HP 3310B Malfunction Generator

Hi tm,

I was just going to post thanking DaveC for pointing me to the yahoo group where I found info pointing me to this link. It is downloading as I type. It is a slightly older copy, but it is much better quality and larger, 72 MB vs. 5 MB!

Thanks for the advice. This site is a treasure trove. I will feel much better about buying old equipment on eBay. In fact, I may work on my oscope to see if I can get the second channel working again. I wish I could find a source for the horizontal position pot. It has been terribly dirty for years. I asked HP about it once and they wanted $50 for a replacement, but that was way back when I could barely afford the scope, much less money for expensive repairs. I think I wouldn't pay $50 now, but only because the scope is barely worth that I think.

I'll say one thing about this unit, it is a field service model with a vertically oriented front panel. So it takes up much less space on the workbench than the horizontal units. Why don't they use this profile with *all* the scopes? The screen fits nicely above most of the controls and inputs with a small panel of buttons beside the screen (power, brightness, etc.). With today's scopes they are very thin, but still are wide horizontally. Why not thin and taller? I guess they might be more tipsy... Makes me want to build my own.

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Rick

Dave,

Thanks a lot for this link. I found some discussions on this unit and one pointed me to a more complete manual! Great suggestion!!!

Now I just need to figure the durn thing out. One of the posts I read seems to be saying that the voltages in the manual require some mods to the circuit and I see what they mean. Voltages on the output are -16V when the output, as we know, should be 0 volts. I may be seeing something similar on the high frequency circuit.

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Rick

Glad to turn on someone else to a great resource.

It looks like you're off and running!

Good luck.

Cheers, Dave

OK; go to:

Ok, I can get to that one. But what is it for? That is not the same unit at all. It looks like a much more modern unit with wide use of op amps rather than a bazillion transistors? I guess it might be a better unit to buy?

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Rick

Yes, i figured that the design was different even tho the function seemed to be the same. Been awhile since i looked at the incomplete Agilent schematic, but the diode array and biasing should be the same. In this schematic, except for Q306 and Q309, all transistors are fully active (no reversed biased E-B or forward biased B-C junctions). Maybe i should look at their crummy schematic..

..still looking at it; will respond later.

See Agilent PDF page 71 TP5 is equivalent to junction on mine described by CR322, CR321, R353, R351 and R350. Likewise, TP7 is equivalent to junction on mine described by CR323, CR319, R352, R346 and R344. Lastly, the "center", (sinewave) of TP6 is my TP13.

Now on mine, it is mostly obvious that the incoming triangle wave via R369 (from output of op amp U301) is/must be symmetrical about ground and (going from left to right) each pair of diodes will "clip" that waveform at a level set by their common resistor at the output line TP13; each clipping point being more severe (lower common R value) and at a higher level (further away from ground). Finally, the peak is clipped at the top, set by R348 and R342.

On the Agilent, PDF page 18, note there is NO "high frequency" monkey business WRT the sine forming, as i seem to have seen mentioned. Ditto with mine. Exception may be small trim caps or such. TP6 appears to be at ground with the waveform symmetrical, just like mine. So...at "low" frequencies (10-1000 cps) the triangle coming from the triangle amp (Pg 18 again) better the hell be EXACTLY symmetrical and well behaved. And it should stay that way all the way to the high end on the top range. I think that may be the key, and so there may be more than one problem - the first being this triangle waveform ain't not nowhere near symmetrical (to use bad Engrish).

TP5 should be as negative as TP7 is positive; i derived that from the necessary biasing for that DFG, and the schematic voltages noted confirm that. Resistor and voltage values from one to the other in the DFG will be different, but more-or-less on a ratio basis, they should track.

Once you get the triangle symmetrical, then it should be fairly easy to find a bad resistor or diode in the DFG (am guessing this as being a secondary problem). Maybe one of the stared capacitors in the sine shaper amplifier is bad, but i doubt it; if there is a problem there HF-wise, it would be due to a transistor (Q2 or Q3).

