Punch 150s/Power 550s

[Perry Babin]

What do you get from the right channel?

 

[neela30]

I'll have to check tomorrow.

 

[seankane]

The source resistors are .1 ohm 3 watt

 

[neela30]

Thanks sean!

No audio but 40v on right output.

 

[Perry Babin]

With the black probe on the amp's ground terminal and the red on the right negative speaker terminal, do you read positive or negative 40v DC?

 

[neela30]

Negative.

 

[Perry Babin]

What's the PC- number on the board?

 

[neela30]

3382-B

 

[Perry Babin]

I don't have this diagram. The one I have labeled 550S is a different board. If no one else has it here, you'll need to get a copy from Rockford and email it to me.

babin_perry@yahoo.com

 

[neela30]

I've requested one from Rockford directly. I have yet to get the email.

 

[neela30]

Email sent.

 

[neela30]

R265,266,274 and 275 check out.

Q220 +40v

Q221 +15.2v

Q222 -13.8v

Q223 -39.8v

 

[Perry Babin]

You need to check those transistors with the meter on diode-check and no power applied.

If you don't know how to test them, use the applet linked from the following page.
Basic Amplifier Repair - Transistor Test Applet Link

 

[neela30]

 

[Perry Babin]

In order from top to bottom...

* shorted/leaky
* open base to emitter
* probably OK but slightly leaky collector to emitter. Could have been caused by touching the probes
* also appears to be leaky

I'd suggest replacing all of them.

 

[neela30]

I'm looking at some of my options (on my phone at the moment) and notice one has a much higher power dissipation rating. Should this be a viable choice?

MMBT3904LT3G ON Semiconductor | Mouser

 

[Perry Babin]

Use/order the MMBTA06 and MMBTA56.

 

[neela30]

I installed and checked everything and it seems the only thing that has changed is the right channel output is now -44v instead of -40v.

I guess this amp is making up for how easy the 150 was to repair!

 

[seankane]

Are you sure you don't have an open source resistor or a bad output?

Sometimes they can fail during replacement.

 

[neela30]

Anything is possible. I haven't had much time for thorough testing. I may need to pick up a magnifier to look over some of the delicate solder points. They look great to the nekkid eye but I also realize that type of soldering shouldn't be done after consuming nearly a pot of coffee ...