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Tuesday, October 1, 2013

Beomaster 8000 Tuner Repair: Exchange of Prescaler U264B

***********************this is a follow-up to this post****************************

Yesterday the U264B prescaler ICs arrived from Germany and the UK. I bought two batches of Telefunken NOS ICs from to make sure I would have something that actually works. It turned out that both batches worked. I guess now I have enough U264Bs to last me for the next 40 years. This does feel good...;-).
I unsoldered the old chip (series TFK 208). Before:



























The new one I put in using a DIP8 socket. I wanted to test all the U264Bs I received, and this enabled a fast swapping of the chips. Here are the pics of the empty socket and with a new old TFK 225 installed:





















































I also got some series 234 and they also worked. This puts the question to rest whether the series number matters...it does not. The tuner works very nicely now. However, I wonder why this IC died. Maybe it is time to consider putting some TVS diodes on the power rails to prevent over-voltages.
On a general note, I always run my B&O on uninterruptible power supplies to keep them safe from the all to often occurring brown outs and voltage spikes in our 3rd world style power grid.

One more comment about the defect U264B: When I measured the voltage at pin 1, the meter showed only about 1.2V instead of the value of 3.3 in the circuit diagram. The replacement chips showed a value of 3.25V. Maybe this can be used to identify a broken chip if one is far from an oscilloscope.

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