Capacitor doubt

[imraneesa]

hi all,

I have this amp with shorted output transistors for one channel.
There is a capacitor that connecting rca input positive signal to the secondary ground via a resiator. The designation on the board shows as it is ceramic disk type capacitor but I found 10uf 16v caps. I found those caps burst for two channels. Others two values gone too low. I expecting if somebody had interfered with them or I dont know if it is factory itself. Attaching image of C301 and C401.
Please suggest what to use.

 

[Mooly]

A 10uF cap would never be found connecting an audio input to ground... it would short the audio.

Small value ceramics are reasonable and would be used to provide RF suppression.

Is this a car amp?

 

[Mooly]

Is this a car amp?

Ignore that bit I thought it was posted somewhere else.

 

[imraneesa]

Yes it is car amplifier. Then this is very strange.

 

[Mooly]

Very strange... it does sound like it has been 'got at' then.

 

[Perry Babin]

Post a photo showing about 1/4 of the bottom of the board, including the RCA jack corner of the board at one corner of the photo.

 

[imraneesa]

Picture attached.

 

[Perry Babin]

Is this a JBL 75.4

 

[imraneesa]

It is infinity Reference series amp.

 

[Perry Babin]

For you or anyone asking for help, PLEASE do all you can to help those who are trying to help you and including the make/model number in the subject line would be a huge help.

What is the model?

 

[imraneesa]

Noted. I did not see model number on amp so did not mention.. after looking around i found it on side plate.. sorry about that.. Reference 7541A

 

[Perry Babin]

The 7541A has 10uF caps in those locations. The older (similar) amps (both JBL and Infinity) have 1000pF caps in those locations.

 

[imraneesa]

So i can 10uf polar electrolytic caps?

 

[Perry Babin]

Are you asking if you can use polarized capacitors?

What was in the amp originally?

The diagram shows polarized caps but the note for them is cut off at the bottom of the page.

 

[imraneesa]

Ok great. Yes it had polorized caps. All the confusion arised as the markings on the amp did not show like it is polorized. Thank you.

 

[Perry Babin]

Before you reassemble the amp, confirm that you have no DC voltage on the RCA shields (black probe on the primary ground). Twist the transformer while monitoring the shield voltage to confirm that it remains at 0v.