In 2001 BMW decided to move from Philips to Becker to supply their radios for the 5-series BMWs. My 2001 530 had a Becker c53 Business radio in it which is a cassette radio with a CD changer in the boot. The new Becker radios have flat pins and a strange “Quad Lock” connector on the back. These radios have a design floor in that the power amplifier ICs overheat and die, loosing you audio in one or more speakers. For reasons known only to Becker, they decided to make the power amp ICs Chip-on-Board – black blobs of stuff bonded to the PCB. This gives them shit heat dissipation and hence after a good bit of antisocial music they often shuffle.
The radios aesthetics make it blends into the dashboard in a way that reassures you that any attempt to replace it with a DIN radio will look shit. It also listens on the BMW i-bus and makes use of the steering wheel controls which is an expensive operation to get working on an aftermarket radio. Hence the options to fix this is to either:
- Buy another C53 radio on eBay with the prospect that it may also be teetering on the edge of death. This is not an option as they fetch ~£100 or so, which for a radio cassette is just silly.
- Get a fascia adapter, wiring loom adapter, i-bus audio-leads protocol converter to get the steering wheel buttons going. Looks tacky and works out expensive…
- Hack another power amp IC into it.
I went with option 3. This is nice as the power amp IC is the last thing in the audio path on Car Radios, the 8 speaker connections on the back (4 channels) go straight to the power amp, along with battery 12v, 4 pre-amp audio signals and a few grounds and standby signals. Lets get hacking. There is a man on eBay who will do this for you for a tidy £100 but if you have an old and tired aftermarket radio like a sony xplod minidisk head unit or a alpine unit with “cd player foobar” written on it then the donor power amp chip is free and the only cost is your time…
Radio pic from google images. You remove it from the car by pulling off the volume knob and using a flat bladed screwdriver in the little hole to rotate a cam that releases some clips :
Once you take the cover off and remove the PCB (don’t forget the metal clip that tries to push the chips back plate down onto the metal casing for some heat dissipation) you will find the power amp ICs in the rear right corner:
If you have a desoldering station, you can make some more room for yourself:
You will notice that all the fat traces go into the connector board, 8 of them are speaker outputs (buzz them out) and there is 2 grounds and 1 battery 12v feeds per chip (iirc – I did this about 2 months ago and am writing this from memory) The 3 SMD components above and between the chips is a thermistor voltage divider to allow the radio to throttle back on power amp overheat.. Yeah, good one. The radio doesn’t seem to mind this being missing, which is good since as the chips are out on a limb, I decided to amputate:
This was then cleaned up and, because tacking the wires onto the PCB tracks doesn’t work in reality, I decided to bind wires on the through hole connections straight on the back of the Quad Lock connector. This radio is quite poorly built in my opinion. Its PCB delaminates quickly and, if you look at it long enough you will notice some very interesting “auto-router-esque” style traces. Designed quickly I would say.
The colourful wires are the new wires for the daughter board power amp to connect to and the grey ones are temp wires running to some bookshelf speakers as I didn’t have a handy quad-lock connector to test with. BTW, these radios power up and run fine with just 12v and ground, no need to sense an i-bus link etc. The power amp IC I am using came from a sony xPlod radio and is marked TA8268A, a custom variant on the Toshiba TA8266H chip for which a datasheet is available. They are all much the same, this one is about 4x40W. They have 8 speaker connectors, 4 power grounds, 2 power VCCs, Mute and Standby TTL inputs, Signal Grounds and 4 signal inputs. Also, because the old power amp chips were capacitively coupled we can do away with the signal input caps and tack off the old ones. Simples.
TA8266H Test CCT from datasheet:
This stolen schematic shows the TDA7386 wired up and is a more involved example. (TDA chips are a popular power amp which I was originally using for this but killed in a foolish move involving a signal ground masquerading as a 12v line)
Get your point-point wiring hat on and get to work. The metal bar seen in the pics above is a convenient signal ground and the 4 large ceramic SMD caps are the signal caps (you can see the brown,orange,blue and aqua wires coming from them in my pic above.
The big caps are decoupling and reservoir caps on the various power rails. The only complication came in getting a standby signal. This is very important as the chips are fed direct battery voltage, not ignition voltage. Very direct and very hefty 12v. Unless you like jump starting, get your standby line sorted! The original chips seem to have a couple of signal lines which didn’t behave in any useful way in regard to standby signals. I may of killed something by this point but in the end I tacked the TA chips standby line to the electric antenna output driving FETs gate as this had the appropriate logic levels and worked well in regard to de-popping (pre-amp signals stable before firing up power amp).
Reassemble and test. Do not underestimate how hot the power amp chips get! The heat sink pictures above is arguably not big enough! It survives my hour long commute with pendulum at antisocial levels though so that’s good enough for me!
C53 Radio Pinouts