SOLVED - Need help with Focal Solo6 Be repair?

[chilidawg]

Hello there good people, I haven't been here for a few years. Not in the pro audio world anymore.

Yesterday a friend brought in a pair of Focal Solo6 Be, and one of them has a bit of an issue. It has a super loud hiss and produce random crackling noise. Happens with or without a connection to the input.

I thought it might have something to do with the power supply, like a failing filter cap perhaps, but nope. They're all tested ok with values are still tightly close. I can't check for voltages because of the way it's assembled together (a garbage design for a thousand bucks of studio monitor, imho), at least not without damaging something in the process or getting myself electrocuted since there are both live AC voltage and high current high DC voltage running on the board.

There are two amps inside: one for the woofer using two pairs of MOSFETs combined together with a 2-way active crossover I think (all SMD parts), and one for the tweeter using an obsolete amplifier IC (National L4780TA), I don't see any physical damage with both circuits, and the speaker still outputs audio very well. Just not usable at all for listening. I haven't tried to isolate from which amp the issue might be generated because the driver cables are too short, and I don't have AWG18 cables at hand to extend them to the board. I could dismantle the drivers off the wooden box, but that will probably freak out my friend. Last time I changed the broken ON-OFF rocker switch, he was sweating like a bucket while watching me doing it, sooo afraid that I would somehow damage the speaker, lol.

Without a schematic, this repair effort is probably futile, but regardless, any kind of help is appreciated.

 

[thomasdf]

I fixed a friend's Solo6 pair because the mains power switches were failing too. I replaced them. After a while, the woofer amp started turning on and off randomly... I inspected the circuit but was discouraged by the tiny components, the hot glue everywhere and the cheap construction...
He contacted Focal and they suggested he upgraded the amps to updated designs, which he did (and also upgraded the tweeters grill).
IIRC the price was around 300e / amp. I'll ask him and edit the post if needed.

Édit : 350€ excl VAT ...!

 

[chilidawg]

Well, the one with a broken main switch that I fixed not long ago is operating normally without issues. These SMD parts don't scare me away because I have been working with SMD parts for a long time now, even down to the tiniest that needed a microscope to solder by hand, however I did saw one or two SOT-23 transistor which has no clear marking, so I have no idea what they are.

Getting a new amp replacement is not a viable option. It's too expensive, after shipping and taxes. If these speakers were mine, I'd dismantle the amps and sell them for parts. Make my own amps for the drivers. Definitely will not be using that heavy toroid power transformer and will be much easier to service in the future, but this is not doable either. Dude is sort of an audiophile, even when I was replacing the broken main switch, he was also worried it might change the "sound", heh.

 

[alphasnk]

I fixed a Krk vxt 6 for a friend, it was the filter caps, but i second everything you said, hot glue everywhere, thru holes components still, but heavy toroid and everything.. It makes you want to start diying your own speakers that's for sure

 

[chilidawg]

No hot glue here, but they used silicone glue, and German UHU all-purpose glue for the nuts.

It's a dirty inside too because the person who soldered the filter caps had just done potting, so his/her fingers were covered in black resin, which of course, smeared that all over the caps. After it has cured and hardened, it became sands.

The thermal paste job is messy as well.

 

[chilidawg]

No more crackling noise (loose female quick connector from the power switch to the board, probably because the cables are very short and over time with tension and gravity kept pulling it...), and confirmed that the hissing noise is from the woofer amp.

Not sure exactly which component is failing but I still suspect that it's a filter(s) cap problem. 5 electrolytics... or perhaps I should replace the ICs (2x NE5532, 1x TL082C) and the MOSFETs (IRF530 + IRF9530) too? argh, this guessing game is so stupid. I have a good working amp that I can take measurements from and compare with, but I can't do it because of the construction that prevents me from doing it.

 

[Khron]

Nothing a couple dummy resistors (to replace the speakers as a load) couldn't fix..?

 

[chilidawg]

Nothing a couple dummy resistors (to replace the speakers as a load) couldn't fix..?

I think you misunderstood my last post, bro. The tweeter and the woofer are in pristine condition. It's the woofer amp that is having a problem.

 

[Khron]

I meant for testing. "Bro"...

 

[chilidawg]

Yeah I know, but at the moment I have the woofer connected to the board by extension cables.

The construction problem that I have with this monitor is the short AWG16 cables from the toroid to the board.
The board itself sits on a piece of thick aluminum U bracket which get screwed on to the monitor's aluminum back plate where the heavy toroid is also bolted on.

If I remove the U bracket, the board is just dangling by them cables, and that's a recipe for a disaster. Because of the weight of the toroid, it could topple over at any time. It has done so a few times.

Anyway, I'm just going to buy the proper male connector header to mate with the female header at the end of the toroid cables, so I can make extension cables. This will allow me to check the board on my bench vise, where I have the freedom to move around.

Some pics.

Last pic is the tweeter amp, and the two pics before that is the woofer amp.

 

[chilidawg]

More pics. Another resin extravaganza to cover up the laser marking on the ICs, but I managed to scrape one clean to reveal an OPA4134UA.

