Video Teardown and Repair of an Agilent 33250A Arbitrary Waveform Generator

[Hugoneus]

In this episode Shahriar repairs an Agilent 33250A function and arbitrary waveform generator which does not power on. The unit is equipped with a soft power switch which might be responsible for the fault. After a brief look at the unit's constructions, the fault is traced to a few possible locations.

The schematic of the soft power circuitry is presented and the internal switching power supply is closely examined. After the fault is located, the repair is presented. The block diagram and operation of a current mode DC-DC switching IC is also presented.

See video here: [51 Minutes]:
http://youtu.be/eMlRnO_bFAI

More videos at The Signal Path:
http://www.TheSignalPath.com

[rstoer]

Excellent! I always enjoy your videos. Right after work I'll be getting my popcorn and curling up in front of the TV. Thanks for taking the time to make these.

[Hugoneus]

Excellent! I always enjoy your videos. Right after work I'll be getting my popcorn and curling up in front of the TV. Thanks for taking the time to make these.

No problem.

[twdotnet]

I've just seen your video and liked it very well - even if the problem wasn't that spectacular. 

[Radio Tech]

Another great video Shahriar.
There are 3 folks I like to watch, Daves, Alans, and yours.
I have learned quite a lot from your videos.

Thanks.

[Hugoneus]

I've just seen your video and liked it very well - even if the problem wasn't that spectacular. 

I have something else which needs repair... I think it might have a more interesting fault!

[Radio Tech]

I have something else which needs repair... I think it might have a more interesting fault!

Can not wait to see it. I am sure it will be great!

[Hugoneus]

I've just seen your video and liked it very well - even if the problem wasn't that spectacular. 

I have something else which needs repair... I think it might have a more interesting fault!

Wasn't the phrase "May you live in interesting times" intended to be a curse?
I found the description of the diagnostic process more generally interesting and educational than the actual fault. I am unlikely to open some high end test equipment but the tip about the charge in the capacitor not bleeding away when the standby circuit has failed was most helpful.

Do you delete comments from YT. I can't find a comment (question really) I left. Is there some rules I should follow before leaving a comment?

Wilfred,

I have never erased a YouTube comment from my channel, except for one incident where a viewer was aggressive and rude to anther viewer. Usually YouTube marks some comments as spam, I try to release those as soon as I see them.

[pickle9000]

Hey Shahriar,

Another good one. Most repairs are simple but the approach is important and you do that well. Of course repairs apply to design as well.

One thing I do often is solder a wire to important test points (and label them). It's a must for some stuff too small to probe. My eyes are not as good as they used to be.

As for the missing screw, could well have been rattling around in the case and removed for that reason. Then time finishes the job.   

[HighVoltage]

Thanks for another great video.

I have a broken 33220A that does not turn on, may be I will find something similar as a problem.

Your 33250A has the 10MHZ output and input in the back but I did not see a separate precision oscillator board.
How is the precision 10 MHZ generated in this unit.
Somehow I expected a PCB directly connected to the BNC connectors of the 10 MHz IN and OUT.

[Yago]

The usual great standard of yours Shahriar.
Thanks for posting, and look forward to more learning

[Macbeth]

Great video as yours always are Shahriar. They don't come as quick and fast as Daves, but the material is always interesting and well worth the wait!

Good call on those mains capacitors as used in SMPS's. Many years ago, as a Bench Service Engineering Apprentice I had they joy of fixing a totally dead top of the line Philips TV. It's SMPS had two massive caps (nice fancy Panasonic ones) coupled to a split supply with 2 bridge rectifiers. Despite the TV being off for at least 20 minutes I had the joy of those capacitors discharging into my thumb as I removed the PCB from the chassis. 

I've had some interesting electric shocks in my time, including full on 240VAC mains, and 30kV EHT, but those caps discharging something like 750V DC was the worst by far. The protruding leads at the bottom of the PCB managed to burrow into my skin a few mm where they settled and carried on arcing through my flesh. I actually had two holes and a kind of underneath the skin "tunnel" that they burned through

I've come to treat SMPS's very gingerly indeed after that incident.