Telefunken HiFi Studio 1 restoration

HiFi Studio 1 is portable boombox manufactured by Telefunken in around 1979. This player consists of 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. The receiver of this unit is built 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. The power amplifier of this boombox is transistor based and it uses a pair of TIP130 and TIP135 transistors in its final stage.

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

A unit is not powering up and completely dead.
Cassette unit is broken and some of the buttons are falling down inside the case.

After going 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 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 the above components, we replace all the electrolytic capacitors in the 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, the 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 the 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 inches 2-way speaker system. The sound quality of this unit is impressive and we really like it's "unique" cassette unit.

Comments

strudbald said…

Is there an equivalent new part for the transformer unit?

September 22, 2020 at 12:28 AM

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