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-   -   Rockford Power 650 Mosfet (http://www.diyaudio.com/forums/car-audio/195812-rockford-power-650-mosfet.html)

seankane 2nd September 2011 01:37 PM

Rockford Power 650 Mosfet
 
Hello everyone.

I recieved a Power 650 in today for repair.

The amp is acting wierd. It powers up fine and produces sound.

It has a pop when turning the volume from zero to sound on and off.

Also The rear channels work fine, but to get the front channels to work right you have to partially unplug the rca's from the rear channels.

If you unplug the rear channel rca's totally or just enough to where the shield is not touching the front channels work great. If you plug the rca's for the rear channels in all the way the front channels get very quiet and you can hear a frequency noise through the speakers.

Also the amp while trying set bias climbs immediately upon moving the pot at all.

Also wondering what the 5th pot is to the left of the bias pots??

Any help would be great.

Perry Babin 2nd September 2011 02:06 PM

Measure the DC on the input signal lines where they come into the board. Is there any significant DC there?

Do you see a shift in DC as you go from 0 to 1?

The other pot is the threshold for the thermal control for the fan.

Do you mean if you move it from fully CCW or just at some point in the rotation?

seankane 3rd September 2011 03:13 AM

Quote:

Originally Posted by Perry Babin (Post 2695133)
Measure the DC on the input signal lines where they come into the board. Is there any significant DC there?

Do you see a shift in DC as you go from 0 to 1?

The other pot is the threshold for the thermal control for the fan.

Do you mean if you move it from fully CCW or just at some point in the rotation?

There is no significant DC on the input pads the highest reading was 0.050 vdc.

I see a tiny shift when going from 0-1 volume but only a couple of numbers.

The bias pots are fully counter clockwise and when you move any of them clockwise at all the amp immediately starts drawing current.

How do I set the threshold hold for the thermal fan?

Perry Babin 3rd September 2011 03:48 AM

Have the output transistors been replaced?

To set the fan, I connect the fan and turn it until the fan starts, then back it off just a bit.

seankane 3rd September 2011 04:05 AM

I do not know the history of the amp, I suppose they could have been replaced. If so what resistor for the pot do I need to change and what value?

Any ideas in why the front channels only perform properly when the rear is unplugged or only partially plugged in to where the shield is not touching?

Perry Babin 3rd September 2011 05:03 AM

If there is no DC on the signal lines or on the shields, I don't know why it would pop. Are you using y-cables to feed all 4 channels at the same time?

I think you'd have to reduce the value of the 470 ohm resistor near the pot.

seankane 3rd September 2011 07:54 AM

Not using Y cables just feeding it from a Rockford head unit using sub output to rear and front output to front.

WHat would be causing the front to be so quiet when the rears are plugged in? This is very strange to me. Maybe something is wrong with the rear section?

seankane 3rd September 2011 08:35 AM

What issues could a bad input selector switch cause?

With speakers hooked up but no signal touching the RCA sheilds with my fingers makes god awful loud humming and wierd noises through the speakers.

When adjusting the threshold for the fan the higher you turn the pot the faster the fan goes. Once the pot gets to half it just barely starts turning. How high do I go or know what rpm the fan should be at?

Perry Babin 3rd September 2011 04:57 PM

The fan setting is a personal preference. Some people may want to allow a higher operating temperature as a tradeoff for lower noise. I set them as I described. You'll have to decide what works best for you.

The TO-92 transistor that stands up against the heatsink must be tight against the heatsink with compound applied between the transistor and the sink. It's the temperature sensor for the fan. If you touch your soldering iron to it, you'll see the fan speed increase rapidly.

A bad selector would likely cause one or more channels to be dead or intermittent.

What resistance do you read between the RCA shield and the main amp ground?

seankane 3rd September 2011 06:52 PM

Do you want me to measure with the black probe on amp main ground and red probe where the rca grounds solder to the board or at the end of the cable itself on the shield?


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