fluke 8842A  IEEE not repsonding - Page 1
Forum section: electronics / repair

author: charlyd
author_rank: Frequent Contributor
timestamp: March 27, 2018, 03:27:05 pm
content: hello last night i tried to dip my 8842A IEEE 488 to Adr 16 after i switched dip A5 i got no response from the 8842A very strange.So after finding a youtube on how to display the GPIB adress of the 8842A just push  and it will display REMOTE XX [where XX is the ADR number.]but also that didnt work.. i opened the DMM and inspected the top-back IEEE board. ...looks ok.i did the test it starts continued from 01 ---> 22 without errors.any one ever experienced this??

author: dacman
author_rank: Frequent Contributor
timestamp: March 29, 2018, 01:20:26 am
content: There is troubleshooting information in the manual.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: March 29, 2018, 01:28:29 pm
content: Has it worked before?Years 'n years ago my 8842A had a problem with the IEE interface as well. Turned out there was a reverse tantalum cap in the POR circuit

author: charlyd
author_rank: Frequent Contributor
timestamp: March 29, 2018, 02:06:36 pm
content: @dacman i saw the troubleshoot info in the table with the 4 test modes ( which i really don t understand what shoot happen......is shows.. A1,A3,A5 switches to put in position: 1,0,x and the shortcut between TP903 and TP905 that pulls pin 22 of the IEEE chip from high to low ( TP903 is ground).but i didn t see anything happen to be honest.@RobNL: this is interresting information, can you tell me something more. as soon as i push the button  after a 1 second the display flashes but NO MESSAGE : REMOTE XXas if the board doesn t respond. I don t know if it ever worked because i bought the 8842A in working condition but never used the GPIB until now. of course i can go for a sort of recap.what is it exactly with the tantals and which tantals are suspious?

author: RobK_NL
author_rank: Frequent Contributor
timestamp: March 29, 2018, 03:27:29 pm
content: In my unit, C901 on the GPIB board had been mounted in reverse. Since it is not on a low impedance node, that will work for some time and it did. Over time, however, the GPIB became more and more unreliable. As the problem could often be solved by switching the meter off and on, the POR circuit was an obvious first candidate.Check the power supply first (5V across TP902 - TP903).

author: charlyd
author_rank: Frequent Contributor
timestamp: March 29, 2018, 07:32:52 pm
content: hello yes yes checkt the 5volt already is ok. i gonna look at the C901 if it is upside down....or do i need to just replace it.i have this board 8840A - 4005 rev. E no piggybag chip (U911 on U901) . so i was looking for the right schematic for this board and i can not find it anywhere....anybody??btw C901 is not upside down on my board...

author: charlyd
author_rank: Frequent Contributor
timestamp: March 30, 2018, 07:39:28 am
content: but my board has the black U901 chip.i don t know if the software inside the U901( U911) is meant to be just for the 8840A and the other only for the 8842A or if they are interchangable.Maybe someone with both 8840 and 8842 both equipt with a GPIB board can do a swap test and see if both boards work in both unit versions.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: March 30, 2018, 09:11:04 am
content: My board is a Rev.B and also only has U901. These boards are interchangeable between the 8840 and 8842.Do you have a 'scope?

author: charlyd
author_rank: Frequent Contributor
timestamp: March 30, 2018, 11:08:00 am
content: yes i have a scope & Logic probe & Logic analyzer, so no problem..But the schematic which is in the manual is totally NOT corresponding with the tracks on the board. and if you look at the board and see 3 resistor arrays ( network chips) .in the schematic is a Pull-Up set 3.3K and Z903 which is on the board Z901 a 10K array. and also the U901 and U911 are in the schematic our board has no U911 :-(so different...that is why i hope to point me to the right schematic about the 8840A-4005 version.but what is saw is.. on my U901 chip i get some voltages from about 3,5 - 4 volt. and that is NOT a HIGH nor LOW. i was wandering what these pin on boards display on het DMM.and maybe you live in my neighbourhood so maybe you could test my board. ( so i know it is not inside the meter itself)

author: charlyd
author_rank: Frequent Contributor
timestamp: April 05, 2018, 09:51:32 pm
content: ...bump....

author: RobK_NL
author_rank: Frequent Contributor
timestamp: April 08, 2018, 06:32:26 pm
content: Sorry, I was extremely busy this week. I also had mislaid my paper manual, but I found it yesterday in my workshop. I'll try and scan the IEEE schematic in the next couple of days.

author: RobK_NL
author_rank: Frequent Contributor
timestamp: April 09, 2018, 01:00:11 pm
content: There you go!

author: RobK_NL
author_rank: Frequent Contributor
timestamp: May 16, 2018, 10:15:58 am
content: Sure, no problem, you're welcome ...

author: Kjo
author_rank: Regular Contributor
timestamp: July 07, 2018, 03:19:13 am
content: FYIThe 488 interface board for the 8840a and 8842a have different rom code. Trust me!There are at least 3 versions of the actual pcbs. In all, there is a Z86 variant on board. This is programmed unique to the pcb and model. If u have them, you can swap 40a and 42a Z86 chips within the same series 488 pcb. If the pcb has a z8613 with piggyback EPROM you can reprogram the EEPROM to either 40a or 42a from bin images on the web.It is well known that Z86 mask/OTP chips have failed in the in-guard and 488 locations.Hope this helps.