Blown Edifier amp repair - Page 1
Forum section: electronics / repair

author: balboni20
author_rank: Newbie
timestamp: July 27, 2021, 09:46:24 am
content: Hello guys,am kindly asking for some help.I have a pair of Edifier R1800T III monitors that are great to pair with my TV.But one day they gone bad and i only hear sound through the tweeters.I have connected the mid/low speaker to the tweeters channel and same high sound is coming through so my guess is that the speakers are ok but the mid/lows channel is blown.I have visually inspected the amp and 2 capacitors are swollen, you can see them in the pic. I have replaced those 2 but problem still persists.On more inspection I can see another capacitor that is not swollen but has a yellowish harden substance on it! You can see it in the second picture. Can this be a glue from manufacturing or is it electrolyte that has harden over time?I appreciate any help or suggestions!

author: BBBbbb
author_rank: Unknown
timestamp: July 27, 2021, 11:22:09 am
content: This is a fairly uneducated guess, but it seems that this yellow-orange coating is around it as well not just the top of that cap. Look at the PCB - you have some yellowish parts as well. And some coating on other components, but because they're not shiny silver, it's not as easy to spot.One thing that could be is that it maybe became conductive, so maybe cleaning it from the PCB first. Especially over the ceramic caps on the left side of that bigger IC bellow that marked cap.Also I'm sure folks with experience on this topic will soon add their opinions.

author: balboni20
author_rank: Newbie
timestamp: July 27, 2021, 12:26:35 pm
content: I must admit i haven't noticed those residues but I am gonna carry an isopropilic alcohol clean.

author: dietert1
author_rank: Super Contributor
timestamp: July 27, 2021, 12:59:10 pm
content: Some active speakers stay on all the time, others have a second small power supply to enable signal detection and the amplifiers are powered only when needed. I'd guess your speakers are of the first kind and you just need new ones every some years. Those electrolytic caps are rated for 5000 hours or so when running at high temperatures. Less than a year. Failure means chemistry on the board eating away copper traces within another year. Bad news, sorry.Regards, Dieter

author: balboni20
author_rank: Newbie
timestamp: July 27, 2021, 02:19:16 pm
content: Thank you for your answers!These speakers have a small power supply that was hidden inside, but I am not sure it has the functionality you are describing @dietert1?I have attached an image with the internals of the speakers, don't know if it is conclusive tho.Now that @BBBbbb has opened my eyes, I can see lots of spilling on the PCB indeed, could all those capacitors be busted? They seem relatively inexpensive to replace so if it could get me another year, I'll take it!I want to add that I like fixing things, even tho electronics are a bit out of my reach.

author: BBBbbb
author_rank: Unknown
timestamp: July 27, 2021, 03:50:24 pm
content: It still doesn't look like cap leak to me, but some glue (it looks parts of it are all over the place)It could be that caps are bad, or maybe glue became conductive or ... but not sure it's the caps based on the photo.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: July 27, 2021, 06:06:02 pm
content: It's hard to tell from a static photo, but C74 and C75 look like they might be bad.Why not change all 5 Electrolytics? It is a no brainer, cheap, and relatively easy for a novice, and a good way to start becoming better at it.And we all know they go bad, especially in a hot powered speaker cabinet.And then if you still have a problem you know it is not one of these capacitors.Often knowing what the problem isn't is invaluable in diagnosis, as you now have some known facts to test the rest of the system with.

author: balboni20
author_rank: Newbie
timestamp: July 27, 2021, 07:17:20 pm
content: I did replaced C74 and C75. You can see on first pic on topic they are black capacitors from Mafcon that I have replaced with blue caps from JRB.I am guessing the yellow stuff is se kind of glue used considering this sits inside the speaker and is subjected to vibrations.I think I am going to replace the other capacitors visible.Also on the power supply I am not noticing any visible damage.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 28, 2021, 05:33:03 am
content: hi,trace wiring from speakers (low) to amplifier, on the the main case, leave the 2'nd case alone for nowi'd bet they used one amplifier IC for high/med/low, so same amp outputs for tweeter and for medium speakers.there's a good chance of finding the decoupling capacitor from amplifier IC to medium speaker(s) deadfor a good job, change all electrolytics with respected ones from farnell, why not adelaida or another serious enough supplier in romania. i use farnell, they sell good caps

author: balboni20
author_rank: Newbie
timestamp: July 28, 2021, 07:35:44 am
content: Thanks for your suggestions!I have made a "drawing" with what I know till now and maybe help you better understand the PCB layout.It seems to have 2 TAS5707 IC, that might be separate to each channel?

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 29, 2021, 06:42:57 am
content: it may be one chip per channel, it may be 1 IC for tweeters and one for low-medium speakers. without you tracing, i can only guessit seems one of the IC's is dead or has no power or some output is shorted (a shorted speaker may do that)you need a multimeter to diagnose (i saw you have 2 connectors for speakers on that pcb, have you tried to reverse them? but be aware, if you got one speaker shorted, you may fry your 2'nd amplifier IC. that's why a multimeter could avoid dangers like this and point the defective part

author: balboni20
author_rank: Newbie
timestamp: July 29, 2021, 07:28:05 am
content: Well, I did connect the MID/Lows loudspeaker to the highs channel and they are working. I mena you can hear high tones just like you hear through the tweeters.I need to add a possible culprit to the mix. In the week that I noticed the speakers are blown I had over the night an electrical outlet blow, it was a blow with a specific noise that woke me up and I've seen the flash. It is a different outlet then the one the speakers are connected but its the same room and I am thinking it might have been a power surge. But the power supply of the speakers seems to be unaffected and its the amp itself that is showing swollen capacitors.I am not sure I have used the speakers after the blow, it might be that it was a coincidence as no other electronic in the house are affected. I did replace the power outlet.I did a search for that IC, and it says:The TAS5707 is a 20-W, efficient, digital-audio power amplifier for driving stereo bridge-tied speakers.What are bridge tied speakers?I can see this IC is also really cheap .. so buying one is a no brainer but I cant replace it myself for sure. Is it hard to replace those ICs?

author: sperb
author_rank: Contributor
timestamp: July 29, 2021, 01:33:10 pm
content: Hi,In simple words, "bridge tied speakers" means that both positive and negative terminals of the speaker are amplified, as shown on the image of the datasheet:It is like the split phase system in USA: use two 120V phases to get 240V.Looking to the images, looks like you have two amplifiers on the board (TAS5707), with 2 channels on each amplifier. So they are probably using one channel for each speaker (Hi and Low, Left and Right). Did you check if you have the same issue on both channels?Regarding changing the IC, unless you have a hot air station, I don't think you be able to replace the IC, as it has a thermal pad to dissipate the heat to the PCB (the big square on the middle of the IC is soldered to the board):Regards.

author: perieanuo
author_rank: Frequent Contributor
timestamp: July 30, 2021, 06:21:22 am
content: i agree, replacing the IC is not for beginners, maybe you find some friend with the tools and the skills to replace him.but, we are not sure amp IC is dead, the board must be examined, can be also another cause the IC is not workingseems one ic handle tweeters, the other one low/med but without tracing speakers to IC's, i repeat myself, we're not sure, and it's pointless. tracing speakers would point the defective IC, that's important.