Help with Genera

Mick,

perhaps if you check the photos in this thread you can compare to what you have built.

Pay particular attention to the way the opamp is inserted in the socket, it could be reversed.

The led should be red so that part is OK.

Cannot help with check voltages etc. - Graham is the man for that.

I assume you do have the cables in and out in the appropriate sockets.

Otherwise best wait for the cavalry. :)

OK, but a bit more trouble shooting.

Since nothing has gone bang and the power led comes on, I think it is probable that you have all the electrolytic caps and the power diode the right way round.

That leaves the most likely things as either a dodgy solder joint or a solder bridge connecting two points that should not be connected.

To check that will require removing the board from the case, if you can take one or two good photos of the solder side of the board and also the top side for a sanity check and post them in this thread, someone may be able to spot a possible problem area.

I feel for you, really disappointing when you wait weeks and then stuff doesn't work.

Still, it is worse if you turn it on and let the magic smoke out.

Edited by tg - 18 Apr 2014 at 4:03pm

As both channels are not working it should be either the voltage of 18V missing at op amp pin 8 (the pin right of the central identifier notch - by the way pin 1 is left of the notch next to a dimple), or no bias at junction R11/R12. If there is 9V here then check pins 3 and 5 of the op amp - with a high impedance multimeter they should read just a bit under 9V. If all measures correct then you should have 9V on pins 1 and 7 (op amp outputs). If so then you may have the turntable plugged to the output and the input going to your amp....

If there is no bias at junction R11/R12 then check you don't have dry joints on these resistors. If you don't have 18V at pin 8 then check for dry joints on that IC socket pin and the voltage regulator pins - if the voltage regulator output pin (goes to R14) is shorted to its centre pin, re-melt the solder so it isn't shorted and it should be working.

If you've been really unlucky you may have shorted op amp socket pins together with solder blobs.

Another thing to check for is bent up op amp pins. If all the pins were not perfectly aligned with the socket hole centres, then on exerting pressure to plug home a pin could have bent up and away, not making any contact. In this case it would be pin 4 or pin 8 (or both...).

Then again, knowing how things go in electronics, it may be none of these, but we usually get there in the end, even if it means return to base (but that has a cost to it so let's persevere )

The circuit diagram with reference voltages is shown here: http://audio-forum.gspaudio.co.uk/phono-preamp-project_topic745_post5723.html#5723

Graham



Edited by Graham Slee - 18 Apr 2014 at 5:54pm