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Telefunken HiFi Studio 1 restoration

Telefunken HiFi Studio 1 restoration
HiFi Studio 1 is portable boombox manufactured by Telefunken in around 1979. This player consist with 4 band radio (with LW, MW, SW and FM), cassette player / recorder and with 2 × 30W audio power amplifier.

Restored HiFi Studio 1

This unit is designed using both ICs and transistors. Receiver of this unit is build around TDA1047, TBA570 and BA1320 ICs. Tape player/recorder is mainly build using NPN transistors and special Telefunken IC and 4066 ICs are used to get Telefunken’s proprietary HIGH COM tape noise reduction feature. Power amplifier of this boombox is transistor based and it uses pair of TIP130 and TIP135 transistors in it’s final stage.

The unit which we restored is Telefunken HiFi Studio 1 (silver) model and it had following problems:

  • Unit is not powering up and completely dead.
  • Cassette unit is broken and some of the buttons are fell down inside the case.

After go through the circuits we figure out that the problem is with the GR501 bridge rectifier of the PSU board. We replace GR501 with KBP206 bridge rectifier module. During further checks we note that most of the components in power amplifier board are damaged and we replace each with new (equivalent) parts. Most of the replaced components are listed in below:

Original part Replaced part
17520 (TIP135) BD646
17521 (TIP130) BD647
BY251 1N5408
BD373 BC338
BC637 BC338
BC338 BC338
0.47Ω resistors 0.47Ω 3W resistors

Apart from above components we replace all the electrolytic capacitors in power amplifier board.


Partially restored power amplifier board.

In cassette mechanism problem is with the button bar axle and we fix it by attaching 3D printed plastic holder into cassette mechanism’s body. Also we replace playback/record head and pinch roller of this mechanism, and after that cassette unit starts to work again.

HiFi Studio 1 test setup (without cassette mechanism)

Restoration of this Telefunken HiFi Studio 1 takes more than 3 weeks because we replace more than 45% of parts in that unit. After above fixes this boombox starts to work again. Unfortunately we don’t have matching speakers for this unit and we test it with some 8 inch 2 way speaker system. Sound quality of this unit is impressive and we really like it’s cassette unit.