Electronics > Repair

B&K Precision 3011 2mhz Function Generator repair

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Seg:
I bought a B&K Precision 3011 2mhz Function Generator as an eBay fixer-upper. Seller said it powered up but did no other testing. Plug it in, and nope, no sign of any signal coming out. Service manuals for vintage B&K Precision equipment seems to be hard to come by, so I get to fly blind here.

Open it up and, hey what happened here?



A voltage regulator seems to have spectacularly de-soldered itself for some reason, splattering beads of solder all over the thick later of flux covering the bottom of the board and cooking the board pretty good. 1986 vintage 7815's apparently didn't have thermal protection... Let's clean that sucker up before we do anything else:



Probing the pads indicates no apparent shorts, and good power going in. Hmmm. Tried soldering in a replacement 7815, with some heat sink paste for good measure, and power it up with probes attached. The output voltage is low and it gets real hot real fast. There must be a short lurking somewhere. I check capacitor C103 that's right on the output, and what do you know, it's shorted. Wasn't immediately apparent because it couples over to a -15v rail or some such rather than directly to ground.



Replace the cap and hey look at that, it's functional again:

mcinque:
Great job!  :-+ Thanks for sharing

SeanB:
1986 78xx regulators did have thermal protection, just it often did not work well. Relying on parameter shifts to switch off the device while the operation is not tested during manufacture is always going to bite you. I bet that if you clean off the leads and test it it still works.

Seg:
Yeah, I tested the regulator with the output pin lifted, it put out something like 4.75v. It's cooked. :P

Stonent:
I'm always concerned if I try to buy something for parts/not working off Ebay I'll open it up and find stuff missing inside, or it will look like it went down with the Titanic.

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