2000 Factory Mopar Spare Tire Sub Help Needed

So I installed a factory spare tire sub into my XJ last year and never had any problem with it until just last week. It was not working and when I looked at the fuse it was blown. I installed a new 5amp fuse and it blew right away. So wanting to fix this I opened up the amp on the sub and found a 1000uf 35v capacitor laying in there and not attached to the circuit board. Noticing where it went I bought 2 new ones at Radioshack that were the same as the broken one and replaced both. I made sure to install them correctly so I do not think that is the problem. Now the sub will work for a bit, but after a few days it blows the fues again.

Does anyone own one of these? Or might know what is wrong? If you do what size fuse is yours running. I have put a picture below of the sub that I am talking about.

I'm not familiar with the sub, but can you take a picture of the circuit board?

I can. It will be a bit till I can remove it again. But I will post pics soon. Any help would be great.

Thanks

You could try a 10amp fuse and if the speaker's voice coil is shorted/melted, or there is a shorted component in the amp, it'll blow just the same. That looks more like a midrange speaker to me.

gradon said:

You could try a 10amp fuse and if the speaker's voice coil is shorted/melted, or there is a shorted component in the amp, it'll blow just the same. That looks more like a midrange speaker to me.

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I might try that. Just don't want to destroy the sub. It is an 8 inch sub, same as the one found in TJ's.

Seconding the pics request - might be a smoked regulator or driver transistor or something. Any discolored-looking parts or areas on the board?

How many watts RMS is this thing supposed to make? A 5w fuse seems small if this amp makes any power at all. My amp has a 60 w fuse, but it's 500w @ 2ohms, and I saw a brief burst of 75w. Do you know anyone with an amp meter? Get it running, and see what it's drawing. Could lead you in another direction.
I've never seen a sub like that. It was factory? Now I have something else to look for at the yards! It would be a good alternative to the coffins we have in ours, my son and I each putting together better and more molar-rattling systems in our XJs. This wouldn't push out windows, but he doesn't have one!

According to the accessory catalog for 2000. It is a "50-watt amplifier powers 8" subwoofer for added bass response" This item was factory, but hard to find. It took me 3 years to find one brand new and now it just is not working right. I will open it this weekend and post pics. I hope to fix it since it is great for added base.

Thanks

I need one of these.

heyhar said:

How many watts RMS is this thing supposed to make? A 5w fuse seems small if this amp makes any power at all. My amp has a 60 w fuse, but it's 500w @ 2ohms, and I saw a brief burst of 75w. Do you know anyone with an amp meter? Get it running, and see what it's drawing. Could lead you in another direction.
I've never seen a sub like that. It was factory? Now I have something else to look for at the yards! It would be a good alternative to the coffins we have in ours, my son and I each putting together better and more molar-rattling systems in our XJs. This wouldn't push out windows, but he doesn't have one!

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Fuses are rated in amps, not watts. Watts equals volts times amps. So 13.5VDC (engine running) times a maximum of 5 amps equals 67.5 watts.

I should know better, I'm an electrician. I've been out of work too much lately. Sorry about the typo!

Ok so I finally opened up the sub amp and made sure all the connections were good. The sub will work for like 6 to 8 days then blow the fuse. The only thing I did to it was replace the 35V capacitors when I found one of them broken off this past summer. Here are the pictures many of you have asked for. Is there any way to fix this or way to test the parts on the board? I know nothing about Circuit boards.

Thanks in advance.

Kudos for taking a stab at it. Finding the broken caps was certainly a good clue.

If the capacitor values and polarization are correct then I would strongly suspect one of the output IC amps is dying. (bottom pic, 2 large grey backed IC's with the hole) Most of the time that is the problem when an amp blows main fuses. IC amp internal short to ground.

Don't overlook the possibility of a cracked solder joint anywhere on the board. Since one of the caps fell off, it might suggest a poor solder job from the factory. Cracked solder joints can be difficult to see with the unaided eye.

If you are uncomfortable with the repair, look for someone in your area that works on CB's, electronics repairs, or even musical instruments like guitar amps. That is a piece of cake repair for an expert.

Do you have the Mopar pn for that amp?

