I'm stuck...Help please (Bose Amp Repair + pics)
 

So today I pulled my pass. side amp and speaker, and removed the amp board from the assembly. My intent was to remove and replace the electrolytic capacitors on the board the same way I've seen it written up before.

1) I thought a blown capacitor looks deformed or different? The black spot on the biggest cap looks like black marker that mixed with the glue when they put the glue on.

2) I did not expect them to have gunked the whole freakin thing with hot glue. Will I damage the board if I try to peel/cut away this stuff? Is this how they all look?

http://www.davidgeesaman.com/maxima/bose/IMG_8074a.JPG
http://www.davidgeesaman.com/maxima/bose/IMG_8075a.JPG
http://www.davidgeesaman.com/maxima/bose/IMG_8076a.JPG

Hmm, after some more research, it seems the hot glue is just to keep things from vibrating. I'm guessing that careful use of a hot air gun will soften or remove it.

After further research, it looks like the MOSFETs (the rectangular black things at the upper-left and upper-right of the first pic) would be a very good thing to replace.

I will report again later as I progress.

Dave

Your replacing items that you don't even know are broken. :tardsmash

Trouble shoot the board to see what's blown before you start replacing unnecessary items. What's the problem your having that makes you think you need to simply replace capacitors and amps?

How do I go about troubleshooting the board? I have a DMM without ESR or capacitance measuring features. All I know is my fronts aren't producing sound except every once in a while when I hit a hard bump. Both speaker coils test around 1.0 Ohm.

I've been reading up on this Bose amp stuff as much as possible, and it sounds like the only reasonable thing to do is replace all the electrolytics and mosfets. Given that the components only add up to a few bucks, and the original Nichicon caps are universally reknowned as junk, it seems quite sensible.

If you know more, I'm certainly interested.

Dave

Well since nobody offered how to troubleshoot the circuit board, I went ahead and removed the capacitors from the board. (I needed to order a couple more sizes of caps, so I'll solder in the new ones another day).

The hot glue is not a big issue - it's less sticky when cold. Some people suggested using that spray-can freeze-it stuff, but a night on the workbench in my unheated garage was enough. I used a razor blade to cut the glue between components (but be very careful to not touch the board!). The wad of glue is fairly easy to remove when pulling the capacitor from the board.

In case you've never done soldering on a circuit board before, (I hadn't), you need a basic iron with a small tip (I have a cheap 25W iron), desoldering braid, and solder. The capacitors are mounted by what is called a through-hole design, (THT) meaning each lead of the component is a bare wire that passes through the a hole in the board that is slightly larger than the lead. Solder is applied, and due to surface tension, it fills that hole. The extra wire is snipped off, leaving a conical wad of shiny stuff on the backside of the board. To remove THT components, it is necessary to remove the solder, break the wire free from the side of the hole (it likes to stick even after most of the solder is gone), then pull the part free from the other side.

To desolder, take the desoldering braid, unroll a few inches from the spool, and use the iron tip to press the end of the braid onto the backside of the through-hole. After a few seconds, it should melt the solder and you'll see the solder wick into the braid. Immediately use a scribe to pull the wire free from the side of the through-hole. If the wire lead doesn't pop off readily, don't force it or else you could tear the leads off the circuit board. Just heat the lead again for a few seconds and use the pick or scribe to unstick it while it's hot. Clip off the portion of the braid that is loaded with solder and pitch it, and repeat for the other lead of the component. Once both leads are desoldered, flip the board over and use the scribe to gently pry the part from the board (again, don't scratch the board). Any glue that is hunked over the part will pry off pretty easily with the part. There was one capacitor that had a surface-mount resistor (a pinhead-sized black block) mounted very near the leads - be careful to keep the heat away from the resistor and not disturb the solder holding it to the board.

It took me about an hour to remove the caps from both front amp boards. None of them have any signs of damage or leakage, but oh well, it wasn't working before so I may as well keep going and replace them. I have nothing to lose but my time. Here is the parts list:
http://www.davidgeesaman.com/maxima/...Amp Repair.gif

Notice I listed the MOSFETs but did not replace them. These require more advanced soldering techniques to avoid damaging them by ESD, so I figured I'll only do that if the capacitor fix doesn't work. So right now I don't recommend replacing them unless you know what you're doing more than I do. Also, the 820microF caps come in tall and short sizes - to fit in the enclosure, you need the short ones. I ordered 10 or 20 of each size, so that I had plenty of spares and to stock up in case I repair the rear amps too. The Digikey part numbers are for the equivalent Panasonic electrolytic capacitors, which are supposedly much better quality than the original Nichicons.

Dave

save your self the hassle and get rid of the BLOSE, youll fix it now, and something else will go wrong later

Hmm, 7,202 posts of s h i t like that? You're a real asset here.

