JL Audio 500/1 v1 Rev. 10 Boards #2

[RiLoWa]

I have 10v square wave on high side gates.

Wave form did get slightly cleaner grounding scope to the low side source. All square waves are probably clean and straight enough on all four gates of course including in front of the 4427.

Now should I re-connect the .010uF caps accross the gate and source of all four outputs again?

 

[Perry Babin]

Yes. That was to load the drive circuit to make sure that the signal stayed clean enough. What you're looking for is a drive signal of sufficient amplitude (~10v) and a falling edge that's close to perfectly vertical. The rising side of the waveform (the left side of the pulse) can and will be more curved.

If you get 4 good drive signals, remove all jumpers (on transistor pads and from the op-amp) and loading capacitors, reinstall the outputs, clamp all heatsink mounted components and see if the amp draws excessive current. Check the outputs for leakage from the gate to the other legs before reinstalling them.

 

[RiLoWa]

Reinstalled the caps as load, the amplifiers idle current is ~1.084A. I do not have good drive signals at the gate pads of the low-side (Q505 & Q506), but appear to have good enough elsewhere. I think that I am back to your suggestion to replace the 4427 because the IC has decent square wave on its inputs. If so, I'm glad I ordered some extra earlier.

Here is what I do have with scope set at 5V, 2uS, pictures labeled according to test points.

 

[Perry Babin]

What does the waveform look like on the output of the 4427?

If it's square and has an amplitude of ~10v, it's likely OK.

 

[RiLoWa]

Here are the outputs of the 4427, 5V and not so square.

 

[Perry Babin]

I think it's defective. It's driving the capacitor through a 100 ohm resistor so it should be almost perfectly square/vertical at the IC, especially on the rising edge.

 

[RiLoWa]

No problem, I'll replace it and post results afterward.

 

[RiLoWa]

That did it, nice ~15V square signal on the output side of the 4427.

Now I am going to check the 540's once more for leakage and undo caps, jumpers, etc and install them.

 

[RiLoWa]

I reinstalled good outputs, the amp draws ~1.585A at idle.
I have < 1mVDC accross the output terminals.
I tested with speakers and seem to have good clean output.