[SOLVED] HP Agilent 53181A  display Fail (wrong segments) - Page 1
Forum section: electronics / repair

author: charlyd
author_rank: Frequent Contributor
timestamp: December 15, 2017, 10:12:44 pm
content: hello today i got a new project it is a HP Agilent 53181A. This unit has a display error ( see picture ) .any advise on were to look for is it the display driver or the processor..or did someone had this problem also on a 53131A or 53132A or 53181A and fixed it?i am curious about the reactions..lots of pictures below

author: ivi_yak
author_rank: Regular Contributor
timestamp: December 15, 2017, 10:27:24 pm
content: seems cable to display is failed? could you teardown for additional photo?

author: HighVoltage
author_rank: Super Contributor
timestamp: December 16, 2017, 11:24:46 am
content: It could be a bad VFD but most likely not.Check all cable and wire connectionAlso, some of these instruments have problems with corrosion and I had one in the past that was corroded on one of the VFD pins and I resoldered all pins and solved a problem that way.

author: charlyd
author_rank: Frequent Contributor
timestamp: December 16, 2017, 02:23:09 pm
content: i am going to check out the flat cable to the front board maybe that is what i overlooked. i will come back on that one.+++ a while later +++i checked the flat cable it is ok check the voltage supplies all ok.i added the schematic part from the display and control chipsthe clock was also there.

author: charlyd
author_rank: Frequent Contributor
timestamp: December 17, 2017, 06:59:53 pm
content: today i took apart the display board and looked underneath the VFD and cleaned the board double checked the flat cable again. but for sure it is not the cable.it is really or the HV518PJ display driver ...or coming from the mainboard. anybody ever had a broken HV518PJ and that it is going to give strange numbers and letters so all messed up? i nearly can not believe that the problem lies with the driver.

author: texaspyro
author_rank: Super Contributor
timestamp: December 17, 2017, 07:46:27 pm
content: I'd bet on the display driver.BTW, I've seen cases where a short in the display driver chip sent the VFD high voltage to the TTL I/O pins and cooked a lot of stuff.

author: charlyd
author_rank: Frequent Contributor
timestamp: December 17, 2017, 10:37:33 pm
content: i hope so today i ordered the display driver chip HV518PJ because it is situated underneath the VFD so probing is not really possible..[ but christmas-period it can take up 30 days shipping now.. pfff.  last week i ordered parts for my Fluke 6062A and these took more then a week from nearly arround the corner :-( ]i wil add more picture now..the bottom pictures numbers are recognizable others are not..

author: duak
author_rank: Super Contributor
timestamp: December 18, 2017, 01:47:00 am
content: Is the cable a ribbon type with IDC connectors or a planar type? ie., metal conductors deposited on a polymer backing? I recently replaced one on a CNC control where one conductor was intermittant.Was the device assembled under the ROHS directive and used lead (Pb) free solder? I understand that Tin whiskers can form and connect two chip leads together. I believe I encountered this once on a memory DIMM and using a small stiff bristle brush on the soldered leads made the DIMM work again.Cheers,

author: charlyd
author_rank: Frequent Contributor
timestamp: December 18, 2017, 01:07:51 pm
content: it is a IDC connector i de-soldered and clean/checked underneath and reinstalled it. at the end beeped all the pins from board to board..(was 100% ok but now for sure.)as i told above i ordered a HV518PJ because it is positioned at a terrible place to probe and cost nothing to replace.But i would more suspect one of the demuxers or the multiplexer chip. but first wait for the VFD driver to arrive, maybe it is an easy one.and my new frontcover is also on the way.

author: Tony_G
author_rank: Super Contributor
timestamp: December 19, 2017, 11:12:05 pm
content: If you're consistently getting the same corrupt display for something fixed like "Selftest Passed" then to me it would seem that the serial data stream into the VFD controller is probably correct and you have a bad VFD controller.If you're getting random errors on that fixed string then U19 is probably the issue (or at least the next step in the chain).TonyG

author: charlyd
author_rank: Frequent Contributor
timestamp: January 13, 2018, 06:06:25 pm
content: +_+_+ one month later +_+_+_today my hv518 chip arrived. last week i placed a chip-socket so i ony had to push it in solder the vfd back and let see what happens...still the same.. i suspect the demuxer much more but this will be later this week...to see.

