Keithley 2015 THD faulty after 2-3hrs when warm - Page 1
Forum section: electronics / testgear

author: holmsn
author_rank: Newbie
timestamp: September 10, 2014, 03:13:56 pm
content: Got this today from ebay on a Buy-it-now so a 14 day return is possible but I'll have to bear the return shipping cost.Initially it worked on Volts AC/DC , Ohms, Frequency then fed it some streamed wave files from an Ipad and measured 0.001% THD on 250 and 1k and 0.006% on 10kHz, quite believable I thought. Came back an hour or so later to use its own source , using the test routine in the manual and got a rather high (0.5%) figure - should be 0.2% @ IkHz and also a bit unstable. Worse, a bit later still, the meter only now seems to work on continuity even after a power reset and factory default setting.Could it be dried up C's in the power supply, I wonder ?, I'm a bit reluctant to break any of the electrical safety stickers yet around the sides of the case, the rear and the rack sides show signs of corrosion

author: jpb
author_rank: Super Contributor
timestamp: September 10, 2014, 03:27:53 pm
content: If you look at the calibration date and count it will give some indication of age. It might well be 20 years old.I changed all the caps in the one I bought as a precaution. (I also ended up replacing the display, the screws and a plastic bit holding the display as well!)Whether it is worth the risk of keeping it and replacing the caps rather than just returning it I suppose depends on how much you paid for it.

author: holmsn
author_rank: Newbie
timestamp: September 10, 2014, 05:50:03 pm
content: You're dead right !, last cal in 2011 and count at 17. And I thought one these was a better bet than a 30-40 year old HP Analyser.On the plus side the VFD display is still decently bright enough( for me anyway ) and it seem to work initially too so my little soak test probably proved too much for the electrolytics, the supply rails are probably crawling with ripple. All the selection logic and display indications are OK and the initial firmware message is displayed.It cost £250 but if I return it I'll end up spending £20+20 on postage for nothing, so since I'm sure its fixable ultimately I'll get cracking in a few days

author: jpb
author_rank: Super Contributor
timestamp: September 10, 2014, 08:52:41 pm
content: The advantage of being that old is that the reference should be pretty stable.If you can avoid changing the display it is all for the best, it is hard to get the board complete and just doing the display is a bit of a pain.I described the trauma in this thread:https://www.eevblog.com/forum/testgear/replacing-a-keithley-2015-thd-display-scary-stuff!/EDIT : the URL doesn't seem to be working correctly, but my several attempts to fix it haven't worked.

author: retiredcaps
author_rank: Super Contributor
timestamp: September 10, 2014, 09:45:19 pm
content: Correct URLhttps://www.eevblog.com/forum/testgear/replacing-a-keithley-2015-thd-display-scary-stuff!

author: retiredcaps
author_rank: Super Contributor
timestamp: September 10, 2014, 09:46:36 pm
content: Quote from: jpb on September 10, 2014, 08:52:41 pmYou need to put the entire url (including !) insideCode:

author: jpb
author_rank: Super Contributor
timestamp: September 11, 2014, 09:50:40 am
content: Quote from: retiredcaps on September 10, 2014, 09:46:36 pmI did try doing that (by shifting the  bit) but for some reason it still kept taking me to the top of the page rather than the thread. I even tried e-mailing the link to myself (which worked) and then pasting it back into the post but it again went wrong. In the end I decided that life is too short and gave up (on the efforts to post - not on life!)Thanks for fixing it.

author: holmsn
author_rank: Newbie
timestamp: September 11, 2014, 03:45:19 pm
content: Got stuck in today, turns out it'sonlya 2003 model, one clear stamp on Display Board for 2003 and a smudged 20** on the DSP, the main board also was vintage 2002 according to the printed traces. All told very clean inside no muck on boards fortunately although any mounting screw shows some corrosion like on the rear panel. C156 6800uF a bit wobbly for my liking still will change all electrolytics including the ones near the back BNC's (output DC Blocks ?). What about the little surface mount (tant ?)100uF near the ADC on the DSP board should that be renewed as well , even if the thing is nearer 10 than 20 years old ?

author: jpb
author_rank: Super Contributor
timestamp: September 11, 2014, 05:11:11 pm
content: I just changed the electrolytics - there were enough of those! Of course I can't say if the tant should be changed until mine blows up - then I'll know that I should have!