Rockford Punch 250x2 repair

[dhamia]

Hi folks I picked up this dead Rockford, internal inspection shows 2 transistors (numbered 2,3) are now toast!

The amp powers up but I haven't tested for sound as I don't want to damage it further.

My questions are-

1-What are the blown transistor details?
2-Would you suggest replacing just the blown transistors or all the power supply transistors?

Thanks in advance for any useful advice.

[Perry Babin]

You must replace all 6 power supply FETs (3/side). The gate resistors (connected to leg 1 of the power supply FETs) have possibly failed (check after removing the FETs). The PNP driver transistors for the power supply FETs may have failed.

Shorted output transistors could have caused the power supply to fail so those need to be checked.

[seankane]

Start by replacing Q6, Q7, Q8, Q9, Q10, Q11 which are the power supply fets. The originals will be either IRFZ40 or MTP50N06V. Replace them with IRF3205 which are readily available and cheap.

Next replace the gate drive resistors for the power supply fets. These are R46, R47, R48, R49, R50, R51 and are hooked to the gate leg of each power supply fet. Use 0805 SMD 47ohm resistors for these.

Always check D100 and D101 as sometimes these blow when the power supply goes, but sometimes they are fine. These are a IN5336B, you can use a close substitute for these.

Next replace Q2, Q3, Q4, Q5 which are the pnp and npn driver transistors for the the power supply. The are usually marked 1AM and 2A or close. You can order them from mouser electronics.

1A or 1AM = MMBT3904

2A = MMBT3906

You can use those part numbers when ordering.

After all this is replaced check for shorted output fets BEFORE powering up the amp. If you find any clip the fet out of the circuit. Turn the bias pots fully counter clockwise they are RV5 and RV6 locations on the board.

Put a 10 amp fuse inline with the B+ and power up the amp. Make sure the amp is clamped tightly back into the heat sink before doing so just to be safe. If all is well then begin repairing the output section.

Common problems are shorted fets and or open gate resistors. Faulty source resistors, etc. when you get to that point I will be glad to assist you.

Keep us posted.

[dhamia]

Thank you gents for the prompt and comprehensive replies, I will go with Seankane's advice and replace all the components in question and reply back soon, thanks to Perry too