Rockford Fosgate Power 1000a2

seankane · 2011-04-05 3:56 am

Hello again Perry. I have a rockford power 1000a2 that is doing something I have never encountered before. The board number is a PC-2392E.

The right channel never had any sound when I recieved the amp about 5 years ago. Since then I have come along way in my repairs, so it was sitting on the shelf collecting dust and I kinda just found it again.

I replaced all the output fets in the right channel years ago and never went any further. The left channel has great sound. The right channel has great sound for about 3 seconds then just fizzes out to nothing at all. Amp idles fine no current issues. Can I get a heads up on where to start??

seankane · 2011-04-05 4:01 am

I must add the right channel will not bias either.

Perry Babin · 2011-04-05 4:13 am

Drive a sine wave into the amp with a speaker (or dummy) load on the right channel. Snap a photo at the point where it begins to fade out.

seankane · 2011-04-05 4:21 am

Ok I will try but it happens so fast. I hear the sine wave clear and loud for a few seconds then it gets real quiet. You can still hear the sound but at very low volume. No matter how loud you turn the volume it just stays at the same low volume. Does not sound distorted either, just really quiet. If you turn the amp down then back up it is loud for a second or 2 then like someone is turning down the volume. Like waiting for a cap to charge then discharge ya know? I will try my best to snap a pic. Scope settings? 5vol/div 5 us ?

Perry Babin · 2011-04-05 4:24 am

I guess I didn't understand 'fizzes out'. I would have expected distortion. If it's not distorted, don't worry about the photo.

Perry Babin · 2011-04-05 4:27 am

Check the signal level on the positive terminals of C304 and C201. Do they remain the same when the output drops on the right channel?

seankane · 2011-04-05 4:28 am

Sorry I should have been more clear.

seankane · 2011-04-05 4:32 am

Ok I will have to pull the board from the sink to get to the + terminals of those 2 caps. Give me a liitle bit, lotta screws to pull

seankane · 2011-04-05 4:45 am

No the signal does not change only in amplitude as you increase the volume. Both sides look identical, when the sounds drops off with a speaker connected and without a speaker connected. The signal is different from idle to volume but I think its just amplification. Would you like a photo of idle and volume output on the scope from the positive terminals from those two caps???

Perry Babin · 2011-04-05 5:01 am

You should have asked if you could use a different test point.

Are you saying that, at that point, the signals remain identical in amplitude at those caps both before and after the signal drops on the right channel?

seankane · 2011-04-05 5:14 am

Correct they remain the same in amplitude before and after the sound drops off. I have the scope set to .2 vol/div and 5us

The sound drops off really fast like almost instant. When you increase the volume the amplitude increases at both points and looks identical at both points.

Shall I use a different test point?

Perry Babin · 2011-04-05 5:29 am

With no audio, does the voltage across R208 and R308 remain the same after the point where the audio would drop off?

Look at the signal on the speaker terminal of the right channel and confirm that there is no distortion after the level drops.

seankane · 2011-04-05 5:43 am

Perry Babin said:
With no audio, does the voltage across R208 and R308 remain the same after the point where the audio would drop off?

Look at the signal on the speaker terminal of the right channel and confirm that there is no distortion after the level drops.

With no audio the voltage on R208 is -8.69vdc
With no audio the voltage on R308 is +8.69vdc

I have not checked these with audio but without they hold that voltage and do not chabge.

The right channel output looks nothing like the left. The left looks just like the signal on the + terminals of the caps I tested.

The right channel at idle has a giant saw tooth wave form and then when volume increses it goes nuts all over the screen and is not readable.

Make any sense?

seankane · 2011-04-05 6:12 am

I am including three pics the first is at idle, second volume at 2, third volume at 4, after that you cant even see it. These are from the faulty channel.

Perry Babin · 2011-04-05 3:07 pm

Do you have rail voltage on that channel after the audio level drops?

seankane · 2011-04-05 9:23 pm

Perry Babin said:
Do you have rail voltage on that channel after the audio level drops?

Hello Perry.

Upon checking the rail voltage, the good channel has rail voltage on the drain which is 65 vdc and 7.5 vdc on the gate but nothing on the source.

The faulty channel has no rail voltage at any time, with or without audio.

Any thoughts??

seankane · 2011-04-05 9:28 pm

The power supply fets for that channel (assuming the amp has separate power supplies for each channel) have 13.87 on the drain and source but 0.00vdc on the gate legs. Is that half of the amp not turning on? Do I have defective power supply fets or a defective transformer for that channel?

seankane · 2011-04-05 9:31 pm

The power supply fets for the good channel have 6.5 vdc on the gates, 13.87 vdc on the drains, and 0.00 vdc on the source.

Kinda odd?

seankane · 2011-04-05 9:58 pm

What supplies the power to the gates of the power supply fets? Obviously that is where I should be looking because the other side is getting power to the gates. There is 2 TL494C PWM chips one for each channel shall I post voltages from the faulty channels PWM chip?

Perry Babin · 2011-04-06 2:17 am

If the source leg isn't at ground, you have an open trace.

Rockford Fosgate Power 1000a2

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