Rockford low power

[imraneesa]

Hi all,

I have this rockford amplifier, it dont have model number on it. problem is one channel not working and the output is very low.

two opamps were bad and after changing i got the other channel to work. but the output is very low. with full volume it only gives 2.5v output. amplifier picture is attached.
there is good rail voltage about 40v and up.

 

[Perry Babin]

What's the PC# under the transformer?

What does 40v and up mean?

 

[imraneesa]

What's the PC# under the transformer?

What does 40v and up mean?

PC-4333-B

i just meant to say that there is good voltage it is actually +49v and -49v.

 

[Perry Babin]

Is the audio clean but low?

Have you tried operating all switches and pots through their entire range while listening to both channels to see if the audio ever got louder?

 

[imraneesa]

Is the audio clean but low?

Have you tried operating all switches and pots through their entire range while listening to both channels to see if the audio ever got louder?

yes audio is clean. i am using 100hz sine and it is very good showing on oscilloscope. i tried gain knob and HP LP selection knob and it have some pots near rca jack and two more pots in centre i tried all but no change .

 

[Perry Babin]

Are you saying that the gain pots make no difference when adjusted?

 

[imraneesa]

Are you saying that the gain pots make no difference when adjusted?

gain pots working but it is not increasing volume so much. maximum it is outputing 3v.

 

[Perry Babin]

What is the AC voltage at the back of the RCA jacks?

 

[imraneesa]

What is the AC voltage at the back of the RCA jacks?

without rca jack plugged there is no voltage on the rca jacks.

rca cable coming from deck have 0.45v AC

 

[Perry Babin]

With the gain at minimum and maximum, what is the AC voltage on pin 1 of U104 and U404? 4 voltages.

Confirm that you still have 0.45v on the RCA input (black probe on the RCA shield).

Do you have the signal source ground connected to the 12v power supply ground?

 

[imraneesa]

With the gain at minimum and maximum, what is the AC voltage on pin 1 of U104 and U404? 4 voltages.

Confirm that you still have 0.45v on the RCA input (black probe on the RCA shield).

Do you have the signal source ground connected to the 12v power supply ground?

RCA Voltage 0.46v
gain at minimum
pin 1 of U104 is 0.375v
Pin 1 of U404 is 0v
Gain at maximum
Pin 1 of U104 is 6v
Pin 1 of U404 is 0v

yes the shied is grounded to 12v power supply

 

[Perry Babin]

What is the AC voltage on pin 3 of those ICs and pin 1 and 7 of U101?

 

[imraneesa]

What is the AC voltage on pin 3 of those ICs and pin 1 and 7 of U101?

i am sorry before voltages were given when only left channel rca jack was hooked.

Now with both left and right rca here are the voltages

U104 Pin1 - 9.5v
u404 pin 1 - 10v

Pin 3 of both IC has about 0.38v

 

[Perry Babin]

Which op-amps did you replace?

 

[imraneesa]

Which op-amps did you replace?

I replaced u102 and u103 to get channel work.

but now i replaced u104 and U404 also just to see if the problem with solve but it did not solve.

 

[Perry Babin]

How do the signal levels compare on C201 and C304?

 

[imraneesa]

How do the signal levels compare on C201 and C304?

both are good. no problem. getting good clean signals. about 9v ~ 10v

 

[Perry Babin]

Which channel is low?

Did you check signal on both sides of the cap?

 

[imraneesa]

Which channel is low?

Did you check signal on both sides of the cap?

both channels are doing same, just gain pot in one channel is giving slight problem but nothing big.
oi checked on both sides of the caps and the signal is very good.

preamp is having good signal but there is only 2.5v ac on output. dont know why.

 

[Perry Babin]

So, is the maximum output from both channels 3v AC?