When STK4241V burn...

First, sorry for my bad english.
One friend of mine bring to me Sharp SX-8000H(GY) for repairing. Left channel not working. Relatively quickly I discovered why. STK is burn out. Аlso it is not original.I buy a new one from e-store, it was described as a original SANIO but it was exactly the same, fake.
I try to repair the burned one. I removed all parts and replaced them with new ones. Complete waste of time and money.
A little :scratch1: and finally :idea:
I must build a new module, based on the internal schematic of STK and fully compatible electrical and mechanical.
Here is the result. Currently running the latest checks. Working steadily and I think that is a good alternative.
 

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The first revision works well. Of course, there is always something to improve.
There should be offset controll.
Should be able to use trimpots with a horizontal and a vertical adjusts.
...
And here's the second revision.
 

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They burn due the limitations imposed by production technology. There is little reserves of power. Not tolerate to overloading. Furthermore, widely sold substituents with unknown parameters.
This development is not an exact copy of STK4241. It is based on it but there are many differences. The components are of great reserves of power and voltage. The output stage is different. Heat is transferred directly from the output transistors to the heatsink. The other components are not stressed thermally.
And so on...

PS One example. In this Sharp SX-8000H (GY) has an external current generators to pins 7 and 17. Current is about 10mA. The supply voltage is 70 volts. This means that in TR3 and TR4 will dissipated 700mW. 700mW in SOT-23 case? WTF
 
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Hello. At the request of a user, I apply the Gerber files and the assembly scheme of version 02.05/16.
By the way, I continue with the improvement of this module. The third version introduces SOA protection. An additional board is provided which allows the addition of parallel output transistors.
Here is a description of the protection scheme (in Bulgarian).
 

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The preparation of prototype of version 0418 was completed. I present: Circuits, PCBs and expected characteristic of built-in protection.
Next step: manifacturing of one set for testing.
 

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