Reseating opamps appears to solve problem in vintage board

[telehumbucker]

I have a 70's Midas mixer and I was having an issue with white noise coming in through the monitors. Narrowed the issue down to one of the stereo out channels. Not knowing quite what I was doing, I looked for anything that looked disconected, burnt, etc....didn't see anything, so just pulled out the four and so op amps, blew the area where they were connected to the board out with air and reseated the opamps......Problem with noise seems to be solved. Is this likely just a coincidence or could an opamp not seated optimally cause a noise issue? The noise issue was also showing up in the eight busses....the noise rose as the busses levels were brought up, but only when the problem channel was in the board.

 

[ruffrecords]

Probably due to corrosion of the contacts of the socket and /or the chips over the years.

Cheers

Ian

 

[JohnRoberts]

yes, pretty common with socketed ICs

JR

 

[telehumbucker]

Seems to have cleared the white noise out....had the board on for quite a few hours with no issues. Thanks for the responses......

 

[Newmarket]

Well sorted. Hopefully ! If it comes back you may want to lightly abrade (and I mean lightly) the ic legs. I'm assuming socketed ? And maybe IPA (alcohol not beer. Yeah I know beer has alcohol in it ) and/or a Caig DeOxit product. The flushing D5 type I guess.
Worst case new sockets. Turned pin types recommended.

 

[telehumbucker]

Well sorted. Hopefully ! If it comes back you may want to lightly abrade (and I mean lightly) the ic legs. I'm assuming socketed ? And maybe IPA (alcohol not beer. Yeah I know beer has alcohol in it ) and/or a Caig DeOxit product. The flushing D5 type I guess.
Worst case new sockets. Turned pin types recommended.

Yep, came back the next day, so I swapped out new op-amps, and so far so good, but was wondering about using deoxit or alcohol or something similar...could one put that in the socket or is that just to be used on the opamp or both? It's really humid here, everything rusts in the South.

 

[Newmarket]

Yep, came back the next day, so I swapped out new op-amps, and so far so good, but was wondering about using deoxit or alcohol or something similar...could one put that in the socket or is that just to be used on the opamp or both? It's really humid here, everything rusts in the South.

What sort of sockets do they look like ? Turned/Machined pins or Spring Leaf ? I'd kick off by saying lightly abrade the ic legs to remove any oxidisation and grease there. Then apply DeOxit to the legs. A bit of IPA into the docket and let it properly evaporate before refitting ics.
I'd leave the DeOxit if you don't already have some. But maybe scrape the socket contacts with a sharp point. I know that's not easy to do.

 

[scott2000]

I had a tiny crack inside the socket on one of the leaf types that had me chasing around once.

 

[telehumbucker]

You can see the little black plastic sockets in the picture.

 

[telehumbucker]

Better pict of the opamps.

 

[Disco Volante]

Oxidized contacts can play all sorts of tricks on you.

I had a Quad33 that was making speakers and girlfriends jump out of their seats, random thumps and stereo/mono coming and going. Was going to replace all the (hard-to-find) push switches, but on a whim I gave it a soak in mild citric acid solution over night, cleaned with water and IPA. Back together, it worked like new. No more fuss, and such little work...

Happy tinkering;-)

 

[JohnRoberts]

At Peavey we stopped using sockets back in the 90s. Our sockets were relatively inexpensive in the quantities we bought them in, and machine inserted so no significant labor cost, but truckloads of them add up.

I worked with the service department repair techs to asses how much it would affect their repair costs if we didn't use sockets. What this investigation revealed was that the vast majority of IC failures occurred to input and output devices. Most likely from static hits and rogue hot grounds. IIRC we ended up leaving those I/O sockets in place. SMD made this all moot.

JR