rockford fosgate 1000bd

[mike49504]

hi on this amp when speakers are connected the subs suck in someone told me the negitive rail is on all the time what do i check on this amp to find the problem amp powers up but speakers suck in

[Perry Babin]

Assuming that you've checked all of the outputs and none are shorted, and it does not draw excessive current when no load is connected to the speaker outputs...

Post the DC voltage on all of the pins of U17 (should be an LM6171).

Do this with the amp powered up and no speaker load.

As a side note, this amp retains significant energy in the caps. They must be discharged before you do any work on the amp. This needs to be done every time the amp is powered down. If you have a high power dummy load, short it across the large red and black (twisted together) wires (after the amp is switched off).

[mike49504]

i checked the outputs 6 irf6215 are blown so im gonna replace thoose what else do i check since the outputs are bad?? and i appericate all your help thanks a million

[Perry Babin]

If all of the 6215s are blown, you must also replace all of the 3415s.

Check the gate resistors for all of the output FETs. They often open with no visible signs of being defective.

On the MIC4420 drivers, you should not have any low resistance (near 0 ohms) between any of the pins except 2 and 4. Check both drivers. You may need to do this after you remove the blown FETs to prevent the shorted FETs from giving false readings. If the driver has shorted, there may be other damage that can be difficult to find. If the drivers survived, it's likely that the only damage is to the outputs and possibly the gate resistors.

[mike49504]

where are the mic4420's located on the board i cant seem to find them maybe i need new glasses lol thanks

[Perry Babin]

They are in a heatsink like the regulators. Instead of having 3 legs, they have 5.

[mike49504]

ok i see them how do u check thoose to see if they are bad what pins do u probe with a multimeter?

[mike49504]

i got this amp back again and doing the same thing once again when the amp is playing it makes the speakers flutter (bounce up and down) i checked the rca shields and there is no ground present at the rca inputs wondering what i might check to find the problem thanks

[Perry Babin]

The shield ground should have no direct connection to chassis ground unless there is a defect like a shorted diode.

You said it's doing the same thing but the top of the post indicated constant DC (pulling the woofer in). Are you sure it's the same problem?

Is the problem the same whether in the vehicle or on the test bench?

[mike49504]

i powerd up the amp on the bench and looked at the sub to see what the guy was talking about with the gain all the way down u can hear a lil distorion on the sub when u start turning the gain up lil by lil the distorion goes away but u can watch the sub flutter move up and down i checked the rca grounds and replaced them due to the fact the rca ground where broke off the board so thats fixed the i was doing a visual on other parts and came across the cap in the power supply thr pf2475-nd 4.7 mf 250 volt with a broken lead on it so i replaced that powerd up the amp and doing same thing the speaker flutters a lil and the lm317 and lm337 get hot really quickly but the amp still plays but with the speaker flutter prob wondering where i might go from here what do i check?