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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #1 ·
The PO-installed Alpine deck on the car used to work sometimes and not other times. I had a newer BT/ipod Alpine deck that I swapped in for the upgrade and I figured the other deck may have been flakey. Well, it turns out the wiring is flakey. The 'new' deck was giving me errors after starting the car but would work. I figured I had the power and constant 12v crossed over .. but I didn't. I ran a multimeter on the original harness (install is proper, not spliced wiring) and discovered that there was 12v on both pos/neg (white, white/black) wires which go to the front left speaker. I pulled the dash cover to check wiring and it was ok. I disconnected the speaker and there was 12v on those wires. I isolated those wires and re-connected everything and the stereo is 'fixed' .. except that I don't have front left. I plan to install all aftermarket amp and run new speaker wires anyway but I'de like to figure out stray voltage .. or I think it is? Anyone ever have this problem?
 

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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #2 ·
I isolated that speakers wiring, ie; disconnected those wires from the harness altogether. Unplugging the speaker didn't change anything, there was still 12V on those wires. The speakers are all aftermarket alpines with all the factory wiring in place. If I install an amp I'm doing all new wiring for speakers and yes, RCA outs. But I'de still like to fix this because my suspicion is frayed wires somewhere or .. something like that?
 

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86 300e Anke
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1,254 Posts
I did some searching and it seems that's in the amp. A bad output transistor can cause live voltage to a channel?
The output transistors bias the voltage to around 1/2 of the 'source'... in our case, around 6v...
This way, the output signal has the ability to fluctuate between 0 and 12v... with the 'zero-crossover point' being the 6v.
This is why you sometimes hear a 'pop' when the system is turned on...

If an output transistor is shorted, it would allow full-voltage at all times... therefore... 12v on all the time.


FYI. :D
 

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'95 E320 Wagon & '98 BMW M3
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929 Posts
Measure right at the head-unit's speaker output with a DVM set on VDC and the unit turned on. Pull the HU out of the center console, find the speaker outputs and measure. If you're getting any DC voltage over a few hundred mV then the HU is toast. Also if the speakers have been connected for any significant period of time (in this condition), I'd suspect they would be blown (i.e., they don't like DC offset).

*Edit* is the OE fader switch still in place and wired up? I know MB did some crazy ground scheme with the fader switch to get 4 channels from a 2 channel HU. Or are the speakers directly connected to the HU?
 

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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #8 ·
Mine doesn't have the fader. I'm familiar with the setup because I worked around it on my old 190e. I'll bust out the multimeter tonight and see what's what at the amp end.
 

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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #12 ·
Factory amp only powers the front side panel woofers (map pocket). However the signal for the amp comes off the front dash speakers. I know factory amps go bad from water/windshield washer fluid getting in to the wheel well and rusting the amp from the bottom.
That's interesting ... maybe the amp is messed and shorted out or something? Another clue, the door speakers do not work!

bmwpowere36m3: I'm getting 12v on the speaker wires with the speaker disconnected and the head unit disconnected. So, the power is coming from somewhere else. I'll check on the amp when i have a chance.
 

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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #14 · (Edited)
My harness looks like this:


Well, picture the male half of that, is what's on the car, the pictured one above is now spliced to the head unit. I don't think it's the wrong harness and it looks factory. Mine's a 95 and I think they moved to a later style harness for the stereo because my searches for w124 stereo harness didn't yeild anything that looked like mine .. but a search for 210 and 202 did...

aha, like this:


At this point I'm pretty sure the amp is fubared.
 

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'95 E320 Wagon & '98 BMW M3
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929 Posts
That's interesting ... maybe the amp is messed and shorted out or something? Another clue, the door speakers do not work!

bmwpowere36m3: I'm getting 12v on the speaker wires with the speaker disconnected and the head unit disconnected. So, the power is coming from somewhere else. I'll check on the amp when i have a chance.
Which speakers exactly? If it's the door woofers, then disconnect the amp. Maybe the amp shorted out, not uncommon for them to rust and that can cause all kinds of problems.
 

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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #16 ·
It's the left dash speaker.

I checked it out. The amp isn't rusted, in fact it's nice and clean back there thankfully. But someone's been in there. The amp was secured with a zip tie on one end and a blitzsafe adapter was worked in there that I'm not sure does what. Didn't have much time tonight. With the amp now disconnected I'm going to check those leads again behind the deck.
 

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1992 190e 2.6, 1995 e320 Wagon
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551 Posts
Discussion Starter · #17 ·
I pulled the amp and opened it up to check for bad solder joints and corrosion, you know, the obvious stuff. I didn't find any of that. There was some corrosion at the pin outs by the connector which I cleaned up. I don't know how to test capacitors but I know that they can fail with age so I did a continuity test on all of them and found that *most* of them had continuity. The ones that didn't were all the same type. Does this test have any value? I don't know.

I buttoned it all up and hooked it back up but I didn't remove the head unit or the dash grill, not enough time. So I haven't checked if the 12v speaker problem is still there or if it's there with the amp removed. I have another problem now, the convenience relay at the back of the relay box behind the fuse seems to be out so there is no power to the windows, sunroof, rear wiper or stereo :(
There's another thread about that because I'm treating the two things as unrelated. Unless you guys think there might be a relation. Can a short break a relay?
 

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'95 E320 Wagon & '98 BMW M3
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929 Posts
To test capacitors, you really need to have them out of the circuit (or PCB). You can test them installed, but the readings are less reliable. Generally if the capacitor (electrolytic) is blown, it'll look like it expanded or exploded out. Some examples here: Blown, Burst and Leaking Motherboard Capacitors - A Serious Problem? - PCSTATS.com
However it could be bad, without any external ques. I would just disconnect the amp and see if you still get 12 V at the speaker. Unless your electronics savvy, if the amp is bad… look for a new/used one.
 
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