# Repairing a BOSE amp - some notes



## en4rab (Jan 24, 2014)

*#include <std/disclaimer.h>*
I am not a repair technician and this isn't an exhaustive step by step guide to repairing your bose amps.
It you try this there is every possibility you will end up destroying the amp, especially if you don't first 
practice the required techniques on some scrap electronics until you are confident of the techniques.
*This is also not an advert, no I wont fix your amp for you*, I believe there is already someone offering this 
service and I would assume since they specialise in this they can probably also bench test the amp.
This information is not authoritative, it is merely an account of what I did to repair a friends amp and indeed 
some or all of it might be flat out wrong, I am a warehouse worker by trade and have no formal electronics training.
If you know a better way please post explaining it.
Some of the materials are toxic so read the MSDS datasheets, wash your hands after soldering, dont drink Isopropyl 
alcohol and if you have alergys to rosin / pine you might want to consider not soldering or at the least wear a 
respirator and ensure solder fumes are blown away from you.
Because it worked for me does not mean it will work for you, if you blow something up trying to replicate this it 
entirely your doing, if you are anything less than 100% confident in you skills don't try this.
Don't pick soldering irons up by the hot end.

*Photos from during the repair.*

01 The damage by en4rab, on Flickr

The first one was taken by tomos8304 of the damaged chips, the rest are mine, closeups of the pcb are from the 
andonstar microscope, its a toy but a good one.
http://www.flickr.com/photos/[email protected] ... 220544544/

*Taking the chips off the board.*




 Dave Jones removing a multi pin chip the medieval way. (from 6 mins to 11min30)
Some thing to note about this, when I cut the psop-36 chips off the board I used a fresh scalpel blade and I didn't try to cut through the pins in one go as I was worried about lifting a pad instead I gently scored along the top "shoulder" of the pins repeatedly until they were cut through. 

02 Cut the pins and desolder by en4rab, on Flickr

One thought I had after the fact was it might be an idea to hold the legs of the chip to the board with the edge of a steel ruler or something while doing this to reduce the chances of a pad being lifted but that isn't how I did it.

Once they were cut I put the blade into the cut and very gently bent all the pins outward a tiny bit so 
they were clear of the body of the chip then I carefully pried the chip off the board. 
The chip is slightly stuck to the board as it has had an acrylic conformal coating applied which runs under the chips and sticks them down, prying with the scalpel resulted in the chip popping off the board leaving the legs in place which I could de-solder one at a time.
The desoldering process is as seen in the video, basically gently heat each pin till the solder melts and then wipe the leg off the pad along the length of the pad not across the pads, then clean up the pads with desolder braid, this will also melt and burn the acrylic conformal coating but this can be cleaned up with a cotton bud and some isopropyl alcohol leaving the board clean and ready for another chip.

03 Removal of the chips by en4rab, on Flickr

This really is butchery and the proper way to do this would be to use a hot air rework station or ChipQuick to desolder it but the chip was ruined and this does work if you are careful.

*Inspecting the damage.*
Once the chip is off and the pads cleaned its time to inspect the traces for damage. 
I did this visually with a £35 Andonstar USB microscope http://www.ebay.co.uk/itm/171190008984 and a cheap multimeter, all you need is the continuity test where it beeps if there is a connection, just test all the pads are connected between the pad and whatever via they connect to.
If you want some more info on the microscope and why the andonstar is better than the £15 ones EEVblog did a 
review on them here: 



 yes im a fan of EEVblog 
In my pictures you can see in pic 03 the tracks at the top right are damaged and a pad at the bottom right has been lifted (probably my fault but the chip was particularly corroded there)


04 Damaged tracks to speaker by en4rab, on Flickr 

05 what good tracks to speaker looks like by en4rab, on Flickr

Pic 04 shows the corrosion to the top right speaker connection and pic 05 shows what it should look like.


06 Looks OK but no connection by en4rab, on Flickr

Pic 06 shows the 2 connections to ground just below the speaker connection, these tested open circuit with a multimeter as the copper track where the pad meets the solder mask had been corroded away completely, see the gap at the bottom right.


