Fluke 8840A - Page 1
Forum section: electronics / repair

author: grafas
author_rank: Newbie
timestamp: August 20, 2015, 07:46:40 pm
content: Hey guys,So... I figured that I needed to upgrade my setup a bit. Since I only had a cheap-ass multimeter, I looked for a proper one on ebay. Following Daves' practice, I bought a "Not working. For spares or repair" (I can change a cap!).Fluke 8840A - 5 1/2 digit. For 65 USD (plus shipping and customs charges :/) - a bargain.Well, it looked battered and the sellers description was "does not power up".After some initial checks, I tried to power it up and - bingo. The thing works. The screen is nice green vacuum, relays are switching and everything. Yay ^^But the reading does not change whatever I do. Looks like, whatever first value on power-up is, it stays pretty much the same. It drifts a bit, but if on power-up it reads, lets say, +70.040mV, then 2V range reads 0.07012; 20V - 0.7014; 200V - 07.021; 2000V - 070.24; mA DC - 702.92 and so on. That is with nothing on the input (checked both, front and rear).Time to read themanual! Chapter 6 - Maintenance, 6-37 initial troubleshooting (page 130). During self test, I get ALL errors. Plus readings are in error (I mean 70V on 2000V range). All power rails seem OK, thus - A/D converter or Track/Hold is the problem. So, as per manual, I connected TP103 to ref. low and got -0.00002V. So, the precision reference and A/D are most likely good. Phew..Next step - Track/Hold (page 143). All the voltages test OK. Oscilloscope trace on TP201 is a nice and square wave. The thing is.... it shouldn't be square. But the manual doesn't say what to do next!I tried to follow the next three steps (presumably you do those however the trace looks like). 1st - done, 2nd - fail, 3rd - should I keep U301-14 grounded? I don't have enough hands :/So, I tried the next paragraph, ignoring 3rd step - lift one end of R318 and apply <+2V to TP103. I used a 1.5V coin cell. Screen shows -1 and blinks. Not a good sign. If A/D converter was OK, 8840A should show the same voltage with the opposite polarity.So now I'm back to A/D converter?

author: retiredcaps
author_rank: Super Contributor
timestamp: August 20, 2015, 07:56:33 pm
content: Quote from: grafas on August 20, 2015, 07:46:40 pmI don't have any Fluke bench meters and I haven't taken any time to look at the manual, but the above ebay seller is a subject of discussion here at eevblog often not in the a positive way. Some members will know what I'm talking about.Battered, doesn't even begin to describe some of the past and likely future auctions from this seller.

author: grafas
author_rank: Newbie
timestamp: August 20, 2015, 08:03:30 pm
content: It was a 3V coin cell....I just tested it with a proper 1,5V - perfect. Shows negative 1,5 :>A/D converter IS OK.The seller... Well, he DID describe it as not working. And I did see the photos, it was risky. And the unit was nicely packed. Looks like this 8840A came out from some destroyed building or something like that. But I mean, I can live with a 5 1/2 digit multimeter even if it doesn't look very shiny, as long as it works.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 20, 2015, 08:10:07 pm
content: Quote from: grafas on August 20, 2015, 08:03:30 pmYes, I understand that part about "as is, parts, not working", but if you have seen some of the past auction pictures, you will understand.QuoteFrom some of the past auction pictures, we speculate it comes from ex military active field use.QuoteI totally agree. Sometimes, based on past auction pictures, there is no way that equipment will ever be made to work again.

author: OldSchoolTechCorner
author_rank: Frequent Contributor
timestamp: August 20, 2015, 09:24:08 pm
content: I would avoid that seller at all cost. That seller is overpriced and most is beyond any means of repair, as they treat their inventory very poorly. Bought a older RF signal generator that was suppose to be working and look to be in good condition and was a Marconi 2022E version, from them a while ago and they sent a completely different unit a D version, had some water damage to the case, lucky it didn't corrode the board and someone was clearly in it and hook up DC fan to AC fan port and was a complete mess. Ended up getting most my money back, but had to put in over $75 in parts, as had to rebuilt power supply, replace buffer IC and replaced 4 modules and over 12 hours of labor to get it within specs again. The second time I bought from them pretty much the same story, but ended up just sending the item back as wasn't worth repair, as came with crushed damage and now avoid that seller at all cost.The best seller to get surplus test gear from is this seller below. They take much better care of the inventory and isn't left outside like the other seller is. Just bought a Keithley 2015 and works with no issues and bright VFD and is in great shape for cheap price for what it is, just have to order a tilting bail and rear feet, which was expected. They have other Multimeters and AS-IS ones cheaper and is a much better bet. Item came in 2 days to the US.http://www.ebay.com/itm/121706248830?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

author: codeboy2k
author_rank: Super Contributor
timestamp: August 21, 2015, 05:51:04 am
content: A lot of that seller's past gear is shown here :https://www.eevblog.com/forum/testgear/abused-test-equipment/

author: grafas
author_rank: Newbie
timestamp: October 12, 2015, 07:52:02 pm
content: It's been quite a long time since the last post, but finally I got some more time to try and fix this one.The A/D converter is OK (like mentioned previously), so the next step was Track-Hold circuit. I measured the waveforms - they do not match the ones you should get according to the manual (page 6-40). Also, following the 6-63 chapter "Track/Hold Troubleshooting" I got Fail on step 2 but not on step 3. That means - "U303 is bad". So that's useful - all I need now is to get the spare chip.And here's the catch - does anyone know what this chip is? Can I get a replacement somewhere? It is not listed in the manual, and all that is written on it is:FLUKE70000132587 104 (as old as me)... and four other chips have the same markings (U301, U302, U402, U403)

author: tautech
author_rank: Super Contributor
timestamp: October 12, 2015, 07:58:05 pm
content: Quote from: grafas on October 12, 2015, 07:52:02 pmSee this thread:https://www.eevblog.com/forum/testgear/old-fluke-multimeters/drtaylorwill know, ask in the thread and/or PM him

author: xwarp
author_rank: Frequent Contributor
timestamp: October 13, 2015, 11:14:01 am
content: I have a spare 8840 parts unit.I can pull those chips if you are sure that is the problem.Send me a message.