Good Luck and that is a cool Amp. I would try to save it too.

X2 on that, though those look like power transistors in a push/pull config rather than ICs to me. Looks like a pair of 2SD718s from what I can see of the markings on the biggest two, since that is a 120Vce 8A 80W NPN power transistor this makes sense.

I don't see any discolored areas except some burnt solder flux around some of the smaller power transistor/regulator packages off to the side, any chance you could read off the part numbers marked on those and post them up? I'm expecting some of them to be something in the 78xxx voltage regulator series and perhaps some more power transistors.

kastein said:

X2 on that, though those look like power transistors in a push/pull config rather than ICs to me. Looks like a pair of 2SD718s from what I can see of the markings on the biggest two, since that is a 120Vce 8A 80W NPN power transistor this makes sense.

I don't see any discolored areas except some burnt solder flux around some of the smaller power transistor/regulator packages off to the side, any chance you could read off the part numbers marked on those and post them up? I'm expecting some of them to be something in the 78xxx voltage regulator series and perhaps some more power transistors.

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I can try to find some numbers. Could you be more specific on what you would like. SInce I have no real clue at what I am looking at. I can try.

Kastein, you are correct, they do look like power transistors not IC's. Good Catch!

I believe the other 2 sets are "pre amp" transistors in the same push/pull configuration. Being a Sub woofer there's no need for 2 channels, therefore power transistors vs IC.

Agree it would be nice to know the part numbers to know for sure.

It would be easier to troubleshoot if it was blowing fuses with power applied, all the time. Then he could just unsolder both large power transistors, apply power, and eliminate the possibility/problem.

2000XJSPORT said:

I can try to find some numbers. Could you be more specific on what you would like. SInce I have no real clue at what I am looking at. I can try.

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Bottom picture:

2 large grey squares with hole

2 smaller grey squares with hole

2 black rectangle with hole

They were held down with a clamp to the heat sink.

Just write down any numbers or leters you can see on them.

Greenz said:

Bottom picture:

2 large grey squares with hole

2 smaller grey squares with hole

2 black rectangle with hole

They were held down with a clamp to the heat sink.

Just write down any numbers or leters you can see on them.

Click to expand...

ok i will take a look asap. thanks.

Greenz said:

Kudos for taking a stab at it. Finding the broken caps was certainly a good clue.

If the capacitor values and polarization are correct then I would strongly suspect one of the output IC amps is dying. (bottom pic, 2 large grey backed IC's with the hole) Most of the time that is the problem when an amp blows main fuses. IC amp internal short to ground.

Don't overlook the possibility of a cracked solder joint anywhere on the board. Since one of the caps fell off, it might suggest a poor solder job from the factory. Cracked solder joints can be difficult to see with the unaided eye.

If you are uncomfortable with the repair, look for someone in your area that works on CB's, electronics repairs, or even musical instruments like guitar amps. That is a piece of cake repair for an expert.

Do you have the Mopar pn for that amp?

Good Luck and that is a cool Amp. I would try to save it too.

Click to expand...

I will look to see if there a Part Number when I look up the other numbers, but I did not see one last time.

Thanks

I agree on the bad solder joints. That would explain an intermittent problem. With a good magnifying glass and bright light check the solder joints, particularly the larger ones and the ones on the transistors or larger components. Bad joints will look dull and have circular cracks around them. You might just take the soldering iron and reflow any suspect joints. You might even notice that some bad joints don't want to melt unless you add a touch more solder (ideally, you'd want to suck the old stuff off, but just adding some more is usually adequate).

I just did this recently on the power control module on my Nissan Frontier. Nissan claims they are non-repairable and charging customers $400 to replace the entire module. It's about to become a major recall for Nissan, covering most of their models for the last 4 years, as when the problem crops up the vehicle shuts down. Being a cheap bastard with some electronics skill, I refused to pay $150 for the part mail order and tore it apart. It had lots of obvious bad solder joints, which I redid and it's been working fine for 4 months now.

The caps in your pictures look okay (not swollen or leaking), but it's also possible some have dried up and lost capacitance too. That's a common problem in some equipment like TVs, Monitors, and VCRs where they used components that weren't rated for the heat.