07 Lifted pad by en4rab, on Flickr

Pic 07 shows a close up of the lifted pad, this is bad and to be avoided at all costs, luckily this pad is just a signal pin which goes to a convenient via nearby and can be patched with a kynar bodge wire. 
But a lifted pad could really ruin your day, if you were to have a go at fixing this yourself first practice on an old graphics card or something similar of no value, until you are sure you can do it.

*Replacement parts.*
For this repair I was replacing chips U24 and U26 which are ST microelectronics TDA7575 amplifiers, 
U25 is also a TDA7575 but I think U27 is a different chip so if that is damaged you'll have to identify and source that yourself but its probably some other ST microelectronics TDA series chip.

I found the datasheet for the TDA7575 here http://pdf.datasheetcatalog.com/datashe ... s/9110.pdf
But the only sources I could find for this out of production chip wanted silly money, but I did find a seller on ebay
selling the newer TDA7575B http://www.st.com/web/en/resource/techn ... 175174.pdf Comparing the datasheets it looked like the revision B chip just added some extra digital diagnostic registers but should be backward compatible as these registers are unused on the older chip, so I bought 2 of the chips from this seller on ebay for about £7.50 each + £3.30 P&P they came from Germany quite quickly:
http://www.ebay.co.uk/itm/360466148291
If you source your own elsewhere you need the PowerSO36 (slug up) package not the flexiwatt package.

*Putting the chips back on.*
I replaced the chips using a flow and wick technique as the pins are tiny.
First apply some flux to the pads on the board then place the chip on the board being careful to make sure it is the right way round pin 1 is marked on the boards silkscreen with a 1 and on the chip with the corner of the chip cut at an angle.

08 Chips replaced by en4rab, on Flickr

Line the chip up with the pads and solder the corner pins down to hold the chip in place, then solder all the other pins dont worry about bridging pins with solder at this point. Once its all soldered down use some desolder braid to remove any excess solder causing bridges between pins, you can see this technique in this video here:





Finally I repaired the broken and corroded tracks by cutting a small bit of wire, I used the leg of a resistor as I had that handy and these connections are fairly high current as they are for the speaker and ground, to bridge from the out2+ pins of the chip to the via for the speaker, and for the 2 corroded vcc pins I carefully scraped away some solder mask from the ground plane to expose the copper and tinned this with solder then again ran a bit of wire from the vcc pins to the ground plane. 
Finally I repaired the lifted pad with a kynar wire from the pin to the via it should connect to this is a signal trace so it doesn't carry any power and a fine wire is ok, then I superglued the kynar wire down so it wouldn't move.
You can see theses fixes in picture 08 on the top left of U26 and the kynar wire on the top right, U24 was also replaced but the corrosion wasn't as bad so it didn't require any tracks rebuilding.

With the soldering done I inspected between the pins with a microscope to look for any signs of bridging, I did see some traces of solder sitting on the solder mask between 2 of the pins but gently scraping this with a pin/cocktail stick dislodged it, a final "light" tap of the board against my desk to make sure there were no stray solder blobs on the board and it was ready for a conformal coating.

*Finishing off*
Since this amp seems to have a real problem with condensation forming on the heatsink above the chips and then dripping onto the legs of the chip I thought it would be a good idea to try to protect it as best as I could so I bought some silicone spray conformal coating, the amp originally used an acrylic one but that seems a bit thin and doesn't seem to coat the legs of the chips as well, the silicone one should be more like the rubbery coating you find in the bosch ecu's used by audi.
I masked off the metal "slugs" of the amplifiers as well as masking off the connectors and the holes in the metal box over the audio processing section as I only wanted to coat the amp chips, then lay the board flat and sprayed the coating over the chips U24 to U27, in theory at least you could do the entire board but with the silicone being thicker I didn't want to risk any heat issues so kept the coating mostly to the chips that get condensation problems, of course everything in that corner gets coated too.
Once the coating had dried which I think was about 12 hours or so, I removed the masking tape and carefully scraped the top slug of the chips where some silicone had got under the tape as its important the slug makes good contact with the heatsink, I then applied some thermal grease to the slug of the chip and a bit to the appropriate spot on the heatsink (I wiped off the old grease as it seemed to have some grit stuck to it) then reassembled the amp.

