STK4141-II pinout?

[orbanp]

Hello Everyone,

I am repairing a JVC RX-150 radio, that uses an STK4141-II hybrid in the final amplifier.
The datasheet by Sanyo shows that the chip has 22 pins.
The actual chip in the radio, that has the correct part number on it, has only 18 pins!
The service manual (same as for the JVC RX-111, available at hifiengine.com) shows an STK4141-II with 18 pins!

What gives?
Are there different versions of that chip?
The Sanyo datasheet shows different versions of the chip (different max supply voltage and rated output power), but all with 22 pins.

Thanks, Peter

[orbanp]

Here are the documents.

Peter

[orbanp]

It looks like that there are indeed two versions of the chip, with the same numbers!
Here is the datasheet on the 18-pin chip.

The 22-pin version looks like an improved version, it has a current mirror for the input pair, a cascade VAS-stage, and a access to other internal points for bypassing and for tweaking the compensation.
Details of such improvements (and others) can be found in Doug Self's essay titled "Distortion In Power Amplifiers" that was available on the net some time ago, and now published in his book on audio amplifiers.

It looks like that the newer version of the chip (22-pin) could be used instead of the old one, just by leaving out the outermost two pins on both sides.
DISCLAIMER: I have not tried it!

Peter