Hi y'all,
I recently bought this 8116A function generator off eBay hoping to 1) fix it 2) learn something in the process and 3) gain a function generator for my bench!
The listing was scant on details but said that it powers on but little detail beyond that. On first inspection of the outside, there is a concerning amount of what looks like corrosion and corrosion-esque residues all along the bottom 1/2 inch of the enclosure, front panel and all over the connectors. Not looking so hot so far. (you'll see in the pics)
But, I was delighted to find it more-or-less working! I don't get a whole lot of time to work on my projects during the week so didn't get to let it really warm up until a couple days later, when I decided to crank it up into higher frequencies, ended up letting it run at 100kHz 75% duty 1V amplitude and would periodically check on it.
Lo and behold after a couple hours maybe, the negative half of the waveform had gone all wonky. Positive side still doing fine. Okay, now we're getting somewhere. Upon reboot it greeted me with E42 but would still output, just nothing below 0V pretty much.
I should mention, soon after those early tests I cracked it open to look around, but not much stood out from the top side. Except it does look like somebody has worked it over a time or two, probably even replacing the pesky HP ASICs I've heard about (evidenced by discolored flux residue underneath). (yay! maybe?)
Upon getting the error code 42 and a quick google, this does seem to indicate a problem with the negative half of the output amp, nice!
Last night I went ahead and paid somebody for a scan of the manual, and happy to have it now. Today I've taken a closer look at the output area and oh boy there's lots of corrosion. My mind jumps to leaking electrolytics ...but maybe not so, as you'll see later. *suspenseful music plays*
I cleaned it up and to me it looks as though the Unknown Past Servicer may have already replaced the output diodes and big electrolytic. I'm judging this a couple ways: 1) the amber flux residue on particular components 2) the slight difference in color of solder joints compared to rest of board and trimmed leads that gives it away
I think there's a story here. Imagine, if you will... brilliant engineer working into the night finally gets the thingamabob to work, and in a moment of ecstacy smacks his beer over, spilling right onto his trusty 8116A (which he just had repaired). He quickly turns off the unit and does a hack job cleaning it. It sits unused while engineer achieves great success and ultimately sells off his old gear for new kit and he lives happily ever after.
But seriously, could the leftover flux and proximity to the chassis in a corrosive environment (humid + degrading battery on top PCB) contribute to this type of failure?
At any rate, next I need to actually go through checking voltages at all the nodes in the negative half of the output amp I reckon. All the power rails checked out good.
I really appreciate any advice you folks can give!
I'll be adding pics here, trying to keep it chronological:
https://imgur.com/a/Tkf4w8F