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1987 560sl
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16 Posts
Discussion Starter #1
I couldn’t find any information on Becker 754 disassembly and battery replacement. So I made a video to chronicle my disassembly and battery location. The last parts are supposed to arrive soon, so hopefully I’ll install the new battery this weekend and go to the dealership next week. I’ll post updates as I go.

Notes:
  • previously I tried grounding all the pins on the 5-pin connector. It did not unlock radio.
  • Mercedes of Alexandria Virginia has said they have the tool to reset.
  • Becker in New Jersey quoted $195 plus shipping to replace battery and deactivate theft
  • new battery was about $5 on amazon, I also bought a battery holder so that I can replace battery without soldering in future. I plan on mounting battery holder on back of radio for very easy access.
  • I considered using a rechargeable lithium polymer battery (sold at micro center cheap, 3.7v adafruit brand, comes in a few capacities, but would need a board for charging, like $20 total). I also considered setting up a solar panel to charge said battery But that was going to be ugly. In the end, lithium polymer batteries don’t do well below freezing and I live too far north.

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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6,743 Posts
Very helpful video, thanks.
I too have a 754 Becker Radio that does not work.
How much does your dealer charge to reprogram the Radio????
 

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w108 & w107
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96 Posts
Nice work. And just in time as i embark on re-fitting the becker in my SL...looking forward to seeing how the battery holder mounts to the rear. Would be good to be able to test the battery without removing the radio as i disconnect my car battery over winter for prolonged periods...
 

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1987 560sl
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16 Posts
Discussion Starter #4 (Edited)
I unfortunately won’t be able to take it to the dealership until next week, but over the phone Mercedes of Alexandria quoted $50 and Mercedes of Arlington said they have the tool but didn’t confirm price. Euro motor cars of Bethesda did not respond.

here are photos of the battery holder. I decided to notch the lid to provide more clearance for the wires. In hindsight, I probably could’ve soldered them to the other side of the board and fit them without modification. Used super glue to attach the holder to the rear of the radio.
Battery Holder, 1/2AA Size, Wire Lead: Battery Holder, 1/2AA Size, Wire Lead: Amazon.com: Industrial & Scientific
2 x Saft LS-14250 1/2 AA 3.6V Lithium Primary Batteries (non Rechargeable): Amazon.com: 2 x Saft LS-14250 1/2 AA 3.6V Lithium Primary Batteries (non Rechargeable): Health & Personal Care

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1987 560sl
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16 Posts
Discussion Starter #5
Nice work. And just in time as i embark on re-fitting the becker in my SL...looking forward to seeing how the battery holder mounts to the rear. Would be good to be able to test the battery without removing the radio as i disconnect my car battery over winter for prolonged periods...
I like your idea of being able to test the battery without removing the radio, I guess you could move the battery holder to inside the ash tray or glove box and test the battery voltage while still in holder. Removing the radio from the dash is pretty easy, so for now It’ll work for me.
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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6,743 Posts
You peaked my interest.
My Becker 754 has been sitting in a box for years.
It stopped working some time ago - I thought it was that it would not power on.
But, after I opened it up, the Battery still showed 3.6 volts.

So I reinstalled it in my 560SL. Now it acts this way:
Powers ON and OFF
Display shows station
No sound from Speakers - can hear a slight pop changing channels though.
Antenna will not go up or down even by the Radio or even by the Antenna switch on the dash.

I had a Radio out of a 380SL installed but it tended to drain the Battery and I just removed #12 fuse.

Wondering if I should remove the old Becker 754 and clean those pins thinking that might be the reason for no sound.

Notes for others who want to do this:
  • the rear of the PCB is hinged
  • there are two screws at the front to remove so you can pull up the PCB from the front
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1987 560sl
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16 Posts
Discussion Starter #7
Sorry Carl,
I’m not experienced with troubleshooting these radios beyond the theft lockout and battery change.

From an inexperienced perspective:
I’d try to isolate the issue further. Does AM or tape work? Did the speakers work with the other radio? Any power or connector issues?Any leaking capacitors on the board? If there’s no audio for all the modes, I’d try to inspect the area near the speaker connectors to see if there were any signs of issues. The other side of the radio also disassembles as easily to show the other circuit boards. You could also contact Becker in New Jersey and see if this is a known issue. Many people have gotten helpful responses from them.
good luck!
 

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
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6,743 Posts
I might try bench testing this radio.
I found a description of the pin outs:

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1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
Joined
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6,743 Posts
My 754 shows the display and changes channels, but no sound, the antenna will not go up, and the cassette deck will not accept a cassette tape. Mine just might be something like a power supply.

EPC shows the part number for the 754 Becker Radio: A 002 820 86 86
Googling shows this radio is used in other Mercedes models. We might get lucky and find a good working one at the Junk Yard.
 

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1987 560sl
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16 Posts
Discussion Starter #11
So I got the radio unlocked at Mercedes Benz of Alexandria. It was a slightly confusing process because multiple people tried to “get the unlock code from the vin”, until they finally got Merv who knew exactly what was needed and got the tool and unlocked in 60 seconds.

Unfortunately my radio is now behaving similar to Carl’s. Displays the radio station. Antenna won’t go up. No sound from speakers. I don’t have a cassette tape.
Next time I have time, I’m going to test the voltage out of the speaker ports to see if the radio is outputting anything. If not, I’m considering switching to a cheap-o crutch field for a while.
 

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Registered
1983 380SL, ivory/dk brown, 46k miles, dual roller timing chain. 1986 560SL, red/white, 190K mile.
Joined
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6,743 Posts
So I got the radio unlocked at Mercedes Benz of Alexandria. It was a slightly confusing process because multiple people tried to “get the unlock code from the vin”, until they finally got Merv who knew exactly what was needed and got the tool and unlocked in 60 seconds.

Unfortunately my radio is now behaving similar to Carl’s. Displays the radio station. Antenna won’t go up. No sound from speakers. I don’t have a cassette tape.
Next time I have time, I’m going to test the voltage out of the speaker ports to see if the radio is outputting anything. If not, I’m considering switching to a cheap-o crutch field for a while.
That is interesting. Maybe something about the unlocking process? Fuse?

Is this a Fuse?
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1987 560sl
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16 Posts
Discussion Starter #13
Hi Carl,

there is a fuse in there. Mine is fine, you should check it just in case.
So I broke down and paid $40 for a cheap head unit and harness from Crutchfield. The harness was perfect fit and soldered the wiring up quickly and easily. The new radio has rear speaker outputs that I taped off and the orange illumination line from the car is not used. Other than that, very straightforward install. The cage press fit in but the clips are not “locked” in. I could modify the cage, but left it for now. The radio works and speakers are working, so confirms that my issue is with the head unit. I’ll probably send the old unit to Becker to get it diagnosed and priced for repair. I’d much prefer the original look. But for now, I have FM, Aux, and usb.

radio Dual XDMA350
Wiring harness Metra 70-1860 Receiver Wiring Harness ($1.99 with purchase of radio!!). No changes to stock wiring. Metra 70-1860 Receiver Wiring Harness Connect a new car stereo in select 1981-94 Mercedes vehicles at Crutchfield

Note: the Dual XDMA350 radio I purchased does not save FM/AM presets after the car battery is disconnected. Kinda disappointing but I guess you get what you pay for.
 
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