Author Topic: Need help with diagnosing subwoofer issues - Monitor Audio R370HD  (Read 2658 times)

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Offline Mithrandir

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Hi everyone, I need help diagnosing issues with my subwoofer which last for years but I've finally decided to tackle them.

Subwoofer is Monitor Audio R370HD
https://www.monitoraudio.com/en/support/past-products/radius-hd/r370hd/

Issues are:
  • Sub is randomly too quiet
  • Sub is randomly too loud (goes berserk)
  • Volume control doesn't work when sub goes berserk

Sometimes it works just fine.
I think the driver is OK and the problem might be in amp.

This is link to user manual (I couldn't find service manual):
https://www.dropbox.com/sh/7kkjnqq6jprqqw2/AAA-wQMptUW1rdrAs8n2tf-0a?dl=0&preview=Radius+HD+Manual.pdf

I've tried to bring subwoofer to local Monitor Audio shop few years ago (I live in Croatia) but they couldn't find the issue and if they could they can only replace the whole board which costs almost as new subwoofer.

I've managed to remove the back plate but I don't know where to go from here.
I have a multimeter and soldering station and forgot all my electronics/EE stuff from college (I mastered computer science 10 years ago, maybe I've should gone EE route instead  |O).

Can anyone help me with troubleshooting the amp?

I've attached the pictures of removed amp board.

Higher resolution images are available here:
https://imgur.com/gallery/d2V5JmD
 

Offline Mkdsime

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #1 on: February 03, 2019, 09:29:06 pm »
hi not a pro here but does the relays makes strange noise ? see if there is burned marks maybe loose connection somewhere
take few more pitures of the smd board. I would suggest taking it slow board by board first with simple measuring like diodes transistors just watchout of those big capacitors can carry charge for some time very dangerous i think you would know that. pozdrav iz balkana
 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #2 on: February 03, 2019, 09:44:37 pm »
hi not a pro here but does the relays makes strange noise ? see if there is burned marks maybe loose connection somewhere
take few more pitures of the smd board. I would suggest taking it slow board by board first with simple measuring like diodes transistors just watchout of those big capacitors can carry charge for some time very dangerous i think you would know that. pozdrav iz balkana

I can't see any burned marks anywhere.
They hotglued all cable connectors between PCB's so I can't take them apart yet.

What's the best approach to remove hot glue? Isopropyl alcohol?
 

Offline Mkdsime

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #3 on: February 03, 2019, 10:03:43 pm »
yes alcohol
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #4 on: February 03, 2019, 11:53:48 pm »
Sounds like a AGC & auto mute problems, you would look at those circuits there.

 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #5 on: February 04, 2019, 10:46:51 am »
Sounds like a AGC & auto mute problems, you would look at those circuits there.

I'm a newbie. Could you explain me what AGC is and where should I find this circuit?
 

Offline Mkdsime

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #6 on: February 04, 2019, 10:53:23 am »
 Automatic Gain Control
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #7 on: February 04, 2019, 12:20:14 pm »
If I have the time, I could have look it for you.
Your circuit has been "raided" by the previous repairer, don't know if everything are fitted back the right way around or missing components, coupled with no schematic, is difficult to communicate thru to you.

But you can begin with taking close up photos of the 3rd photo left board, breaking up into sections so that the ICs number and Transistors numbers can be clearly seen.
If this is done, many people here can spot it for you and advice you accordingly.

I think is a cheap problem. For that I mean, some cheap components but no promises.  ;D

Sounds like a AGC & auto mute problems, you would look at those circuits there.

I'm a newbie. Could you explain me what AGC is and where should I find this circuit?
 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #8 on: February 04, 2019, 01:18:53 pm »
If I have the time, I could have look it for you.
Your circuit has been "raided" by the previous repairer, don't know if everything are fitted back the right way around or missing components, coupled with no schematic, is difficult to communicate thru to you.

But you can begin with taking close up photos of the 3rd photo left board, breaking up into sections so that the ICs number and Transistors numbers can be clearly seen.
If this is done, many people here can spot it for you and advice you accordingly.

I think is a cheap problem. For that I mean, some cheap components but no promises.  ;D

First, thank you for your detailed help.
I'll take photos you requested when I come back from work.
Also, I'll buy isopropyl alcohol to remove the hot glue from cable connectors so I can disassemble everything.

