HP 3310A Function Generator Repair (FIXED)

[Nirios]

I finally got around to purchasing my first function generator.  It was won off Ebay and is in good shape.  Everything appears to function except for the sine output.

See attached images.

I followed the service manual found at: http://elektrotanya.com/hp-3310a-b_function_generator_op-sm.pdf/download.html
The service manual said to troubleshoot the sine shaping network and amplifier.  My problem is the schematics in the manual appear to be missing pieces.  I think I am supposed to start with the A3 board, but not certain.

Anyone have a good scan of the service manual?  Or knowledge of the steps to troubleshoot the sine wave section.

Thanks.

[grenert]

You can get the manual from the mothership:
http://www.home.agilent.com/agilent/techSupport.jspx?pid=3310B:epsg:pro&pageMode=MN&lc=eng&cc=GB

The manual is the same for A and B models.

Congratulations on your find!  The simple and clear, analog user interface makes it a pleasure to use.

EDIT:  It looks like the Agilent version is the one you got from elektrotanya.  There is a gigantic 27MB manual at KO4BB's site:
http://www.ko4bb.com/Manuals/HP_Agilent/HP_3310AB_OS.pdf

[Nirios]

There is a gigantic 27MB manual at KO4BB's site:
http://www.ko4bb.com/Manuals/HP_Agilent/HP_3310AB_OS.pdf

Thank you!  I was about to poke my eyes out looking at the other manual.  Its amazing how much easier it is to read when you have the reference designations chart to use and full schematic pages.   

The decision tree says I need to troubleshoot the sine shaper network since there IS a good triangle signal on A1TP4.

[Nirios]

Now I have a few question concerning my troubleshooting of the sine shaping network on the A3 board.

TP5 measures -2.335 V
TP7 measures 2.338 V
TP6 shows the attached scope capture which is not the correct waveform according to the schematic.

Am I correct to assume that the left and right green portions are working correctly?
Would a faulty component in the yellow section cause the wrong waveform at TP6 or could a failing component in the above sine shaper amplifier cause the issue?

EDIT: Typo on the 2.338 V point.

[lowimpedance]

 Now you have 2.338V on TP6 ?? , the same as TP7 ?.
TP6 should be around 0V. This TP6 waveform appear at the sine amp output TP1?.
If not and you do indeed have 2.338V at TP6 I would test for a shorted diode in the shaper cct. (right hand side of schematic most likely).

Use the diode function on your DMM.
Also a quick test that the transistors are still good
You should also do a quick in cct test for any resistors that may have drifted well out of tolerance which would alter the dc operating conditions.

(note, I'm sure you have confirmed all the supply rails are fine?)

Also note that the sine shaper diodes are all selected as a set to provide the best symmetry and lowest possible distortion with this method.
However if one is shorted then for hobby use you could just play with something similar and adjust for best performance.

Above all have fun fault finding , you will end up with a handy little generator.
LowZ

[Nirios]

Now you have 2.338V on TP6 ?? , the same as TP7 ?.

Sorry, that was a typo. 2.338V was on TP7.  I just double checked, 0V DC shows on TP6.

TP6 should be around 0V. This TP6 waveform appear at the sine amp output TP1?.
If not and you do indeed have 2.338V at TP6 I would test for a shorted diode in the shaper cct. (right hand side of schematic most likely).

TP6, does measure as 0V DC on my DMM.  The non-sinus waveform measured at TP6 does NOT show up at TP1 on A2.  TP1 on A2 measures 0.055 V DC

Use the diode function on your DMM.
Also a quick test that the transistors are still good

Can the diodes be tested in-circuit?  For example, I tested CR2 (yellow section) in circuit and my DMM showed 0.288 V in both directions.

And I did test the supply rails in the beginning, but going to re-test them just to be sure.

[lowimpedance]

 AH yes it could be tricky with the low resistor values to check in cct, do you get the same reading across CR2 in both directions?.
Check the dc voltages around the sine amp, I would suspect something dead there.
Post your results.
LowZ

[Nirios]

Fixed it.  It was a shorted variable capacitor.  Thanks to everyone who provided assistance. 

Here is my logic flow, process, whatever, on how I found the problem in case someone else runs across similar issues with this model or other generators.

The problem had to be in either the sine shaping network or sine shaper amplifier section.  I decided to isolate the sine shaper amplifier by cutting the lead on L1 on board A2.  I then probed TP6 on A3, this showed the correct sine wave display.  So the problem is in the sine shaper amplifier.  I powered off the device, and noticed a 0.2 ohm resistance between the connected side of L1 on board A2.  The short was traced to C3 on board A2.  For whatever reason, the plates on the trim capacitor were touching each other.  I fixed it by rotating the screw so the plates no longer touched and soldering the cut lead on L1.

How important is a working C3?  The service manual states it is for adjusting frequency response of the sine wave output.  The output looks OK to me but I do not have a reference sine wave source to compare with.  Is this something I should be concerned about?