HP 33120a – s/n question & do’s and don’ts in cleaning the instrument - Page 1
Forum section: electronics / general

author: Christe4nM
author_rank: Unknown
timestamp: July 07, 2012, 10:30:56 am
content: Hello everyone,Yesterday I received my HP 33120a AWG I won on eBay. This particular one also has option 001, which include a PLL and TCXO timebase. I haven’t had the chance to turn it on, or better yet to take it apart, but I’ll do a teardown soon. For now I will ask your help:I understand that there are several versions of the service manual around, mainly since there are slight differences in some components between HP and Agilent branded units. This unit’s s/n starts with US3602, so if I understand correctly that means it’s 1996, week 2 right? Which HP service manual do I need? These are the ones I could find: 33120-90017 and 33120-90014. Alas the latter is only found in printed form on eBay.Now the unit looks like it has been in a lab/warehouse for quite some time, and when handling it leaves a dark residue on your hands. In some spots the plastic is not at all (light) grey anymore. Nothing out of the ordinary but I want to clean it thoroughly. I just have no idea what the do’s and don’ts are. So1) What is the best way to clean the enclosure, frontpanel, knobs etc?2) Any idea how to get rid of the scratches in the black display cover; polish maybe?3) All the connectors are both dusty (the kind that sticks) and a tiny bit corroded. How can I clean those without damaging any connected circuits?Thanks for your help!- Christean

author: Unknown
author_rank: Unknown
timestamp: July 07, 2012, 10:43:37 am
content: From the 90017 service manual:QuoteThe date of the serial number indicates the last major revision, not the production date. The date codes on semiconductors is usually a better indication.I would use a moist cloth (for external parts) or IPA to clean it. I would not use anything abrasive on connectors, it will strip off the plating. IPA with a brush or Q-tip should be safe.

author: Psi
author_rank: Super Contributor
timestamp: July 07, 2012, 10:50:03 am
content: Don't use acetone, it will dissolve most plastics and ruin their finish.

author: Rerouter
author_rank: Super Contributor
timestamp: July 07, 2012, 11:03:44 am
content: Quote from: Christe4nM on July 07, 2012, 10:30:56 am1. Isopropyl Alcohol is my prefered chemical for cleaning front panels and knobs of unknown materials, (isocol under some chemists is fairly additive free)2. Brasso metal polish, the stuff can lift scratches out of just about anything,3. If exposed enough, a light touch of high grit sand paper can help, the sticky dust well no matter how you approach it that gets hard to clean,

author: JuiceKing
author_rank: Regular Contributor
timestamp: July 07, 2012, 11:14:44 am
content: Windex works well and in my experience doesn't harm panel markings. Spray it on a paper towel or q-tip and wipe lightly. Use an X-Acto knife to lift stickers--it's much better than simply trying to pull them off. Goo-gone will remove most sticker residue and doesn't seem to harm paint, but even with these gentle solvents, use them sparingly. I find that alcohol is good for cleaning metal contacts but it harms plastic more than Windex so be careful with it.

author: Christe4nM
author_rank: Unknown
timestamp: July 07, 2012, 03:53:29 pm
content: Thanks people: I will start with IPA, and find out if that is enough. Concerning the panel markings: there seems to be an extra transparant layer on top of them so they won't wear off. But I'll be careful and try Windex (or Glassex as it is named in the Netherlands) first.Quote from: alm on July 07, 2012, 10:43:37 amYes I read that too, but then I found this posthttp://www.edaboard.com/thread179383.htmlfrom someone we're familiar with on the EEVblog forums. So I wanted to find out whether free_electron's statement there can be confirmed.

author: free_electron
author_rank: Super Contributor
timestamp: July 07, 2012, 04:02:16 pm
content: yep. that is a printed manual only. and i have one. i fixed my two generators >and i have those transistors as well should you need them. they are obsolete but i found abunch at the local surplus partsstote.if you ever need obsolete semiconductors :www.acecomponents.com. it's a monster text file with thousands of parts ...cleaning : IPA , windex or clorox wipes. works wonders. 409 works fine too since there is ammonia in it.

author: Unknown
author_rank: Unknown
timestamp: July 07, 2012, 04:46:05 pm
content: I would only spend money on the 90014 manual if you find a problem in a circuit not covered by the 90017 manual. I have been able to fix minor problems in HP branded instruments with the 90017 manual without coming across any differences. If the only changes are limited to the output stage (I haven't seen the 90014 manual), then it doesn't make sense to buy the 90014 manual unless you have a damaged output stage. You could also try to ask f_e to scan the relevant page(s) covering this circuit.

