Datron 1081 and 1065 repair help. huge offset on readings

[ThunderMink]

Hello.

Was wondering if anyone have seen this problem on Datron multimeters.

I have a 1081 and 1065 that is having similar problems

The 1065 had a relay problem a while back that resulted in an huge offset in the readings about several 100 volts in the 1000v range. actually all ranges was the same. with shorted inputs the readings was like 0.2 / 2 / 20 / 200 ,  i thought that it was the relay on the analog board that was acting up again but when i replaced it nothing changed.

The only thing positive is that my 1081 is having the exact same problem so i need to find the root cause on the 1065 and hopefully it is the same fault on the 1081

Any help would be very helpful

[Gyro]

Hi,

Your first stop should be the service manuals... http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=06_Misc_Test_Equipment/Datron if you haven't already found them.

Tantalum beads caps with high leakage and degrading Opto-isolators are common failures on Datron meters of that vintage. Your best bet is a methodical rather than shotgun approach, eg. Check the main analogue supplies and the bootstrap supplies. try to find the offset at the input of the A/D circuit block with another meter and either trace backwards across the analogue board or diagnose the issue with the A/D circuit.


P.S. A forum search for Datron should bring up a few relevant threads, from what I remember.

[ThunderMink]

Thank you for the reply Gyro

I have the manuals and have went through the common faults. Powersupplies, Optocouplers and relevant logic ic's. i think i will replace all tantalums on every board as i have repaired  a 1061 and 1071 before and both had problems with unstable tantalum caps.

i will try to re-seat all ic's again as the 1065, was working fine last week and have been working for over two year since the first repair.

As for the 1081 i need to re check all the power rails again using my scope. May be the lm309 that is acting up. or maybe a bridge rectifier or tantalums.

I have went through most of the datron posts here and they are of great help

On my 1071 the main problem was the bootstrap power supply that produced about + - 12v on the outputs. The problem was IC M16 on the analog board