kx 800.4 issues

have issues with a kicker kx 800.4 amp keeps going into protection mode the amp is bridged running 2 10" cerwin vegas 4 ohms svc rms 1200watts. Amp was working fine for 3 months. I unhooked subs turn on head unit still goes in to protect mode. checked my ground my meter its good. I have 4 ga power & ground. I hooked the vegas to the other amp KX 600.2 the worked fine the amp did not go in to protect mode. The KX 600 is working fine no issues. The gains on the 800 set less than 1/4 of the way up. So thats the problem I have any

help would be great ( yes I know there kickers that could be the issue, Told my son should have got Memphis

The amp has shorted output transistors.   It is a very simple repair if you have even basic soldering skills.  Let me know if you are going to attempt the repair, I can walk you through it.

This is a picture of the 650.4, for all practical purposes it is the same as your amp.  https://ampguts.realmofexcursion.com/Kicker_KX650.4/inside1.jpg  The area to the left of the picture is the power supply section.  To the right of the yellow capacitors are the output transistors.  You can easily get to 2 channels of the amp, the other 2 channels are located below the preamp board.  To remove the preamp board there are 3 machine screws that go through that board.  Remove them and put separate of the other screws.  Then remove the 4 screws that secure the endcap to the heat sink, then remove the screws from the RCA jacks.  Remove the end cap and lift the preamp board straight up.  Now you can get to all 4 channels of the amp.  Using a meter set to the diode test function, place the black meter lead to the center leg of one of the outputs, now the red lead to the rightmost leg of the same output transistor.  Notice the reading, repeat for the other 7 output transistors.  One or 2 of them will read significantly lower than the others.  Before you remove the clamps off of the transistors, notice the difference of the 2 clamps under the preamp board.  Make sure you put those clamps back in the same place and in the same manner they came out.   If you find the shorted ones, they need to be replaced.  If only one is shorted, I would still reccommend replacing both on that channel.  I do not remember if they are TIP35C and TIP36Cs  or  2SB688 and 2SD718s.  Either should be easy enough to locate.  Do not attempt to remove the board from the heat sink without further instructions.  Let me know what you find out.

What are the numbers on the transistors?   If they are TIP35 and 36 I would look into Motorola brand.  Available at digikey.com or mouser.com.  The 2SB688 and 2SD718 are available at MCM Electronics.  They do have a website you will have to search for it.  1-800-543-4330 

Yes you are correct.  The only pic I had access to was the 650.  It has one each per channel.  Your amp has 2 each 35 and 36 on each channel.  Using your meter you can figure out which of the 2 are shorted by following this procedure.  Black lead on middle leg red lead on the leftmost leg of the same teransistor.  One of the 35s will read lower than the other.  Figure out which one is reading the lowest and cut the legs off of it.   Do the same for the 36s.  Then you can clamp the transistors back down, put a single 10 amp fuse in the amp and power it up and see if it works again.  Do not play it loud at all.  Just make sure it has clean audio and no protect light.  If it is as stated, all you need to do is replace the 2  35s and 2 36s.

The green stuff behind the transistors is a heat conductive tape.  The transistors are probably stuck to the heat sink with that tape.  The safest way to get them up is to take a pair of pliers and grab the transistor on the sides and rock it genly off of the heat sink.  Make sure you do not tear the tape.

I just looked at your picture and noticed that your amp unlike the 650 has 2 power supplies.  Try putting 5 amp fuses in every slot.  Let me knwo what happens.