WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

[rlb245]

I bought this unit of Ebay for about $90.00. Was supposed to be a working unit but after receiving it. Started it up ran the calibration after the 20 min wait for worm up and got this error reading. (ERROR OFSTGAIN) I've download the schematic and some other technical sheets on the unit. I getting ready to start the reading of all this in hopes that it may bring me to a solution to this problem. if anyone has any prier experience with this unit please share your experience. i assure you it will greatly appreciated.

[stj]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

if you want help, hit the "go advanced" button and upload the technical info/schems

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Newbe: not sure where to find that advance button youngman

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Never mind da, found it! The schematic is a complete PDF with the prints in the final pages. It's way to much to post I think so maybe just a link to the PDF for it. is there rules governing links in the forum?

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

this is where you can get the manual which has all the schismatics for this unit

https://www.google.com/url?sa=t&rct=...qGAAVA8wkM7ZJw

[stj]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

pdf limit here is about 20meg.

sooo........

now where are the other parts?

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

There aren't other parts, That the hole thing. Operation, maintenance, Trouble shooting, board views and schematics

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

I found this Doc helpful in understanding whats going on

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

OK i've read this manual front to back along with other items i found on this subject. I think my best coarse of action is to climb into my chair at the bench tomorrow and fire up the scope and start probing my way through this puppy. The schematics in this manual are really great with point to point reading and views of what should be seen on the scope. It doesn't get much better than that. I think my plan of attack will be to start probing the power rails just to verify correct power is being supplied. The manual calls out 3 different boards to look at for this error so i thing I will start at the out put and work my way back though the circuit. I'll keep ya posted on my finding If your interested.

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Well didn't get much done today. Forgot about the Sunday dinner thing with my girl friends sister. how ever i did get a chance to confirm the primary power rails in the unit.
all measurement were taken with a Fluke model 8050 and check for ripple and noise with a Tektronics 460A Ocsiliscope on channel 1 with a probe set to 1X, after a 30 min warm up and a calibration cycale ran. All power rails clear of ripple and noise,
reading as follows
+5 volt = actual reading +4.98 volt
+12 volt = actual reading +11.97 volt
-12 volt = actual reading -11.98 volt
+22 volt = actual reading +22 volt
-22 volt = actual reading -22 volt

Now! I noticed that i'm going to need a signal generator to complete the trouble shooting on this instrument. Many of the test points require a signal of 1KHz, 1MHz and 4KHz to be feed to the unit to varifye the circuit is operating correctly. Ill have to buy or barrow a signal generator for some place, This unit that supposedly worked was going to be my generator, Life is just full of little inconveniences, RIGHT!

[stj]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

you can get the KHz range from your computer headphone socket.

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Thanks for the heads up.

[Longbow]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

I would ask if the unit works, or is disabled until the error message is fixed? You have confirmed that the supplies are fine. I'd start looking at the various output waveforms to see what it is that might be triggering the error. As usual, don't take the error message literally. The guide pretty much tells you that the problem is inside the unit somewhere. Helpful, isn't it?

[Longbow]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

While the article on DAC calibration is instructive, it would be surprising if the generator message is actually referring to a subtle change inside one of the DACs. I would be looking for a really obvious level change that would show up right away at the output.

Manual page 4-3, top right-hand column. This talks about the 8 analog control voltages that range from -5 to +5, which are used in the POST. That would be an interesting place to look also. There is also a local -5 volt regulator in that circuit.

Interesting that this unit is not a fully synthesized design. For all its digital fanfare, the triangle is created with a diode ring and +/- current sources. Sine waves are created from triangle waves by analog shaping networks. HP did it like this for years before fully digital synthesis was practical.

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Thanks longbow for that insight. I've been vary busy on a 1987 Ford F350 6.9 Diesel I'm restoring this past week. changed the differential to a 1033 gear for better highway speed. But I spent most of the morning probing and found 2 tantalum capacitors out of spec. one in the calibration circuit its that you mentioned in you last post. given this units age and the amount of tantalum capacitors in the system I've decided to just do a hole sale replacement on them. I am going to change the 2 that I've found and see if that cures my problem. But since I don't normally carry that capacitors in stock Ill have to wait for them to come in. Thanks a bunch for jumping in! both of you! your willingness to help and old fart out is greatly appreciated.

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Thought I should mention that I got a full refund from the seller on this unit the other day. I've made 4 purchases from him in the past month that were supposed to be working units and 3 have not been. My project table is kinda full right now thanks to them.

[Longbow]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

A couple of comments: on an older unit like this I would expect a project, and not be amazed that it might need a little work to bring it back to life. On the high-end test equipments you can count on the fact that they were used continuously for years in a lab environment.

As for tantalum capacitors, they fail by shorting and blowing up. They generally don't change value or partially fail, but you may have some special types I have never seen. Designers use them because they are low leakage, which would be desirable in test equipment, but they don't withstand overvoltage or reverse voltage as well as typical aluminum electrolytics. Do you really have failed tantalums? Besides, replacing them with new tantalums is going to cost a fortune. I would re-assess.

[slburris]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

I have a 288 with the same OFSTGAIN error, so I'm interested in what it turns out to be for you.

Scott

[rlb245]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Ill give you a shout if this cures it

[Longbow]

Re: WaveTek Synthesized Function Generator Model 288 20Hz to 20Mhz

Which 2 capacitors are you referring to? What were their measured values and/or ESR? The shotgun method has occasionally worked in the past, and might work this time but I don't recommend it. The troubleshooting guide lists 3 boards that might generate your error. A quick check of the test points on those boards should provide some good information. Also with anything this old, replacing the backup battery is always a great idea.