Rebuilt Amp & Head Unit but no sound

[Aleman]

Hey E30 hive,
I have installed in my E30 a professionally refurbished CM5908 head unit (HU) and factory premium sound amp. The system worked beautifully for a couple of days then stopped outputting sound. Now when I turn on the radio, I hear the amp power on with a click, but I get no sound from the speakers.

I've checked the connections on the back of the HU many times, and looked for broken wires in the dash behind the HU. Where would you check next?

E30 Model: 1990 325is
HU Model: CM5908 (rebuild and doublechecked by Dr Don's - I sent it back to them, and it's confirmed to work)
Amp: Factory (rebuild by bradnic of OEM HiFi)

Thanks for the advice.

[bradnic]

Hey E30 hive,
I have installed in my E30 a professionally refurbished CM5908 head unit (HU) and factory premium sound amp. The system worked beautifully for a couple of days then stopped outputting sound. Now when I turn on the radio, I hear the amp power on with a click, but I get no sound from the speakers.

I've checked the connections on the back of the HU many times, and looked for broken wires in the dash behind the HU. Where would you check next?

E30 Model: 1990 325is
HU Model: CM5908 (rebuild and doublechecked by Dr Don's - I sent it back to them, and it's confirmed to work)
Amp: Factory (rebuild by bradnic of OEM HiFi)

Thanks for the advice.

Dude give me a call happy to assist.
Working install, rebuilt radio and amp, you hear the amp click, no sound?
All 4 channels going silent with rebuild equipment is unusual for sure. Try switching the input source on the radio first (tuner, tape). If you have a BT retrofit check BT and aux too.

If changing sources doesn't help, then I'd start with the amp. I can send you an amp bypass adapter for testing.

[Aleman]

Dude give me a call happy to assist.
Working install, rebuilt radio and amp, you hear the amp click, no sound?
All 4 channels going silent with rebuild equipment is unusual for sure. Try switching the input source on the radio first (tuner, tape). If you have a BT retrofit check BT and aux too.

If changing sources doesn't help, then I'd start with the amp. I can send you an amp bypass adapter for testing.

Thanks! I gave the tape play function a try but still no sound. Is this the bypass adapter you mentioned? I don't think I got it from you, but it may do the same thing... I'll have to mess around with it this weekend.

[bradnic]

Thanks! I gave the tape play function a try but still no sound. Is this the bypass adapter you mentioned? I don't think I got it from you, but it may do the same thing... I'll have to mess around with it this weekend.

ha cool that's Ryan's adapter. I ended up going with my own design as the pins he was using cost $2 a pop and are overkill for the application. I have a pre-wired bypass adapter that costs less, plus a bunch of different access harnesses. If you just want to test then yeah you can wire it up or I'll send you a loaner.

[Vincenze]

The PCBs in the E30 amplifier are connected using multiple wires. They can easily break.
Then, you can supply 12V to the Remote pin, and check the resistance between the relay power pins. It seems you can hear the sound of the relay.

[Aleman]

ha cool that's Ryan's adapter. I ended up going with my own design as the pins he was using cost $2 a pop and are overkill for the application. I have a pre-wired bypass adapter that costs less, plus a bunch of different access harnesses. If you just want to test then yeah you can wire it up or I'll send you a loaner.

Hey Bradnic, I got your bypass adapter, and it worked great. Would like to get the amp looked at by an expert. DM'ing you to coordinate a hand-off. Thanks again for your help!

[bradnic]

Hey Bradnic, I got your bypass adapter, and it worked great. Would like to get the amp looked at by an expert. DM'ing you to coordinate a hand-off. Thanks again for your help!

This is exactly why I do loaner bypass adapters - give folks a chance to know if wiring or equipment is the main issue. It's quite unusual for the OEM trunk amp to 'click on' and you not have any sound output on any/all channel(s). That is almost always due to a no power situation. The only other wiring explanation I can think of is the radio output ground wire being cut, but that would still likely produce some sound. Looking forward to getting the amp on the bench.

Vincenze's post above is spot on regarding the potential root cause here. A bad relay winding could explain the behavior you've seen - relay clicks on but no sound because the amp internals aren't powered properly.