fli audio amp 900s autoprotect on ?

[rob737673]

hi all, new to site but been interested in car audio since way back.my question was to see if anyone can help diagnose and possibly fix problem i.m having with my fli amp which was working fine but has now decided to stay on protection with red light. the power,remote ground are all sound and was installed professionally.i did have amp apart but made mistake of powering with board off heat sink and managed to burn out 3 fets?
(irz44n,s) which i have replaced but can anyone help with step by step checks to see if amp can be saved.thanks for reading.rob

 

[Perry Babin]

The output transistors likely failed causing the amp to go into protect. Can you post a photo of the inside of the amp?

 

[rob737673]

thanks, trying to upload but think my file size to big what best way to import pic

 

[rob737673]

pic

 

[rob737673]

should the 3 fet,s blown even without heat sink? only them three went red hot ,others fine

 

[Perry Babin]

Email me the photo.
babin_perry@yahoo.com

They were more likely to fail if they weren't clamped tightly to the heatsink.

 

[rob737673]

send it

 

[rob737673]

the pcb board not sure which is output fet is prob cause of problem?

 

[Perry Babin]

With your multimeter set to ohms, measure the resistance between the legs of each of the output transistors (large, black, fully encapsulated components clamped to the heatsink).

If you read anything near 0 ohms between the legs of any individual transistor, it's likely shorted. Remove it from the board and re-check it.

 

[rob737673]

did you recieve pic would they be the smaller one,s with silver face or larger all black ones. i think i had 0.65 ohm across one across 2 legs

 

[rob737673]

i got 0.67ohm across one set of legs and around 3 ohms across set on second transistor would that likely be fault is 3ohms considererd shorted out/faulty it only that set the other three pairs have identical readings alot higher

 

[smd1979]

I have similar problems with an FLI 800s, stuck in protect mode. Did you manage to get yours working Rob??

I currently have mined opened up, board is identical to your 900s.

 

[Mx5Mayhem]

I have a similar problem too and mine's a 900S.
Do you have any pictures from underneath the smaller PCB board of the larger board? One of my resistors under there have melted and I haven't got a clue what size it is for me to be able to replace it. It's on the left of that picture, 1st resistor on the left under the smaller board. Any help much appreciated. Thanks