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JBL S412P studio speakers repair


knightrider200's Avatar
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11-10-17, 12:41 AM   #1 (permalink)  
JBL S412P studio speakers repair

Hello,

i'd like to get some more information about an amplifier insides. I added a link of a pdf file with info about this amplifier.


Grtz,

knightrider

 
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11-10-17, 07:08 AM   #2 (permalink)  
What's happening with the speakers? I don't know what you can do with that system. I only buy separate components.

 
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11-10-17, 12:04 PM   #3 (permalink)  
Welcome to the forums.

You left a link to the owners manual. You need the service manual.
service manual_S412P.pdf


~ Pete ~

 
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11-11-17, 01:11 AM   #4 (permalink)  
Hello PJMax and Donato,

as far as i can remember, the lfe input wouldn't work anymore. And that input was getting loose. Then when getting the module out of the speaker, i removed 2 screws that were holding a transistor against the coolingback. When doing that, the metal plates (2) fell off on the inside of the speaker, with the amp unit still installed. So there were shortcircuiting, cause of falling/lying on the pcb and components. I was carefull with taking out the amplifier unit, that didn't work and turned on the amplifier still. Then the fuse blew, probably because of the 2 metal plates still lying somewhere on the pcb and shortcircuiting.
Have gotten the amplifier out of the speaker, and reinstalled the 2 metal plates, with the screws on the backsidie. And tightened the plastic thing, housing of the lef input. Just had to install it and put the screw in. Now the lfe input is steady.
When pulling out the cables of the amp, there was a spark on the connection plug leading to the speaker(12 inch woofer). So there was still voltage on the speaker. Probably should have waited longer before pulling out the cables.
I read the guide and it shows exclamation marks at certain components. So that would mean those parts are more sensitive to getting broken. And are the first parts to be measured if they aren't broken.
It seems like at least some parts are overdimenioned and the fuse is the first part that gets the hit. The voltage rectifier can stand much more power than the fuse. When inspecting the pcb, there were black marks, but it wasn't really clear if that was a broken component. There is a lot of gel/dried glue that is on the pcb, so that could have been there from the making of the speaker.
I really wasn't to carefull with the speaker as you probably think now. Still they're quality speakers that i have bought like in 2000.In all that time the speakers have been working fine.
Some say, bad speaker cables are causing often trouble with speakers. That may also be the case. Hence the lfe input getting loose. Either i have been using a to short tulip cable and stepped on the cable. Or i used tulip cables that are to tight, so i had to use more force to get them connected to the speaker.
My question is, if it's still possible that the amp works, despite of the spark and the blown fuse.

 
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11-11-17, 05:33 AM   #5 (permalink)  
With all that short circuiting, anything can happen. Do you have a small AC DC meter to trace the juice? Another trick is to swap the speakers to see if the sound follows the channel.

 
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11-11-17, 05:53 AM   #6 (permalink)  
Follow the juice, yes i do have a standard voltage meter. Swap speakers, it's a build in amplifier. It's a subfrequency amplifier build in the speaker housing driving the 12 inch woofer. The speaker has a power cord too, for supplying the juice to the internal amp.

 
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11-11-17, 06:01 AM   #7 (permalink)  
In the drawing i saw 2 diodes in paralell. This is to get rid of the left energy right? So leaving the speaker/sub amp powerless for like half an hour will result in zero voltage anywhere in the pcb.
Then, for a pc power supply it is possible with a shorcutting two pins of the psu to run the psu without anything connected. It doesn't really harm the psu. Is this also possible for an amplifier? So becaues the wires from amp to speaker are very short. To short to be able to measure anything. When put the ampliifer on a desk with power connected and turned on, it's more easy to measure voltages.

 
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11-11-17, 06:53 AM   #8 (permalink)  
I have no experience with that type of speaker. I would have to depend on a meter to tell me what's wrong.

 
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11-11-17, 07:35 AM   #9 (permalink)  
ok, didn't know that yet. Some people fix things with a drawing, others with a voltage meter.

