Amp turns on for 1ms then shuts off - Works on external battery but not in the car
Hi everyone,
I'm hitting a wall with my car audio setup and could really use some expert advice. I have a Blaupunkt amplifier (around 750W) powering a JBL 1000W peak subwoofer. Everything was working perfectly for 3-4 months, and then it suddenly stopped while I was driving.
My setup:
- Power: 12V constant from the battery via an inline fuse.
- Ground: Connected to the car chassis (Peugeot 106), going through a capacitor before hitting the amp.
- Remote: Connected to the head unit's ignition wire (plus après contact).
- Vehicle: 1999 Peugeot 106 (very humid environment recently due to heavy rain).
Voltage measurements at the amp terminals:
- B+ to GND: 12.5V (engine off) / 14V (engine running).
- Remote to GND: 12.5V (radio on) / 0.3V (radio off).
- The capacitor display shows stable voltage even when I try to start the amp.
The Mystery: When I try to turn it on in the car, the power LED flashes for a millisecond, the sub makes a tiny "thump" sound, and the amp immediately shuts down.
What I've already tested:
- Bench test: I took the amp out and connected it directly to an external car battery. It works perfectly there.
- Without Capacitor: I bypassed the capacitor in the car—same issue.
- Without Speakers/RCA: I tested the amp "naked" (only Power, Ground, and a jumper for Remote)—same issue, it won't stay on.
- Jump start: I tried jumping the Remote terminal directly to the Amp's 12V B+ terminal—still shuts off.
- Battery variation: Strangely, it works on some external batteries but not on others, and definitely not on my car's battery (even though the car starts fine and the multimeter shows 14V when running).
I suspect a grounding issue or a "phantom voltage" that collapses under load, but I can't find where. Does anyone have an idea why an amp would work on a bench but refuse to stay on in the car despite having 12V-14V at the terminals?
Thanks for your help!