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Help with Bob's (DS) ESR meter kit?

Discussion in 'Hobby Electronics' started by DaveC, May 16, 2007.

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  1. DaveC

    DaveC Guest

    Someone who is familiar with this kit, would you lend some assistance?

    I purchased and assembled the Mk.II version of Bob Parker's widely-praised
    ESR meter kit. Assembly went swimmingly.

    The first test (with ICs removed) is to see what the power draw of the board
    is. It registered about 4.2 mA, whereas the instructions say that ~6.0 mA is
    typical. After installing the ICs and then doing the power-on diagnostic
    (holding the switch leads together), I get "F2" displayed on the LEDs. The
    instructions say that this means that there is a problem with the C10 cap
    charging too slowly, or not at all.

    Following the clues of the troubleshooting section of the instructions, I've
    unsoldered the transistors Q9, Q10, and Q11 as well as C10. The transistors
    all check OK using my DMM in diode check mode (all junctions show approx.
    0.6v bias in one direction only).

    I noted on first install that some of the transistors had some adhesive
    residue from the tape that held them in a roll (I presume they were purchased
    in a roll quantity). I ignored this on first install, but cleaned all of
    these transistor leads with contact cleaner before reinstalling them.

    I checked C10 with my DMM in cap measure mode, and it is spot-on at 47 uF.

    Likewise, I removed R19, R20, and R22, examined their resistance, and
    reinstalled them.

    I can find nothing wrong with any of the components in this part of the
    circuit.

    Both ICs have 5.02v at their power pin.

    I've examined the solder job I did, many times, with several different power
    loupes; it's excellent. I've re-flowed all solder joints. I de-fluxed the
    board hoping that maybe the flux affected the circuit somehow. No joy.

    I looked at some of the points in and around these components (Q9, Q10, Q11,
    C10, R19, R20, R22) using a scope, but I'm not sure what I should see. I
    looked at pin 4 of the u-processor: it transitions irregularly a few times a
    second. Is pin 4 the u-processor sense input of the charging cap? Should this
    voltage be a ramp (slow decay) of regular period?

    To conclude I'll only add that I modified the board via Bob's follow-up
    instructions by replacing the 78L05 regulator with the micro-power,
    low-drop-out version (LP2950CZ-5.0) and changed R25 to 27K.

    Some suggestions as to what I should see at certain pins, or where to look
    next would be greatly appreciated.

    Thanks,
     
  2. DaveC

    DaveC Guest

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