The speaker is from back 2000. At that time they were i guess for a year on the dutch market. They're very hard to get these days. Would be awesome to get the same pair of speakers for surround speakers. Right now i have jbl control 1g speakers as surround. They're connected to a passive sub with filter to the receiver. When using pioneer mcacc and set the calibration mode to 'align to front speakers', the sound is quite nice.
Right now i disconnected the two jbl s412 speakers and connected some really old bose acoustimass speakers. The sound is still nice. The base is a little less.
I was thinking of putting the whole drawing of parts and connections into i thought it was mathlab. Then run the circuit. That way all of the voltages through the pcb become visible. You can just add virtual voltage and amp meters to the circuit. But it's a lot of work i think.
I'm having the european type of the speaker. The manual is of the american speaker.
The mcacc is from 2012 pioneer receiver. It's become better then older versions. It only measures one position and can do all the calibrating of the sound.
Getting back to the speaker. There are 3 wires leading from amp into the speaker. You can't follow them, cause there's plastic between the amp and the rest of the speaker. So 3 wires are glued in the plastic.
One wire is green yellow i thought, is the 12 inch woofer speaker cable. One is red black, it's from the normal speaker input. Then there's a third wire, not sure were that one goes. Can't see nothing of it in the drawing. But should be leading to the 2 front leds.
Funny thing of the speaker, is that i saw few of them on our craig's list, and there's just no one that is mentioning that the sound of the speakers is incredible or very good. But they're quite expensive though, at least back then. Must say, they last very long. The bose acoustimas speakers i have, aren't very much older, but they looks like ****. Sound is reasonable, still a bit of bass in them, remakably much.

 
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11-11-17, 08:01 AM   #10 (permalink)  
it's not mathlab, but spice, elektronic workbench or multisim.
*edit; it seems electronic workbench is an open source program, free downloadable here: https://archive.org/details/ElectronicWorkbenchEwb5.12


Last edited by knightrider200; 11-11-17 at 08:36 AM.
 
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11-11-17, 08:28 AM   #11 (permalink)  
I'm the one that troubleshoots and repairs electronics. You've written a short story. Tough to follow. Let me offer a few pointers.

1) there should be 0vdc measured across any speaker leads or amp outputs. Any voltage on the speaker leads signifies shorted output transistors. The amp should go into protection and not allow any voltage but it does happen. ANY DC voltage on the speakers will burn them up.

2) there should be 0vdc measured from any speaker lead to ground or amp chassis.

3) you can check the speakers themselves with an ohmmeter. They should measure 4-8 ohms not connected to the amp.

4) you mentioned that the link was for the U.S. version. That is all I have access to.

If you have any other questions.... ask.


~ Pete ~

 
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11-11-17, 08:54 AM   #12 (permalink)  
then ry101 (the relais before the speaker) is broken. There's also an exclamation mark at that relais on the drawing.
Next question, how to measure all the components of the drawings with a meter?
That would be the following components:
- diode rectifiers kbl405 (D112 + D113)
- C119, C120, C121 and C122
- powertransformator (PT001)
- C001
- switch and fuse should still work or are replacable
- Transistors Q108 through Q123

These are all marked as most fragile components.

 
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11-11-17, 11:02 AM   #13 (permalink)  
You have two of these speakers. Each one has three passive speakers and the subwoofer. Is that correct ?
Do you have a problem with both of them or just one ?

RY-101 is the speaker protection relay. It doesn't close and connect the speaker if there is any DC present on the speaker line. It also delays the connection of the speaker on turn-on to eliminate turn-on thumps. That's a problem if it's broken. No big deal to replace. It's a DPST relay... probably 12vdc coil. You can sub to a different relay and hard wire it in.

Instead of randomly checking parts... check the +15vdc and the -15vdc supplies. You check them from each line to ground. Then check the AC voltage too. It should be very close to 0v. If you see anything over 1/2vac then you may need filter caps.


~ Pete ~

 
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11-11-17, 11:16 AM   #14 (permalink)  
three passive speakers and one active woofer, yes. Yes both the speakers have trouble. The other speaker has power off thumbs(deloading over the 12 inch sub), probably also due to a broken relais. The three passive speakers on the first speaker are working fine.
I get the measuring of ac and dc of the +15 and -15 volt lines. What are filter caps and hard wiring, is that bridging the relais?

*edit: seems like the hls signal is continuously on the speaker, the ap0 signal is going through the relaisswitches also to the speaker.
*edit2: the relais is texted with something like 2 times 12 volt, but then '@22", what would that @22 mean?


Last edited by knightrider200; 11-11-17 at 11:56 AM.
 
