B&W Subwoofer Amp Repair - identify SMD resistors - Page 1
Forum section: electronics / repair

author: MetalToby
author_rank: Newbie
timestamp: March 19, 2023, 02:30:54 am
content: Hi all,I have a dead B&W ASW610XP Subwoofer. Original plan was to just sell the driver and not attempt to repair it. However while stripping it I found some burnt SMD resistors on the power amp board. They are quite large so I think I can replace them, but reading the numbers is difficult (see image). I think they say R280, but what do you guys think?I guess these resistors don't go bad like that for no reason. The second image is the other side of the board and I notice there are some MOSFETs close by. Might they be the root cause? From what I've read they do fail. I've read about testing them with a multimeter, do they need to be removed before testing? Or can they be tested in situ?I'm not an electronics engineer, just a curious guy having a go. I am happy to replace a few components, but that is as far as my knowledge goes. No big deal if I cant get it working.Any advice appreciated.Many thanks

author: beatman
author_rank: Regular Contributor
timestamp: March 19, 2023, 04:19:20 am
content: looks like R820.check all suround components for short.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 19, 2023, 08:18:54 am
content: Mosfets can easily be checked without removal, check there're no pins shorted.Large picture, could be useful:http://bilder.hifi-forum.de/max/607287/asw-10cm-s1-asw-10cm-s2-asw610-xp_1169032.jpg

author: MetalToby
author_rank: Newbie
timestamp: March 19, 2023, 09:12:48 am
content: Thanks for the replies.@DavidAlfa that image is exactly what I have. A couple of the MOSFETS in the top left corner are shorted between any combination of pins, so I will add them to my shopping list. Those MOSFETS are close to the burnt resistors on the back, so maybe they are the cause of the failures.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 19, 2023, 09:29:17 am
content: It's really seems like R820, so 0.82Ohm.

author: geggi1
author_rank: Frequent Contributor
timestamp: March 19, 2023, 10:57:36 am
content: You should also look into getting resistors with a higher wattage or maybe just add one additional resistor since there is solder pads for one more.The resistance of the new resistor would be 820*4/3=1,093but you will most likely get a way with 1,1

author: Swake
author_rank: Frequent Contributor
timestamp: March 19, 2023, 11:10:01 am
content: Indeed you have to check those mosfets and caps for shorts. Those resistors are likely collateral damage.The resistors have a somewhat unusual format. Connections are along the long side instead of the short side. Any idea of their physical size? If you could measure them with a caliper that would be ideal.

author: MetalToby
author_rank: Newbie
timestamp: March 20, 2023, 01:57:45 am
content: The resistors are roughly 4.5mm x 3mm

author: Chris56000
author_rank: Frequent Contributor
timestamp: March 21, 2023, 10:05:28 pm
content: Hi!I think you'll find the originals were "R020" for "0.02 Ω", in 1812 case size, as sub–woofers are fairly high power devices, and me thinks that "R820" as well as being a fairly uncommon value not often stocked, will be too high for the high–power amplifiers used in these units!"R020" is quite commonly stocked amongst suppliers as its a value very commonly used in power supply circuits for current sensing!Me thinks if you search "R020 SMD" in Mouser or Digikey you'll find replacements in the correct format, as the sorts of circuits where these resistors are employed pass a very high current, implying much wider than usual track widths!Chris Williams

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 22, 2023, 07:51:51 am
content: If it was 20mOhm, 3 in parallel (7mOhm), it would be imposible to blow them like that, you'd need a really serious amperage, which the supply wouldn't be able to supply except for a very short peak.

author: MetalToby
author_rank: Newbie
timestamp: March 22, 2023, 09:55:30 am
content: I'll order some of each then worry about which one to try....

author: beatman
author_rank: Regular Contributor
timestamp: March 24, 2023, 04:17:16 am
content: R020 looks another option.if other forum member have the same subwoofer to look inside what is the value of the resistors.

author: MetalToby
author_rank: Newbie
timestamp: March 24, 2023, 04:27:03 am
content: Yes, I've ordered some R020 as well.Annoying how all three of them have damage in just the right spot to confuse 8s and 0s.

author: Vicus
author_rank: Regular Contributor
timestamp: March 26, 2023, 07:06:19 am
content: The power amp / psu is a icepower 1000asp (I guess) that is not easy to repair. That resistors blown to a short somewhere, I suggest to find it before replace the resistor.By the way when I think is not easy to find resistor with the same form factor.

author: MetalToby
author_rank: Newbie
timestamp: March 26, 2023, 09:49:36 am
content: Thanks for the info, from the ICEPower website I can see its a 500ASP.Sounds like I dint have much chance fixing it. I'll replace the shorted MOSFETs and the burnt resistors and see what happens. Being in Australia means everything takes forever to arrive...The cabinet and woofer are good so I just buy a new amp for it.

author: coppercone2
author_rank: Super Contributor
timestamp: March 26, 2023, 09:53:53 am
content: impossible to blow a shunt?! I think thats a very wishful idea...i think its 0.02

author: MetalToby
author_rank: Newbie
timestamp: March 28, 2023, 09:11:44 pm
content: I gave up.After replacing the 3 resistors and the shorted MOSFETs I turned it on and the resistors all popped as soon as the music started.Plan B is to just find a new amp, probably not the 500asp as they are pretty expensive.Thanks for all the replies, I've learnt a lot from you all!

author: AzGuy
author_rank: Newbie
timestamp: May 20, 2023, 09:30:01 pm
content: Did you check C308 and the two electrolytic caps? By the look of the residue beside the first resistor, it took some major current before burning. Are the two electrolytic caps connected to the input bridge rectifier in any way? And, where does C308 connect? There was certainly a major short somewhere. Replacing the resistors will do no good until you find the short or the cause of it.

author: jeffjmr
author_rank: Regular Contributor
timestamp: May 22, 2023, 01:05:39 pm
content: Just be careful to keep soldering temps to the minimum necessary. If that B&W amp is anything like the others I have repaired the PCB burns and traces and donuts lift much easier than other brand PCBs in my limited experience.Jeff

author: krisskross
author_rank: Newbie
timestamp: May 24, 2023, 10:16:10 am
content: Definitely R020 if connected to mosfet. Check for shorted diodes as well. dont forget the power IC

author: strawberry
author_rank: Super Contributor
timestamp: May 24, 2023, 03:41:29 pm
content: did someone really expected that none of IC's blown?