Talk:Unitra M 2405 S
A very well-known company of the entertainment electronics was from Poland the company Unitra. In addition to radios and tape recorders that were mainly built under license of the German company Grundig and others. The ZK or ZKR series of tape recorders were produced under license. Whether the TK series was also manufactured in Poland for Grundig and then sold in the West should not be in question. Many countries of the Eastern alliance operated with it a foreign exchange market and brought additionally profit to the state. Even today there are still many fans of the Unitra brand. Especially they are to be found among the tape recorder friends who have grown fond of the good old analogue technology. Very robust were the tape recorders from the series ZK 120 up to the ZK 246 without stable power supply. Among them is also the first series of the M 2405 S. With the production change of the built-in amplifier and equipment of the IC TBA 810 of the company Tesla began the unrest among the tape recorder friends. The IC does not stand the high voltage peaks in the long run for a long time and was therefore equipped with the GDR IC A 210 E in the workshops. There were and are still today workshops with it a problem have because a construction error in the circuit is present and not recognized. The error was none, eigendlich ingenious - the transformer was part of the engine! Repair and modification of the tape recorder Unitra M 2405 S 1. and 2. generation
Amplifier: When using the IC A 210 E DDR production, on the amplifier board it is best for the IC if it is embedded with electrolide and not soldered in. This avoids damages caused by soldering. Afterwards the connections sealed with Elektrolid after the hardening time with protective lacquer provide.
Power supply: The power supply has an error in the circuit by the manufacturer!
The R 56 regulator does not provide an accurate control range for regulating the voltage to 16 Volts. This voltage is the maximum voltage for the ICs A 210 E.
Attention! Higher voltage can lead to the destruction of the ICs!
If the BD 355 B transistor is replaced, always apply heat-conducting paste to the underside of the transistor and to the insulating washer. The heat-conducting paste ensures optimum heat dissipation. The resistor R55 and capacitor C69/70 can be removed. Transistor T6 BC 147 B/C can be replaced by transistor BC 107.
Preamplifier: Check the components for full functionality.
If there is no input signal at the amplifier board, there is a fault in the volume control which must be replaced.
Ps:Same estimation as for the TESLA115.Technically more mature,because of GRUNDIG,resp.Philips.They were able to sell these units from Poland(technically from the 60-70's),in various catalogues,until the middle of the 80's.There was for example a black market in the GDR - the price was hot - probably the units were simply TAKEN from the assembly line!!??HW