Fluke 3330B questions

[wictor]

Hi,

I'm repairing Fluke 3330B DC calibrator and I have some questions. When unit is powered on and in standby state, should I limit/V trip light be on all the time? When unit is in operate state, it will turn off and unit will give proper output. But I cannot get it to trip in operate state, when I'm adjusting the voltage limit on the front panel.

There has been broken parts and some modifications that are added afterwards by some previous owner. I'm trying to get it back to original state, but there seems to be still some faults.

Right now I'm using it with variac to provide 115V, but I would like to convert it to 230V. According to manual you only need to connect few poles in transformer differently and change the fuse to smaller one. I tried this already, but for some reason fuse is blowing about 5 seconds from startup, when some relay is connecting power to main circuits. I'm suspecting that this has something to do with grounding, because device should not know what is the input voltage, when transformer is properly wired. With variac, only N and L are connected, there is no protective earth. With 230V I have all in place.

AC input connector has two filter capacitors.  I didn't find any image of this in service manual, but one is connected between outer terminals(L & N)  and one is connected between center(earth) and with one outer pin(I don't know is that L or N, because connector is very old oval shaped and we don't have that here in Europe). In US you can connect plug with protective earth only with one way, but here in Finland we can plug the either way so L and N can be switch places depending the plug position. So my question is that should the capacitors be connected so that one is connected from L to earth and one is connected from N to earth or do it really matter? With current configuration earth voltage level will change depending how your plug is connected...
Connector is like this:


What is the purpose of the potentiometer in the following image between transformer pins 23 and 24? Is it adjusting guard voltage and compared to what?

Wictor

[pelule]

Hi if the 3330B is in stand-by state, the I limit/V trip should be on. I can rmember exactly where, but there is a note in the UM describing that.
If you shift the I-Trip and V-trip levels to the most left position (min) the gear should trip immediately, if you select operation.
/PeLuLe

[wictor]

Thanks PeLuLe!

[SeanB]

I will take a flyer that the pot is there to minimise AC noise on the output. Adjust for the lowest AC noise between the common terminal and Mains earth. It just adds an AC signal in antiphase to the windings, so the coupled through AC mains common mode signal is minimised.

[wictor]

I will take a flyer that the pot is there to minimise AC noise on the output. Adjust for the lowest AC noise between the common terminal and Mains earth. It just adds an AC signal in antiphase to the windings, so the coupled through AC mains common mode signal is minimised.

Oh yes, I found it... You connect 10k resistor between + and - outputs and then adjust for minimum rms voltage.

[dacman]

The power socket looks like a PH-163.  Pinouts would be N-G-L if the center pin is offset low.  (From the rear, solder side, it would be L-G-N.)  The phase of the transformer needs to be correct (same side towards L for both primaries in both 230 V and 115 V configurations)

[wictor]

When unit is in operate state, it will turn off and unit will give proper output. But I cannot get it to trip in operate state, when I'm adjusting the voltage limit on the front panel.

Q2 was open on series pass driver board. Now voltage trip is working.