Newsome79

iTrader: (3)

This is my first post on instructions on how I am repairing my rear BOSE amps. I found some other sights for Corvettes and NSXs where they repaired the amps. However every BOSE amp is a little different according to the power and frequency response that was designed for the car and location. i.e. the filtering for the rear sub is much different than the center tweeter. Unless your amps have way overheated shorted and burned up the circuit board or the BOSE Integrated circuits. The most likely culprit for failure is one or more of the Nichicon aluminum electrolytic capacitors (little green or black cans), the one Tantulum capacitor (orange bulb) or one or more of the 4 N-type MOSFET drivers (rectangular flat black plastic thing with 3 leads).

Why these components do you ask? Electrolytic, and tantulum capacitors have a lifetime measured in hours at XXX degrees Celcius i.e. 5000 hrs @ 105 C. If the operation temp is actually higher then the lifetime is degraded dramatically. I would not be surprised if these amps in that crowded trunk space in the middle of summer get near or over that temp. The lifetime is degraded even when not in operation. Think about how hot that hatchback gets just sitting in a parking lot in the sun. Its not 105 C, but it reduces the life of the caps. So basically the electrolyte dries out and they short out and stuff oozes out the bottom of the cap onto the circuit bored and starts to corrode the leads and eat off the green colored resin covering the copper runs. I saw this especially under one of the large 820 uF cap when I removed it. The MOSFETs just die because they are insulated packages with poor heat transfer with an even poorer heat sinking. If you push them hard they die. I’m sure there are cases where the other film capacitors on the board fail but most of them when you look them up have no lifetime expectancy just operating temps. So as long as they stay under that temp they last a long long time.

Bose is kinda annoying how they remove the marking of the MOSFETs but I could tell that the rear BOSE amps MOSFETs were ST microelectronics. However, I couldn’t find info that referenced STmicroelectronics replacement MOSFETs. What I did find was that International Rectifier makes a MOSFET that can be used. I looked for an equivalent from STmicro for the IR version but I could find none. The significance of the IR MOSFET is the low input and output capacitance this will allow for a fast response by the MOSFET to ensure good frequency response and the Junction Operation Temp of 175 C for operating in the extremely hot environment. If I was so inclined I could probably find another replacement from another company but why bother since the IR one is basically $1. So here is the parts list from Digikey of all the electrolytic capacitors the one tantulum that should be replaced and the MOSFETs for both rear amplifiers along with the values of the original parts.

Part Number ***** Price ***** Total ***** Qty ***** My Parts ***** BOSE Original ***** Designation

EEU-FC1C821S ***** 0.80000 ***** $3.20 ***** 4 ***** 820uF 16V ***** 820uF 16V ***** C19,C25

EEU-EB1H100S ***** 0.11000 ***** $0.66 ***** 6 ***** 10uF 50V ***** 10uF 16V ***** C172, C183, C31

EEU-EB1E470S ***** 0.11000 ***** $0.44 ***** 4 ***** 47uf 50V ***** 47uF 16V ***** C7, C8

EEU-EB1H4R7S ***** 0.11000 ***** $0.44 ***** 4 ***** 4.7uf 50V ***** 4.7uF 35V ***** C203, C150

IRFIZ24NPBF ***** 1.17000 ***** $9.36 ***** 8 ***** 55V 14A ***** ????? ***** Q1-Q4

EEU-EB1H1R0S ***** 0.11000 ***** $0.22 ***** 2 ***** 1uF 50V ***** 1uF 50V ***** C16
T
AP106K035CCS ***** 1.28000 ***** $2.56 ***** 2 ***** 10uF 35V ***** 10uF 35V ***** C34


So how did I find out all these capacitor values? I carefully dug through all the silicone goop that was structurally reinforcing the caps and the wire wound inductors (round things with wire coiled on it) I matched all the capacitance values but in some cases i chose a higher voltage model. Why would I do that you ask? The higher voltage models when derated for heat maintain integrity at higher voltage. With that said the lower voltage models are available if you wish to match them exactly. In the 820uF's case I did not get a higher voltage model do to space considerations. After all these things have to fit under that metal cover you will find over the amps. Any radial capacitor with a height more than 15mm will bump the cover and probably not fit without cutting a hole in the cover. The Nichicon caps are still available but I chose the Panasonic versions because they are cost effective and from my research more reliable. I’m sure there are a lot of others out there by AVX, Vishay, NEC and so on, but these are decent enough and cheap. If you have a favorite manufacture choose them it matters not but make sure the electrolytics are rated for at least 5000hrs @105 C. If you get like 1000hr @85 C. Expect them to fail very quickly. The tantulum is another story just get the longest rated highest temp you can find for a reasonable price.