When you say "raided" you want to say that it was messed up with?

I bought this subwoofer brand new 7 or 8 years ago in local shop in Croatia.
They went out of business soon after that. If what you are saying is true then I'm glad they went out of business.

What is the sign the board has been messed up with?
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #9 on: February 04, 2019, 01:29:55 pm »
I meant they are signs of desoldering works being done especially on the board I asked you to take photos on.
You said you had sent it to a repair shop before right?.

Especially without a schematic, if some small components are not in circuit, it's very difficult to detect it,
not that I am accusing anything here. I mean, the repair job become more "uncertain". Luckily it's just a simple preamp board to deal with.
Cross fingers, it could be everything are just there.... and nothing to worry about.   :D

Let's look on the bright side, cheers.





 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #10 on: February 04, 2019, 01:49:13 pm »
I meant they are signs of desoldering works being done especially on the board I asked you to take photos on.
You said you had sent it to a repair shop before right?.

Especially without a schematic, if some small components are not in circuit, it's very difficult to detect it,
not that I am accusing anything here. I mean, the repair job become more "uncertain". Luckily it's just a simple preamp board to deal with.
Cross fingers, it could be everything are just there.... and nothing to worry about.   :D

Let's look on the bright side, cheers.

Yes, I've sent it to repair shop but they didn't touch anything because they couldn't identify the issue :D
I'll do my best to repair it. If it doesn't work, it's just a subwoofer in the end :D
 

Offline drknob

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #11 on: February 04, 2019, 04:10:13 pm »
Common powered speaker intermittent failure points:
1) dirty switches. check all those toggle switches.
2) cold/broken solder joints on switches and rca connectors.
3) cold/broken solder joints on interconnects and board traces.

Extreme vibration in subwoofer can cause all of the above.
 
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Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #12 on: February 04, 2019, 07:07:05 pm »
I've taken photos off preamp section.
Don't know why all connectors are hot glued, had to be careful not to break smth :D

I did 5 pictures:
1. Amp backplate
2. Whole preamp board
3. Top preamp section
4. Middle preamp section
5. Bot preamp section

Picture 4 Con1 is going to amp board.
On picture 5 Con2 is connection to volume control on top of the subwoofer box.

Parts on Picture3 (above R8) seem like flux residue, but I'm not sure if that was being resoldered - on the backplate in the same position is crossover control (40Hz -120Hz)
Similar for bottom of Picture 4 and top of Picture 5 (above Q5) - on the backplate in the same position is Auto On switch (On, Off, 12V trigger).

Analyzing the pictures i see that similar connections (from top to bottom):
1. Right from C36 (Picture 3 and 4) two joints are soldered together.
2. Above R13 (Picture 3 and 4) two joints are soldered together
3. Left from R45 (Picture 4) two joints are soldered together
4. Above R79 and R80 (Picture 4) two joints are soldered together
5. Below R79 and R80 (bottom of picture 4) and above Q5 (top of picture 5) seems like these two joints are not soldered together (there is also some flux residue I think).


If you need higher resolution images, they are on:
https://imgur.com/a/cStiKlL

I think I can't do better pictures with my mobile phone in this lighting.
If you need better resolution/clarity I can try borrowing Nikon from my parents.

What should I do next?
 

Offline Mkdsime

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #13 on: February 05, 2019, 12:00:01 am »
3rd picture is the IC blown ?
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #14 on: February 05, 2019, 12:14:23 am »
Look at picture 3, the Red "RoHs" side, the resistor R84 big lump solder blot and the flux residues rampage over there. That's why I use the word "raided".

I think you should clean up the flux residues with IPA and cotton Qtip, clean all the top of the ICs and Transistors so that the numbers can be clearly seen. Then take nice clear pictures with the Nikon [with IC and transistor numbers clearly visible].

You should put everything back up connected up, carefully, power up , play some bassy and discover again,  whether the fault is still the same or new faults has develop.

How confident are you if you will to measure those Big capacitors voltage while is powered on? Think about it how you can measure it safely. Knowing that the capacitor carries big charges and if you accidentally shorted it, its going to make held lots of a spark. Do you have a isolation transformer?

NO rush, enjoy the troubleshooting, reading from the part board pictures takes times anyway.
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #15 on: February 05, 2019, 07:31:00 am »
The voltage measurement of the caps will be difficult for you. So forget it at the moment.