All that is left then is to plug it back in and cross your fingers that it is now working, its not really possible to bench test it as its all wired into the can bus and the head unit.


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## en4rab (Jan 24, 2014)

*Tools and materials used.*
This list is not necessarily the best or the cheapest but is a list of what I used in fixing this so you have an idea of what is needed.
Some of it I already had and a few things I bought in to do this (conformal coating and thermal grease and the replacement chips)

*Tools:*
Soldering iron: (I used an old antex I think its a CS18 that I was given years ago and has I think an 1106 1mm tip fitted) you can buy these new on ebay with a slightly bigger tip for about £23 or as a kit with stand/sponge from RS for £28 
http://uk.rs-online.com/web/p/soldering ... s/7683570/?
I'm not saying this is a good soldering iron but it will do, if you want good look at hakko and weller but they cost.

Andonstar USB microscope: Not essential but very handy and your kids will like it once your done with it 
£35 ebay, http://r.ebay.com/B6lKE3

Scalpel with fresh blade: to cut the legs of the chip, its a brutal way to do it but it worked, buy from local craft store.

*Materials:*
Solder: Avoid the lead free shit and get the thinnest you can reasonably find, I used this 0.5mm but its a bit much for one job http://uk.rs-online.com/web/p/solders/4364881/ something like this is a bit cheaper http://r.ebay.com/wJx1kv I am a fan of the multicore brand stuff but only because it is what I have always used and its never given me problems, you can also get this at maplin, try to get the 0.7mm in the blue tube, the 1.2mm http://r.ebay.com/1CMXiU will also do but is a bit fiddlyer to control how much goes on the pins, whatever you choose go for 60%/40% tin/lead as lead free is shit, and wash your hands after use!

Flux: I used CW8100 no clean flux from ITW chemtronics £9, http://uk.rs-online.com/web/p/solder-fl ... s/3217289/ about the same price on ebay.

Desolder braid: http://uk.rs-online.com/web/p/desolderi ... s/7622682/ the actual one i used was servisol soldamop no clean 1.5mm size and brand within reason dont matter, for flood and wick 1.5mm width seems right to me, others may have their own thoughts on the matter. http://r.ebay.com/6wvKXM ,an example on ebay.

Silicone conformal coating: http://uk.rs-online.com/web/p/conformal ... s/0494714/ £10.78 I chose that one through an abundance of caution as its rated to 200°C and the amp chips shutdown at 170°C so worst case there shouldn't be any issues with the coating catching fire  there is a brush on coating for around £4 but its only rated to 125°C so I decided against it.

Thermal grease: http://r.ebay.com/rQLyfQ the one I used came from RS http://uk.rs-online.com/web/p/thermal-grease/7074733/ but thats way way way more than you need the thermal conductivity is 1.8W/m·K which seems to be enough as the amp is working, I didnt use any of the higher conductivity ones you see on ebay as I had concerns they may be electrically conductive at the higher voltages an amp chip runs at compared to a pc processor, these concerns may be entirely unfounded but the ebay link above has a thermal conductivity >1.829 W/m-k and costs 99p and should do fine.

Isopropyl alcohol: For cleaning up the board before and after soldering http://uk.rs-online.com/web/p/precision ... s/0567890/ also on ebay from £3.40 for 100ml avoid the 70% stuff as that is 30% water.

Cotton buds: steal off your missus or buy from the shop down the road. dip the bud in isopropyl alcohol and use it to clean the grot off the board.

Kynar wire: incase you need to rebuild a signal trace http://www.ebay.co.uk/sch/i.html?_sacat ... re&_sop=15 pick the colour you like. For power connections you should use a thicker wire, see the TDA7575 datasheet for the chip pinout.


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## -:[KM]:- (May 16, 2010)

Absolutely bloody fantastic!! What a write up!
Thanks a lot. I've a spare amp or two and might try this in summer. 
I didn't know we could source the chips. 

