HELP! Fosgate 600A4

[Brain Fried]

I picked up a 600a4 the guy i got it from told me it gettint really hot and shutting off so i did a bench test and it drawing 9amp's at idol so i take a look inside the amp and to my surprise someone turned all four gains all the way up so i turned them down new it's only drawing 1/2amp. Here my question how do i set them back right without a oscilloscope ?

[Perry Babin]

The potentiometers that are not accessible with the cover in place are the bias potentiometers. If you have an amp meter on your 12v power supply, turn them clockwise until you just BARELY see an increase in current draw. Do this for all 4 channels. The current draw should be well below 2 amps after they're all set.

You MUST have all semiconductors clamped tightly to the heatsink when doing this.

[Brain Fried]

Originally Posted by Perry Babin

The potentiometers that are not accessible with the cover in place are the bias potentiometers. If you have an amp meter on your 12v power supply, turn them clockwise until you just BARELY see an increase in current draw. Do this for all 4 channels. The current draw should be well below 2 amps after they're all set.

You MUST have all semiconductors clamped tightly to the heatsink when doing this.

So like 1.5 amps what i should aim for?

[Perry Babin]

You should adjust each one to the point to where the current draw just BARELY increases. The total current draw isn't critical but it shouldn't be excessive.

[Ground Zero]

Hi

for my punch 200.4 i set the bias current to 4.5mv with my multimeter on each 0.1ohms resistors and it works good without heat, i use the service manual of rockford to do that

[Brain Fried]

OK i think i got it now it idling at 1.57amp's and i let it set for a hour at idol and it stayed the same and the bias on all four is set at 3.61mv any higher and it starts draw a lot of current then i let the amp run for a hour at 3.4 volume it got nice and warm but did not shut down the one thing i did notice the rear right & left is running hotter then the front right & left is that some thing i need to worry about? and the two transistor's in the center of the 600@4 U3 & U4 get quite warm at idol is that normal? And all four channels nice and clear.

[Perry Babin]

Did the idle current remain at ~1.5 amps after the amp was hot (you need to run it until it's too hot to touch)?

The bias current on the rear channels may be drifting when it's hot. If it's not holding, you need to reduce it a bit.

Do the regulators get hot when clamped to the heatsink?

[Brain Fried]

Originally Posted by Perry Babin

Did the idle current remain at ~1.5 amps after the amp was hot (you need to run it until it's too hot to touch)?

The bias current on the rear channels may be drifting when it's hot. If it's not holding, you need to reduce it a bit.

Do the regulators get hot when clamped to the heatsink?

The regulators and the output transistor's are cool to the touch even when the heatsink is hot and the idle current go's to 1.73amp's after i get the amp really hot but drop's back to 1.57amp's pretty quick after input signal is off the only two that get hot at idle is in the picture below i am not sure what they are regulators or transistor's i can't read the numbers because of the heatsink

[Perry Babin]

If that's U3 and U4, those are regulators. It's normal for them to produce a lot of heat.

[Brain Fried]

Thanks Perry everthing seems to be good the amp is running a lot cooler and idle is staying about 1.60V and all four channel's are playing clear.