Repairing HP 3310A Function Generator

It is not uncommon that lab TA's report that their lab equipment is broken in some way or another. Usually it's some trivial thing like they forgot to check if it's properly powered or didn't know how to check if the fuse is blown, but from time to time the equipment is in need of some serious maintenance.

So this was brought into the back and the TA just mentioned that he couldn't get it to work. This older model function generator are usually pretty solid and don't have fuses so if they're broken then they are super broken. After some initial tests just to double check if the TA was not using it correctly, it was found that there was no output for any of the waves.

After taking the thing apart, and I would just like to give kudos to HP for their work in designing their function generator in such a way that it was a huge pain to take apart. I mean this this is a rock solid piece of equipment and my guess is they really didn't want it to be taken apart unless it really had to because it was a mystery box of sliding parts to get this jigsaw box apart. Anyways, it is pretty common for the countless detaching and reattaching of cables to the output by students just naturally wears them down and in this particular case, breaks the connection so that new leads need to be soldered. To the right, there is my handiwork with a new resistor in place. The original connector that was attached was just destroyed so I had to fashion a new connector to the board as well. This actually solved part of the problem because I was able to get the function generator to output a square wave, but the Sine and Triangle wave parts were still flat lining.

Well that was the easy task, now I had to look for something a little more malicious as to why this thing wasn't working and you can see it in this picture to the left. Some old military grade tantalum capacitors leaked and corroded away at the copper trace. On the right you can see that the trace was just eaten away.

So the service manual was found, but wasn't really necessary in this particular case because it was fairly obvious what was the culprit for the bunk outputs. I thought it was kind of interesting though and figured I would show the photo of the schematic, C2 and C3 should be the caps that I needed to replace if I remember correctly.

The only thing that needed to be done to repair this would be to fly wire the two separated traces together and drop in some new tantalum capacitors. Not too tricky.

The above photo is the new wire soldered to connect the two traces, and to the right are the new two orange caps that were soldered in.

And would you know it, everything started working again. Successful repair job to keep this HP function generator up and going for at least another year before someone drops it or something.

Big thanks to Dave Azpell for keeping the service manual and giving me guidance on what to check for to get this guy up and running again.