Thumbs up from me. [smiley=thumbsup.gif]


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## sico (Feb 6, 2003)

Ok I have followed your instructions:










Hang on.......


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## naughts4187 (Apr 26, 2013)

Who makes posts stickies? 
This and a few other how to's are going to slip into the thread history if they aren't archived for all to reference for years to come.


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## brittan (May 18, 2007)

naughts4187 said:


> Who makes posts stickies?


Me.

en4rab - do you mind if I add this repair procedure to the Knowledge Base?


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## en4rab (Jan 24, 2014)

brittan said:


> en4rab - do you mind if I add this repair procedure to the Knowledge Base?


Of course not, the post and the photos are entirely free for use as anyone sees fit, I hope they help you all in fixing your amps.

I didnt know I was going to make this post or I would have taken more pictures/video of fixing it, especially as I stupidly didnt look up or photograph U27 so im not sure what chip that is, if that needs replacing you will have to identify it first.


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## tomos8304 (Mar 1, 2013)

Brad that's an awesome right up after repairing it for me it works even better cheers fella


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## naughts4187 (Apr 26, 2013)

brittan said:


> naughts4187 said:
> 
> 
> > Who makes posts stickies?
> ...


Ah great stuff. I did a how to recently, may be of interest too for rear diffuser projects http://www.ttforum.co.uk/forum/viewtopic.php?f=19&t=544578&p=3727066#p3727066


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## brittan (May 18, 2007)

en4rab said:


> brittan said:
> 
> 
> > en4rab - do you mind if I add this repair procedure to the Knowledge Base?
> ...


Thanks; all done. View it here: viewtopic.php?f=43&t=556713



naughts4187 said:


> I did a how to recently, may be of interest too for rear diffuser projects http://www.ttforum.co.uk/forum/viewtopic.php?f=19&t=544578&p=3727066#p3727066


I'll get round to this one soon.

Thanks, done now. View it here: viewtopic.php?f=43&t=556809


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## en4rab (Jan 24, 2014)

A few of the links seem to have got eaten in the process of copying this post to the tutorial section.
I have shortened all the problem links so they shouldn't get eaten by the forum.
Im still in 2 minds about the ebay links at they will tend to be a bit ephemeral but I wanted people to see that you can get stuff from more than one place, I like RS and the service they offer but didnt want it to appear they were the only place to get stuff.

*In the section "Photos from during the repair."*
The link to the album on flickr: http://flic.kr/s/aHsjRm4qwu

*In the section "replacement parts."*
The link to the TDA7575 datasheet: http://goo.gl/Ugi9JR
The link to the TDA7575B datasheet: http://goo.gl/BAQ3Nc

*In the section "Tools and materials used."*
The link to the Antex soldering iron kit at RS: http://goo.gl/JyrkjV

The link to the CW8100 flux at RS: http://goo.gl/jrYuQ
The link to the desolder braid at RS: http://goo.gl/Y9khbY
The link to the Silicone conformal coating at RS: http://goo.gl/X8z0Ln
The link to Isopropyl alcohol at RS: http://goo.gl/yk2Y3U
The link to Kynar wire on ebay: http://goo.gl/Dhntxc


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## brittan (May 18, 2007)

Hmmm, that was the easy part: a simple cut and paste. :?

Not sure why some links didn't work but I've replaced them.

The photos are re-hosted, as is every other picture in the KB, so I omitted the link to the flickr album.


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## en4rab (Jan 24, 2014)

The long urls getting eaten when cutting and pasting is I think a side effect of the way the forum parses urls in posts, when the forum software sees a url it converts this into a link with the link text being the url but if the url is beyond a certain length it truncates the printed text. so for example the link to the filckr album:
http://www.flickr.com/photos/[email protected]/sets/72157640220544544/
once parsed becomes:
http://www.flickr.com/photos/[email protected] ... 220544544/

note the link text has been truncated at the "@N ... 22" part, if you then copy and paste this it then parses this truncated text as a URL which creates a broken link, so shorter links that dont trigger this truncation work but longer ones will break on copy and paste.