Please just focus clearly on this area as shown.

BTW, are you able to unsolder smd component?
 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #16 on: February 05, 2019, 11:19:05 am »
Look at picture 3, the Red "RoHs" side, the resistor R84 big lump solder blot and the flux residues rampage over there. That's why I use the word "raided".

I think you should clean up the flux residues with IPA and cotton Qtip, clean all the top of the ICs and Transistors so that the numbers can be clearly seen. Then take nice clear pictures with the Nikon [with IC and transistor numbers clearly visible].
I've cleaned everything with Ethanol alcohol (70% from local pharma) and Qtip yesterday.
I don't have IPA at hand and only 1 shop in town sells it :D Does IPA cleans better than ethanol?

I'll also have Nikon today and reshoot everything after work.

You should put everything back up connected up, carefully, power up , play some bassy and discover again,  whether the fault is still the same or new faults has develop.

How confident are you if you will to measure those Big capacitors voltage while is powered on? Think about it how you can measure it safely. Knowing that the capacitor carries big charges and if you accidentally shorted it, its going to make held lots of a spark. Do you have a isolation transformer?

I don't have any isolation transformer.
I never did measurements of large caps. 2 large caps on the amp board are rated at 3300uF/80V and other 2 are 3300uF/200V if I remember it correctly. It's best seen on pictures I took earlier:


If there is safe way to do measurements I'm confident that I could to it.

I'll clean, take pictures with Nikon and put everything back together and post back results.

The voltage measurement of the caps will be difficult for you. So forget it at the moment.

Please just focus clearly on this area as shown.

BTW, are you able to unsolder smd component?

Well I bought Hakko FX888d soldering station week ago for RPi project :)
Last time I soldered anything was in high school (15 years ago :D)

I think I could do it, but maybe better question is how to solder it back again?
I only have 1mm soldering wire. Guess that's too thick for SMD work.

The shop that has IPA is only electronics shop in town (and it's on other end from where I live).
So if I need anything for troubleshooting feel free to list it and I'll buy it.

What is the reason to focus on that area? (I'm not questioning your skill, I'm just curious :))
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #17 on: February 05, 2019, 11:30:21 am »
Oh!, to focus on that area means I would like to see clearly that area [IC and transistors numbering, you can photoshop those in] as I think is the area where I "guess" is the area that I can isolate the fault to narrow down of search. I could be wrong with that area but at least is the area of focus and imagination since is multi-layered board.

But you also need to confirm by powering the subwoofer up so that we know is the only fault you have previously described and nothing new from the raiding.

IPA is an alcohol used for removing flux residue. As long as it cleaned up, is OK with me, we are not that petty right?   :D. Other solvent may attack the plastic material or circuit labelling.

I have not use ethanol before so I am not certain to advice you properly about it.

 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #18 on: February 05, 2019, 09:17:16 pm »
Oh!, to focus on that area means I would like to see clearly that area [IC and transistors numbering, you can photoshop those in] as I think is the area where I "guess" is the area that I can isolate the fault to narrow down of search. I could be wrong with that area but at least is the area of focus and imagination since is multi-layered board.

But you also need to confirm by powering the subwoofer up so that we know is the only fault you have previously described and nothing new from the raiding.

IPA is an alcohol used for removing flux residue. As long as it cleaned up, is OK with me, we are not that petty right?   :D. Other solvent may attack the plastic material or circuit labelling.

I have not use ethanol before so I am not certain to advice you properly about it.

OK, I've cleaned board with IPA, took photos then cleaned a bit more after looking at photos :D

Here are all the photos in very high resolution, taken with Nikon D5100.
https://www.dropbox.com/sh/tdmb4fouw2w7ql6/AABHR0dN5zULOvzH0QIcugmua?dl=0

First 5 photos are most important, they show board from top to bottom (ROHS side is top) and 5th is largest chip photo.
I took more if you need details of any part of the board.

Largest chip says:
NXP (vertical text)
HEF4052BT (top row)
L0A8E406 (mid row)
UnG10156 (bot row)

I think this might be this chip:
https://assets.nexperia.com/documents/data-sheet/HEF4052B.pdf

I think that on all U labeled chips (U1, U2, U3, U4...) says:
4560 (top row)
0066 (bot row)

But it's really hard to see and I don't have magnifying glass so I've read it from photos best I could.

