Have a Fosgate on the bench, came in with blown pair of PS FETs. Replaced those, the gate resistors and driver transistors, but still has an odd symptom- scoping the drain leg of the FETs reveals a sine wave not a square wave.
With the drivers removed I’m getting good square waves from the 494 so that’s still good, and the PNP side of the totem has good continuity to ground. What resistance should the NPN drivers have to B+ though? I would have expected 10-100 ohms or something like that, but it just keeps counting up like it’s charging a cap somewhere.
With the drivers removed I’m getting good square waves from the 494 so that’s still good, and the PNP side of the totem has good continuity to ground. What resistance should the NPN drivers have to B+ though? I would have expected 10-100 ohms or something like that, but it just keeps counting up like it’s charging a cap somewhere.
Didn’t think it would, but I got down to around 5v input and it changed into a square wave. Bringing the voltage back up only results in it screaming at me and drawing a bunch of current, WTF?
The amp shouldn't run at 5v. The low voltage protection should engage about 8-9v.
I don't know why it it's having a problem with the increasing voltage. What's the DC voltage on pin 12 of the 494 when the amp is at 5v?
I don't know why it it's having a problem with the increasing voltage. What's the DC voltage on pin 12 of the 494 when the amp is at 5v?
Pin 12 stays at 13v no matter what input voltage is doing, guessing there’s an internal power supply for the control circuits?
Initially (before PS start), the PS ICs are powered by remote (which is why you can get drive without B+).
After the PS comes starts, the positive regulator (LM317) supplies power to the ICs.
Check the voltage on the voltage divider resistors for the high/low voltage protection. The low voltage protection doesn't seem to work if the amp operates at 5v.
After the PS comes starts, the positive regulator (LM317) supplies power to the ICs.
Check the voltage on the voltage divider resistors for the high/low voltage protection. The low voltage protection doesn't seem to work if the amp operates at 5v.