Laney L5-112T efx loop problem.

[Prairie Dawg]

I'm working on a Laney L5 with an effects loop issue. The customer reports that the effects loop worked off and on, then quit working all together. So I get it here, and I find out that the effects loop would work with the cord plugged about 2/3 the way in to the FX return jack. So I figure "fine. It's got a bad jack." and I replace it along with the send jack.

No joy. Then I figure maybe I can jury rig it to work and get it out of my hair. No such luck. I tried a series of three-contact jacks (which this is) where I'd selectively removed the contacts in each position, and I had no joy there either.

So I'm looking at the schematic and I see that there is/are an IC associated with the efx send and the efx return circuits, they're marked TL072SM on the schematic.

The other point of information that would help is whether all TL072s are the same.

Is this IC the direction I'm going? Bear in mind I know nothing at all about this stuff, but it sure looks like it could be surface mount. I peeked under the board with a mirror.

Thanks for the assistance everyone.

ps while researching this I found a very interesting site that gives specifics on soldering and desoldering surface mount devices-they also have a youtube video.

http://curiousinventor.com/forums/3

L5T-112 (2).pdf

[52 Bill]

If you look at the schematic, the FX loop is a parallel loop where the straight signal is not shut off by the loop. If the IC was bad there would be no straight signal or reverb signal making it through the preamp.

The problem is probably in the return jack, or the pc traces or r15.

[Jazz P Bass]

I agree with Bill.
That " worked when 2/3 inserted" doesn't make sense.
The jack requires a 1/4" tip/ring plug.
Now if you where using a tip/ring/sleeve plug that may explain what you saw.

[Prairie Dawg]

I've been using the jacks that are illustrated in the lower part of the picture below, i.e., common guitar cords. I also checked the 100k resistor (R15) and it is OK.

Ooooooooh....why do I do these things to myself?

TRS - Bose L1 Encyclopedia FAQ & Wiki