Here are some links I drug up from the forum and google that I found useful. They are not the how to fix the amps just good info I used to start my quest.

Nice rough diagram of a BOSE amp. However ours is a little different.
http://www.zr1netregistry.com/Bose2.pdf

Nice explanation of how to replace the caps without destroying the rest of the board
http://www.zr1netregistry.com/amp.htm

Nice pictures of the amps from an NSX.
http://www.nsxprime.com/FAQ/DIY/bose_rr.htm

The reason I started my quest. The amps I purchased also died, not the forum members fault they worked when I got them.
https://www.rx7club.com/showthread.p...ferrerid=90185

Here is a series of videos for the person who never soldered before. http://www.ehow.com/video_4435735_solder.html

Some random info about my soldering. I use a soldering iron at my work with a very narrow tip set at 800 degrees. It is very hot but the small tip does not transfer heat as fast so I had to make it hotter to get the results I wanted. The method I used to remove the caps was pretty simple I would heat from the back side of board with the board in a soft vise (i.e. vise with rubber padding to grab the board by the sides and hold it steady) and grab the cap with pliers and pull out the lead I was heating then I would heat the other lead and put it out and repeat back an forth till the cap was out. This also works with the FETs. Be careful with the iron and don’t melt the solder on the surface mount chips on the bottom of the board. After I had all the components I wanted to replace out, I used a solder sucker by heating on one side and placing the sucker on the other and sucked out the thru holes. After all the holes were open, I used a .050 wide solder wick to remove excess solder left around the holes. Once again be careful with this stuff is will suck the solder right off the surface mount components if you get it hot and on them. I then used isopropyl alcohol and an acid brush to clean off the flux, small bits of solder stuck to the board, and the electrolytic compounds leaked by the caps.

For soldering back in I used a Lead free, no clean, Silver solder. It was a pretty small gauge 21. I was not sure whether the original solder had Lead but I didn’t want to contaminate it with lead if it didn’t have it before.


So far I have replaced the MOSFETs and the caps on the two amps on rear BOSE acoustic wave tube thing. I plugged them in and amazingly they both worked well the first time. I still have some work to do before I put them back in permanently. First, I need to get some electrical grade silicone to replace the goop that I removed during disassembly. Be careful not to use non electrical grade. The solvents used to cure it will corrode exposed copper and silver. Not a good thing considering most solder is full of silver and the runs on the board are copper.

One example of what I will use

GC electronics PN# 19-155

http://www.altex.com/GC-Electronic-G...5-P141838.aspx


The IR MOSFETs are rated at 29 Watts at 25 C. With a derating of 0.19 Watts per Celcius degree above that. What does this mean? If you let the things get hot there power handling goes down. Each speaker is running at 1 Ohm. With the car running you have a 14.4V input voltage to the FETs. Each speaker is running off of 4 FETs. The maximum instaneous power that can be delivered is 207 Watts. The maximum RMS power delivery is .707*207 = 146 Watts. 146/4=36.5 Watts per FET. In reality music has varying amplitude and frequencies and the system will never truly be put in that high a demand unless you feed it the amps resonance frequency continuously from some sort of frequency generator. If you assume that the actual RMS power delivered is something more like 35% of the max you get 12.78 Watts per FET. Sounds like it should handle it right? Well it will only if you keep its temp under 110 C [12.78 = 29 - 0.19*(X-25)] X=110 C. Heat destroys these FETs. The only option is to try to keep the heat down or replace it with a higher wattage FET. The problem I found was all the isolated packages were basically 30 Watts or less power handling. The higher wattage FETs all have metal housings that are electrically connected to the drain of the FET. If you notice the heat sink frame that covers the amp connects back to the board ground plane. If you connected the drain of the FET back to the ground plane of the board you now have a direct short to ground fuses blow and most likely your amp is now beyond repair.

