Fluke 8600A

[GEBevis]

Hi everyone,
I have a Fluke 8600A and the display flashes random values and then flashes to the overload display "1.8888" When I select the different ranges the appropriate LED lights in the proper decimal place, and the LED indicating DC, or AC, or OHMs lights up when the different mode buttons are pressed. Due to the way it displays the measured A/D converted DC voltage vs time slope I think it might be problems with the timing in the U4 or U5 and U6 A/D converter circuit.  If anyone has any experience with this problem I would very much appreciate your input. Any ideas will be appreciated.  I have done a thorough cleaning of all buttons and switches and recapped the old electrolytics in the P/S.  All voltages check nominal at all test points. I am now plowing thru the manual to familiarize myself with the operational theory and the block/schematic diagrams.

Thanks for any help

Gary

[med6753]

I also have an 8600A but I have not experienced the issue you have so unfortunately I can't provide much help. But I would be very interested in what you find for the benefit of "just in case". 

[halexa]

Hi,

Try to measure the input resistance on each range/function. To see if something in the input circuit is dodgy.
I have a working 8600 unit we can compare the result with.

[GEBevis]

I have done some trouble shooting with the manual referring to sections 4-56 to 4-60. I hooked a scope probe to the test point and discovered that the logic level +5vdc is supposed to remain high for 200mS and the signal is only high for 120/125mS. Which is somewhat expected as the meter cycles between overload display and random numbers.  I need to find data sheets on some of the obscure discrete components such as U4 and U5 both precision op-amps in an 8-pin can package. I will keep poking about as time allows.  I have begun to put a test bench together again and pulled this old guy out and would really love to put it back in working order.  Again thanks for any help.