emitter) with an ohmmeter it should read open circuit. in diode check mode, you should read open circuit in one direction and possibly about 0.5 to 0,8 volts (diode check tells you the voltage drop of a forward biased semiconductor junction). also, be aware that if the output transistors are shorted, there are probably other components that were damaged. other transistors and diodes could be shorted and some resistors burned open.
 
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