Solution:
I bought some diamond base thermal compound that I will put under the MOSFETs and on top of them between the FET and the metal cover that sits on top to try to keep them from overheating and being destroyed.
http://www.heatsinkfactory.com/ic-di...m-p-16605.html

Why did I choose the diamond base instead of silver, ceramic or silicon? Diamond has a higher thermal conductivity than silver and it is an insulator. Silicon and ceramics are insulators just not as effective. Since the FETs used are isolated the compound needs to be isolated too to make sure there are no shorts to the other leads or copper runs.

My next installment some info on the application of the diamond heat sink compound and electrical grade silicone and maybe info on the center channel amp if I can get it out of the dash. I know everyone wants pics I will try to get the digicam out and take some example photos.

Newsome79

iTrader: (3)

Here is a Panasonic part number for a 820uF 25V capacitor that is the same size as the 16V. The 16V is marginal when filtering alternator output (which is what these caps do) that normally sits at about 14.3-14.4V. I would recommend you get this one if you can find it. Newark has it but they charge 20 bucks to buy from them which defeats the purpose since Im trying to be on a budget.

EEUFK1E821S

Before I go through all the trouble of sealing up these amps I'm going to do a quick bench test to check the gain and the distortion of a 1-2 Ohm resistive load on the output.

Newsome79

iTrader: (3)

Ok update.

I changed the components on two amps. One that made slight buzzing noises in the BOSE tube and the other did not work all. The amp that was buzzing initially was now working great. I hooked it up to a frequency generator a 14.4 V power supply and a 1 ohm wire wound resistive load. It had its highest gain at 50 Hz rolled off slighty down to 20Hz and also rolled off significantly above 100 Hz. The gain is slighty greater than 2. so when you put in a wave of about 4.5-4.8 V amplitude you get the output amplitude maxed out at 14.1-14.4V. there is a lot of high frequency ripple visible on the output. I suppose you would expect that with a cheap class D amp. I installed this amp into the tube and it sounded pretty good.

The other amp sounded ok in the tube along with the amp described above but when i looked at it on the bench i found that it was clipping at high volume. I troubleshot it till I found that one of the four output stages of the Class D BOSE Pulse Width Modulation chip the one marked 134499 had no PWM output. So why did this output stage not work?

Before i changed the MOSFET drivers I measured them and found that the one connected to that output stage had shorted internally thereby effectivelly putting 14.4V power onto that pin of the chip. Bad Class D chip which I could not replace.

I happen to have 4 amps handy. So I tried to move the caps and MOSFETs to another amp and I kept having problems. One of the other amps seemed to have a good PWM chip but then the other chip marked 131454 the compression and equalization preamplifier was putting a very noisy signal into the 134499 chip which in then tried to pass on to the MOSFETS very messy signal. Im sure it would sound like $hi$. There were bad input power caps (C7, C8, C19, C25) on this board that normally isolate signal ground for power ground. I hypothesize that when they failed they damaged the 131454. I could go on and on moving parts around and hope that finally I get another good working amp which I believe I could do by switching one of the good 134499 chips to the first board I tested. By now I probably have well over 30 hours of time involved. Since I'm an electrical engineer it was interesting but def not cost effective. I could have mailed off 2 amps to carstereohelp had them both repaired for 80 dollars each with lifetime warranty for probably about 180 bucks total. I make about 32 dollars an hour at work with overtime. So its pretty obvious it was more of a see if I can do it project than a necessary one.

The conclusion I have come to is that if your amps have never been repaired and they are working either do one of three things. Take them out now and change those components and put them back before they die and take the BOSE chips with them. Or just turn it up loud as possible on the hottest day of the year and watch those babies fry. Then send them to carstereohelp to repair and never worry again. Or do what I am gonna do. save the 80 dollars times 5 for all the amps being repaired and install current technology speakers and amps.
All three are a lot of work or money or both but the everyone knows

"BOSE Blows"

or one of my other favorites.

