Punch 500x part location?

[KyferEz]

I've got this RF Punch 500x that some idiot screwed up. The guy obviously put in the output transistors all out of order. I'd just like some verification on which is which. I think I've figured out where they go, but I would like some confirmation if anyone has any data on them.

Q310=IRF540
Q311=IRF9540
Q410=IRF540
Q411=IRF9540

THX!

 

[Perry Babin]

http://bcae1.com/temp/IMG_4129.JPG

I don't know what model this is but it has the same components/designations as your amp.

If you want to confirm, all of the IRF540s will have their source resistors connected together. The same goes for the IRF9540s.

 

[KyferEz]

These are the EXACT same boards, except that mine has 4 3300uf SMPS caps and all of the outputs are IRF540 / IRF9540. It looks like RF had two models of this amp and just used cheaper components in the lower power model. Mine is 62.5WRMS/ch@4ohm and 125WRMS/ch@2ohm.

Thanks as always Perry!

 

[Perry Babin]

If the 0.1 ohm source resistors have been replaced or opened when the outputs failed, check the 12 and 20 ohm resistors connected to them. If the source resistors are in the circuit, read the resistance carefully to determine if the resistors are intact. Generally, they show signs of damage when they open. If both are intact, you'll read ~7.5 ohms across either the 12 or 20 ohm resistor. If one is open (likely the 20 ohm), you'll read ~12 ohms.

You can contact Rockford for the schematic of any amplifier that's no longer in production.

 

[KyferEz]

Pery, you are GOOD!

3 of the 0.1ohm resistors had been replaced by the guy who butchered the outputs and on every one of them the 20 ohm resistor was bad.

Thanks for the schematic tip.

 

[KyferEz]

Ok, I ordered parts for this amp a while back, and just now am getting to it... Been too busy...

Anyway, I've replaced the IRF540 and IRF9540 with brand new parts on the bad channel and replaced all bad 20 ohm resistors so that now all of them read ~7.5ohms. All of the output resistors are good.

The amp powers up and does not draw excessive current, and plays audio out of all channels.

One problem:
One of the channels is distorted and shows about 50mV of DC on it. What could be the cause? This is on the same channel the guy had the IRF540 and IRF9540 transposed... I don't see any damage to the drivers transistors: MPSA006 & MPSA56. Not sure what else could have been damaged.

Thanks!

 

[Perry Babin]

The MPSA06 and 56 are probably not the drivers. The SMD transistors that are connected to the 20 ohm resistors are likely the drivers. Check them. Expect at least one to be defective.

 

[KyferEz]

Alrighty Perry. I've checked out all the sot23 transistors and found one that is bad in that channel. I don't know what it is though. It says 2AK but the K is turned 90degrees counter clockwise. What would that be?

Thanks!

 

[Perry Babin]

MMBT3906

The K probably means that it was manufactured by KEC semiconductors. You can use MMBT3906s from any manufacturer.

Also replace the 1A (MMBT3904).

 

[KyferEz]

Replaced them and now the amp resets itself constantly... ugh. Do you have the schematic? If not, I'll email it to you.

 

[Perry Babin]

I don't have the 500x schematic.

Is the power supply voltage dropping significantly to trigger the low voltage shutdown or is it remaining above 12v?

If you set the bias pot fully counter-clockwise, does the amp remain on?