Rockford 1501bd >>> Problems e service manual

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TasoTaso

Member
Joined 2018
...i have a problem... this is the situation.

I have switch on the amplifier...the sound output but...

1- Q1 - Q3 - Q13 - Q14 (LM317 and LM 337) is very very hot, i can't touch!

2- When i turn the potentiometer of Gain up and down...the audio output increases and decreased but the subwoofer connected moves up and down....i have DC on output..

3- If i switch on the subsonic filter the subwoofer no up and down.

4 - When touch the knob of frequency crossover i can hear a buzz-humm......the knob is plastic!

..can you help me?

Sorry for my english..i'm from italy!
 
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TasoTaso

Member
Joined 2018
Hi, i'm here! :)

I measured, this the situation with amplifier without speaker and connector rca.
Only power on.

Switch Subsonic: ON
Switch Phase: 180°

TL072 - U1 output A = 0.4mV
TL072 - U1 output B = 3.3mV


TL072 - U2 output A = 5.7mV (Gain turned Left) / 0,23V (Gain turned Right )
TL072 - U2 output B = 10,4mV (Gain turned Left) / 0,24V (Gain turned Right )


TL072 - U3 output A = 12,0mV (Gain turned Left) / 0,24V (Gain turned Right )
TL072 - U3 output B = 13,0mV (Gain turned Left) / 0,24V (Gain turned Right )


TL072 - U4 output A = 0,64V
TL072 - U4 output B = 5,8mV

I have change the original potentiometer (5k)...with new potentiometer (10k)...but
but the situation is the same.
I made the measurements with the 10k potentiometer.


and now? :(
 
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Perry Babin

Member
Joined 2003
bcae1.com
U2 is likely the most significant problem.

Sometimes, the TL072s age badly and all have to be replaced.

As a side note, it won't do any harm to leave the subsonic filter engaged.

What is the DC voltage across the speaker terminals with the amp at idle?

Does it change with the position of the gain (after it has had a few seconds to settle after changing its position)?
 
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TasoTaso

Member
Joined 2018
Across the speaker terminal (without connected speaker and without signal in imput) i have 89,1mV with gain at minimum ad 89,0mV with gain at maximum.

I can't see voltage peak because i have a digital tester but..when mouve the gain knob from minimum to maximum a can see on multimiter an increase in tension which then returns to 89.1mV.

What can I do? I proceed to replace all 4 TL072? or just U2? What should I buy in TL072? Which brand? Do they have to be all the same?

Many thanks :)
 
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