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Stereo generator board using AN612 ICs

S

Studio1

I have a stereo encoder board here that belongs to an associate, who has asked me to repair it.

It arrived on my bench with a blown out tantalum capacitor (supply rail decoupling) so I have completely recapped
it and removed all tantalums (being used in decoupling) - total of about 12 caps.

I've powered it up but it has no MPX output and the AN612 ICs are both getting quite warm.
I have no manual or schematic for this board.

Does anyone recognise these ICs as being used in a commercial stereo generator for which you have a schematic?

I have the datasheet for the IC - and it's helped me identify the various pins and what should be on them.
 
Hi,

If you only have the board, and not the chassis I presume it plugs into, could that be the reason you see no output? Maybe the only thing wrong was the bad capacitor. External pots, carrier supply, etc., may be off the board you are fixing.

While looking for a data sheet in English, I found that the NTE1249 is a replacement for the AN612.

Good luck.
 
Thanks Bill.

This board is a stand-alone encoder - ie throw +/-15V at it, left and right audio and it gives an mpx output at the other end. Everything it needs is onboard.

I've sourced some AN612s off Ebay - so first step will be replacing them and seeing if it cures the problem.

My associate wasn't aware that it needed split-rail power and he applied only +12V to the +15V line. In theory this shouldn't have been an issue as the AN612 is a single supply device - ie has Vcc and Gnd connections only.
However, the way it's been configured, the Vcc connection goes to the +15V rail via a 180R resistor, and the Gnd connection goes to the -15V rail via a 120R resistor - which is effectively giving +9V across the IC. Weird, but I suppose it works.

The 180R resistors show signs of being quite hot at some point (even now) as they are a little brown and with these ICs getting quite warm I can only conclude they are drawing too much current.
 
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