Rockford 500a2

[Frycztech]

Did you check the driver transistors for shorts and open junctions?

Do you have a scope?

I checked R265,R266,R267,R250,R279
R274,R275,R268,R252,R280

Is there something i missed?

No I do not have a scope yet.

 

[Perry Babin]

You have to check all parts in the red rectangles (and maybe others).

 

[Frycztech]

You have to check all parts in the red rectangles (and maybe others).

For Q220,Q221,Q222,Q223 do I test for voltage passing through? or iam I checking for the one leg of the diode?

 

[Perry Babin]

You test to make sure that there are no shorted junctions and no open junctions just like any other BJT transistor.

 

[Frycztech]

You test to make sure that there are no shorted junctions and no open junctions just like any other BJT transistor.

I belive that Q222, and Q223 are bad. They are open both ways on both legs.

Would these be good replacements?
MMBT 3906 LT1 Infineon Technologies | Mouser

SMMBT3904LT1G ON Semiconductor | Mouser

 

[Perry Babin]

I don't know what the S prefix is. The following has the original part number:
863-MMBT3904LT1G

 

[Frycztech]

what about the 3906's?

 

[Perry Babin]

The 3906 is OK.

 

[Frycztech]

Perry,

I replaced Q220,Q221,Q222,Q223, and iam still getting distortion on the right channel.

The only thing that I havent replaced in the red box's Is C225 and C226. Could these be causing the distortion/static?

 

[Perry Babin]

Without seeing the distorted waveform on a scope, it makes it difficult to know where to check. At this point, you're left to compare readings between the two channels.

Do you have an amp meter on your 12v power supply?

 

[Frycztech]

No I do not I was looking at new power supplies for something that has one built in but at this time I do not have one.

 

[Perry Babin]

Do you have any kind of current limiter that you could install in series with the supply?

A large 2 ohm resistor, an old car headlamp...

 

[Frycztech]

I have some 10ohm 3w resistors. I should have an old headlamp around somewhere.

 

[Perry Babin]

5 of the 10 ohm in parallel would be OK.

 

[Frycztech]

ok I have 5

 

[Perry Babin]

You will connect the resistors in parallel to each other then the group in series with the B+ wire going to the amp. You will then connect your voltmeter (set to DC volts) across the resistor.

The voltage across the resistor will give you an indication of the current through the resistors.

What is the DC voltage across the resistors at idle?

 

[Frycztech]

Am I trying to see the amperage coming into the amp? Can I put my DDM in series with the B+ wire to get that reading?

 

[Perry Babin]

Measure the voltage across the resistor.

 

[Frycztech]

Should I power up the remote turn on for the reading?

 

[Perry Babin]

Without remote voltage, the amp won't turn on.