A600 / 1200 Audio preamp

Solderbro · 08 July 2018, 19:49

Hello,

if things become broken rare parts are involded. One of my A600 won't play sound at right channel. So i checked the recapped capacitors back to the LF347 opamp. Here i found out that the first opamp did get a sound signal from Paula, between sits a MPF102 Mos FET that pulls the signal down to zero. The second opamp only get the zero on it's input pin.
At left channel the audio signal is seen at both opamp and the MPF102.

So i think the MPF102 is shot through in some way, problem is that this piece is EOL. A search have shown that the MMBFJ113 is available, seems to have similar pinning, so i ordered 3 of them.

Do anyone had some repair in the audio amplifier and what compatible parts can be used today?

Daedalus · 08 July 2018, 21:23

To be honest, any dual rail (i.e., not explicitly single-rail) audio op-amp should do the job once it has the correct pinout. There's a good chance the ones you ordered should do the job just fine.

Solderbro · 11 July 2018, 15:43

Can report success here, the MMBFJ113 is cheap and come with same pinout. The sound volume and frequency is the same as before, does not differ from my other A600 with old FET's inside.
Take care for 260°C max for the parts.

08 July 2018, 19:49	#1
Solderbro Registered User Join Date: Jun 2018 Location: Hamburg Age: 55 Posts: 56	A600 / 1200 Audio preamp Hello, if things become broken rare parts are involded. One of my A600 won't play sound at right channel. So i checked the recapped capacitors back to the LF347 opamp. Here i found out that the first opamp did get a sound signal from Paula, between sits a MPF102 Mos FET that pulls the signal down to zero. The second opamp only get the zero on it's input pin. At left channel the audio signal is seen at both opamp and the MPF102. So i think the MPF102 is shot through in some way, problem is that this piece is EOL. A search have shown that the MMBFJ113 is available, seems to have similar pinning, so i ordered 3 of them. Do anyone had some repair in the audio amplifier and what compatible parts can be used today?

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08 July 2018, 21:23	#2
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,335	To be honest, any dual rail (i.e., not explicitly single-rail) audio op-amp should do the job once it has the correct pinout. There's a good chance the ones you ordered should do the job just fine.

11 July 2018, 15:43	#3
Solderbro Registered User Join Date: Jun 2018 Location: Hamburg Age: 55 Posts: 56	Can report success here, the MMBFJ113 is cheap and come with same pinout. The sound volume and frequency is the same as before, does not differ from my other A600 with old FET's inside. Take care for 260°C max for the parts.

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