"No Highs, No Lows, Must Be BOSE"

For me this is gonna be Alpine Type R 6.5 inch components in the doors and install a 8 inch sub in a damonB style box. Im going with a kicker L7 8 inch It should have the SPL of a round 10 inch because if the increase cone area of the square woofer. (We need someone to make the rotor shaped woofer so i can have a 4 rotor RX7) It fits in a shorter box than damonBs 9 inches is tall enough and it will be easier to fit under the strut bar. Hell I could even go with two of them but i think that's way overkill. Driving all three with a bridged Kicker ZX 700.5 five channel amp.

DMoneyRX-7

iTrader: (2)

This is a long post so correct me if I'm wrong but...you fixed 2 broken Amps correct?

I just want to know if your procedure and everything resulted in a fixed amp. If so I'm going to merge the posts and sticky this

Newsome79

iTrader: (3)

I could only repair one of the rear amps without replacing the BOSE chips 134499 and 131454 If anyone can chime in with a replacement chip for those Im pretty sure i could fix the other amps I have. At the age of these amps repair should be looked at like maintenance if you just got to keep the car original take out the amps and replace the limited lifetime parts before they fail and take out the out of production bose chips

sc_frontier

iTrader: (3)

I just rebuilt and tested my sub amps and they work GREAT!! I used the exact parts listed above and ordered from digikey. I used hot glue to secure the inductors and capacitors. Before, my subs would pop and start to distort at about half volume, now I can crank it up and it sounds good. The frequency response is better than a system I built in my truck. Sad to say during the test my only functioning door speaker quit

sc_frontier

iTrader: (3)

Center channel:

Part Number ***** Price ***** Total ***** Qty ***** My Parts ***** BOSE Original ***** Designation

EEU-EB1H100S ***** 0.11000 ***** $0.66 ***** 1 ***** 10uF 50V ***** 10uF 16V ***** C501

EEU-EB1E470S ***** 0.11000 ***** $0.44 ***** 3 ***** 47uf 50V ***** 47uF 16V ***** C035, C037, C810

EEU-EB1H4R7S ***** 0.11000 ***** $0.44 ***** 1 ***** 4.7uf 50V ***** 4.7uF 35V ***** C021

EEU-EB1H101S ***** 0.11000 ***** $0.44 ***** 2 ***** 100uf 50V ***** 100uF 25V ***** C813, 811

EEU-EB1C102 ***** 0.11000 ***** $0.44 ***** 1 ***** 1000uf 16V ***** 1000uF 16V ***** C033

EEU-EB1E221S ***** 0.11000 ***** $0.44 ***** 1 ***** 220uf 25V ***** 220uF 16V ***** C812

sc_frontier

iTrader: (3)

A pair of door speakers:

Part Number ***** Price ***** Total ***** Qty ***** My Parts ***** BOSE Original ***** Designation

EEU-FC1C821S ***** 0.80000 ***** $3.20 ***** 4 ***** 820uF 16V ***** 820uF 16V ***** C19,C25

EEU-EB1H100S ***** 0.11000 ***** $0.66 ***** 6 ***** 10uF 50V ***** 10uF 16V ***** C172, C183, C31

EEU-EB1E470S ***** 0.11000 ***** $0.44 ***** 4 ***** 47uf 50V ***** 47uF 16V ***** C7, C8

EEU-EB1H4R7S ***** 0.11000 ***** $0.44 ***** 2 ***** 4.7uf 50V ***** 4.7uF 35V ***** C203

IRFIZ24NPBF ***** 1.17000 ***** $9.36 ***** 8 ***** 55V 14A ***** ????? ***** Q1-Q4

EEU-EB1H1R0S ***** 0.11000 ***** $0.22 ***** 2 ***** 1uF 50V ***** 1uF 50V ***** C16

TAP106K035CCS ***** 1.28000 ***** $2.56 ***** 2 ***** 10uF 35V ***** 10uF 35V ***** C34

sc_frontier

iTrader: (3)

First picture is a door amp (very similar to sub amps). Second picture is center channel amp which is located left of glove box.