I think this board is definitely the active crossover circuit.

 

[Khron]

Give your lens a wipe sometime.

Extensions for the toroid cables is a good idea.

"Cute" factory bodge with those stood-up-and-soldered resistors on the crossover board.

Now it would be interesting to see (on a scope as well) whether the noise issues come from the crossover board, or the amp(s).

 

[chilidawg]

Give your lens a wipe sometime.

Extensions for the toroid cables is a good idea.

"Cute" factory bodge with those stood-up-and-soldered resistors on the crossover board.

Now it would be interesting to see (on a scope as well) whether the noise issues come from the crossover board, or the amp(s).

Nothing is wrong with my lens. I reduced the pics quality so that they will upload faster. I lost my job because of Covid, and with what I'm doing right now to make money, I'm barely hanging on to get by every month. I had to cut down on some luxuries and one of them being an ultra-fast fiber optic internet connection. My mobile data provider locks the upload speed at 1Mbps, so if the pics stay at their original resolution and pixel density (33Mbytes per pic), it will take forever to upload.

The noise issue is only from the woofer amp.

 

[alphasnk]

It's only a matter of time and it will be running, you've got it! Courage for everything.

 

[chilidawg]

Thank you!

When I removed the crossover circuit box from the back plate yesterday, I saw that it opened up enough room for my probes to poke around the woofer amp section without the need to take the board off the U bracket or make extension cables for the toroid, so I'm gonna be spending the next few days of my available spare time, taking measurements from the good working amp, then compare them with this one.

 

[chilidawg]

I just don't understand the necessity to remove important information by sanding a few numbers off the surface of the parts, or the unwillingness to share a working schematic of the design, especially if your products are being distributed and sold all over the world where there are no company representative and qualified service technicians living in those countries. Not every end-user has the luxury to ship the stuff back and forth just to get it repaired, and no one is going to bin away a $1,500 speaker or a $1,000 amplifier board (after shipping and tax) just like that.

My guess the IC is UC3842B, a current mode PWM controller. And from what I have just read about BASH amplifiers and Focal Solo6 Be manual stated that only its LF amplifier is a BASH amplifier, this board and the components sitting nearby which makes up the whole class D amplifier like switching behavior, may just be what's causing that loud hissing noise going into the class A/B woofer (LF) amplifier. *grunt* more work... think I'm way over my head in attempting to repair this studio monitor.

 

[chilidawg]

So, the crackling noise came back...

And I also found two problematic power transistors. Both are overheating after turning on, especially the TIP112 which happens within seconds. The ones in the other Solo6 are not even warm at all.

Local part stores don't sell TIP112, but plenty of TIP102, TIP122 and TIP142. I went with TIP122, because slightly cheaper than TIP102 and TIP142 is TO-247

Hopefully I only need to replace these two, and the noise problem will go away for good.

 

[Khron]

Could the TIP112 be involved in regulating the gate drive voltage for the class-D output stage?

What transistors are used in the class-D woofer amp? Are all four IRF540's, or..?

 

[chilidawg]

Woofer amp is a BASH amplifier, and from what I read about it, supposedly a class A/B amplifier with a class D power efficiency. The gimmick term they used to describe it is "switching pulse that dance with the music.", lol.

There's only one IRF540 next to a 100V Schottky rectifier, and it's in the power supply section together with the TIP112. In between them is that little proprietary INDIGO board and two (15A I think) bridge rectifiers that feeds into it.

The woofer amp has a lot of BAS16 fast switching diodes, 2N4401 + 2N4403, 2N5551S + 2N5401S, and two pairs of MOSFETs to drive the negative and positive signal output. IRF530 + IRF9530 makes up one pair.

 

[ccaudle]

guess the IC is UC3842B

UC3842 is a power supply controller. With that big toroid the amp definitely does not have a switching power supply, so don't see how a UC3842 could be used in this amp.

whole class D amplifier...the class A/B woofer (LF) amplifier

I couldn't figure out what you were saying at first, but from what I gathered elsewhere there is something like a switching power supply which supplies a varying supply voltage to the linear amplifier to improve efficiency of the amp. If something happened to that supply it could cause problems for the amp. You should be able to see by looking at the power supply rails for the bass amp if the voltage is stable, if the switching frequency looks reasonable and stable, etc. I would think that with no input the supply voltage should be pretty low and stable, and as you give an input signal the supply rail should increase as the input signal amplitude increases. Would have to go look for the BASH patents to be sure, but the description Focal gives indicates that the supply voltage follows the input signal pretty closely. I'm not sure if the UC3842 can track reference voltage changes that quickly, but the picture you showed is definitely an ST part and not a UC3842, so if you thought you were taking a picture of something with a UC3842 on it I can't see it.

I removed the crossover circuit box from the back plate yesterday

So you completely disconnected the input circuitry with crossover from the amplifiers? Your wording was a little big vague on whether you actually were able to disconnect enough to make absolutely sure the noise was from the amplifier and not the input/crossover circuit.