PPI 6600.2 Turns on and off

[Perry Babin]

Sometimes, only 1 of each shorts and reinstalling the remaining ones that weren't defective allows you to continue troubleshooting.

Order replacements. Also order several of the small transistors in that area (MPSA06 and MPSA56?). Check all of the resistors near the outputs.

Digikey and mouser are good distributors. Don't buy semiconductors from eBay.

 

[cory1504]

I'll go ahead and order these replacements from mouser. Should this fix my problem once these are replaced? By the way what part of Louisiana are you in? I'm originally from New Orleans, but moved to Texa about 5yrs ago.

 

[cory1504]

One more thing. The number on these transistors is 2N 6491 and 2N 6488. There's a 2N6488G and a 2N6491G from Mouser. Does the "G" make a difference?

 

[Perry Babin]

It may be the only problem but you may also have defective driver transistors. That's why I suggested that you order them.

When you power it up initially, you'll need to do so with a 15 amp fuse (nothing larger) in series with the B+ line. The cover will have to be clamped tightly on the transistors. Don't crossthread the screws when reinstalling them. If you strip the threads, it can be a pain to repair and the amp won't be reliable without having all screws applying pressure.

I'm in Gonzales.

 

[Perry Babin]

The G means that they're lead free. They're essentially the same as the ones that contained lead.

 

[cory1504]

Hey Perry, I just finished changing those transistors. Is there anything else I need to do before testing?

 

[Perry Babin]

Did you replace the driver transistors?

 

[cory1504]

I changed four of the transistors. The four that are on the bottom right of the pictures. Which ones are the driver transistors?

 

[Perry Babin]

The drivers are the MPSA06s and MPSA56s. At least check them to confirm that none of the drivers for that channel are shorted.

If none are shorted, replace the cover and tighten all of the screws. Insert nothing larger than a 15 amp fuse in the B+ line and power up the amp.

Does it blow the fuse?

Does it produce clean audio from that channel?

 

[cory1504]

No, I didn't change those, but I do remember you said to earlier. Can you tell me where they are from this picture? I have no idea what MPSA06 or MPSA56 means or looks like and I don't see anything in here with those #s on it.

 

[Perry Babin]

They look like the MPSA06/56 that you ordered and should actually be MPSA06s and MPSA56s.

They will have their first leg connected to a 100 ohm resistor (brown, black brown, gold) if this amp is like the 4400.2.

 

[Dr Zeus]

MPSA06/56 should be much smaller than the outputs you just replaced. They are likely about 1-2 inches inword from the outputs you just placed. They are three legged transistors... Perhaps the MPSA portion says something else, but they should still have 06 or 56 written on the transistor.

I just fixed two of these; you are on the right track and very close!

Also, it looks like someone already replaced some pieces in your amp; two of the large resistors are different from all the others. Make sure all are w/i tollerance as well as the transistors measuring equally next to any previously changed out. Make sure all those large resistors are w/i tollerance.