M-Audio EX-66 studio monitor

[electrojas]

Good day to you all.
I have a pair of these ex-66 monitors and one day I turned them on and the left monitor would only give me about a third of the volume at full power and the sound that did come out was quite distorted. As this is a powered monitor there is a preamp board and the amp board. I am really looking for some ideas as to where to begin and or if anyone else has dealt with these monitors.
Obviously I have scoured the web but came up short. M-Audio was apparently bought by another company who now refuses to support this model....(go figure). Anyway, thanks in advance for any ideas. I have no schematic for them. but I do have the right channel monitor to use as a reference but again I am not very familiar with troubleshooting circuits I have done plenty of component replacement and soldering but the issues were pretty obvious. This one isnt so easily apparent.

[Kiriakos GR]

Re: M-Audio EX-66 studio monitor

It is supposed that such sound circuits are using high quality capacitors that is hard to fail.
The speaker it self is another item than needs testing.

If you are willing to get the actual speaker out of the damaged monitor, and test it with the good one, if it works properly .... only then it worth to replace all the capacitors of the broken and hope for the best.

I am also an M-Audio customer and own one Oxygen 49 USB keyboard that up to date still goes strong.


Edit:
In your third picture I can clearly see one 10uF 16V that possibly needs to be replaced.. top two

[electrojas]

Re: M-Audio EX-66 studio monitor

Actually, I did take the entire assembly pictured from the right channel monitor, and install it in this box and both drivers and tweeter are performing flawlessly. I did think about beginning a board swap with the two one at a time but they are silicone glued in and that is going to be a heck of a mess. They really blobbed that stuff in there for vibration reduction I am assuming.

[ben7]

Re: M-Audio EX-66 studio monitor

My guess is one of the amplifiers is bad.

Compare the voltage across the two biggest electrolytic caps, between the broken board and the working board. If they are the same, then the problem is most likely in the amp. If one of them is low, then that might have to do with the problem.

[electrojas]

Re: M-Audio EX-66 studio monitor

so off the transformer there is the connector going to the amp board 2 15v yellow and a black I assume is a neutral or ground, AC correct? here is another pic. Clarification: On the transformer, it states. 15.8 - 0 - 15.8v /Yel blk yel

[Kiriakos GR]

Re: M-Audio EX-66 studio monitor

My first and last suggestion to you: measure how many 10uF capacitors are over the amplifier PCB and replace them all.

I have Yamaha monitors and my plan is to do the same.

[Khron]

Re: M-Audio EX-66 studio monitor

Class-D amplifiers, i'm impressed. Acon capacitors - not so impressed...

I don't suppose you have / you can borrow an oscilloscope, right?

[electrojas]

Re: M-Audio EX-66 studio monitor

no I sure dont. I am a real amateur testing circuits thats why I came to the forum. you guys are the real deal here out of everywhere I have been on the web.

[budm]

Re: M-Audio EX-66 studio monitor

Since this is BI-AMP powered speakers which has two amplifiers, one amp for low frequency driver, one amp for High frequency driver. So to have BOTH Amps go bad at the same time is not likely, it has to be something in common to both amplifiers such as the pre-amp section before the electronics cross-over circuits, power supply. Scope will help to locate where the audio signal disappear in the path to the amplifiers.
The power transformer is 31.6V (15.8-0-.15.8) center tap for Bi-polar power supply that generates about +/-22VDC which what you should have on the large filter caps 6800uF 25Vdc (these two caps should have been rated at 35VDC, look like they cheap out on the parts)
What is the P/N of the IC mounted on the heatsink?

[electrojas]

Re: M-Audio EX-66 studio monitor

it says: tda8927a
n2c5h3
hs0221 1

[budm]

Re: M-Audio EX-66 studio monitor

Yep, two channel amplifiers. You can check the DC voltages on the two main filter caps, then the voltages on the IC pins.

[lexwalker]

Re: M-Audio EX-66 studio monitor

Good day to you all.
I have a pair of these ex-66 monitors and one day I turned them on and the left monitor would only give me about a third of the volume at full power and the sound that did come out was quite distorted. As this is a powered monitor there is a preamp board and the amp board. I am really looking for some ideas as to where to begin and or if anyone else has dealt with these monitors.
Obviously I have scoured the web but came up short. M-Audio was apparently bought by another company who now refuses to support this model....(go figure). Anyway, thanks in advance for any ideas. I have no schematic for them. but I do have the right channel monitor to use as a reference but again I am not very familiar with troubleshooting circuits I have done plenty of component replacement and soldering but the issues were pretty obvious. This one isnt so easily apparent.

