Fishman Loudbox PRO-LBX-300

[gibson17]

Where does the blue wire next to it go, perhaps to the tweeter? And if so is there a second wire on the tweeter? It looks like the male pin for the female on the yellow wire broke off of something, perhaps off the tweeter?

To assist my theory, do the red and black wires go to the woofer? I mean the red and black right with the blue and yellow, not the lone red and black to the left.

This is just a thought, it might be something else of course.

After looking closer at the small tweeter, the lug is definitely broken off of there. The red and black in question goto the woofer. Is it possible that I just had the bad luck of the lug breaking off of the tweeter and falling down near the mains and it made some intermittent contact?

What about the caps that a broken off the trace? Should I replace them, or just try to reconnect them?

[gibson17]

Is there a 'fuse holder' in thar IEC socket.
If so, then that is the fuse out power wire. (broken off)

There is a fuse holder in the socket. A 2a 250v slow blow.

[Enzo]

Then the yellow wire is the output of the tweeter amp, and if you connected it to the mains fuse holder, you probably blew the tweeter amp.

[gibson17]

Then the yellow wire is the output of the tweeter amp, and if you connected it to the mains fuse holder, you probably blew the tweeter amp.

How do I test to see if that's the case? ... and if so, what needs to be replaced to repair it?

[gibson17]

Could contact of the output with the mains caused the caps to pop off like that?

[Mick Bailey]

Maybe, but who knows. All you know is that if the connector didn't accidentally touch the mains you made sure that it did and you could have more damage than you began with. Disconnect the speaker and tweeter outputs and see if there's DC on either output. Which part of the circuit are the damaged caps located?

[gibson17]

Maybe, but who knows. All you know is that if the connector didn't accidentally touch the mains you made sure that it did and you could have more damage than you began with. Disconnect the speaker and tweeter outputs and see if there's DC on either output. Which part of the circuit are the damaged caps located?

True. Speakers are disconnected. The connector that has red/black/blue/yellow goes to the small tweeter and the small mid. The connector that is away from the 4 wire connector that is a two wire connector that is Red/Black goes to the woofer.

On the 4 wire connector, there was DC voltage present on Blue/Yellow even at very low voltage, but much less on Red/black and not so much at low voltage.

On the 2 wire connector for the woofer there was DC voltage present even at low voltage. The unit was also drawing quite a few amps even at low voltage. 4amps before the 2a slow blow gave way.

The damaged caps seems to be right near the r58 resistor and right below the vr2 trim pot.

[Mick Bailey]

You have three power amps that need to be checked. Plus your mains voltage could have appeared on the main PSU rails momentarily (by way of an output to supply short in U5) prior to the fuse blowing. You'll need to establish that all the DC voltages are correct and that you're not missing one of the supply rails and eliminate the possibility of excessive current draw in the PSU. The only way to do this is either to isolate the power supply or remove the excessive load so that the amp can power up. The tweeter amp chip is almost certainly blown and I'd carefully remove it to eliminate it. Sometimes the supply pins read low resistance to the output pin and give a clearer indication of failure. Worthwhile just to take a measurement. The output devices on the other two amps need checking for shorts. You should also carefully inspect the board for any other visible damage. Before embarking on any repair I would establish what's shorted/damaged. Could be you have multiple faults. Sometimes it's necessary to remove the output transistors just to get to the point where an amp can be powered without blowing the fuse and then work from there.

What's your mains voltage?

[gibson17]

You have three power amps that need to be checked. Plus your mains voltage could have appeared on the main PSU rails momentarily (by way of an output to supply short in U5) prior to the fuse blowing. You'll need to establish that all the DC voltages are correct and that you're not missing one of the supply rails and eliminate the possibility of excessive current draw in the PSU. The only way to do this is either to isolate the power supply or remove the excessive load so that the amp can power up. The tweeter amp chip is almost certainly blown and I'd carefully remove it to eliminate it. Sometimes the supply pins read low resistance to the output pin and give a clearer indication of failure. Worthwhile just to take a measurement. The output devices on the other two amps need checking for shorts. You should also carefully inspect the board for any other visible damage. Before embarking on any repair I would establish what's shorted/damaged. Could be you have multiple faults. Sometimes it's necessary to remove the output transistors just to get to the point where an amp can be powered without blowing the fuse and then work from there.