Yes, that is exactly the problem. The triangle is not symmetrical. The high speed circuit is not about clipping the triangle into a sine wave, it "adjusts" the circuit that detects the triangle has reached +-5 volts and reverses the direction of the waveform. The -5 volt detect seems to work ok on the lower ranges. On the 10k and 100k ranges the high speed circuit kicks in to modify the operation of the +-5 volt detect circuit so that it triggers just early enough to give a proper +-5 volt triangle in spite of whatever delays it has. This is when it malfunctions and looks like it is not going far enough negative, which is confirmed on the scope. The trigger level seems to vary erratically which is also seen on the internal test points.

The symptom is clearly a malfunction of the high speed circuit, plus, I can see erratic drift of the DC values both on the meter and with the scope. The drift is small, but the DC values are also wrong on the -5 volt half of this circuit. I just can't pin any of this down since I'm not clear on how the circuit works. The parts I understand will all affect each other if any of them malfunction.

I'm not worried about the DFG actually, I'm confident the problem is in the high speed circuit. I just can't figure out which part is bad. Someone suggested the caps often fail, at least the electrolytics anyway. There is one cap that looks like an electrolytic, but the schematic says it is 0.1 uF and the parts list says it is a 1.0 uF part. I'm starting to loose confidence in HP docs. I may have to shotgun it... or just use it on the lower ranges only.

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Rick

mine.

range.

-

confirm

to

bad,

to

May i presume that you are using this document for the schematic?:

So that we can all be on the same pages.

?-)

May i presume that you are using this document for the schematic?:

So that we can all be on the same pages.

?-)

+++++++++++++++++++++++++++++++++++

This is a better copy.

Yes, better, but still a lot missing. At least, see page 76 there for a complete DFG schematic, and pages

79 & 80 for a complete A3 (order is srdawkcab).

HF problems aside, fix the triangle FIRST and make it as perfect as possible.

That schematic has missing info. I found a better copy at KO4BB.com and edited the pages a bit to make it easier to view.

HP_3310AB_OS_1971_edited.pdf

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Rick

The HF circuit is the *cause* of the triangle problems. The triangle is just a constant current into a cap. When it reaches +5 volts the detect circuit switches the current source to ramp down to -5 volts, then the cycle repeats. The HF circuit modifies the threshold of the +-5 volt detect circuit which is part of forming the triangle wave. The problem is the -5 volt detect is happening too soon and the triangle is not going far enough negative. The *only* happens when switched to the 10k or 100k ranges. The only difference in the ranges is that the HF circuit is kicked in (and the value of the integrating cap, but they are different between the 10k and 100k ranges).

Just to be clear, the triangle still looks just like a triangle. The symptoms are:

1) doesn't go negative enough, 2) faster than it should be, 3) frequency is erratic, 4) sine wave is truncated on the negative half

To me, this clearly points to the HF circuit. The wave shaper only affects the sine wave and won't change the frequency. The sine wave is affected because the triangle doesn't go negative enough.

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Rick

Yeah, I thought it was pretty impressive too. BTW, are you British? That sounds like a British expression to me... "Good site, that". Or maybe an Aussie?

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Rick

LOL!

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Rick

Good site, thats.. Put that in my Book marks.

Jamie

My grand father was British born (Holmes), but I was born in Maine where every one is related. THe tree does not branch out too far!!!!!!!!!!

Some one told me the other day they don't bother to do crime investigations with DNA in Maine any more, the results are always inconclusive.

Jamie

Well, then work on the negative threshold sense circuit as well as its "compensation": threshold first at low frequencies for symmetry and then the comp.

Little late but I have fixed these 3310's in the past (instrumentation tech since 1960) and your failure is fairly common; transistor(s) 2N3904 or 06 in the output stage driving the power output transistors have opened up pro ducing a halfwave rectified like sinewave. These are Q13 & 14; replace wit h better 2N4401 and 03 respectively to reduce these failures.

1941WISEOWL