Hi All,

I have a older discontinued HP 3301A function generator that cosmetically looks in excellent condition except it does not work properly. It has never been serviced because the unbroken manufacturers warrenty seal is still over a lower case screw head. That has to come off to service it.

Having said all the above I dont have the expertise to repair it myself. Test equipment repair shops charge a arm and leg for any repair.

Does anyone have the skills to repair it at minimal charge? I dont need calibration just a bad part replacement. I have printed out schematics showing the internal circuitry.

Let me know if you are interested and what you might charge.

Thanks, Tom

 

Hello,

What is the generator doing at the moment?
What is your location? (if someone near you wants to help).

Greetings,
Bertus

 

The generator has problems generating the lower frequency square waves. Needs a on/off indicator light replacement also. Also very weak amplitude output I live in Canton, Michigan, near Ann Arbor.

 

No guts, no glory! I don't think you can void the warranty by removing the screws any more!

If I'm not mistaken, there's a tiny INLINE fuse right on the output of the generator. Part of the feedback circuit is extracted AFTER the fuse, oddly enough...and when it goes, you get all kinds of bizarre symptoms.

Check that fuse first...it will probably look like a tiny resistor. It should read less than an ohm or so if it's good. If not, stick a clip lead across it and see if the generator comes to life.

Of course it COULD be something else, but I've seen this on a few HP products.

Eric

 

Check that fuse first...it will probably look like a tiny resistor. It should read less than an ohm or so if it's good. If not, stick a clip lead across it and see if the generator comes to life.

ACK!! NO, don't do that!!

If you are going to jumper across a fuse, you better be using a fuse as a jumper, or you may release the magic smoke from the components!

I suggest that you may have some (or many) electrolytic capacitors that have high leakage current, or may have leaked their electrolyte. Look for caps with bulging tops or corroded-looking areas around them.

 

Thanks for your help guys,

I will look at both suggested areas. I can see the caps from the top but will have to take the bottom cover off to really inspect them. As far as the inline fuse is -- Is it in some kind of metal clip or directly soldered in? I dont plan to smoke anything as I would replace the fuse and see if it blows again

Tom

 

I will look at both suggested areas. I can see the caps from the top but will have to take the bottom cover off to really inspect them. As far as the inline fuse is -- Is it in some kind of metal clip or directly soldered in? I dont plan to smoke anything as I would replace the fuse and see if it blows again

Here is the 3310A schematic circuit link. I see the caps but can find the fuse?? Can you reference the page the fuse is shown on?

http://www.home.agilent.com/agilent/techSupport.jspx?pid=3310A:epsg:pro&pageMode=MN&cc=US&lc=eng


Tom

 

As far as the inline fuse is -- Is it in some kind of metal clip or directly soldered in?

If you don't see the typical AGC-style glass fuse, it's likely to be a small component that's roughly the size of a 1/8 W resistor. The ones I've seen were often a green color.

 

I found there is one transformer powering 4 individual power supplys. The 4 power supplys in turn feed all generator components. If any one power supply goes bad everything gets screwed up. Each power supply has a large 500uf electrolytic capacitor in its circuit. Two of the power supplys show no voltage. Looks like I will be changing some large caps. Given the age of the generator I just might change all 4 caps at the same time to be sure I dont have trouble later. Thanks for your help again guys Tom

 

What is the voltage rating for the 500uF capacitors?

If the electrolyte hasn't leaked and the cases are not bulged, you may be able to re-form the dielectric by using a current-limited voltage to slowly charge them up to their rated voltage. If you can get the current leakage down to an acceptable rate, you could still use them.

I looked at the service manual; HP/Agilent did a really poor job on scanning the schematics to .pdf format. Practically all of them are missing at least half of the information.

 

Two of the caps are rated at 30 volts and the other two are rated at 50 volts.

I scoured the internet and I found some caps that match the 50 volt 500uf rated caps. They are much newer and smaller unlike the older caps in the generator.

I also see two rectifying diodes with each large cap. I wonder if they might be shot also?? 10 volts each is required from two of the four power supplys. Thats present. 25 volts is required from each of the other two power supplys. Thats not present.

