HP 6227B - 'cloudy' (micro-scratches) meter windows - Page 1
Forum section: electronics / testgear

author: Sparky
author_rank: Frequent Contributor
timestamp: May 16, 2014, 06:14:15 pm
content: Hello fellow enthusiasts,I recently acquired a HP 6227B on eBay; it is in pretty good condition. The voltage/current potentiometers and knobs have been swapped from the default double pot. fine/coarse controls, to 10-turn single pot variants. I didn't know it at the time, but later found this is official options 007, 008 listed in the service manual. The master channel meter reads about 0.5V different compared to readings at the output terminal using a multimeter. I will be following through the service manual and hope to correct this. The slave channel is spot on.In the meantime, during cleaning of the enclosure I used a "magic eraser" (melamine foam) which did a great job cleaning away dirt and stain marks. However, I made the poor decision of using it to clean the windows of the panel meters. In the photo attached the window on the left is clear, whereas the one on the right is considerably cloudy --- microscratches from the melamine foam.I didn't realize how soft the plastic of these panel meters was.It's quite bad and I want to restore it to original condition. I wonder why my options are? Is the window part of the meter housing itself? Is it possible to replace the window, perhaps from other meters of the same size? Or, would I have to somehow polish/buff the microscratches out, e.g. using a polishing brush on a Dremel tool or similar. I hope to get some advice from others here before I attempt fixing it.I notice some other tips on HP 6227B restorationhere; I will check this out when I open my unit to troubleshoot the meter reading for the master channel I mentioned above.Thanks for further tips folks!Sparky

author: rdl
author_rank: Super Contributor
timestamp: May 16, 2014, 06:39:56 pm
content: I would try polishing first. Do not use a dremel, It'll probably run too fast and may melt the plastic. Just do it by hand. If you can open the meter up and find a way to remove the plastic front from the meter, that would be best. Otherwise just mask off the front panel around the window and buff it by hand.edit: You can usually find plastic polish in small quantities at a hobby shop that sells plastic models. As a first shot, you might even try a bit of toothpaste.

author: krivx
author_rank: Frequent Contributor
timestamp: May 16, 2014, 06:54:24 pm
content: You can sometimes get PlastX at fueling stations, it's used for polishing headlights.

author: casinada
author_rank: Frequent Contributor
timestamp: May 16, 2014, 07:03:07 pm
content: U're in the USA:http://www.autozone.com/autozone/accessories/Meguiar-s-PlastX-clear-plastic-cleaner-and-polish/_/N-25ke?itemIdentifier=419400_0_0_Or any other Car store, Hobby store, etc.

author: retiredcaps
author_rank: Super Contributor
timestamp: May 16, 2014, 07:06:54 pm
content: Quote from: Sparky on May 16, 2014, 06:14:15 pmCheck out mrmodemhead's blog entry.http://mrmodemhead.com/blog/dirty-multimeter-clean-up/with real world results athttp://mrmodemhead.com/blog/gallery/uni-t-ut70b-dmm/

author: Sparky
author_rank: Frequent Contributor
timestamp: May 16, 2014, 07:31:56 pm
content: Awesome! Thank you, Guys! These are all really helpful pointers in the right direction! Especially the webpages mentioned byretiredcaps, which lists the exact problem with the magic eraser I had ("will haze clear plastic"). It seems my best option is the PlastX plastic polish mentioned in the replies and also on the webpage. Once I have done it, I will post a follow-up picture!

author: sdg
author_rank: Regular Contributor
timestamp: May 16, 2014, 08:47:49 pm
content: Quote from: rdl on May 16, 2014, 06:39:56 pmTamiya Polishing Compound.Every self-respecting scale models shop should have it.

author: Sparky
author_rank: Frequent Contributor
timestamp: May 16, 2014, 09:00:28 pm
content: Update! I was rather excited to try this out, so I went and got the PlastX polish from an auto shop a couple of minutes away. Instant improvement! It did not take a lot of polishing to get this improvement --- only a few minutes. See the photo attached.When I take the unit apart to fix the calibration issue I have on the master channel, I will remove the panel meters from the enclosure so I can polish the windows to the edges. I am relieved though, to have corrected to quite good condition the problem I created already.Quote from: sdg on May 16, 2014, 08:47:49 pmthank you for this extra tip! I wonder if this polishing compound will improve clarify even further? I imagine it might, as the small scale models I've seen usually have very highly polished windows. I will have a look for this and try it when I do the disassembly I mentioned above.I will update with further progress once the repair is complete.Thanks all!Sparky

author: PedroDaGr8
author_rank: Super Contributor
timestamp: May 16, 2014, 09:16:04 pm
content: Yeah PlastX is your best bet.

author: sdg
author_rank: Regular Contributor
timestamp: May 16, 2014, 09:37:48 pm
content: Quote from: Sparky on May 16, 2014, 09:00:28 pmThat's not polishing, at least not only : a common trick with scale modelers is to dip transparent parts in Johnson's Klear -- it's basically a gloss acrylic varnish that dries to a very hard finish. Degrease the parts, dip in Klear, soak the excess and let dry overnight away from dust. And if the result is not to your liking, Klear can be stripped with propanol or ammonia.

author: Sparky
author_rank: Frequent Contributor
timestamp: May 16, 2014, 09:51:24 pm
content: Quote from: sdg on May 16, 2014, 09:37:48 pmOh, I see. Thanks for the further insight. I won't be dipping the meters in anything that's for sure. But, I'll see what, if any, improvement the Tamiya Polishing Compound makes over the PlastX.