I picked up this used Bose Acoustimass 10 IV speaker system. Speakers seem to work fine, but the subwoofer does not make any noise. So I took apart the unit and found some obviously failed (burnt) components:
So plan is to just replace the components listed above, help identifying what diode and transistor to use appreciated. Everything else on the board otherwise looks fine. If there's other thoughts, let me know? Thanks!
See attached picture.
EDIT: I also just discovered that the small SMD resistor below the "O" in Bose may also be blow. See my post #15 below.
- 1x 3.14 A @ 250V main circuit fuse
- 1x bridge rectifier GBU601. there's actually two of these on the board, one is obviously burnt and the other does not seem to have any anomalies like shorts. However I figure may as well replace both.
- 2x diode. This is tricky because the only markings I see on it are: "617 402". No current rating or anything else. How do I figure what to replace this with?
So plan is to just replace the components listed above, help identifying what diode and transistor to use appreciated. Everything else on the board otherwise looks fine. If there's other thoughts, let me know? Thanks!
See attached picture.
EDIT: I also just discovered that the small SMD resistor below the "O" in Bose may also be blow. See my post #15 below.
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I would remove D702 and read the type number. They are the same diode just one for each polarity.
Don't forget to replace the bridge rectifier and probably the output transistors.
They are darlington pairs, NPN and PNP.
Unfortunately for you, obsolete. If they are for sale on fleabay or Aliexpress etc, probably fakes.
Don't forget to replace the bridge rectifier and probably the output transistors.
They are darlington pairs, NPN and PNP.
Unfortunately for you, obsolete. If they are for sale on fleabay or Aliexpress etc, probably fakes.
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MJH6287 / 84 seem a proper match, stock at digikey. the board is a single channel classH amplifier with 20V and 40V rails. the diodes look like 100V 20A types, not sure whether schottky or normal diodes, measure the forward voltage of the good one. this schematic seems to fit the board in the picture.
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Typical diode test doesn’t always work on darlingtons with internal Rbe’s.
Best bet today are OnSemi MJH6284/6287. Gain is somewhat lower, but they will probably work. These things don’t put out crazy wattage. The preferred types, Sanken 2SD2083 and it’s PNP are also unfortunately gone gone gone.
Best bet today are OnSemi MJH6284/6287. Gain is somewhat lower, but they will probably work. These things don’t put out crazy wattage. The preferred types, Sanken 2SD2083 and it’s PNP are also unfortunately gone gone gone.
The diodes in question should be schottky. A fast diode is required, and on such low rail one cannot afford the high drop of a typical epitaxial ultrafast and schottky leakage isn’t an issue if 60 or 100V parts are used.
Thanks! I can't measure the diodes. Hard to see in the picture, but they are both blown.
I'm assuming you mean D202. This is the same diode and it's also blown. It also has only the same markings of "617 402" which is meaningless.
Is there any issue buying knockoff transistors on Aliexpress? I'm guessing I should stick with the alternative parts mentioned by the other commenters here.
the knockoffs at aliX are mostlikely knockedoff in die size , power rating and amp rating, best to stay away from.
I couldn't find anything similar either.
Could I just jerry rig another in stock diode with 2 pins and of the highest rating in a different packaging? Eg. TO-252 or TO-220? I'm guessing I just want something with the highest DC reverse voltage, the highest current, and the lowest forward voltage + reverse current leakage. Example: MBRF20100
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2 or 3 pin TO-220’s can be used, or even TO-247. 2 pin TO-220’s would be the best fit for the PCB. It has only got to block 20-ish volts, but if the speaker is 2 ohms it would have to deal with 10A peaks without it’s Vf going too high (and therefore running hot). Your basic 60V 15 amp part would be fine, and there should be a dozen to choose from.
the diode does not see more than 60V, but this looks after further inspection as a bit unusual classH with each half switching, so indeed only 20V.
a dual to220 diode can be used in paralell to lower the forward voltage like the MBR220CT
a dual to220 diode can be used in paralell to lower the forward voltage like the MBR220CT
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Single TO-220 is easier to jack into the board, and they do make them. Just not as common as dual common cathode. And if you do use a dual, do parallel them. Might as well use both sides to carry current.
Thanks for everyone's help so far! So I just discovered that small SMD resistor below the "O" in "BOSE" may also be blown. It's testing ~50 ohms, but I'm guessing there's almost no way to verify what it should be without the schematic?
A poster put a similar Acoustimass 10 III schematic above (also attached), but upon further tracing it's not 100% the same. I believe it may be R73, based on my tracing starting from Q209...but I can't verify for sure? The components downstream of R73 don't seem to follow that schematic 100%, so I'm not sure if I should just throw in a 2.00K resistor and hope for the best.
