Electronics > Repair

Multimeter FluKe 233 Remote Display Off

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papi:
Hi all,

I have 2 Fluke 233 in one the remote display does not turn on both when it is on the base and when it should communicate in RF ( 2.4Ghz) detached from the base. The two testers are dated and are from two different PCB versions but having one working I tried to make a comparison between the TEST points to simplify the fault analysis.

I suppose I have identified that the problem lies on the remote display since by exchanging between the two bases the working display shows ID error, so the base attempts communication (It turn on the red HV LED) but finds a different code in the MP430 micro.

I am sending test point verification scheme with comparison with the working model which has two additional Test Points, the TP217 and the TP216, the only differences are with the TP215 which on the non-working display is 0V instead of 3.3V and the IR diode DS202 which is in conduction instead of interdiction due to the conduction of the BJT PNP Q203 which is driven by pin 75 of the MP430 micro at 0V level instead of being at 3.3Vdc.

I am sending the picture of the remote Display PCB.

At the moment the display doesn't work and since I don't have any diagrams I don't know where to take action.

Do you have any suggestions.

Thank you very much for your help.

Andrea Papi

m k:
Are both modules missing R212 under Q203?

Maybe battery info is missing.

papi:
Thank you very much for your help,

yes you are right, I removed two resistors the base resistor of Q203 and the limiting resistor for the IR Led DS 202 for test the MCU pin out (pin 75) it is not 3.3V but 0.35mV and it means that the IR Led is On (PNP BJT Q203 On). The remote display that is working fine it is in the off state.

I am not able to solve the problems for the time being.

Kind regards.
Andrea Papi.

m k:
Normally battery power is selected passively.
There battery voltage is lower.

If both power sources are batteries the situation can be more difficult.
But not much, one PNP can do the trick, there base is main battery pulling pulldown up.
Or two NPN types can do the same if voltages don't match.
There first base is main battery and so first collector pulls the second base down if main battery is present.

Can you follow how remote power is enabled?

papi:
Hi,

thank you for your hints, in the picture I sent in my previous posto of the Fluke 233 Remote display PCB the power is coming from two AA Battery 3V. On board there is a boost IC U202 that provide 3.3Vdc for the MCU U201 (M430F488) and the Low Power 2.4Ghz Transceiver U204 (MC13201).

The power is only from battery, now I am testing the board using and external power supply 3V @100mA (current limit). The whyte packages are IR Led DS202 and Q204 IR BJT I suppose they are used when the remote display in inserted on the base.

Kind regards and thanks a lot.
Andrea Papi.

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