samerag
05-31-2004, 01:13 PM
Hello :
I have bought two JBL LSR25P studio monitors from about three years, they were working fine - in fact they were extra fine - but badly that I have these problem with one of them .
The main cause that I didn't contact the local support in my area this time ( I’m living in Syria ) is that these guys here really know nothing about maintenance and repairing ... I don't know how JBL can work with them as agents.
The first trouble appeared from about one year, one speaker has run out of sound, no sound at all, just a cracks and hisses, I took the speaker to those JBL LOCAL SUPORT guys and they told me that the power amp ICs were damaged, I couldn't trust that ( no way three ICs could be damaged in the same time..). so the only thing I had to do is fix it by myself ( I have some good experience in electronics and repairing), even I knew that I will lost the warranty, and what ?? the problem was in the 10k volume resistance and that just cost me $0.5 to replace and it worked fine. ( the locale JBL guys told my that the cost would be about $100 beside that they damaged the tweeter foil when they shipped the speaker back to me).
Now I'm having this new problem : the tweeter's sound gone very load ( even when removing the line-in cable ), this loudness was just come and go frequently ( sometimes and somehow it disappears when turning the volume high, yet it burned up the tweeter, again I tried to solve this by myself .. but unfortunately I couldn't, and here the steps I took :
First I downloaded PDF’s from JBL’s website, an exploded view and a schematic view for the LSR25p.
I studied the amp circuit well, so can figure out how the signal goes through the main-board and its sections.
I checked the power supply, before and after the power section (the bridging and the regulators) and they all were O.K
I checked the board for any cracks, broken parts or cold soldered points. All were O.K.
I attached a tweeter with a cheap 4 ohms one to do the other tests and I do it through the hi-freq amp sections one be one by this way :
I attached a 10mf chemical capacitor to the board's grounding and earthed the pre-amps one after the other (through the hi-freq section), that made some differences in the tweeter's sound but the loud noise still existed.
I de-attached that capacitor and yet de-attached the main C-141 capacitor (the main line before the hi-signal goes to the power-amp IC, again the high noise still existed.
I suspected that the Hi-freq power-amp IC (the LM3886T) is somehow could has been damaged, so I replaced it ( I was lucky I could found one in my local market). and again the problem wouldn't go and the noise was too loud.
After I burned up the tweeter that I'm testing with .... I gave up.
So ... I know this is not legal and shouldn't have opened up the speaker's chase in first place, but looking at my situation here and being really too far from any REAL experienced guys, Can I have some help from any one knows what the problem is, like telling me what part that obviously causes this problem.
Please I need this speaker, it's the best I can have.
Thank you and sorry for the long story ....
Samer Ajouri
Off-Line DV Editor and PostProduction Eng.
I have bought two JBL LSR25P studio monitors from about three years, they were working fine - in fact they were extra fine - but badly that I have these problem with one of them .
The main cause that I didn't contact the local support in my area this time ( I’m living in Syria ) is that these guys here really know nothing about maintenance and repairing ... I don't know how JBL can work with them as agents.
The first trouble appeared from about one year, one speaker has run out of sound, no sound at all, just a cracks and hisses, I took the speaker to those JBL LOCAL SUPORT guys and they told me that the power amp ICs were damaged, I couldn't trust that ( no way three ICs could be damaged in the same time..). so the only thing I had to do is fix it by myself ( I have some good experience in electronics and repairing), even I knew that I will lost the warranty, and what ?? the problem was in the 10k volume resistance and that just cost me $0.5 to replace and it worked fine. ( the locale JBL guys told my that the cost would be about $100 beside that they damaged the tweeter foil when they shipped the speaker back to me).
Now I'm having this new problem : the tweeter's sound gone very load ( even when removing the line-in cable ), this loudness was just come and go frequently ( sometimes and somehow it disappears when turning the volume high, yet it burned up the tweeter, again I tried to solve this by myself .. but unfortunately I couldn't, and here the steps I took :
First I downloaded PDF’s from JBL’s website, an exploded view and a schematic view for the LSR25p.
I studied the amp circuit well, so can figure out how the signal goes through the main-board and its sections.
I checked the power supply, before and after the power section (the bridging and the regulators) and they all were O.K
I checked the board for any cracks, broken parts or cold soldered points. All were O.K.
I attached a tweeter with a cheap 4 ohms one to do the other tests and I do it through the hi-freq amp sections one be one by this way :
I attached a 10mf chemical capacitor to the board's grounding and earthed the pre-amps one after the other (through the hi-freq section), that made some differences in the tweeter's sound but the loud noise still existed.
I de-attached that capacitor and yet de-attached the main C-141 capacitor (the main line before the hi-signal goes to the power-amp IC, again the high noise still existed.
I suspected that the Hi-freq power-amp IC (the LM3886T) is somehow could has been damaged, so I replaced it ( I was lucky I could found one in my local market). and again the problem wouldn't go and the noise was too loud.
After I burned up the tweeter that I'm testing with .... I gave up.
So ... I know this is not legal and shouldn't have opened up the speaker's chase in first place, but looking at my situation here and being really too far from any REAL experienced guys, Can I have some help from any one knows what the problem is, like telling me what part that obviously causes this problem.
Please I need this speaker, it's the best I can have.
Thank you and sorry for the long story ....
Samer Ajouri
Off-Line DV Editor and PostProduction Eng.