Newsome79

iTrader: (3)

Nice continuation. Looks like the preamp stage for the center and door speakers is the 121661 instead of the 131454 used in the rear sub. Can you remove that heat sink from the center channel speaker amp. Looks like Bose used an integrated PWM and H-bridge output chip instead of the 134499 and external H-bridge FETs. I have done another extensive search and apparently even the people who repair these amps for $80 use old chips. I have not found a 20 pin DIP H-bridge PWM that has the same type of pinout as the 134499.

sc_frontier

iTrader: (3)

Glad to see you are still around! The H-bridge FET can be removed. The heat sink is screwed to the board and mated to the FET with thermal paste and a clip. It is another ST chip:
TDA7256
ST W88AD
9148

Feel free to state any corrections needed on my previous post. I tried to stay around the same series and manufacturer for the capacitors. I called Bose the other day and ordered some new sub-woofer speakers ($60 each) and they said that any new amp cost $80 (same as a repair facility). They also said every speaker in the car is $60. There is one large capacitor on the door boards that I couldn't figure out. It is the big red one next to the connector pins. It says:
475K
35 (a "n" inside a circle) N
From my research, I believe it is a tantalum capacitor, 4.7uf, ~10%, 35v made by Vishay?

Newsome79

iTrader: (3)

I believe you are correct on the tantalum capacitor value. 475K is broken down into 47 X 10^(+5) picoFarads with K=10% tolarance in EIA standards. A picoFarad is 1.0 X 10^(-12) Farads. Now to finish all this math up you have -12 plus the +5 from the markings 47 X 10^(-12+5) = 47 X 10^(-7). For the ease of searching for replacements 1 microFarad or (uF) for abbreviation = 1 X 10^(-6) Farads. So basically moving the decimal point to the left adds one to the exponent. 47 X 10^(-7+1) = 4.7 X 10^(-6)= 4.7 uF.

Bottom line is get as 4.7 uF 10% radial Cap with a temp rating that matches the others and the manufacturer is not important. Vishay, AVX, and CEMET all make quality product just find the one that matches.

sc_frontier

iTrader: (3)

Well, I just installed the remaining 3 amps, and all I can say is HOT DAMN! I have owned this car for 10 years and always contemplated replacing the stereo system, but I am thoroughly impressed with the bose system now that it is working properly. I can turn rap/electronic beats up as much as I want and the frequency response is great, and distortion is almost nonexistent . Rock music sounds slightly muddy but that is the compromise with ported enclosures I gather. My parents also remember this sound system and their faces lit up when I demoed it for them. They couldn't believe it! Just to clarify, this is not the best sounding sound system I have ever heard, but it is definitely something I will thoroughly enjoy and I think it is neat to have a piece of history working again! Thanks for all your help Newsome79. Maybe someday I will get an electrical engineering degree too

P.S. Still not sure about the big red capacitor on the door amp, but both sides looked to be in good shape so I didn't mess with them. I ordered a vishay 4.7uf and it was one tenth the size of the red ones...

chips

Hi guys,

very interesting thread you've been working on.

Here's my situation: I bought the car in 1997 and the Bose system was awesome. Over the years it seems to not sound as good, but currently I have some issues and some may be due to the amps.

I have a 94' with bose. Everything is stock.

My right door amp is blown.

My center channel speaker does not work. The paper on the speaker is torn. I don't know if the amp is inoperable as well. Any ideas on how to check the center amp to determine if its ok or not?

BTW, where is the Center amp located?

Bose has replacement speakers for $60/each and replacement amps for $80/each.

If I buy a replacement center channel speaker from Bose and install it and the amp is bad, will it blow the new speaker?


A few technical questions please:

SC: How long did it take you per board to replace the components? Did you solder all of the parts in? I saw that you used hot glue. Not sure if that was for an insulator or if you hot glued in the new electronics. You seemed to have a lot of success and I'm interested in redoing my amps. Did you replace all of the parts on the list for all of the amps? or just the amps that weren't working?

Thank you both for your expertise and comments.

Chips

sc_frontier

iTrader: (3)

Rebuilding an amp could be considered a restoration. Some components wear out over time. I replaced all the components on the list, just like I would replace all pistons rings in an old engine with only one weak cylinder. You might have one capacitor that is dead, but the others on the board could last a day or 5 years. I used a pencil tip solder iron and a solder sucker to remove all the old components, and re-soldered in the new. The hot glue was just to secure top-heavy inductors and capacitors so they would not bend while driving.

The center amp is to the left of the glove box, somewhat behind the hvac controls, and is tricky to remove.

