BMW E65/E66 LOGIC 7 AMPLIFIER REPAIR
 
Models Affected:
BMW 7 Series E65 / E66 (manufactured between 2002 and 2008)
 
Introduction:
The unreliability of the Harman Becker LOGIC7 amplifier is well known and very well documented across the internet. To give it credit, the amplifier design is ingenious, nobody can disagree the performance and spatial surround experience is fantastic, but it could also be considered a marvel of high volume cost cutting design. Most aspects of the design were simply to make it as cheap as reasonably possible to mass produce. 
 
With this in mind, and the pleasant thought that Harman Becker haven’t diversified into the medical equipment and life support market, this all comes at a price, that of course is reliability.
 
The amplifier utilises 'chip on board' technology, cost saving and simple assembly were the major factors for this, but this is also the major weakness in the design. Repeated thermal cycling simply breaks the wire bonds between the amplifier IC die and the PCB substrate resulting in loss of speaker channels.
 
The simple solution is to replace these faulty IC's, many vendors offer LOGIC7 repairs, and this is exactly what they do. However, the TDA1562 amplifier used is rather unique, it’s a Class H amplifier that utilises a 'charge pump' method to effectively increase the supply rails to achieve a maximum output power of 70W.
 
And this is the problem, the TDA1562 has been obsolete for roughly ten years, they are expensive and difficult to source, and many are counterfeit or don’t even work at all. Therefore, literally every other vendor, or repair kit you will find on eBay, use a Class A/B amplifier instead, cheap and very easy to source. 
 
The real issue now is that the Class A/B amplifiers can only produce 20-25W of RMS power from a 12 - 14.4 V supply. This results in underpowered subwoofers and heavy distortion when the volume approaches around 50%. It's not really a repair, arguably you will have bass, just not very much of it!
 
The BAVtronik Solution
This where the BAVtronik repair is different, the subwoofer channels are now powered by a custom designed Class D amplifier module. To realise this, an entirely new power amplifier card has been designed. This new card improves many aspects of the original design:
 
Class D amplifier module producing 20% more bass
Class A/B midrange amplifiers in standard packaging (no ‘chip on board’)
Dual speed fan control for improved cooling
Improved ground routing to remove fan ‘noise’ allowing it to run continuously
Automotive grade over voltage and over current protection for the subwoofer amplifiers
 
The replacement board is designed to occupy the footprint of the original board and all electrical interfaces are identical, the 20 way main connector, four power inductors and the TVS protection diode are recovered from your original board and fitted to the replacement.
 
The midrange Class A/B amplifiers are mounted to a custom heatsink which is screwed to the side of the case, with the fan now running continuously at low speed the heatsink allows lateral airflow across its surface and ensures the A/B amplifiers remain cool. The fan circuit is dual speed, if the internal amplifier temperature exceeds the threshold governed by the processor card, then it switches to full speed.
 
All repairs are covered by a 12 month warranty, this is limited to replacement board and work/repair undertaken, I cannot offer a warranty on the entire unit, i.e. the processor card. However, the later style 4 clip amplifier processor cards have proved to be very reliable.
Please get in touch using the ‘Contact’ form if you have any questions.