Need help solving Genelec 1032a problem - No bass, but speaker works. [SOLVED]

[jphansen]

Hi all

I'm new here.. and i novice to electronics.. sorry.. or.. I know how to solder and repair stuff.. But I know nothing about the electronics it self..

Anyway.. Some stupid kid was at our studio alone for 10 min. and when I got back our right side Genelec 1032a bass was dead.. (he killed it with some crazy snare sound he told me) - it must have been REALLY loud.
I have now tested the speaker it self - and both the 10" woofer and treble horn works.. So I guess it must be the preamp in the speaker that have a fried component somewhere.. I just DL the 1031A service manual from here.. and it seems somewhat indetical to the 1032A print..

Could someone point me in the right direction on how to troubleshoot the missing bass? None of the capacitors looks blown..

Any help would be nice.. I have a hard time finding any good electronics exports here in my area in Denmark.

 

[jphansen]

No one? 

 

[moamps]

No one? 

You should first swap the amps boards and check the sound to be sure that the speakers are fine and one board is faulty.
If you are 100% positive  that amp board is faulty, usually the problem is in one output amplifier (for bass speaker in your case) (output transistors, etc.), not the preamp or crossover.  Did you check the fuses in the power supply? 

 

[bruno2000]

Check all of the Molex solder connections on the PCB.  The factory doesn't put enough solder on the joints and they fracture.
My $0.02, but maybe that's too much........

 

[jphansen]

Good idea switching the amp boards.. I switched the woofer it self and it was OK.. What about the "big coil" in the back.. How can I check if that one works? Should there be a current flow through that? Like - Should I be able to "bib" test the flow with the multimeter? (dont know what it's called in english sorry)

No one? 

You should first swap the amps boards and check the sound to be sure that the speakers are fine and one board is faulty.
If you are 100% positive  that amp board is faulty, usually the problem is in one output amplifier (for bass speaker in your case) (output transistors, etc.), not the preamp or crossover.  Did you check the fuses in the power supply?

 

[jphansen]

Is there any way to test if the Power Amp (STK442-130) is fried?

 

[Walrus]

From experience, I would be fairly confident that the left hand STK442-130 is dead. It has always been the culprit when a session blows one of our Genelecs.
In the UK, the Genelec distributor will only supply a complete amplifier board. But I have successfully repaired boards before with just the chip. Make sure you buy the STK from a reputable source as there are copies out there! Also you will need a new sheet of heatsink material, as the old sheet will disintegrate when you remove the STK.....

 

[jphansen]

Thanx a lot.. Does this look right?
http://elektronik-lavpris.dk/p99676/STK442-130_POWER_AMP_2x150W_6ohm_63V_10_14-pin/? or this https://www.elextra.dk/main.aspx?page=article&artno=H40532 They are both reliable danish shops..
Isn't it just "normal" thermal paste you use?

From experience, I would be fairly confident that the left hand STK442-130 is dead. It has always been the culprit when a session blows one of our Genelecs.
In the UK, the Genelec distributor will only supply a complete amplifier board. But I have successfully repaired boards before with just the chip. Make sure you buy the STK from a reputable source as there are copies out there! Also you will need a new sheet of heatsink material, as the old sheet will disintegrate when you remove the STK.....

 

[Walrus]

Yes, that looks fine.
Re the paste, I think you can use ordinary paste as the back plate (substrate) of the STK is isolated from the internal circuitry. However, it always looked like Genelec had made sure the substrate was fully insulated from the speaker chassis, so I've always erred on the side of caution.....

 

[jphansen]

IT WOOOORKED... Thank all.. We are back up running.. Changed the STK442-130 and BOOOOM.. it's back up running..