[ibm_jennifer]

Friends,

One of the capacitor in my JBL 75.4 Amp is busted and I got some white smoke from the unit. Can i replace it myself or do you know any place to service it in Chennai? Will a local made capacitor work? Its written something like C102.

The Amp is not under warranty and the capacitor located near the Front Chanel RCA input pin. The capacitor is rated 16v and 10uF

[Sam Kapasi]

I'm not so sure if you can do it yourself. Have you any experience in repairing car amplifiers?
Removing and desoldering a capacitor is a job only for someone with experience, but taking apart a car amplifier successfully and reassembling it defintely requires someone with advanced knowledge of electronics and mechanical disassembly.

In any case, C102 in a GTO75.4 is 22mfd/16V electrolytic. See?

[ibm_jennifer]

I have opened the amplifier and found the place and broken/busted pieces of the capacitor. But I cant install it myself. Do anybody have any idea where I can repair it in chennai?

And I am sorry, it is C201. Am i right? is it blow usually, if my two wires(may be RCA inputs/Woofer output) touches by mistake?

[greenhorn]

technically, any 22mfd 16V cap will work ( just ask an electronics service centre to do it if you're not confident) . if the board(or at least the cap in question) is not soldered using surface mount, it shouldnt be too complex.

the problem is, most local electronics shops will substitute some cheap electrolytic, and electrolytics in the signal path affect sound the most. Elna, Panasonic, Nippon Chemicon, Rubycon, Nichicon, Sanyo are among the better ones,but be aware that fakes exist. Of course if you REALLY want to go overboard, something exotic like black gate...... never mind , I've gone overboard with this already

[greenhorn]

hey wait, now you're confusing me. C201 seems to be a smaller ( 102= 1nF ) polymer/ceramic capacitor. should should look like a brown disc/ rectangular green tablet with wires

[ibm_jennifer]

Friends, We have replaced two 10uf/16V capacitors, but unfortunately the amp not working for long. It cut off automatically after 2-5 minutes.

But the amp works fine(No cut off or no hum sound) without the PREAMP board(where all the Gain/control knobs are available). We have to replace the PREAMP board. Will it available anywhere, Can I get it from the official JBL distributor/pro Musicals?

[Sam Kapasi]

Hey, who gave you the figure of 10mfd.16v??

Greenhorn is correct. C101 and 201 are CERAMIC disk capacitors, 102pF (pico farad)/ 50V

[ibm_jennifer]

Its written in the capacitor itself. It also has letters like JUNZL, Am i right?

[greenhorn]

I guess we are missing something. care to post the pictures of the board? I wonder how C201 could end up as 10mfd electrolytics....Product revisions ?

btw, the failed caps maybe a symptom of something deeper. IF you are sure you replaced the caps correctly ( with the correct polarity etc) , then something else might be at fault

[DerAlte]

I think we should look at the pics of the board AND the failed component to be sure the right thing is being done.

Capacitors do fail sometimes on their own (component failure), but that is extremely rare. The only thing that can make a cap fail usually is a massive spike, which usually ruptures or dislocates body of the cap. It is highly unlikely that a 102pF 50V ceramic fails in 12VDC equipment. If one applies upwards of 200V DC or AC on a 50V ceramic cap, one will find only the leads on the PCB and minute pieces scattered on the PCB, but no smoke.

@ibmjennifer, what made you infer that there indeed was "white smoke"? Were you testing the amp when you observed it? Specifically, under what conditions did this failure occur?

[ibm_jennifer]

The capacitor failed because of my mistakes:

1. Even after I removed the SUBWOOFER, the speaker wires are left unprotected.

2. The fornt speakers are not working, instead they provide "dup dup" sound with high vibration in the diaphragm

3. The power cables are loose when I attempt to recover

4. So I went to the amplifier and try to loosen the RCA input for the front speakers. At that time the capacitor blown out with white smoke. So the problem may be because of the short circuit in woofer wire or power/ground wire or RCA wire.

We have replaced the blown out capacitors, but the original problem (dup dup sound in front speakers) still exists. Once the amp is switched on, I can hear deep dup dup sound from the front speakers even if the volume level is zero.

The electrician tested the amp and told me that one of the IC in the preamp board(there are 8 ICs) blown out and he cant replace it(as its molded). We need to provide a new PREAMP board.

So my question is, will this preamp board(which has all the Gain control knobs) available anywhere? Sam please help me.

[DerAlte]

Originally Posted by ibm_jennifer

The capacitor failed because of my mistakes: ...
The electrician tested the amp and told me that one of the IC in the preamp board ...

Thalaivar, you can take the amp to one of these 2 places:
1. Kooum
2. JBL authorized dealer (even if it is not under warranty)

There seems to be more to it than meets your eye, and definitely that of the electrician. In the circumstances you have described, the pre-amp board would be the last suspect. What did the electrician check the ICs with to infer that 1 of the ICs is bad? The 'dhup-dhup' sound is most likely to do with the output section.

Anyhow, instead of speculating, it is better that you steel your heart for a bit of expense and take the advise of the authorized dealer for the repairs, instead of making matters worse by trial and error.

[ibm_jennifer]

Fine. The electrician is not a roadside mechanic as he is servicing car ECU units himself. If he removed the preamp board, the amp is working fine and no HUM/Dump sound from the speakers. If he connects the preamp board, there is dup dup sound with hum from the front speakers without even any Audio Input. (Remember, this problem exists before the capacitor blown out and still exists even after replacing the capacitors)

The only problem is we cant source the PREAMP board in chennai. Also we cant replace the IC Chip in the board as its molded into the board.

Will this board available separately anywhere in the world?

Anyway, can you please help me to find the JBL authorized service center in Chennai?

[ibm_jennifer]

Friends,

I have One more doubt. Can I use the Amp without this PREAMP Board, Will it provide the default gain?

I have 4 JBL 607c Speakers. Can I use this Amp to power up this speakers without any Gain control or Freq. cutoff?

[ibm_jennifer]

Guys,

This what I got from the electrician:



Sam, is there anything called JBL 75.4 II