author: free_electron
author_rank: Super Contributor
timestamp: July 07, 2012, 06:23:32 pm
content: yep , it's only the output amlifier that has changes. i needed the manual because my transsitors were fried beyond reading the type numbers ..the service manual has the part numbers..the schematic is identical ! no parts added or values changed appart from the typenumber of the transistor ( and the package of the transisotr. went from sot89 to sot223 )

author: Christe4nM
author_rank: Unknown
timestamp: July 07, 2012, 07:38:32 pm
content: I just checked: my 33120a has the PZT3906 in SOT223 in the output stage. The unit works well, so I don't have the need for a service manual as of yet but it's good to know I've got the right one just in case.It seems my idea to do a teardown has become obsolete though since f_e is clearly doing one already. Looking forward to it ;-)

author: pickle9000
author_rank: Super Contributor
timestamp: July 07, 2012, 07:57:46 pm
content: The standard for cleaning plastic panels is 1 drop of sunlight liquid to 2 oz water. It will remove most grime. Apply to a clean cloth and go at it. A clean natural bristle brush can also be used as a gentle scrubber. A clean dry brush can be used to pull wet grime out afterwards, dab the brush on a towel to clean. Don't use artificial brushes (nylon for example) because the bristles can scratch surfaces. Avoid soaking any panels.If you are going to use any cleaner test it on the back or underneath of the case to ensure that it will not cause any problems....mike

author: codeboy2k
author_rank: Super Contributor
timestamp: July 07, 2012, 10:29:31 pm
content: Quote from: pickle9000 on July 07, 2012, 07:57:46 pmput that sunlight solution into a plastic tank, duct tape a peizo onto the side of it and use your benchtop function generator to send a 50kHz sine wave through the tank. Voila! instant ultrasonic cleaner. Drop all the knobs and little bits into the tank, come back in a few hours.. you can thank me laterone of these things from a kid's toy..

author: Christe4nM
author_rank: Unknown
timestamp: July 08, 2012, 02:28:06 pm
content: So the unit has been taken apart, cleaned with IPA (worked well), put together and turned on for the first time in my ownership.Worked perfect, as expected.

author: nctnico
author_rank: Super Contributor
timestamp: July 08, 2012, 02:38:20 pm
content: I see you are from NL. Next time you clean equipment use this:http://www.eco-logisch.nl/St-Marc-Sint-marc-verfreiniger-1227In the US something similar is sold under the name 'simple green'.

author: SeanB
author_rank: Super Contributor
timestamp: July 08, 2012, 02:44:12 pm
content: Codeboy, i did that with a bigger transducer and a tank, works well enough, but I definitely can use a better power source to drive the big transducer.

author: codeboy2k
author_rank: Super Contributor
timestamp: July 09, 2012, 12:02:09 am
content: Quote from: SeanB on July 08, 2012, 02:44:12 pmHaha.. I was half joking, I knew the concept was sound, but I've never tried it. I don't know if such a small transducer can move the mass of solution in the tank. Probably not.Good to know that it works with a bigger transducer. What frequency did you use? Maybe next time you could enhance it with an external NPN-PNP push-pull driver and hook that to a bipolar power supply, and drive the push-pull from the function generator.

author: SeanB
author_rank: Super Contributor
timestamp: July 09, 2012, 04:47:35 am
content: Blocking oscillator to drive it with around 400pp at about 25kHz, the transducer is the C in the LC tank of the oscillator. Was a kit i ordered as parts from RE in the USA about 20 odd years ago, and ir had a 110V oscillator that I redid to run off 24V from a scrapped switcher.

author: codeboy2k
author_rank: Super Contributor
timestamp: July 09, 2012, 05:49:04 am
content: Quote from: SeanB on July 09, 2012, 04:47:35 am<- Wow. That's me raising an eyebrow. I hardly expected to need a 400V pp oscillator ...

author: SeanB
author_rank: Super Contributor
timestamp: July 09, 2012, 03:44:39 pm
content: Well, it is a pretty poor coupling to the tank, as you are driving a high impedance load ( the resonator0 and trying to get around 50W of power into the tank. I used a nice tank unit that had a pair of 200W transducers per oscillator, and 2 oscillators. They used a 60V power supply that went to a simple colpitts oscillator using a ginormous heatsink and a 2N3773 transistor as a power driver. Brute force, if a little hard on the transistors, as they would pop if the tank was turned on empty. Only did that once, it was not in the thin manual it came with. Used 200l of TCE per fill, and did vapour distillation of it in use with a refrigerant circuit.

author: Dawn
author_rank: Regular Contributor
timestamp: July 11, 2012, 05:19:37 am
content: Going a bit back to the OP, Clear Ammonia is a pretty safe, but effective cleaner that leaves no residue for exteriors. A solution of ammonia and water is a very good cleaner for knobs and external hardware with a lot of hand soil in ultrasonic cleaners. It's also excellent for cigarette smoke yellowing. I haven't ever seen it bother markings or the finish. Many of the other cleaners like recommended bathroom foaming cleaners leave a sticky residue. Some of the strong houshold cleaners like 409 and Fantastic here in the states can discolor finishes.