Any thoughts?
A poster put a similar Acoustimass 10 III schematic above (also attached), but upon further tracing it's not 100% the same. I believe it may be R73, based on my tracing starting from Q209...but I can't verify for sure? The components downstream of R73 don't seem to follow that schematic 100%, so I'm not sure if I should just throw in a 2.00K resistor and hope for the best.
Any thoughts?
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Is the driver working? Check its continuity...blown transistors may have damaged the driver. That can complicate matters.
You can think of replacing the entire board with another Class H plate amplifier, it may be easier to do so, and the parts procurement / search stage can then be avoided.
Some of the circuits used by Bose are described as 'typical', which can mean unique to eccentric.
Further, many versions seem to exist, and the production may have been done at a contract manufacturer in the Far East, so quality may be an issue.
Cost, and practicality, let the other members, who have actual experience, decide and give their advice.
I just checked, 12 / 24V Class H plate amps start about $ 60, here in India.
You can think of replacing the entire board with another Class H plate amplifier, it may be easier to do so, and the parts procurement / search stage can then be avoided.
Some of the circuits used by Bose are described as 'typical', which can mean unique to eccentric.
Further, many versions seem to exist, and the production may have been done at a contract manufacturer in the Far East, so quality may be an issue.
Cost, and practicality, let the other members, who have actual experience, decide and give their advice.
I just checked, 12 / 24V Class H plate amps start about $ 60, here in India.
A 12/24V amp will put out about 1/3 of the power. A 40/80 V class H amp will be harder to find, but not all that hard to make if you are so inclined. A class D full bridge board running off 40V would do it and be a turnkey, if it was happy with the speaker impedance. Get one that runs off 48, and run it off the high rails configured as a single 40 V supply. A half bridge would need the full +/-40. Move the preamp voltage regulators over to the low rail winding. You will need to keep whatever EQ Bose was using to make the small speaker sound big, or it will sound like 4” woofer. It’s probably just a couple of cheap op amps. It could be reverse engineered and added as a separate module, if you go with something decent like the ICEPower stuff. The matching power supplies even have +/-15 for your front end.
The board is probably not all that hard to rebuild, though.
The board is probably not all that hard to rebuild, though.
I got a 2.1 board here, three D2030s (Chinese CRC make 2030 equivalents).
The third chip amp is for the woofer, it uses a 4558 to filter out the bass from the main stereo channels, to supply the woofer with a bass signal.
So, I agree a cheap dull 4558 should be adequate. Or something similar.
As for the voltage, that was just an example.
For security reasons, and due to a strained relationship with China, we cannot browse or access Ali Express and other Chinese sites.
The OP is welcome to find the suitable 40/80V plate amp, and use it instead of hunting for obsolete parts.
And a 40V Class D plate amp might be a stupid low priced common item, for all I know.
The third chip amp is for the woofer, it uses a 4558 to filter out the bass from the main stereo channels, to supply the woofer with a bass signal.
So, I agree a cheap dull 4558 should be adequate. Or something similar.
As for the voltage, that was just an example.
For security reasons, and due to a strained relationship with China, we cannot browse or access Ali Express and other Chinese sites.
The OP is welcome to find the suitable 40/80V plate amp, and use it instead of hunting for obsolete parts.
And a 40V Class D plate amp might be a stupid low priced common item, for all I know.
That 2.1 board was about $3 when I bought it, 12-0-12V supply, rectified to about 19V across rails.
It has a 7805 as well, to supply the FM module, which also has USB / SD Card / Bluetooth.
There are Indian sellers offering 2.1 plate amplifiers in various topolgies, for small to large wattage users.
I expect Chinese sellers can offer something similar, which might be useful and readily available.
It has a 7805 as well, to supply the FM module, which also has USB / SD Card / Bluetooth.
There are Indian sellers offering 2.1 plate amplifiers in various topolgies, for small to large wattage users.
I expect Chinese sellers can offer something similar, which might be useful and readily available.
Yes, if this repair doesn't work then probably rebuilding it using a separate amp entirely would make sense. However, I got this unit pretty much for free and repairing it to like OE Bose, fetches a much higher premium if I were to resell it. I know alot of people aren't fans of Bose but there is a certain allure to keeping things original.
Right now the only unknown is that burnt SMD resistor. I'm probably in it for ~$50 in parts right now, so it's worth taking a chance IMO.
Right now the only unknown is that burnt SMD resistor. I'm probably in it for ~$50 in parts right now, so it's worth taking a chance IMO.