 

Two caps are rated at 50 volts and two at 30 volts. I found newer much smaller caps on the internet rated 500Uf at 50 volts. I could use 4 of these to replace all 4 four caps.

The (2) 50 volt cap power supply side of the generator is supposed to deliver 25 volts at the output in 2 places. ---No voltage present.

The (2) 30 volt cap power supply side of the generator is supposed to deliver 10 volts at the output in 2 places. --- 10 volts present.

Each cap has two diodes within its rectification circuitry. I wander if all 4 might be shot if both of the 50 volt caps went bad??

Tom

 

It's hard to say from here whether they are blown or not.

Replacing old electrolytic caps is really pretty easy to do. As long as the new caps are rated for at least the same voltage as the old caps, you're OK. You could also use 470uF caps to replace the 500uF caps; that's an easier size to find. I suggest that you buy capacitors from companies that are authorized distributors and that have a large sales volume; otherwise you may receive capacitors that are beyond their shelf life.
Digikey.com
Mouser.com
Newark.com
Alliedelec.com
are all major suppliers, authorized distributors for many companies, and have a large sales volume.

It's possible that you may have one or more blown diodes if the caps have failed shorted.
Check for blown fuses first.

What makes this restoration project particularly difficult is that the published schematics are incomplete.

If you have a digital camera, it may help if you can post well-focused images of the areas under scrutiny.

 

Two caps are rated at 50 volts. Each supply 25 volts to the generator circuit
Two caps are rated at 30 volts. Each supply 10 volts to the generators circuit. Four seperate power supplys feed the generators circitry. Any one or more goies out the generator fails.

There is "NO" 25 volts present at 2 locations. 10 volts "IS" present at 2 locations. 1/2 of my power supply is dead. Having said that I narrowed the problem down to both 50 volt electrolytic caps and two diodes that work with each cap in a rectifier circuit.

Looking at the 3310A link schematic I referenced before the power supply circuit is plain to see. Other parts of the circuitry are not.

Question: Is there a quick way to see if any part is good without unsoldering it from the circuit board? I have a digital multimeter to work with and know how to use it.

Tom

 

Tom,
OK, I'm looking at page 77 of the manual.
1) Turn on power to the signal generator.
2) The output of T1; measure across pins 2 and 24. You should measure roughly 60VAC,+/-10%. If you can't get to it, skip to the next step.
3) Then on the A4 board, measure voltage between pins 2 and 5. You should measure roughly 60VAC,+/-10%.
4) Measure from A4 pin 4, to pin 2, then from pin 4 to pin 5. You should measure roughly 30VAC both places,+/-10%.
5) Measure from pin 4 to ground (the + side of C2, or the - side of C1) - you should measure 0v.
6) Turn off the power to the signal generator.

If the voltages are way low from what they're supposed to be, the diodes may be shorted or the transformer is burned out. If they're about where they should be, the diodes are most likely burned open.

Unplug the A3 board from the A4 board.
Unplug the A4 board from the signal generator. I can't tell from the manual whether the transformer is soldered to the board, or if it has a connector.
Use your meter in diode check mode to measure CR1 through CR4 both ways, forwards & backwards. One way they should show open, the other way read somewhere between 300 and 700; that's their Vf when a certain current is applied to them.

If any of the diodes are open or shorted, you might as well replace them all.
Use 1N4004, 1N4005, 1N4006 or 1N4007 diodes.
The original diodes for CR1-CR8 were specified as 200 PIV 0.75A diodes.
The 1N4004 thru 1N4007 are all 1A diodes, 400 PIV to 1000 PIV; so they are better than HP's original specifications. They are also dirt cheap.

 

Hi Guys

I found one of the 30 volt?? electrolytics bad (open) and a loose wire connecting the power transformer to the circuit that needed resoldering.

I decided to replace all 8 of the power rectifying diodes and all four caps.

The generator is quite old but in like new condition. To be on the safe side later I should not have any power supply problems pop up. I am now waiting on 4 ordered caps that match what was in the generator. I already replaced the diodes using a new Weller battery powered solder iron. Its perfect for "small jobs" and does not burn the circuit board. Its been a long time since I did something like this but I really enjoyed it. Tom