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11-11-17, 10:01 PM   #15 (permalink)  
Still don't know if the amp can be measured unconnected to the speaker. Will any speaker/woofer with about 4ohm resistance do?

*edit: transistor i want to measure, from base to collector/emitter, or from collector/emitter to base should be 0,7 volt. Then measure shortcircuit between each of the c,b and e. So base being the middle pinout and collector/emitter the ones on the side. Do i have to use the 2kohm/diode selector on the meter?
Then i want to measure the capacitor if they're shortcircuited. With measuring the resistance.
*edit2: the dpst relais, i thought wrong. It's more probable that the speaker is either connected with the AP0 or the HLS. HLS, would be the speakersignal, the AP0 would be some kind of park connection. In other words, the speaker is always connected to some kind of power.


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11-12-17, 12:24 AM   #16 (permalink)  
The components on the drawing with an exclamtion mark, aren't marked because they're the most fragile, but when those components are broken, there isn't comming any good sound out of the speaker. So they should function well for the speaker to function good.

 
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11-12-17, 06:00 AM   #17 (permalink)  
RY101, i figured that one out. It's depowering the HLS (speakersignal) with the AP0 signal, or it's not depowering the speakersignal and passing it through to the speaker. In both cases the speakersignal is fed to the speaker.
The relais is according to the specs rated at 5 Amps, but here it's used as 22 Amps( 12 volt times 22 is 264 Watts, going to the speaker). Does this mean you can just use a 5 Amp version as 22 Amp?

*edit: transistor, the first on the left is the base, the others are collector and emitter.


Last edited by knightrider200; 11-12-17 at 08:23 AM.
 
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11-12-17, 09:59 AM   #18 (permalink)  
short story of what happened: a little metal bracket fell on a transistor, shortcircuiting it, and caused DC voltage on the loudspeakerpole. Thus broke the fuse.

 
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11-13-17, 05:08 AM   #19 (permalink)  
Ater an inspection of the amplifier and some testing, it seemed all right. But there was a capacitor fried. The spark probably was from the relais.. So the amplifier is still working.


Last edited by knightrider200; 11-13-17 at 06:16 AM.
 
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11-13-17, 09:29 PM   #20 (permalink)  
Sounds like you are making progress there.


~ Pete ~

 
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11-14-17, 02:33 AM   #21 (permalink)  
Yep, it's amazing. But i have one question, that is: what does the capacitor parallel to R147 do? But maybe it isn't even broken yet. Still there was a lot of black on the backside of the relais RY101. I could easily rub it off though.
Then for the working of the speakers, there comes some DC voltage on the 12 inch speaker conus, making it contract. Then it doesn't contract, but it's completely normal for these speakers. What isn't completely normal i think, is that the other speaker unloads through the 12 inch speaker if turned off.
Further, if i read the schema right, it seems like the loudspeaker signal is always on the 12 inch speaker. In both states of the relais RY101. But in on state, it is fed back negative into the amplification section. So there comes less signal on the speaker.
The schematics is for 120v60hz (GB voltage) so it's not the same as for 230v50hz version. That also looks that way cause of when i look at the pcb and at R147, there is only one capacitor running over it parallel. So not also the diodes.
Then something to owners of this type of speakers, it's quite hard to make the right sound come from it. You really have to use MCACC or some kind of microphone used calibration for that. I also have some Bose speakers, they are more easily giving the right sound.

Have a nice day! Knighrtider

 
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11-14-17, 11:15 AM   #22 (permalink)  
I don't see any cap in parallel with R 147.

The amplifier audio output is only connected to the speaker when the relay closes. When the relay is open there appears to be the HL S connected to the speaker.


~ Pete ~

 
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11-15-17, 06:32 AM   #23 (permalink)  
Well, on my jbl s412pch pcb, there definately was one cap welded over R147. Maybe it's another revision or the 230volts schematics is a bit more different than the 110Volt schematics. If this one is solely for the 110volt version, it seems like you could almost make the amplifier for yourself. You can even make the pcb yourself with it. Then put all the components on it. But i don't think a print of the wired diagram is working out for that. It's a bit hard to read. I'm used to either bows or points at connections of wires. Here it's all just lines. If you have the project file and load it up in electronic workbench or some programm like that, you can select a line and it glows or something like that so you can make difference from were the wires go and were they have connection and where not.

Anyway, the speaker works still good, even the auto shut off works the way it should.

 
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