Focal FPP5300 5 Channel amplifier

Good day to all. I hope all is well and good and having good repairs this past days. I have a Focal FPP5300 5 channel all in one amp. Been troubleshooting it for a couple of day now. The issue was it is in protect mode , after troubleshooting there was an input capacitor 10uf 25volts going to the sub driver ckt. output section which was deffective, after replacing I can now see the signal after the capacitor going to the sub driver circuit but does not go through the output terminal of the sub, that means no signal coming from the sub amplifier section output, and still in protect mode. But when I connect a sub woofer on the output terminal. The amp is good and goes out of protect mode. Make an audio test and all channel are working perfectly. Removing the subwoofer from the terminal then again it goes protect mode. Can anybody have an idea why this happens? Why it needs an impedance connected to the sub output terminal on order for it to work>
After further troubleshooting , I found a deffective SMD transistor connected to Pin4 of the TL494, pin 4 previously measures 5.5 volts which was to high , after replacing the transistor it went to normal 0 volt and the amp powered on normally, Funny thing was I tested the SMD transistor in my transistor tester and it was showing a good transistor but since I was not sure because I encountred the same problem of transistor in an Stetsom amp , i went ahead and replaced the transistor and thank God i found the culprit. Thank you Perry and providing the link as well.