Memphis 16-ST500D

[mike49504]

Im working on this amp someone brought to me. Im wondering what power supply fets go in it since everyone of them were cut of the board.

Second question is: what size are the internal fuses suppose to be

Any help would greatly be appericated

[Perry Babin]

I've never worked on a 500 but it's likely they used IRF3205s like the 1000.

From what I found on line, it appears that it would use two 25 amp fuses.

At least one of the driver transistors on the power supply driver board has likely failed also.

[mike49504]

Thanks Perry,
Now the other question is they also cut all the outputs off the board i believe they are 640's and 9640's But wondering if you or anyone else might know what order they go in?? Any help would greatly be appericated

[Perry Babin]

There are likely more 9640s than 640s (the amp may use 540s and 9540s if the rail voltage is less than ±50v).

All of the source legs for the 9640s will be connected directly (~0 ohms) to the center leg of the positive rectifier.

The source legs of the 640s will be connected to the center leg of the negative rectifier.

[mike49504]

Ok cool thank you perry.

! more question i was checking the driver board and a transistor marked a1023 has a leg broke off it Wondering what the part number is thata i need to order . Or can i sub this part for a differnt one ?? I have alot of a916 but not sure its the same

[Perry Babin]

The 2SA916 is not a suitable substitute.

The original (KTA1023 or 2SA1023) is difficult to find.

If you have a 2n6491, you can use that but you'll have to install it facing the opposite direction since the pin configuration is reversed.

I use the 6491s as replacements for the 2SA1266 drivers also when there is sufficient clearance. Sometimes, I have to cut the tabs off of the transistors to make them fit.

[mike49504]

With no outputs in the amp. I put in the irf3205's in the power supply and checked the drivers as soo as u apply the remote power it blows the 3205's.

Wondering what might cause this

[Perry Babin]

You should not be blowing FETs. If you clamp the FETs to the sink and either use a current limiter or a 10 amp fuse, you're unlikely to ever blow another power supply FET.

Did you check the drive signal before installing the FETs?

Have you checked all of the gate resistors?

[mike49504]

I checked all the gate resistors all check fine 47 ohm. Its been along time since i used my scope dont even remember how to use the thing wondering if u could tell me what i need the setting on to test any help would greatly be appericated

[Perry Babin]

Since some of the FETs are blown, remove all of them.

Set the timebase to 10uS.

Set the vertical amplifier to 5v/div.

When you touch the probe to the chassis ground, do you get a straight line trace with no vertical deflection (the trace remains at the reference line)?

When you touch the probe to the B+, do you get a straight line trace that's deflected ~2.5 divisions above the center reference line?