Crossfire XP1400 D

[S Merlington]

This amp powers up and plays perfectly on the bench..

Once installed in a vehicle it does some crazy things..

First thing it does is cut on and off it also gets really hot fast and it has feekback thru the sube almost like theres a rca shield ground issue..

I removed the board from the sink and first thing i noticed is the amp has been repaired before..

The amp uses IRF640N's and IRF9640's as the outputs..

1 side of the outputs are the orginals IRF640N's and IRF9640's
the other side has been replaced with IRF640's (no N suffix) and IRF9640's

Since some of the 640's have the N suffix and some dont would that cause a problem that im having with this amp?

Also i found some 1 watt resistors that are 4.7K But are measuring 3.88K
So think about replacing them..

Wondering if the outputs could cause this or wondering where i should start checking ?

[Perry Babin]

Did you check the shield ground for the signal source?

Does it make any strange noises or get hot with no RCAs plugged in?

[S Merlington]

I hooked the amp up in 3 seperate cars with different head units and sub woofers..

Amp does the same thing..

It gets warm even with no RCA's plugged in..

Thoose resistors i refered to in Post 1 Measure 3.83K but are suppose to be 4.7K Wondering are they out of tolerance?

[Perry Babin]

Post a photo of the inside of the amp.

The tolerance is determined by the last color band. Most are ±5%.

[S Merlington]

Here are some pics of the board

[Perry Babin]

For the 4.7k resistors that have the over-heated solder connections, remove them, clean the terminals (with sandpaper if necessary) and resolder them from both sides of the board. Clean the pads up before resoldering them.

[S Merlington]

Ok I cleaned the pads and resolderd the resistors in from both sides of the board..

Anything else i should check before putting the amp back together?

[Perry Babin]

Look for anything obvious.

You could confirm that the 12v zeners have approximately 12v across them. They are the SMD diodes near the large 4.7k resistors (not the ones you cleaned up).

[S Merlington]

I checked the diodes everyone of them has 11.65 volts across it..

I noticed all the IRF640's get really hot within a min with the amp just idling no rca's plugged in

[Perry Babin]

If it's not drawing excessive current, this may be normal. After clamping the FETs to the sink, let it idle for several minutes. Does the part of the heatsink behind the 640s get appreciably hotter than the rest of the heatsink?