Toshiba Transistor Fakes – another case
February 2004, somewhere in Germany
I used freshly bought Thoshiba transistors as drivers in the final stage of a Fine Arts A9000 amplifier. The types 2SC3182 and 2SA1265 corresponded exactly to the original service documents. A few seconds after switching on power the base-collector paths of these transistors blow. As a result immediately also the complementary driver transistors burned through, as they experienced a short circuit to the supply voltage against which they tried to work what they can not do. This happened with aconsiderable production of heat.
After all of the transistors and resistors were replaced (almost the entire stage) the same process happened with the new transistors in an identical manner a second time! The heat damaged the PCB so that some pads were pulled, and a repair of my amp got more difficult.
Figure 1: Extract from the circuit diagram of the power amplifier
The following reasons suggest that the delivered transistors did not meet the specified parameters, so that they were declared as the wrong types:
- This amplifier were operated without load. So the transistors emitter current ICE could not be high. This also excludes a excessive power dissipation. The cross-current of the stage was only 30 mA. (60 V × 30 mA = 1,8 W). On the other hand the limits of both transistor types were ICE = 10 A and Pv = 100 W.(!)
- The corresponding emitter resistors (0.33 ohm / 3 Watt) would have been blow up with a current of approximately 3 A. But they all were untouched. Accordingly, no significant emitter current can be flowed.
- According to the technical data for both transistors a limit voltage of UCE = 140 V is guaranteed. The amplifier had only 125 V (± 62.5 V).
- The second channel of the amplifier was running without any trouble with the same type original parts for 10 years.
- The circuit was gradually put into operation. Without soldered output transistors, the circuit still worked up to the preceding driver stage properly. (For this purpose the negative feedback loop has been returned from the drivers. Voltage and current gain and operating points were correct.)
Everything pointed out that the amplifier transistors were beaten simply by applying the working voltage.
After some research I came across a web site about Toshiba transistor fakes.
The descriptions were practically identical with my experiences.
Evidence for a fakes
The burnt-out transistors from the outside ...
- The transistors already blow at voltages that are significantly below the nominal voltage (140 V here)
- The letters
Toshibawere printed in poorly readable brown color, Toshiba transistors are usually printed with white color.
- Chip size of the SA1265 is too small (see below)
- The chips of the 1265-types have not the meander structures that provide current distribution as you can see at the 3182 chips (see below)
- It was clearly visible that the transistors on the chip are burned, although not a strong emitter current can be paid for it (see circuit)
... And from within. 2SC3182 (left) and 2SA1265 (right)
I had luck that that the transistors blow immediatly and not a few hours later. At this amp I was running my brand new speakers ME25, where a damage would be eally expensive (price of the speakers was 783 € each).
As a gesture of goodwill I received pin-compatible transistors 2SC5200 and 2SA1943 from the supplier, which have more power and higher limits. They worked.
More cases of Thoshiba Transistor Fakes:
sound.westhost.com/counterfeit.htm – Site of Scott Elliott
www.planet-kuehne.de/martin/audio/counterfeit.htm – German translation of Scotts site