author: charlyd
author_rank: Frequent Contributor
timestamp: January 15, 2018, 11:10:27 pm
content: today i checked out the 3x 74138 ( U15,U16,U17 )and 1x 74251( U19) but none of them. :-(

author: HighVoltage
author_rank: Super Contributor
timestamp: January 16, 2018, 07:51:57 am
content: Did you test the display manually on each segment?

author: charlyd
author_rank: Frequent Contributor
timestamp: January 16, 2018, 10:07:25 pm
content: how can i do that my display expects a clock and data Train...i replaced the display controller chip under the vfd.so please give me hints to test the display manually.. ;-)

author: HighVoltage
author_rank: Super Contributor
timestamp: January 17, 2018, 08:09:49 am
content: Its very simple:Apply ground and supply voltage to the VFDThen apply voltage to a particular grid.Then apply 12V signal to any of the input wires (segments input) of that particular grid and you can see each display element light up.Go through each segment on that grid and then switch over to the next grid and repeat.

author: Tony_G
author_rank: Super Contributor
timestamp: January 17, 2018, 04:17:03 pm
content: Quote from: HighVoltage on January 17, 2018, 08:09:49 amIsn't this what happens on device start-up when all segments are lit?TonyG

author: charlyd
author_rank: Frequent Contributor
timestamp: January 18, 2018, 01:08:05 pm
content: hello yes i passed that station already i think and i am now looking into the signals from the input amp & count ic these signals are inputted on the U19 and partly on het U16,17,18.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 18, 2018, 03:12:20 pm
content: You have a short between the left and right bottom segments (not sure what they are called). So it's either the display, the board or the shift register.

author: Tony_G
author_rank: Super Contributor
timestamp: January 18, 2018, 03:51:46 pm
content: Quote from: PA0PBZ on January 18, 2018, 03:12:20 pmAhh I see what you and HighVoltage are saying now - If there were shorts then the wrong or additional segments would turn on - Looking at the images for example, you can see that the bottom right segment of the 3rd numeral is shown as always on (it's turning the E into a 6) - By testing individual segments you could confirm if this was coming on and part of a different segment drive.Charlyd - You might just want to try that 3rd numeral first and see if you can manually bring on only 1 segment at a time.TonyG

author: free_electron
author_rank: Super Contributor
timestamp: January 18, 2018, 04:54:23 pm
content: segment C is shorted the segment E. either in the display, or in the driver ....

author: HighVoltage
author_rank: Super Contributor
timestamp: January 19, 2018, 01:29:28 pm
content: Quote from: Tony_G on January 18, 2018, 03:51:46 pmExactly!I should have been more clear on the explanation.

author: charlyd
author_rank: Frequent Contributor
timestamp: January 19, 2018, 10:36:38 pm
content: i am going to pull the display off again and test it on the bench. come back with the results ;-)

author: charlyd
author_rank: Frequent Contributor
timestamp: January 20, 2018, 01:10:32 pm
content: hi today i found what is wrong , thanks to PA0PBZ . i thought let's take it apart again and test all segments one by one..and indead it went wrong. i was puzzle-ing arround how to test here is how this VFD can be tested. (see picture)i gave the picture some blue lines on some random digits just to show you what happenedon every gridthey lite up together.so next is to order a new VFD.i just renewed the HV518PJ could this have killed my controller chip again?? High-Voltage outputs shorted.

author: HighVoltage
author_rank: Super Contributor
timestamp: January 20, 2018, 01:35:03 pm
content: Great that it worked out by manually testing.I still have a used display, if you are interested.

author: Tony_G
author_rank: Super Contributor
timestamp: January 20, 2018, 04:06:54 pm
content: Good to hear (well good that you found the fault not that it was faulty). I wonder where in the VFD it shorted.TonyG

author: charlyd
author_rank: Frequent Contributor
timestamp: January 21, 2018, 09:10:31 am
content: yes i share a sort of same feeling, i never heared of this type of faulty VFD.. but ok.yep after replacing the VFD-display the unit worked like a charm.