Repairin Keithly 2001

[rroland]

Hello guys,

I am new to this forum and I need help repairing my Keithly 2001.
I tried to find case like my, here on forum, but no luck.
My DMM is working cca. 1,5 - 2 minutes, than turns off and starts again (like reset).
After few this cycles does not turns on any more.
As I tried to repair it, I found that U629 (LM2940CT low drop 5V voltage regulator) is heating to much.
This (U629), as i understood, is 5V for digital board.
I did not found anything else to be heated to much except U629, not on digital neither on analog board.

Can someone please help me with this.

Thank you very much.

[Shock]

Heating up but providing the correct output voltage still? Where exactly does the voltage drop out?

Look for input and output caps on the regulator as well as resistors or diodes that could be pulling high current. After replacing any defective components remove the regulator and power that rail from a current limited bench supply (current limited to something sensible). You can also measure resistance across that rail when the regulator is out as well for obvious shorts.

If it stays up on the bench supply it's more than likely the LM2940CT, you can load test it out of circuit if you like, but it's best to replace it to be sure even if it was a cap. With caps check for C, ESR, leakage then check for electrolyte contamination on the PCB if applicable and consider replacing all caps similar to the defective one.

[rroland]

Hi Shock.
Thank you for answer. You helped me to find failure.
It was DC-DC converter who draw to much current.
It is replaceable part so I will order one.

Thank you ones again.

[TiN]

If your meter old (made before 2010) - replace ALL large electrolytic capacitors, or you will end up destroying the meter. This is known issue in these meters.
Some data can be found here and of course here on forum.