I'll attach resized photos, full resolution ones are on dropbox link on top of the post.

I'm gonna assemble it now. If you need any more details I'm gonna take it apart again :)


 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #19 on: February 05, 2019, 09:57:06 pm »
Hi thanks but the center part is clear outer part is blur.
Please take it at an angle of say 40 deg so that the numbers can be seen because the parts are reflective.
otherwise you need to get a magnifying glass [a cheap one] to see it and write it down.

Normally if you flash it at an angle you can see the numbering.

 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #20 on: February 06, 2019, 12:36:23 am »
Hi thanks but the center part is clear outer part is blur.
Please take it at an angle of say 40 deg so that the numbers can be seen because the parts are reflective.
otherwise you need to get a magnifying glass [a cheap one] to see it and write it down.

Normally if you flash it at an angle you can see the numbering.

I think all components labeled with Q are the same (Q1, Q2, Q3...)

If you look at pictures 19 (at the top) and 20 (top left) I think its says: BR30.

https://www.dropbox.com/home/Public/sub%20repair?preview=DSC_0019.JPG
https://www.dropbox.com/home/Public/sub%20repair?preview=DSC_0020.JPG

I've taken the screenshot also.

 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #21 on: February 06, 2019, 09:06:11 am »
Much more difficult than I could have thought.
I can't do it. Sorry, I'm out.

No worries, many experts here, Next Better Guy should be able to help you out.
thanks.   :-+
 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #22 on: February 06, 2019, 11:42:21 am »
Much more difficult than I could have thought.
I can't do it. Sorry, I'm out.

No worries, many experts here, Next Better Guy should be able to help you out.
thanks.   :-+

Thank you so much for your help, I didn't even expect that someone would try to understand it without schematics.
If it means anything to you, I assembled the speaker yesterday and watched 1 episode of TV show and it didn't show any of usual issues. I'll try more during the weekend and post the results.

In case it starts to show issues again do you have any mono class D amps to recommend for subwoofer? I think we can agree I don't have required skills to repair this :D
On subwoofer page it says:
  • 250 W RMS Class D amplifier with switching power supply
  • Downward firing 10” Ultra long throw, C-CAM bass driver
 

Offline Armadillo

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #23 on: February 06, 2019, 12:48:22 pm »
Hi, nothing to do with your skill,
I discover that mine skill has reach the limit to understand the circuit fast enough.
We're on same boat, cheers!;  :D
 

Offline David_AVD

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #24 on: February 06, 2019, 08:11:57 pm »
If the volume goes intermittently full level and uncontrollable by the volume control, I'd actually suspect the volume control itself.  Another possibility is the solder joint for the CCW connection of the pot if it's wired in the common voltage divider way.  If the volume control is wired in the feedback path of an opamp instead, then an open circuit control could also give that symptom.

I don't think I've ever seen a subwoofer with an AGC as why would you ever want that.  Similarly I don't think it's a mute line issue as that would only cause a reduction in volume.  This is all assuming your statement that the volume goes full and can't be controlled is accurate.
 

Offline Mithrandir

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #25 on: February 07, 2019, 06:14:12 pm »
If the volume goes intermittently full level and uncontrollable by the volume control, I'd actually suspect the volume control itself.  Another possibility is the solder joint for the CCW connection of the pot if it's wired in the common voltage divider way.  If the volume control is wired in the feedback path of an opamp instead, then an open circuit control could also give that symptom.

I don't think I've ever seen a subwoofer with an AGC as why would you ever want that.  Similarly I don't think it's a mute line issue as that would only cause a reduction in volume.  This is all assuming your statement that the volume goes full and can't be controlled is accurate.

I'm not 100% sure it's full volume but it goes very loud. Volume control is maybe on 30%.
Whenever it goes loud volume control doesn't work at all. I can turn it all up or down and it doesn't change volume.
When that happens I have to turn subwoofer off/on and then it works correctly again.

I'm a newbie so forgive me for asking, but what's an CCW connection?
 

Offline David_AVD

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Re: Need help with diagnosing subwoofer issues - Monitor Audio R370HD
« Reply #26 on: February 07, 2019, 08:50:40 pm »
CCW means "Counter Clock Wise".  :)

It is odd that the unit resumes normal operation when the power is cycled.  I missed that in your original post.

It would be a lot easier to guess what may be wrong if we had a schematic.
 


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