Rockford 500a2

[Frycztech]

Those resistors you linked to should be OK.

Hey Perry,

I finally got around to repairing this amp. So I replaced all the 0.1ohm resistors, all of the IRF540 and the IRF9540's.

The amp turns on the both channels play music but the right channel has static and sounds distorted.

Where is a good place to start?

Thanks for your help getting me this far.

 

[Perry Babin]

Check all of the resistors back to the driver transistors and the driver transistors.

 

[Frycztech]

What resistors would thous be? The SMD ones like R150?

 

[Perry Babin]

In red rectangles in attached diagram.

 

[Frycztech]

It seems that R274 and R275 are open and have no resistance.

 

[Frycztech]

Q120, 121 and those in similar locations in the circuit commonly fail.

R165, 166 and similar commonly fail.

All gate resistors commonly fail when the output transistors they drive fail.

D3 is likely a 33v zener in a sot-23 package.

See attached.

Perry,

Iam a little confused trying to find a replacement for D3 and the SMD resistors for R274 and R275. Iam not sure on the ratings. Is it possible for a part number?

Thank you!

 

[Perry Babin]

What is confusing?

 

[Frycztech]

I do not know the type (Thick Film, Thin Film or Metal Foil) and not sure on the power rating and tolerance. This is my first time with sms's

 

[Perry Babin]

Order by size and you will get the right power handling. They're likely 0805.

The diagram gives the power but the right size is good enough.

Thick or thin film will work.

Tolerance is the same as with through-hole. 3-value indicators = 5%. 4 indicators, 1%.

 

[Frycztech]

Order by size and you will get the right power handling. They're likely 0805.

The diagram gives the power but the right size is good enough.

Thick or thin film will work.

Tolerance is the same as with through-hole. 3-value indicators = 5%. 4 indicators, 1%.

Perry,

Would this be a good replacement?

CHP0805-JW-200ELF Bourns | Mouser

 

[Frycztech]

Order by size and you will get the right power handling. They're likely 0805.

The diagram gives the power but the right size is good enough.

Thick or thin film will work.

Tolerance is the same as with through-hole. 3-value indicators = 5%. 4 indicators, 1%.

What value in the diagram gives the power rating?

 

[Perry Babin]

The resistors are 0805 in size. That's all you need to order. The value is given in watts.

RM/10-200B - 1/10 watt 20 ohm.

RM3 for the 0.1 ohm source resistors (for comparison), are 3w.

 

[Frycztech]

The resistors are 0805 in size. That's all you need to order. The value is given in watts.

RM/10-200B - 1/10 watt 20 ohm.

RM3 for the 0.1 ohm source resistors (for comparison), are 3w.

Thank you for that Perry.

I found this:
CHP0805-JW-200ELF Bourns | Mouser

Would this be a good replacement for the amp?

 

[Perry Babin]

Yes but I'd suggest buying them in large quantities if you intend to repair more Rockford amps. Also, you can use much cheaper resistors. $2.50/100 vishay resistors are good enough.

 

[Frycztech]

Ok thank you Perry I will buy extras.

Would this be a good replacement for the D3 Zener Diode?

BZX84C33-7-F Diodes Incorporated | Mouser

 

[Perry Babin]

This is more likely identical to the original (same 81H marking).

MMBZ5257BL

 

[Frycztech]

Thank you Perry!

What do you recommend for a heat sink compound?

 

[Perry Babin]

Dow Corning 340.

 

[Frycztech]

Perry,

I replaced the 2 resisters and check all the others and iam still getting static on the right channel when playing audio through the amp.

 

[Perry Babin]

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

Do you have a scope?