Becker Mexico Alive

After rebuilding the power supply, time came to rebuild the radio. Again, these units are made of simple electronics components (resistors, capacitors and some semi-conductors) in addition to the tubes. The Becker Mexico contains 7 tubes and complex circuits that are much difficult to follow without the correct schematics. 

The Becker Mexico view from above; 2 tubes and the Wunderbar mechanism are visible

Thanks to Jeff Miller for posting on www.mbzponton.org the schematics of the various Becker Tube radios (Mexico, Brescia, Europa and LeMans), without them I couldn’t perform any reparation accurately. 

Here is a quick history of the Becker Mexico installed in my car:

1.  I bought it in 1999 from a retired taxi driver who had kept it for more than 35 years untouched, unused to replace the original Becker LeMans (AM, LW) radio which was beyond reparation
2. I was 19 back then and had only very basic knowledge in electronics, no schematics and no testers. I only had a soldering iron and an ohmmeter. To my luck, visually a tube was broken (replaced it), cleaned the vibrator pins and plugged in the radio listening to beautiful music.
3. I changed the power supply's vibrator in 2004 after finding a solid state replacement in Canada.
4. The radio worked well from 1999 up till 2014 when problems started appearing:

              a-      The radio’s sound started becoming unclear (bad quality of sound)  
              b-      Then the Wunderbar (automatic electromechanical search system) stopped detecting any  station              
              c-       Finally, the radio died on the FM band followed by an extremely weak AM reception

I sent the radio to two repairmen (one of them mentioned in a previous article on this blog) who both failed to do the repair after leaving it at their shops for more than a month; I lost hope and decided to give it a try myself.

I started by studying well the schematics; understanding the different currents, how things work and how the radio is designed. I was lucky enough to find a very interesting website on old radios’ restoration (http://antiqueradio.org) that Philip Nelson runs. I exchanged few emails with Phil who suggested I start by replacing all the electrolytic and paper capacitors and see if anything changes.

The radio contains the following electrolytic capacitors:

• One 50uF 350V
• Two 10uF 25V
• One 5uF 30V
• One 100uF 25V

Replacements were easily found and installed; of course the new capacitors are much smaller making their installation easier than expected. 

100uF new electrolytic capacitor installed

New 4.7uF electrolytic capacitor installed

After replacing these capacitors I turned on the radio to only hear a hum from the speaker.

I continued recapping and changed the several 0.022uF and 0.01uF paper capacitors; the replacements are the smaller much more efficient orange and green drop models that are not polarity sensitive (no + or – connections as the electrolytic ones).

Green drop newly installed capacitors along with an electrolytic one

Orange drop newly installed capacitors

On a side note, always make sure to install the new capacitors in a way that makes them look nice in these “board-less” circuits.

Once this job done, I powered the radio without succeeding in getting anything different than the “hum” on the AM and very far FM reception (barely noticeable and accompanied by the hum).

At this stage I was starting to lose hope; the resistors were the only left components that I didn’t test thoroughly; the tubes were out of any suspicion since I tested them all on my working Blaupunkt Santos radio.  

Before doing so, and to get an idea on the status of the old capacitors, I placed each old one on the tester only to discover that the 100uF capacitor had drifted in value to 500uF and the 50uF one was shorted. 

The old paper and electrolytic replaced capacitors; notice the bottom of the Blaupunkt Santos tube radio

I took few days off then started again examining the values of the many resistors. After 3 long hours of examining and noting values, I found a 500K resistor that seemed completely open! This resistor (R104 on the diagram) connects Tubes EF89 to ECC85 indirectly; hence it plays a major role in the FM Band’s operation.   

The famous 500K dead resistor

100K resistors were the closest I found among the ones I had on hand; I connected 5 of them in series, soldered them to the respective points and powered up the radio…Eureka! Music was heard on the FM with very strong reception and excellent quality of sound!

5 x 100K resistors installed temporarily in series. Notice the 6 new orange drop capacitors
and the new 47uF electrolytic capacitor

5 x 100K resistors installed temporarily in series. Notice the 6 new orange drop capacitors
and the new 47uF electrolytic capacitor

I bought few 500K resistors, installed one adequately and started tackling the AM issue. The AM issue wasn’t as difficult as expected; a good hour spent on testing resistors showed that a well hidden (under many wires and other components) resistor R9 (70K - 2W) was completely fried! I wasn’t surprised when I found out that, especially that it is directly connected to the 50uF capacitor which was shorted. I changed the fried resistor and got strong signal on the AM.

70K Ohms (2W)  fried resistor

Finally, I addressed the Wunderbar issue which was extremely easy as it needed a bit of calibration (calibrating potentiometers P2 & P3 and variable capacitor C126) as indicated in the second page of the radio's schematics. 

Rheostat P3 surrounded by 2 resistors. Watch out this area as it contains high voltage 
(Photo courtesy Becker Autosound)

I tested the radio for few hours and was very satisfied with its performance. I lubed the Wunderbar mechanism, assembled it all and installed it in my car ready for additional years of playing music...

To conclude on this Becker Mexico Tube Radio adventure; I can say that most of these radios are easily repairable and can live for so many years. All what one needs is some logic, basic electronic knowledge (resistors, capacitors), specific testers, a soldering iron and a lot of patience. I admit it was a challenging project/ job to complete but on the other hand, I learned a lot and covered an additional aspect of maintaining my car and all of its components in a perfect shape. 

Enjoying the sound of the Becker Mexico Tube Radio