Slightly too easy HP 3312A function generator repair

[SingedFingers]

Well this was a bit easy. I decided to finally take a look at the sweep function on my HP3312A which has not functioned since I acquired it. The rest of the unit was fine and operating normally. These are simply the pinnacle of analogue function generators and were pretty much a "nothing is too expensive" job by HP. This one appears to have been made in about 1990 with the design originating from 1974, that's a 16 year run for a product at least which is pretty amazing.

As it was before with the previous owner's unknown brown goop on the front. I suspect it may have been owned by a stoner as it was a bit whiffy:



Had a quick look inside and looked for obvious damage and decayed components. The thing is 100% immaculate. Typical quality HP design here:

Top of unit



Bottom on unit



So on to the fix. It worked on AM, FM modulation but not on sweep. I checked the modulation generator test point with the scope and it was working. Clearly it wasn't getting to the main generator for modulation in certain modes. A quick wiggle of the sweep switch on the front and it started sweeping intermittently. Being latching changeover switches, they are usually the culprit so I lifted the corner of the switch assembly (4th switch from the top) and shot some contact cleaner in it and pressed it a few times. This is plastic and rubber safe zero residue contact cleaner (WD40 brand but NOT standard WD40!).



Bingo. Sweep reliable again. In fact all modulation functions were spot on after this.

So reattached sides of unit and proceeded to clean it. All that was used was a sable paint brush, some dettol and some kitchen roll. Quick artificial dry with the wife's hair dryer and sorted:



Slightly disappointed that it was that easy but hey, one fully working function generator at last.

[mtdoc]

I got a good deal on one of these on eBay a few years ago. It worked well for a while then suddenly no output..

They really are beatiful examples of vintage HP engineering.

This was the second old school FG I've bought on eBay (the first was a Wavetek) that initially worked then stopped

I've been meaning for sometime to open it up and see if it's something I can find and fix but in the meantime  I purchased a Siglent SDG-2042x so somehow fixing it became low priority.

Thanks for posting this as it will get me to move this up on the "To Do" list. Maybe it will be an easy fix..

[SingedFingers]

I've seen a few function generators with blown output transistors and resistors. May be as simple as that. My last one, made by Exact came with those blown. Was a cheap resistor and a 2n2219/2905 pair to replace and good as new.

I've actually got my eye on a Siglent SDG1020 at some point in the future. I've got a Marconi 2019A floating around, well actually lumbering around. I could sell that to fund it as well. Hmm interesting

[Cubdriver]

Nice cleanup job, SF - that front panel looks like new.     Cool that it was a simple problem.

-Pat

[tautech]

I've actually got my eye on a Siglent SDG1020 at some point in the future.

I'd suggest you scrap that idea and take a hard look at what is it's replacement that has a # of features that surpass the much older SDG1000 series.
http://siglentamerica.com/pdxx.aspx?id=4705&T=2&tid=16

[SingedFingers]

Thanks for the tip - will take a look at at that unit.