Rockford Fosgate Punch 240x4 DSM

[seankane]

Hello everyone.

I have a Rockford 240x4 board number PC-0952-D REV D Punch 240x4 transoar 05/23/95.

This amp is stumping me. The amp has no sound. The amp powers up and idles fine, does not draw excess current. There is no DC on the output terminals.

The amp has 61.7 vdc rail voltage. The positive and negative regulators are out putting fine. I have +/- voltage on the supply pins of all the op-amps.

Checking with my scope, I have audio on pins 1 and 7 of all the op-amps. I also have audio signal on the bridging output terminals. All signals look just like the input.

I have audio signal on the drains of the output fets too.

I have 0.000 vdc from gate to source (blk prb on srce) on all of the output fets.

U2 LM339M reads as follows:

pin 1: 3.850 vdc
Pin 2: 6.06 vdc
pin 3: 18.36 vdc
pin 4: 0.318 vdc
pin 5: 2.580 vdc
pin 6: 4.98 vdc
pin 7: 6.40 vdc
pin 8: 4.34 vdc
pin 9: 4.98 vdc
pin10: 4.98 vdc
pin11: 8.20 vdc
pin12: 0.002 vdc
pin13: 6.06 vdc
pin14: 6.06 vdc

The transformer is not getting hot, but it remains warm to the touch after the amp idles for a few minutes.

I find it very strange that I have audio signal on the bridging terminals but no sound. Is there something I am missing?? Any help would be great.

[Perry Babin]

I think you have a blown speaker or a bad connection if you connect the speaker and have signal on the bridging terminal and no signal on the non-bridging terminal.

[seankane]

The speakers are good they are the speakers I use on a daily basis for testing on my repairs. I tried changing the 2 channel 4 channel switch on the board and I have tried different x-over cards. The scope will trigger fine showing audio and clipping.........but no sound.

I dont understand. My scope settings are 50m vol/div 5us probe set to 10x.

[Perry Babin]

Turn the amp off and measure the resistance across the speaker terminals (speaker connected). What's the resistance?

At 50mv and 5us, you're not likely to see anything significant. Set it to 5v/div. Touch the probe to the positive terminal of your power supply and confirm that the trace deflects up about 2.5 divisions. Set the timebase to 2ms. With these settings, what do you see on the bridging speaker terminals?

[seankane]

I noticed someone has changed the output fets before I got the amp. The IRF540N and IRF9540N were used. Maybe they are in the wrong location?

[seankane]

Originally Posted by Perry Babin

Turn the amp off and measure the resistance across the speaker terminals (speaker connected). What's the resistance?

At 50mv and 5us, you're not likely to see anything significant. Set it to 5v/div. Touch the probe to the positive terminal of your power supply and confirm that the trace deflects up about 2.5 divisions. Set the timebase to 2ms. With these settings, what do you see on the bridging speaker terminals?

Im sorry my scope setting were 50m vol/div and 5ms not us. Probe set to 10x. I bridged the speaker to the bridging terminals amp off and it measures 4.1 ohms. With the amp powered up with the settings you requested I cannot get the scope to trigger at all touching the positive terminal on the power supply. With the same settings I see nothing but the basline wobbling a little on the bridging terminals. If I set the scope to .2 vol/div 2ms and 10x probe then I see signal on the bridging terminals.

Thoughts??

[seankane]

Moving the probe to 1x scope set at 5vol/div and 2ms I see a signal on the bridging terminal but it only deflects 1/2 a division. It is audio from what I can tell and does clip at full volume but not much of a signal. I get alot better wave form on 2 or 1 vol/div.

[seankane]

I have 7.50 vdc on the gate legs of the p/s fets. Isnt that a bit much or no?

[Perry Babin]

Did you touch the probe to the B+ terminal and confirmed that it deflected 2.5 divisions?

[seankane]

Yes in my reply above I mentioned that I did and was not able to get the scope to trigger at all. The baseline jumps up 3 divisions but remains flat no wave form and the scope does not trigger.