old Fluke 8842A - advice request - Page 1
Forum section: electronics / testgear

author: not1xor1
author_rank: Frequent Contributor
timestamp: April 16, 2017, 08:14:25 am
content: Hiin few days I should get an old Fluke 8842A I bought from ebayI've no experience about bench multimeters and so would be glad to get a few advices about checking/hacking/improving the device.The device has both GPIB and AC options installed.The seller wrote it is in full working condition although there is no data about calibration and the calibration seal is brokenBTW where can I get the manufacture date? From the serial number?Or... should I just guess it from the date on the ICs inside?The best DMM I have so far is just a fairly new Brymen 867S that, according to a few different voltage reference ICs (3 MAX6250ACPA+ and 1 AD588BQ - 0.02% and 0.01% initial accuracy), seems to be within specifics.Besides that I have a few 0.1% 15ppm metal film resistors.I downloaded the 8842A manual from the net and plan to do the following:1) Set the AC supply to 240VAC (now we have 230VAC here in Europe).2) power on the device and see if it is still alive and smokeless3) run the test routine described in the manual and if no error are displayed...4) measure various DC/AC voltages, currents and resistors comparing the values with the Brymen ones5) check and in case of high ESR replace the PSU electrolitic capacitors? Or replace them in any case?in case of problems I'll obviously ask for more detailsBTW I think it would be quite useful if the more experienced guys made a sticky thread regarding most common advices for second hand equipment buyersthanks

author: tautech
author_rank: Super Contributor
timestamp: April 16, 2017, 08:48:31 am
content: You pretty much have the right ideas and they're a good place to start.Some further things I could offer:For old and unknown operational state, use adim bulb testerin series with the mains supply. It will prevent a major meltdown if something is seriously wrong. Google it.Linear PSU electrolytic caps are not low ESR variety and ESR readings will be higher in them, normally an Ohm or three. Let visual inspection be your guide to start with, look for bulges and leaks. Wholesale replacement of caps is not normally necessary unless the supply rails are not to spec and not exhibiting low ripple levels.Sometimes cap reforming with a variac or time on a dim bulb tester can prevent cap replacements.Get her running and check accuracy before hunting for something that might not even exist.A thread that might help and get replies from members that know your instrument intimately:https://www.eevblog.com/forum/testgear/old-fluke-multimeters/Others that might have the same model might hang out here:https://www.eevblog.com/forum/metrology/

author: mzacharias
author_rank: Frequent Contributor
timestamp: April 16, 2017, 12:56:25 pm
content: I would say since you bought it on eBay if you saw pictures of it working, don't worry about any "dim bulb tester" in this case. Just plug it in, check it's operation and enjoy. This series of mutimeter does have a history of bad solder connections at the main power transformer - which may not even appear bad. So if there is any problems, hard fail or intermittent, resolder these first.

author: not1xor1
author_rank: Frequent Contributor
timestamp: April 20, 2017, 09:34:06 am
content: thanks to both of you for your suggestionsI got the DMM yesterday and it looks like it is working as due, with a bright display and probably still within or quite close to specifications (see attachments below), psu capacitors are like new and the interior is very clean5volts MAX6250ACPA+ reference5volts MAX6250ACPA+ reference with 1:3 voltage divider (3 20k 0.1% resistors)20k 0.1% resistorThe only problem is the aluminium case that is really dirtyThe manual says to use just water, but I tried IPA although it seems to degrade slightly the grey coating (some kind of soft polymer, IPA probably dissolves phthalates or other plasticizer?).I wonder if I can just cover it with some acrylic spray.Any experience, any advice against that?thanks

author: GreyWoolfe
author_rank: Unknown
timestamp: April 20, 2017, 12:01:35 pm
content: Have you tried a bit of dish soap and water with a non abrasive pad? If they are available, Mr Clean Magic Eraser pads do a really good job.

author: not1xor1
author_rank: Frequent Contributor
timestamp: April 21, 2017, 11:48:07 am
content: Quote from: GreyWoolfe on April 20, 2017, 12:01:35 pmI unsuccesfully tried dish soap and will buy magic eraser, but the coating is fairly soft, almost like rubber and not smooth, it looks like artificial leather so I doubt magic eraser would work.In any case thank you for your suggestion.