What's your mains voltage?

Hello there. I've been quite busy so haven't gotten a chance to reply until now. I removed the Power Amp board from the amplifier to get a clearer look at what's going on. The caps on the backside look to be the only things that have sustained any visible damage. While the power amp board was removed, I powered up the amp so I could take some measurements off of the power connector board, which is what I assume you were asking for. When I took measurements from pins 1 and 2, the meter jumped to 5 acv then dropped to zero. Measurements from 4 to 3 provided no voltage, and pins 1 to 4 produced 120v. Pins 3 and 2 also produced 120v. Without the power amp board connected no fuses blew.

I have not gotten around to removing U5 yet. Should I reconnect the caps on the back since there are two that need attention or should I wait to get walked through it?

[Mick Bailey]

I think you're measuring the input voltage and assume you're on 120v mains.

I'm referring to checking the DC output voltages. Take a look at the PSU and you should have +/- 33v and +/- 14v. Also check for AC - those supplies should be pretty ripple-free with no load. These voltages have to be correct before moving on. Don't reconnect the old caps - they need replacing.

[gibson17]

I think you're measuring the input voltage and assume you're on 120v mains.

I'm referring to checking the DC output voltages. Take a look at the PSU and you should have +/- 33v and +/- 14v. Also check for AC - those supplies should be pretty ripple-free with no load. These voltages have to be correct before moving on. Don't reconnect the old caps - they need replacing.

Hello there, been pretty busy so haven't gotten a chance to get to doing more work to this until the last few days. I removed U5, but was still blowing fuses. There amp was still drawing over 2a at about 40v. I did the smell test and Q18 was stinky and very hot. So I removed it. The amp will now idle at full power at .18 amp draw. I tried testing various points now that the amp would stay running. I took a look at the schematic and it looked like to test for those values that I should test U10, U11, BR1 areas to get the values you are looking for. I tested for both AC and DC. I did not get the numbers exactly, I came in at 35.8vdc and 14.5vdc. The outside legs of BR1 had VDC while the inside legs had VAC. Am I testing the correct points? Please advise.

[gibson17]

Hello all. I sent the board into fishman for repairs. I received it, and installed it into the amp. Upon power up, the amp is buzzing and there are no lights coming on for power or mute and the controls do nothing. When I push the phantom power in, the buzzing is about half of what it is without it the button depressed. Transformer issue? Please advise.

[The Dude]

I doubt a transformer failure. Measure the "buzz" at the speaker jack. Is it AC or DC and what is the level.

[gibson17]

Hello Dude, It looks like with the phantom off it's 64.6mv AC, and with phantom on, it's 39.3mv AC. I also measured on DC and got .7mv with both phantom on and off. Also was starting to get an overheating electronics smell, which I suppose could be from the board getting serviced. Also, still no lights on the control panel, which is odd.

[The Dude]

Ok. Nothing ridiculous like full rail voltage. Double check that you hooked everything up correctly when you installed the new board. Make sure there are no bent pins in any connector. If you don't find any problems there, You'll need to troubleshoot the amp just as you normally would- new board or not. First check power supplies, etc.
One thing to note and not talking specifically about Fishman: I have in the past gotten replacement modules that were missing parts. Are all the fuses, filter caps, etc. installed? I think my first step would be to visually scrutinize everything and make sure nothing was forgotten and that everything is hooked up correctly. Also, do you have it assembled? Sometimes grounds are carried by jacks, screws, etc. and partial assembly just won't do. The problem could be as simple as something isn't grounded.