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mike49504 5th December 2008 01:33 AM

rockford fosgate 550x
Im working on a fosgate 550x. Ive replaced the power supply fets, checked the gate resistors,and checked all mpsa 56's and 06's. When power and ground are applied NO remote the amp draws 20 amps or more of current. Wondering what do i check next im stummped

mike49504 5th December 2008 01:35 AM

Sorry forgot to metion in last post i checked all outputs, the 317's 337's and u1620's and 1620r's all check fine

Perry Babin 5th December 2008 02:21 AM

Connect ONLY remote and ground. With your black meter probe on chassis ground, what is the DC voltage on each of the gate legs of the power supply FETs?

Are all PS FET gate resistors within tolerance?

mike49504 5th December 2008 02:44 AM

All the gates measure 3.82 volts. the other two legs on all power supply fets read 13.91 volts. the gate resistors all read 10.1 ohms

Further checking in this amp it looks like the torriod got hot at one time and melted the coating off one of the leads.

So wondering where do i go from here?

mike49504 5th December 2008 02:56 AM

Sorry did that wrong the first time the gates read 10.08 volts.

The other two leads on the fets are 0 volts.

Looks like the torriod got hot at one point it melted the coating off one of the leads.

Wondering where do i go from here

Perry Babin 5th December 2008 03:08 AM

If you're reading 10v on the gates, the PNP driver transistors (likely marked 2A) are open. They will be near the TL494.

Is only one turn damaged or do you have multiple turns damaged on the transformer?

Can you post a photo of it?

mike49504 5th December 2008 03:46 AM

2 Attachment(s)
i found a couple 2a's shorted. and heres a pic of the torriod sorry my camera isnt the best

mike49504 5th December 2008 03:50 AM

2 Attachment(s)
heres a lil larger pic if needed

Perry Babin 5th December 2008 03:52 AM

I can't see enough detail on the transformer.

If only 1 winding (the terminal winding) is shorted, you may be able to desolder it and insulate it with heatshrink tubing or Kapton tape to prevent it from shorting. If there is more significant damage, you will have to get a replacement transformer from Rockford or rewind the one you have.

If you have replacements for the driver transistors, replace them and measure the gate voltage again.

Perry Babin 5th December 2008 03:55 AM

Email me the photo at the highest resolution. What camera do you have?

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