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Old 21st April 2008, 01:54 PM   #1
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Default New User, Blowing Fuses!

Hello. As the title states, I am a new user here. I was directed to these forums by the Basic Car Audio Electronics web site.

I have an issue, well, 2 actualy, with a Jensen 500w Bridgeable power amplifier. It's model XA 2250.

My more major issue is, if I have the level set to anything over half way, it will immediatly blow the inline fuse. It does not matter if it has remote or not. It's basically, plug the fuse in, and as soon as the blades complete the circuit, it blows the fuse. Again, ONLY when the level is set to over half way on the amp.

It is not dependant on what speakers I have connected. I've also been able to recreat it many times using my test bed consisting of a 500w computer power supply (sends the PSU into protect/short mode).

Problem #2. The right channel positive output doesnt' seem to have anything going to it. I dont know if thise is related to the original problem or not.

There is not scoring inside the amp, no debris, or any telling smell.
Any help is appreciated. I would like to get this corrected so I dont have to buy a new amp, being that I'm broke.
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Old 21st April 2008, 02:14 PM   #2
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Default the info

you provide is incomplete ....

i can give you some advice but there is a lot to be done to troubleshoot an amplifier like that

are you equal to the task ???
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Old 21st April 2008, 05:51 PM   #3
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What do you mean by 'level' (gain control position, input level from head unit)?

Without the remote, no level control/input should make a difference. Are you sure the amp is switching off when remote voltage is removed?

At a low 'level' (where the fuse won't blow), are you saying that the left channel works properly but the right channel has no output? If so, have you tried moving all controls and switches to determine if a dirty contact is causing the right channel to lose signal?

Also try moving the RCAs where they plug into the amp. Sometimes they get loose and cause one channel to go out.

Do you have a multimeter?
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Old 22nd April 2008, 03:24 AM   #4
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Quote:
Originally posted by Perry Babin
What do you mean by 'level' (gain control position, input level from head unit)?

Without the remote, no level control/input should make a difference. Are you sure the amp is switching off when remote voltage is removed?

At a low 'level' (where the fuse won't blow), are you saying that the left channel works properly but the right channel has no output? If so, have you tried moving all controls and switches to determine if a dirty contact is causing the right channel to lose signal?

Also try moving the RCAs where they plug into the amp. Sometimes they get loose and cause one channel to go out.

Do you have a multimeter?
Alright, lemme see if I can answer this systematically.

The level I am talking about is on the amp itself, grouped with the High and Low pass filter setting knobs.

I'm fairly certain it's switching off, no power lights are on, and no output is there when I use an MP3 player with it.

The left and bridged both work fine when the amp isn't blowing fuses. The bridged uses the left channel + with the right channel -. And I have moved each and every switch and pot multiple times. I've used this amp to power everything from subs to mids and tweeters, using the appropriate settings for each

And I am fairly certain that it's not the cables since I have used quite a few different sets. And have also run it with just left and just right plugged in.

And last question, yes, I have a multimeter. I just wish I still had my good one, but that got stolen a while back, so the one I have will have to do.
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Old 22nd April 2008, 04:07 AM   #5
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Will the amp blow the fuse with nothing plugged into the RCA jacks?

Will it blow the fuse with the ipod plugged in but with no speakers connected?

A signal source with an isolated ground (like an ipod) can cause some amps to do strange things. Have you tried a different signal source (standard head unit)?

Pull the cover and measure the DC voltage from the left negative speaker terminal to the center leg of the output transistors. The output transistors are the large 3-legged devices under the clamps. Check all 8 of them with the remote on and with the remote off. Wait ~1 minute after removing the remote voltage before checking the voltage. You should read something near plus/minus 35v with the remote on and ~0v with the remote off.

With the amp disconnected from the supply, measure the resistance from the left - to the B+ terminal of the amp. It should read something significantly higher than 0 ohms.

Measure the resistance from the RCA shield to the L- speaker terminal. It should read ~0 ohms.

Measure the resistance from the chassis ground terminal to the L- speaker terminal. It should be well above 0 ohms.

Since the amplifier works properly in bridged mode, the power amplifier for the right channel is probably working properly. The fault is likely in-between the input circuit and the front end of the power amplifier circuit. It could be a defect in the muting circuit or a broken connection.
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Old 22nd April 2008, 08:00 AM   #6
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Yes, it blows the fuse with nothing at all plugged in. And I was using it with my standard pioneer hu. I only plugged in my mp3 player when I was tinkerying around with it.

And how do you want me to measure it. With the level down to the point where it's stable? Or what? Cause if I dont, all it will be getting is the negative and remote.

And what exactly do you mean by RCA shield? the outer ring on the input connector?
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Old 22nd April 2008, 08:10 AM   #7
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Measure the resistance with no power applied.

Measure the DC voltage where the amp is stable.

Yes, shield = outer ring of RCA inputs.

Does the gain control feel like it's in good condition or does it feel rough?
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Old 22nd April 2008, 08:15 AM   #8
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Default to my understanding

our friends problem should be located not in the outputs but mostly in the power supply .....

should be one of the mosfets leacky or something and at low levels is working and then more current draw drives to almost shortcircuit .....

it could just as well be a mosfet drive issue and goes on ....

but from what i see here our friend will be not able to locate such a problem ....

mostly issues like that are no cable/gain.source related .....
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Old 23rd April 2008, 06:48 AM   #9
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Default Re: to my understanding

Quote:
Originally posted by sakis
but from what i see here our friend will be not able to locate such a problem ....

Well, thank you for writing me off before I've even managed to really start this project. I cannot tell you how much your faith in me fills me with joy!


Anyways, back to the real problem at hand: Apparently, the last time I tried this, the amp actualy managed to blow out my PSU, and I dont have another one. So doing anything on the bench is out.

Also, I have one fuse, and as I said before, I am broke... So it looks like I am going to have to put this project off untill I can either pick up another PSU or grab some more fuses.
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Old 23rd April 2008, 07:19 AM   #10
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You can still measure the resistance from point to point as I suggested in a previous post. Post the results for each.

You can also answer the other question about the gain control.

Don't get discouraged. Do the other tests when you get a new supply.
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