huh .. thanks a lot , as my first assumption was to take a board need literally unscrew everything, but it seems need to do it anyway ... it very dirty
is my understanding correct that there no schematic for True RMS board ?
Picture attached
I really have a little hope
This is a mess and I can't guarantee that it is exactly correct for your version. If someone is ambitious and willing to splice the sheets together we'd all be appreciative. But here it is:
how did you physically connect to the data bus and how are you triggering the LA?
Sorry miss it, simply solder cut off wire on the back of mainframe board , as 4 connectors the same , it easy spread across all 4, and then connect LA ChXX input to that improvised pins,
im not triggering, it simply running , then i press reset button recording sequence.
all my sniffing done on guarded bus , where analog board , slots 1-4 , and not included digital , as I not interested about , so control bus on analog side are 0-4 , 5 lines , 5 bits seems only 3 "1" bits in use for addressing.
When TRMS is away can you switch back to V DC from Ohms?
yes i can
basically the device operate as voltmeter without ohm ,AC board and interface. minimal need: controller, isolator, A/D, Conditioning, Active_Filtr (5 boards)
Saving another vintage Fluke from the scrap bins?
I too tried to save one. That long switch show previously on mine was bad. I flushed it with Proclean then put about 20mA through each contact and cycled it several times. Then once more flush. That took care of it.
The ohms board on mine would not change relay states. All analog design and once I understood how it worked, I ended up changing I think an RC to increase the one-shot pulse time. That solved that problem.
Last thing I was looking at was the decoder PROM and some of their firmware. It was such a tangled web and the meter was so old, I abandoned it.
We had a thread going. Maybe there is something useful in it.
https://www.eevblog.com/forum/testgear/some-old-school-instruments-showing-how-its-done-(hp-3325a-and-fluke-8506a)/
unbelievable ... everything works .....
AC board even good numbers till 3-4Mhz
but ... the funniest part , the last cal label are 1996 , and seal on screw intact ...
so when i hook my 3xLM399 it shows exact number after a few min of running .... well see what would be after warmup and week of so
and then probably total cleanup, review \ add capacitors (a modern one) and i think get rid of input switch and broken connector on back
and total adjustment ...
(maybe ... a modern opamp would be not a bad idea, somewhere ... )
Hello everyone ...
I'm back
here is some fun glitch after 2days of running -
Led segment "A" (top one) on 6 and 7 digits indicator ( in my understanding U10 , U13 )
as well "sample" LED started blinks sporadically, then stops at all .....
im tirelessly try to dig over schematic but can not really figureout a common element , mostly due to unknown pinout.
I would be really appreciated. if some guide my miserable mind in the right direction !
I assume you mean U34, U24 and U13?
So I poked at my spare panel board. The three displays don't share a high-side driver, but they are all multiplexed through the 'J' circuit of U30, U25 and U20. I tested using pin 12 of U20 for my low side and the collectors of Q2-Q8 in turn. If the problem is in the 'J' circuit, you should also see the REMOTE (pin 19 U26), HI ACCURACY and NORMAL (pins 2 and 4 of U14) fail to operate. Hopefully you have a clear schematic you can see all of that on.
I had once a problem where certain number turned on segments elsewhere, error segments were bright.
Reason was too high 5V, finally everything went blank and 5V was 7V, or something like that.
Thanks bdunham !!!
correct U 34 , 24, 13
and exact the thing - AC: HI ACC, NORMAL - not lit up (remote -not up, getting err-4)
I attached stitched schematic for the front board , will dig now ....
had replace all caps on PSU and adjust it ... but will check again
finally ...
i fix everything , clean everything , assemble everything ... a small job need on ohm board .. but so far all great
shorted\soldered front-back switch no need it
add a lot SMD caps on digital part of ADC , and a lot additional caps on power analog ADC parts ; same for digital isolator board.
as well replace electrolytic caps on boards, for some i wasn't sure and left it ...
seems all in a normal order,
at first - noise about 0.3 microvolts , and cold-hot drift about -4ppm ; I think it good numbers
plans to leave it to for a month or more in "ON" state then do adjustment
maybe ... as an option to do something with Vref ... make it better a bit. or... more likely use embedded option to switch to Ext ref.