A new speaker could be blown by a bad amp. If the amp is putting out a dc current instead of an ac current the speaker will suck in or raise up until it gets so hot it melts the voice coil. More likely a bad amp will have a lot of distortion which would have dc currents mixed in with ac currents and can also kill your speaker. The nice thing about distortion is you can usually hear it before you damage a speaker. You could test the amp with another cheap speaker that has a voice coil resistance similar to the bose. Realistically, the amp needs rebuilding if it show signs of life, or replaced if it is dead. As Newsome79 has stated, the heat and age on these amps makes very few, if any, in good condition.

milano maroon

iTrader: (1)

I have been watching this thread for awhile and finally decided to try it. I bought all of the replacement capacitors listed for the two rear amps (Digikey is the greatest with $2.50 shipping), taught myself to de-solder and solder, and replaced them - 11 on each board (I think). I did not replace the Mosfets at this time, wanted to see if this would be enough. I did check some of the caps after taking them out and saw a few that weren't testing well.

Anyway, I put everything back in and tried it out. Here's my question - all I hear when I put my ear to the rear wave outlets is a low pitched beating, drumming, etc. Should there be any mid range? I have never had the pleasure of hearing a working Bose system so I have nothing to compare mine to. When I sit in the driver's seat I can't seem to hear much sound coming directly from the rear, but overall the whole system doesn't sound bad.

Or should I go ahead and change out the mosfets too? Can they be tested in place? And if I change them how do you remove them? With three connections they don't look as easy as removing a cap.

By the way, I have tried two different head units and two different sets of rear speakers. I have 12 volts coming in on the black connector from the relay up front, and almost 6 volts coming in from the radio to each channel.

Thanks for your help, Jeff.

Newsome79

iTrader: (3)

When I checked a working amp on a bench with a scope it rolled off heavily at 100Hz So I would not expect to hear much mid range at all from the snake. Most of your mid range comes from the door speakers and the highs come from the center channel. But you should hear some pretty decent 80-40 Hz bass from it. You will want to check each amp separately and make sure both are working. The snake will not really have a lot of punchy bass like you would want listening to double bass pedals. But you should hear a pretty nice response to things like Bass Guitar. Good test song Metallica "The God that Failed".

One thing you can use to test the FETs is just measure the resistance between the three leads on each FET. None of them should be shorted together.

Removing the MOSFETs is really easy. With some needle nose pliers grab a single lead from the top. Put the solder tip on the bottom until the solder melts then pull out the lead. Repeat for the other two leads.

milano maroon

iTrader: (1)

Thank you for the reply. This really is an interesting process. When I started this I had 4 amps to choose from. One had a blown Mosfet, had burnt up on the board. 3 just seemed dead and didn't produce any output that I could tell. So I chose two of them (actually the two that weren't in the car at the time) and replaced all of the caps. Put them in and as I said earlier, did have output but it seemed awfully faint and one side seemed to have some distortion.

So I looked at the one that I didn't use (which didn't have the melted Mosfet) saw a black mark under one of the medium size caps and replaced it with one of the caps I took out from the other two. By the way, I went back and re-checked all the caps I removed. All of them (even the one I just removed) seemed to at least charge up, but ones of the same values did not always start and charge the same. Anyway, I tried the 3rd amp which just had one cap replaced and it seems to work. My volume out of the rear wave is louder, and I was able to isolate the amp which was causing some of the "distortion". Anyway, I think the rear wave sounds much better than before and certainly better than before I tried to fix anything.

So I wonder, what exactly do the Modfets do? Could the amp still work with a bad one but just not very well?

Now I just need to find a new front center speaker (mine is dead) and amp (maybe) and everything should work.

I'm sure an electronics tech will have a laugh reading about me stumbling through something I know absolutely nothing about but it's like my old boss used to say, "even a blind pig finds an acorn once in a while"!

Thanks for your help.

milano maroon

iTrader: (1)

One other thing I forgot to mention - I checked voltages at the 6 pin connector at each amp. Looks like I have 5.5v going into the amp from the head unit and about 6v out of the amp to each rear speaker. Does that sound about right?