FWIW, it's the Nichicon capacitors that are universally blamed for Bose problems. If you look closely, they are now all gone. The Panasonic capacitors I spec'd last much longer.

Dave

Well I'll be cowkicked - that fixed them. :hs:

http://www.davidgeesaman.com/maxima/bose/IMG_8124a.JPG

You can see here the repaired circuit board with the Panasonic caps. The soldering was easy to get the knack for, as long as you put the heat on the wire/hole for a few seconds before applying the solder. The solder size I listed above seemed to work really well.

I think when I'm bored I'll take out the rear amps and redo them with the spares I have left. I'll make sure to list them too for the 14 people on this forum who might actually use the search and find this thread.

Dave

good job man, my partner can use your post to get his amp back on line, thanks

I just did the rear speakers, and it turns out they have the exact same circuit boards. So the parts listed in the chart can be multiplied by four to do all the amps.

http://davidgeesaman.com/maxima/bose/IMG_8126a.jpg

I do suggest using maybe a thinner desoldering braid (say, .050" instead of the .075"). Also, be careful to fully desolder each connection, but if it's taking too long to get the solder moving, take off the heat. Come back to that one again in a couple of minutes - if the heat is going to the wrong place, you can cause the circuit board traces to peel up.

Dave

I like the inorganic sound of base provided by BOSE, till I get a blowout or the stereo overheats from my scratched CDs. :-P

Dave - I just saw this - since it got bumped... great work!

thats excellent work. im saving the pics and numbers for parts...

i dont liek adding boxes and allthat junk in the trunk... my girl has all i need.. = )

heh anyhow its not for me.. i lov eht sound of BOSE.. and they put alot of work into the system when designing it and it noticeable from the sound.. and it sounds beautiful...

anyhow thanks for the pics and all.. consider doing a writeup and contacting MODS to make it into a HOW to... this would be sensational to have in teh howto....

P.S. 2 Da Max... hey man i saw ur car in the drive way the other day... is she up and running... hit me up soemtime.. im gonna finally put int hte navigation OEM nissan one.. and i need help tapping into speed sensors etc.. i figure u and the guys u knwo might be able to point me int eh right direction.

Dave - would you mind if I linked this thread as a "Bose amp repair howto" in the appropriate sticky?

Of course I wouldn't mind. I'll make sure to leave the pics on my website (which is prepaid for at least 2 more years)

Dave

even though im close to removing all the bose stuff i should fix the clipping i get at high volumes. its not typical farty distortion, but more of a scratching of the higher frequencies. i wonder what it is. it happed with my bose HU and still does it sometimes with my alpine.

then you should add some tweeters to the rear. just get some front ones off ebay and wire them in under the rear grilles. they help so much.

Also putting the 6 3/4"'s in a baffle helps alot with bass responalso(check crutchfeilds for the baffles).

Great work you did in replacing those caps. Interesting that the FETs are so cheap and available. Bipolar output transistors cost a mint and are hard to come by, the Chinese have flooded the market with inferior copies. I'm seriously tempted to see if I can find some cheap Bose amps on EBay and make bass boomers out of them.
Interesting also that the Bose speakers are 1 ohm. Impossible to find replacements with that impedance. I will have mine re-coned when the rubber surround fails.

I read somewhere else that the speaker units themselves are interchangeable from car to car, but the amp design is what differentiates them. So in theory, you might do very well at a junkyard if you have an idea what models use similarly sized Bose speakers.

Dave

could you just wire two 2ohm speakers together to get it down to 1 ohm?

- If you wire them in parallel yes, but you'll have to find the space to fit two speakers each side instead of one. And make sure you get the phase right! (Plus to plus and minus to minus.)
2 ohm speakers usually come as dual-voicecoil items, they actually have 2 x 4 ohm windings so you can wire the coils in parallel to get a 2 ohm driver or in series to get an 8 ohm driver. I have never seen a commercial 1 ohm driver except these Bose units (Bose manufacture their own drivers, have done for many years).

Dave,

Did you even figure out how to test the individual capacitors? I'd rather only replace the one(s) that are bad.

Nope, I didn't. The fact that they are part of a circuit makes measuring them difficult or impossible (can't recall which - I'm a mechanical engineer, not electrical).

In any case, when you have the whole thing apart and your stuff set up, it's really not hard to take the extra half hour to replace all of the caps. The Nichicon caps on the board are known for high failure rate - it would suck to have to do the job again.

Dave

I noticed you didn't mention using a de-soldering pump or vacuum. When you melted the solder and applied the braid what happens to the solder you melt? Don't you have to suck it up somehow? I've done my fair share of soldering but I've never de-soldered.

I used desoldering braid which wicks up the solder when it's molten. A solder sucker might work better, but I was too cheap to buy one.

Dave

5 years later and the Bose are still running strong. Can't say the same for the rest of the car.