STK4050V and it's use in Definitive Tech PF15TL subwoofer - Page 3 - diyAudio
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Old 1st November 2008, 06:11 PM   #21
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Im probably not looking hard enough, but where on the PCB is the STK4050v? Besides all the capacitors and resistors on the board I only see the op-amps and some little motorola IC's.

mine is the PF15TL "plus", I dont think that would really make any difference though.
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Old 1st November 2008, 10:38 PM   #22
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duratothemax,

I am reasonably sure that Definitive Technology moved from those chip amps to designs without mains transformers.

ie be careful!

sp
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Old 1st November 2008, 10:40 PM   #23
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Yeah I definetly wont touch any of the capacitors or stuff like that. Hopefully the original poster will see this and maybe post some pics of the repair.

Only half of the resistors are labled it seems, Ill keep looking for R89

thanks
Ben
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Old 1st November 2008, 11:43 PM   #24
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Mine is a PF15TL "plus" model. After going over the PCB schematics it seems there are quite a few differences...

Ben
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Old 2nd November 2008, 12:11 AM   #25
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Quote:
Originally posted by duratothemax
I dont know if those two resistors are supposed to be that color, they look a little brown???
They should definitely not look like that and need to be replaced. Before that you should try to determine, why they look like that. Maybe U3 has to be replaced. And right below Q4 (on the right side in the photo) there is another resistor that looks overheated.

Quote:
Originally posted by duratothemax
Only half of the resistors are labled it seems
The labels are below the resistors. You will have to lift them out to read their labels.

Quote:
Originally posted by duratothemax
but where on the PCB is the STK4050v?
Should be screwed or clamped to the heatsink.
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Old 2nd November 2008, 02:48 AM   #26
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duratothemax, there must be an amplifier section that either uses an IC Power Amp (that is STK series or equivalent) or Mosfets to drive the subwoofer. The pictures are only showing the pre-amplifier section with multi-stage op amps (IC's). This PCB is probably the preamp section, try and look for another PCB that will have the amplifier section... the IC or the transistor is attached to the heat sink to dissipate heat. There you will find the R89 resistor. By the way, it is 19.1 kohms and not 19.5. Do not attempt to change it to 20 kohms because I think the design was for it to give way (you know, like a fuse?) is the sub is played to point of clipping. All the best.
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Old 2nd November 2008, 03:13 AM   #27
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Duratothemax, with respect to post of Pacificblue, Q4 (transistor) is involved with power supply- the fact that your unit powers up only tells you that this component is not defective. U3 (the IC close to the suspicious looking resistors) is responsible for turning the red power light on when the unit detect a signal from the inputs. Again, since you unit turns on when it detects a signal this tells you this is not at fault. I still believe the previous post that the culprit is R89- it is connect to pin 4 of the STK4050v and to the mute of U3- with this info alone, you know it is involved with sound production because when it opens, it will mute the system. Happy fixing. Hope this helps.
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Old 2nd November 2008, 06:50 PM   #28
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Thats great thanks for the help everyone! Yes the output stage is separate on the PF15TL "plus", wheras I think on the non-plus model its all integrated into one module that has the heat sinks sticking out the back of the sub box itself.

the "plus" model is supposedly 500w RMS. Its actually inside the box, I think ill have to take the driver out to get the heatsinks and stuff out to diagnose it. Being double the rated wattage Would it use a different power amp circuit than the STK4050V? Would my "Plus" model use the same 66v rails and power supply as the non-plus model? Ill pull it out and take some pictures.

I see now the resistor labels are underneath the resistors themselves, I feel pretty stupid for not realizing that!

thanks
Ben
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Old 3rd November 2008, 02:25 AM   #29
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If it uses two 10,000 mFd 80 volts capacitors, its voltage is playing around 66 to max of 70 volts. Company won't be using 80 volts caps and load it a 75 volts...that's a meager 5 volts + or - fluctuation...the caps might burst (although not usually). Please be very careful not touching the contacts of the caps unless you discharge them... it's quite a painful jolt...may disrupt your pacemaker if you have one. As I learned from the experts posting here in diyaudio, the 500 RMS of the PF15TL + can be achieved by increasing power supply, so probably the limiter IC was adjusted or the power supply itself was changed. But this is a guess, the STK4050v will probably be still used in your amp. Happy fixing. Will await your pictures. By the way, the amps of the Definitive Tech PF15TL and the PF15TL + are probably one of the best sounding amp for a subwoofer I've heard...for the price it sells. They are better than the latest Supercube amps (which are even rated at 600 to 1000 watts but use a 32 ohm driver!).
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Old 3rd November 2008, 05:58 PM   #30
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Ok so I heard back from Definitive. They were a huge help and gave me the schematics no questions asked. Downside is the replacment amp is like 350 bucks.

thats more than I paid for it, so Ill try to diagnose it myself.

the schematics look different from the PF15TL non-plus, maybe someone can make sense of them?

thanks
Ben
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