Well, looking at those pictures, many may forget the first rule in troubleshooting audio equipment. And my first rule is always to remove those degraded glue when I find them. This will eliminate many other possible variables before further troubleshooting, searching for failed/faulty components and extensive diagnostics. That degraded glue can cause all sorts of problems (since it becomes conductive) such as creating phantom circuits and phantom components. Quite often I've easily solved many audio equipment problems by just removing that degraded glue stuff...

[budm]

Re: M-Audio EX-66 studio monitor

Bad glue.

[lexwalker]

Re: M-Audio EX-66 studio monitor

Bad glue.

Yups, hate them especially cleaning up that mess the degraded glue caused. Currently working on a Corsair SP2500, with (again) very bad degraded glue problems (blobs of them, some were wet) that caused major power supply failure as well as audio problems on the amplifier board. After some degraded glue cleanup, can visually make out at least 4 burned resistors, one resistor with one lead corroded until broken and a ceramic disc capacitor also with one lead corroded until broken. Can sense more failed components there.

There are simpler cases I've handled that by just removing the degraded glue the audio hardware comes back to life. Some examples below. From left to right...

Altec Lansing VS2321: subwoofer bass crackling, the woofer connection is corroded
Altec Lansing MX5021: no sound at all, degraded glue visibly the culprit
Altec Lansing MX5021: after a bit of cleanup, corroded traces found
Edifier M3200: very weak sound, hardly audible bass, blob of degraded glue stands out
Edifier M3200: cleanup process, components temporarily removed, notice the stains

[budm]

Re: M-Audio EX-66 studio monitor

Yep, have been dealing with bad glue since the 70's.

[electrojas]

Re: M-Audio EX-66 studio monitor

I never Thought of that as even a possibility. Here, take a look at this shotty business and tell me what you think. I took the other assembly out of the other one and the amp board is different and has none of these three things in it. any ideas?????????????

[Khron]

Re: M-Audio EX-66 studio monitor

Looks like a factory bodge - it happens when it's easier (not to mention cheaper) to just tack on a few parts that fix the issue, than recall / recycle / redesign / remanufacture all the boards, etc.

So this board with the extra parts is from the monitor that works fine? "Worst case", you could try "grafting" that group of parts onto the misbehaving board, and see if it makes any difference.

[budm]

Re: M-Audio EX-66 studio monitor

Since you have working board, I would try fixing the board first to get the sound back to normal first since it was working fine for years without the mod, then I would install the mod later. You have the good board that you can take voltage readings and compare then to the non-working board, I would also remove those glues first.

[drfred]

Re: M-Audio EX-66 studio monitor

It doesn't look as if this issue was resolved, but I have three EX66s myself (having bought the review samples), which have all become similarly flaky. I'm about to open up the worst offender, but my theory is that it's the switch which chooses between analog and the left/right channels of the digital input. I'm trying to imagine--without a schematic--where that switch would be (right after the ADC, before..?), but the wiper is certainly having trouble wiping..and I use only the digital input, so I could also just hard-wire two of them as "left" and "right" digital inputs only. Right now I can make the connection by "wiggling" the switch a tiny bit, putting pressure on it, but when I let go, so does the sound.
I'm thinking I'll put in a good quality switch (once I figure out what I need), and while I'm at it, perhaps replace all the other similar, cheap switches. I know, I should probably do the caps as well.
Anyone replaced the switches? Results?
Thanks!
"Dr. Fred"

[ben7]

Re: M-Audio EX-66 studio monitor

It doesn't look as if this issue was resolved, but I have three EX66s myself (having bought the review samples), which have all become similarly flaky. I'm about to open up the worst offender, but my theory is that it's the switch which chooses between analog and the left/right channels of the digital input. I'm trying to imagine--without a schematic--where that switch would be (right after the ADC, before..?), but the wiper is certainly having trouble wiping..and I use only the digital input, so I could also just hard-wire two of them as "left" and "right" digital inputs only. Right now I can make the connection by "wiggling" the switch a tiny bit, putting pressure on it, but when I let go, so does the sound.
I'm thinking I'll put in a good quality switch (once I figure out what I need), and while I'm at it, perhaps replace all the other similar, cheap switches. I know, I should probably do the caps as well.
Anyone replaced the switches? Results?
Thanks!
"Dr. Fred"

I've never worked on one of these, but yes, I've seen numerous failures of switches in cheaply built products.

It could also be bad solder joints not the switch itself.