JBL CS60.4 repair guide

[amitverma]

my ICE woes doesnt seem to cease. well this is part II of the deal. my 60.4 JBL amp has a dead MOSFET [i hope this is what it is called, the golden screw thingie..?]. the ones operating the sub are alright. the ones doing duty for the components have said goodbye.
pls let me know where to get it fixed in new delhi? i dont want to goto local electrical-walaa. i have been referred to a lot of these guys but i am fairly confident that they will wreck my amp for sure. also pls dont suggest some ultra hi-fi techno-jargon-buster, who would rip me off by boggling certain cool sounding abbreviations.
if u want a peek at my financial situations regarding ICE, refer here (Pioneer HU upgrade/woes)

[Sam Kapasi]

I'm assuming it isn't under warranty.

Firstly a Metal Oxide Field Effect Transistor is not a golden screw thingy lol. It is a transistor and is proud to be something like this.


Secondly - how do you know that the MOSFET has failed? Yes it is quite possible but not necessary. My question is - how can you be sure?

[navin]

Originally Posted by Sam Kapasi

Firstly a Metal Oxide Field Effect Transistor

correction: it is
Metal Oxide Semiconductor Field Effect Transistor

MOFET is Jewish/Yiddish/Herbew word (something I learnt while at Yeshiva Univ, NY) that has something to do with educatation (I believe it is Maths and Physics) and culture.

[Technocrat]

Have had this changed in my Sony amp too, it seems this is cheap as the installer did it free of cost to me(as I was anyways paying him for speakers & cables) SO hsould not bea problem, others can advise better on place & price.

[amitverma]

Originally Posted by Sam Kapasi

Secondly - how do you know that the MOSFET has failed? Yes it is quite possible but not necessary. My question is - how can you be sure?

i might know the technical aspects of this but let me just give u a peek into the problem im facing. the 60.4 has a pair of 4 gold screws to which i attach the speaker cable to. on the upper set of screws i have bridged the subwoofer while on the lower set reside the front components. now the LEFT front comp always turned on and off and on...whenever i increased the volume, it comes back to life. i inquired abt this with a couple of local accessory shops and they all told me that the "mosquito" is dead. at first i was a bit sceptical about my amplifier renting out space to a bunch of mosquitos to live but then the working side of my brain intervened and i realised that he must be referring to the MOSFETs.

now when i asked about the repair bills, teh mosquito guy tells me "Sir, yeh JBL-shey-BL ke amp imported maal hai. inko repair karne ka kharcha bhi imported hi hai. pata nahi uske level ka part milta bhi hai yaa kuch jugaaaad chalaana padta hai"
that line was enough for me to walk out of that store.

anybody can throw some light as to what i need to do now?

[navin]

Originally Posted by amitverma

now the LEFT front comp always turned on and off and on...whenever i increased the volume, it comes back to life.

this sounds like a leaky cap in the amp. any good technician should be able to diagnose and fix this. amp circuits are really not all that complicated. since it is only 1 channel that is malfunctioning one can use the voltages of the working channels to ascertain which part needs replacement.

[Sam Kapasi]

Change your RCA cables.

[amitverma]

Originally Posted by navin

this sounds like a leaky cap in the amp. any good technician should be able to diagnose and fix this. amp circuits are really not all that complicated. since it is only 1 channel that is malfunctioning one can use the voltages of the working channels to ascertain which part needs replacement.

Originally Posted by Sam Kapasi

Change your RCA cables.

2 different suggestions.
Sam, how did u arrive on the faulty RCA cable situation?

[DerAlte]

Originally Posted by amitverma

2 different suggestions.
Sam, how did u arrive on the faulty RCA cable situation?

2 different valid possibilities!

"Faulty RCA cable situation" means a loose connection can also show this behaviour. "whenever i increased the volume, it comes back to life" could be a coincidence - vibrations from the louder sound could be causing the connection to reconnect!

[greenhorn]

question, when you pump up the volume and it comes back to life, does it play clean, or is there any distortion?

[low_bass_makker]

It can be RCA or some dirt in the switches which is used for HPF, FLAT, LPF setting.

Try fiddle with them while playing and check for the sound.