Blaupunkt520 repair

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A little success story of a car radio repair gone right.

A few weeks ago my girlfriend's car radio stopped working. The car is a Holden Astra model ST from 2001 released for the Australian market. On the (UK-based) 'Astra Owners Website' they also refer to this model as either a Vauxhall Astra Fourth Generation (or Mk 4) or Opel Astra G.


Funnily enough, there are even three pages on Wikipedia, each for a particular market:

The car radio is a Blaupunkt 520. It's a smart-ish radio in that it communicates with an external display higher up in the centre console and shows things like radio station, volume, CD track etc..

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So at one point a few weeks ago the output volume suddenly started dropping. I was listening to some music on CD and the volume coming out of the speakers dropped to almost nothing over a period of maybe 10 seconds. I tried compensating by turning the volume up but it really was getting quieter and quieter. I switched on the FM radio but it was also very very quiet; almost no output volume. I switched off the radio and drove home.

This couldn't be a fuse or so because the radio and all the controls still worked; it was just very very quiet. Since the symptoms were the same when either listening to CD or radio I assumed that the fault was in the final output power amplifier.

Since I didn't really wanted to open up the radio and swap out these chips I thought it would be simpler to just look around for a second-hand Blaupunkt 520 radio. Someone on eBay had one on sale for $20 ex shipping. Unfortunately he didn't have the security code.

The security code is important because it locks down the radio if the battery power is removed. I knew our radio's code but that didn't help for this other radio as a unique code is programmed inside each radio. Change the radio and you'll need a new code. There are usually ways to recover (or maybe reset) the code through the official car dealership, e.g. in case you've lost your code or bought a car without knowing the code from the previous owner.

I decided to take the risk and buy the radio on eBay in the hopes of being able to reset it through a local Holden dealer. My girlfriend is the first owner of her Astra and has all the official paperwork to prove so. I thought it would be a (perhaps somewhat costly) breeze to recover the replacement radio's code.

The radio from eBay arrived shortly after the purchase and we began inquiring with several Holden dealers in the area to get an idea of what it would cost to have the radio code recovered. I must say this was a very unsatisfying experience. The feedback from the local dealers can be summarised as a mix of hostility, unhelpfulness, rudeness and sheer incompetence. Some seemed to insinuate that we had a stolen radio, others flat-out refused to help and some gave us the idea that our problem wasn't worth their time even though we were well prepared to pay for the recovery service.

The next step was to look for an online radio-code recovery service. Yes they exist, but we weren't successful with them either. Websites that offer these services ask for a couple of details and then (if all goes well) instantly produce a code that you can use straight away to unlock your radio. The website I found asked for the Blaupunkt 520's serial number and part number. Well, the serial number was printed on a sticker, but the part number was missing. I looked everywhere, even inside the radio, but was not able to find the part number. I figured that probably any website that offers these instant-code-generator services operates in the same way and not having a critical piece of information will probably mean that any other code generating website would also not be able to help.

After calling another Holden dealer I finally got some good information. In order to recover the radio code they would also need the VIN (chassis number) of the car that the radio originally came out of. I asked the eBay seller but he said he was unable to recover this information.

Hmm... what to do.

Since I already had the radio open at this stage I noticed the two final amplifier ICs.

(Grey and black ICs that are backed up against the two copper heat sinks)

Blaupunkt520 repair1.jpg

Standing up vertically, on the right side is the AM and FM radio module, but apart from that there was no easy swapping of modules that could help me repair the original radio with the one I just bought.

The Final Power Amplifier is the component in the radio that amplifies the (relatively weak) audio signals from the AM and FM radio or CD player and drives the loudspeakers. It was my guess to think that the fault was in these chips as the radio controls all worked; there just wasn't any audio out.

Investigating the part numbers on these chips it was clear that these were two identical chips, the TDA7375A. I recognised the 'ST' manufacturer logo and had a look on the ST MicroElectronics website to find the component. They now sell the TDA7375V and TDA7375AV, but not the plain 'A' series anymore. The datasheet for the 'AV' product did reveal that it is indeed a 'class AB car radio amplifier able to work either in dual bridge or quad single ended configuration.' (see here for product website on the ST website:

They are able to drive about 35W into a speaker and since there are two I think that it's 35W for the left and 35W for the right audio channel. A quick search on Mouser, a big online electronics parts supplier, showed that these chips retail for about $8 a piece.

At least I now knew that these were indeed the chips responsible for the final output Power Amplifiers and that the 'easiest' fix was to swap them over from the eBay radio (assuming that the PA chips in the Ebay radio were still good). I could have bought two new chips from Mouser, but I wasn't 100 per cent sure that the problem was indeed these chips. The most cost-effective way was just to salvage the chips from the eBay radio. This also meant that I didn't have to chase up radio codes as all I was going to do was replace the amplifier chips.

Let the (un)soldering begin..

Using a 40W soldering iron, a tin-sucker and a lot of patience I am able to take out the tin surrounding the pins one by one.. Blaupunkt520 repair2.jpg

..until all the pins are freed and I'm able to wiggle out the first chip.

(bottom view)

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(top view)

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Rinse and repeat until both chips from both radios are unsoldered.

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Finally! Both chips are unsoldered and ready to be swapped.

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The holes in the circuit board were clean enough for the replacement chips and after re-soldering them in place I began assembling the radio back together again.

I slotted the radio back into the car dashboard and the moment of truth came..

As expected, the clock-display in the top console asked for 'RADIO CODE - - - -'. I entered the radio code and it was accepted. So far so good.

I then turned on the radio to an FM station and... IT PLAYED SOUNDS THROUGH THE SPEAKERS!! YAAAY!!!

This is a very good outcome.

Apart from the frustration of talking to Holden dealers and the realisation that Blaupunkt doesn't make it easy for their radios to be re-used (even in identical cars!), it took me a few hours to do the soldering.