Newsome79

iTrader: (3)

To answer one question. The MOSFETS are part of an H bridge. The amplifier is a Class D amp which uses Pulse Width Modulation (PWM) to turn the fets on and off with a varying duty cycle to create the sign waves required for sound. If you loose one of the fets you you could short the + or - side of the speaker terminal to ground or +12V according to which fet it is. Or the fet could just be an Open and then you get only half of the signal on that side of the H bridge. Its really hard to determine without looking at the signals with a scope or taking the fets out and checking if they work.

So the voltage you see coming into the amp has two measurements to take. The + and - inputs to the chassis of the car. Those should be near identical. In the Electrical world we call that Common Mode voltage. Common being that it is the same on both. That voltage should be around 5.5V - 6.5V in a system that is 0-12V. If you want to amplify a sine wave you have the room to go negative from your reference. Since this system is a 0-12V system 6V is ideal to give maximum room to swing up and down. Otherwise you will loose all the negative swings of the input signal. The next measurement should actually be an AC measurement while playing a constant tone. Preferably 60 Hz so the amp can amplify it and most meters work well at that frequency for measuring AC voltage. So now that you have your constant 60 Hz tone, you can measure the + to - differentially and get what the input amplitude is using the AC voltage measurement function. That measurement should be 4.5V - 6.0V at full volume.
(NOTE: some high end aftermarket stereos preouts are capable of more than that but that's all you need with the Bose Amps to get full volume out.)

The output measurement should also be an AC measurement and should be between 12 and 14.5 V at full volume according to your battery / alternator and if the car is running.

M_Rex

iTrader: (5)

I should start with the fact that I've never done anything like this before.

So I'm replacing caps in my rear amps. When I searched Digikey for product# EEU-EB1E470S, the description came up as [47uf 25V], but in the main post, it quotes [47uf 50V]. I'm wondering if the [47uf 25V] cap is acceptable or if I should buy the [47uf 50V] option. I think I've found the [47uf 50V], however wanted to double check on the differences in size, ripple current(?).

From main post:
EEU-EB1E470S ***** 0.11000 ***** $0.44 ***** 4 ***** 47uf 50V ***** 47uF 16V ***** C7, C8

From Digikey:
EEU-EB1E470S -- 47uf 25V -- CAP ALUM 47UF 25V 20% RADIAL
Digi-Key Part Search

EEU-EB1H470 -- 47uf 50V -- CAP ALUM 47UF 50V 20% RADIAL
Digi-Key Part Search

The differences between these are voltage rating, lifetime@temp, ripple current, size/dimension, height-seated, lead spacing.

Any input is appreciated and thanks!

Newsome79

iTrader: (3)

So I am looking at the caps.

EEU-EB1E470S 25V 5000hr This cap will work fine but with less margin

EEU-EB1H470S 50V 5000hr This cap seems like the best option

EEU-EB1H470 50V 7000hr This one is really tall, as tall as the 820uF caps I think there may be less room under that section of the amp cover. It also has different lead spacing that may make it stand taller than will fit.

Seems like I typoed the original post or ordered the wrong part but for all of you that got the 25V cap you can rest easy it should work just fine.

On a side note I checked again for the 25V 820uF capacitor with 15mm height or less and 5mm lead spacing.

Newark now has the EEUFK1E821S I would go with that one instead if possible. I checked shipping to CO and its 13.50 for for FexEx Ground.

chicagozer

iTrader: (3)

You should open a repair service. I'll bet there's plenty of 90s Bose amps from several makes that need new caps.

I wound up just gutting the Bose from my 300ZX. At the time it was too hard to find anyone who wanted to tackle fixing it.

M_Rex

iTrader: (5)

Thanks for this write-up Newsome and the updates. Not trying to call you out, because this is not my expertise at all. If you didn't spell out the steps like in this thread I'd also be gutting out my Bose, so thanks for saving me a couple hundred bucks.

Newsome79

iTrader: (3)

I still never found replacement parts for the pre-amp equalizer IC or the Pulse Width Modulator Class D Amp chip. If those are damaged because the caps shorted out or the MOSFETs shorted out I have no way fix the amps. Since someone else out there will do it for $80 and guarantee it for life its basically a DiY deal since the time required is pretty significant.

<http://www.carstereohelp.com/mazda.htm>

I just figured I would share what I had learned with everyone.