|My OEM bose speakers served me so well during the ~8 years of owning my old silver Z. I've always thought sound quality was great, and you never needed any more, especially with the Z singing its own song when you drive. I use an aftermarket Pioneer headunit bought in ~2009 with a Scoshe adapter to plug directly into the headunit. The Pioneer also has Sirius connectivity, which has really ended up being an integral component of enjoying daily-driving and commuting in the Z for me.
In any case, my rear passenger-side speaker started popping and screeching and making insane noises, as everyone tends to experience. I drove around like this for a year or longer, only because it wasn't bad at first but did progressively get worse. Once I built up my new car and reinstalled the old speakers, I realized I had forgotten how bad the popping and screeching was and I needed to do something.
My friend Matt, who likes clown shoe BMWs but loves all car parts, helped me out with this. We first tried some new capacitors, even though the stock caps didn't appear to be blown or damaged. No difference, the speaker/amp still worked, but the new capacitors didn't affect anything, still plenty of popping and screeching. Matt then recommended we try replacing the transistors. He bought some that he thought were the right ones. After installing them, they kept on blowing the speaker fuse in the driver footwell the second they were powered on.
There is only one post on TT.net from a member referencing the transistors in the amp. If you look for it, he too was experiencing popping and screeching before the speaker started smoking. He opened it up and found a busted transistor. Further evidenced the transistors are what cause our issues.
In any case, Matt found some info online and ordered another set of transistors, and they worked! I have since installed these replacement transistors on all four of my speakers and they all work great. I think I might have found the same info he did, but all the credit goes to him for finding and ordering the right parts. The OEM transistors have the following info printed on them:
Doing some googling, you'll find several posts about the "137110" transistor on other forums. On one particular page here: La-Z-Link, "Dieter Wiedmann" mentioned that a part "IRFIZ24N" should be a good replacement. Well, that part is what seems to work for me. Good call, Dieter!
Here is where Matt originally ordered, but now out of stock: La-Z-Link
Here are two other sources for them with plenty in-stock: La-Z-Link La-Z-Link
Here is good site for international sources: La-Z-Link
The replacement procedure is not that bad. Please bear with me as I have very novice soldering skills, but think that this fix is totally possible for anyone with novice soldering skills. You will need the following:
Soldering Iron with Solder and Flux
Copper Solder Wick
Hot Glue gun
Pick tool/Dental tool
Small pair of Pliers
Small pair of Snips
OPTIONAL: Silicone Modified Conformal Coating
This photo shows both the front and rear amps out of old 94 TT. They are slightly different, which is interesting. The top unit has been modified with aftermarket capacitors which is not necessary or referenced at all in this guide. That was the initial fix that did nothing for me. The bottom unit is unmodified.
The first thing you need to do is remove the orange goop. Use your pick tool to pick away at all the goop near the transistors. Do your best not to scratch and mar the surface of the PCB when removing this stuff, but it can be inevitable depending how it is applied:
On this next photo, you can see I removed the orange goop, and also just bent off the transistors. I scratched up a bit of the PCB, which we'll come back to. This is just mainly to show removal of the goop, you don't necessarily need to bend off the transistors like I did.
Once orange goop is gone, time to remove the transistors themselves. This is the hardest part of the procedure I think. There are several ways to do this, and takes some figuring out. I would love some advice from an expert on what the best way to get these out are. First I was just bending off the transistor, putting the amp in the vice, pliers on one side, soldering iron on the other side and pull out the pin once it is free. If you can't get a grip on the pin with pliers, you can use your pick tool to push one side, and soldering iron on the other side to melt the solder enough to get it free. They'll push out and be much easier to grab with pliers.
I eventually just started leaving the transistor installed, holding it with my fingers and try to pull out just the one pin that I was de-soldering. This ended up working way better than my previous method. You'll just need to work out what works best for you.
The folloing photo is when I was using the method of pushing them out from the back-side, while heating up the solder from the front-side. You can see they're all sticking out here now and easy to grab.
Once they're out, you'll have a lot of solder left over that needs to be cleaned up:
This is where you use your copper wick. Just place a small section of wick over the hole/solder that you need to clean up, heat it up with the soldering iron and the copper sucks the solder right up. It will clean up the holes pretty well, you'll be left with something like this:
Slightly tricky to bend the transistors' pins in the correct orientation to install, but becomes easy after the first one:
I slightly bent the pins to hold in place while I solder. Little bit of flux applied before soldering.
I only solder from the back of the PCB because there isn't any space on the front. Be sure enough flows through the hole to get the front side.
Once they're soldered up, snip off the excess solder and pins off the back. All done:
On the front, this is the optional step of using the silicone modified conformal coating. This may really not be necessary, but I wanted to seal up any surfaces of the PCB that I scored earlier. It is more for waterproofing electronics like a PCB of a drone that could crash in water, but I just wanted to do something for the obvious scratches I made. Just brush over all the areas that you touched.
Lastly, you need hot-glue the areas where you picked off the goop from earlier. I used way too much. Don't use as much as me. Just be sure not to get any on the front-portion of the transistor. All done!
One thing to note that I didn't realize at first, is the aluminum shroud that is installed on the amp actually makes contact with the transistors and must act as a heat sink. Two of the screws that mount the amp and shroud actually go right in between the transistors on each side of the amp, putting pressure on the transistors from the amp. So when you go to reinstall these, make sure the screws are nice and tight and putting good pressure on the transistors from the shroud so they're properly cooled.
I'm very curious for someone else to try these transistors out on see if the fix works for them. I've only had them in for a week, but they work great so far.