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## Tevildo (Feb 8, 2014)

Excellent guide, en4rab - thanks for posting!

One point I would make, though - you don't mention static protection. The ideal solution is a proper field service kit (available from RS for £55, part number 681-1235 - http://uk.rs-online.com/web/p/esd-safe-field-kits/6811235/), but failing that a metal baking tray or similar should be sufficient. The important thing is not to do the work on a plastic table-top, especially when handling the chips themselves, otherwise there's a risk that they'll be destroyed before getting near the board.


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## poder (Mar 18, 2015)

I just replaced the U26 chip on mine with one of these: http://www.ebay.de/itm/integrato-TDA-75 ... 0683771218
A couple of the pins had gone completely away...

Before









After









Thank you for the guide


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## Yesj (Nov 12, 2014)

Nice Job.
Can I ask where you van find the amp? I want to check what state mine is in. If i listen to a CD the sound is much louder than then I listen to the Radio..


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## poder (Mar 18, 2015)

It is in the boot behind the left side panel. There is a description somewhere on here, that describes how to get to it.


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## Yesj (Nov 12, 2014)

Thanks!


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## stona1 (Nov 1, 2015)

Hi,

I have problem with my Bose Amp too. I did deasembly it and found only very small problem with corrosion. For sure paths are not damaged. It playing OK but subwoofer sound is very, very week. I suppose in my case some of TDA7575 chips is damaged. I am going to replace it using this excellent tutorial. Can anybody point me which TDA chips is responsible for subwoofer? Is it U24, U26 or another one?

BR
Stona


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## auditt (May 10, 2012)

Before you can repair your amp you will need to remove it. Here are some instructions on how to remove your interior without breaking all your fixing clips.

*INSTRUCTIONS ON HOW TO PHYSICALLY REMOVE YOUR BOSE AMP*

Here is a video on how to properly remove the side panel and Bose amp.


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## Rene Pogel (Aug 27, 2015)

Many thanks for a very well written posting!

I bought the exact same Andonstar USB microscope (after having a different one that was useless) - the Andonstar is brilliant. No idea how they do it, but it can go from being used as a normal webcam all the way to 200x magnification. I use it for reading resistor colour codes, what's written on chips etc. For anyone looking to buy, this is the one.

What you say about avoiding the lead-free solder is so, so true - the stuff's utterly useless. There were rumours of an EU ban on the regular tin/lead stuff, so being a responsible tree-hugging citizen, I stocked up on the proper stuff! There's still plenty of tin/lead solder, it's worth getting the right stuff.

You were looking for a straight replacement for the TD7575 chip - is this what you're after?: http://www.ebay.co.uk/itm/TDA7575-SMD-I ... SwEK9T~jCx

Hope this helps,

RP


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## tttony (Dec 21, 2014)

If anyone is going to attempt amp chip replacement themselves it will pay to source the chip(s) from a major supplier. Fake and remarked chips are a big problem in the industry.


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## Detailninja (Jul 15, 2020)

I have just bought a 2008 TTS and the Amp is toast. When i read this I was inspired to do the chips but when i removed and stripped the Amp unit I found that the power had shorted and was seriously burned out. 
Now I need to find an amp, any amp, that could provide the unit to use even if I have to swap out the chips.

Any ideas?


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## StollySMO (Nov 11, 2020)

After suffering a dead sound system in Jan 2020. I was fortunate to land on this post. I removed my Bose amp and found 2 amp chips with corroded legs. Just as everyone else had found. I ordered my chips off eBay (China Long-Sheng electronic), as a total gamble. They came after several weeks. I then went about finding an audio electrician. I came across Midlands Electronics Repair Specialists in Burton on Trent DE150JR. The guy successfully fixed the amp and for only £50. 
A year on though, what with the bad weather my amp died again. I opened it up and found gritty heat sink. I gave the amp chips a good blast of PCB cleaner and a gentle brushing of the chip legs. Thankfully, it is back working without issue. I have now coated the legs with silicone spray, re-applied heat sink paste and fitted a plastic bottle around the amp for further protection. Thanks to this post I have saved myself a small fortune! Thank you!!! Great information!


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