Attn DaveC re ESR meter

[Bob Parker]

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,

Hi Dave,
<[email protected]> is the fake e-mail address of one of the trolls
which have been trying to destroy this newsgroup, so my filters have
been deleting your posting(s). I only saw what you wrote by chance.
It would be preferable to discuss your ESR meter problems by direct
e-mail. You can contact me through this temporary e-mail address:

[email protected]

Bob

 

[Bob Parker]

Just a quick follow-up... there's probably nothing wrong with your
ESR meter.
I hope you haven't wasted too much of your time chasing this
'fault'. When the 78L05 regulator is replaced with a LP2950CZ-5.0
and R26 is changed, the self-test function falsely shows an "F2" fault code.
Unfortunately this wasn't realized until after a lot of Mk2 kits
went out, because very few people make that modification. I've had a
warning about this on my website's ESR meter hints page for quite a long
time.
If your meter's reading the 5.6 ohm and 68 ohm test resistors
reasonably accurately and doing all the things it's supposed to do,
there's nothing wrong with it. If it still has a problem, please e-mail
me at [email protected]
Sorry for the inconvenience this has caused.
BTW, C10 is 0.47uF not 47uF.

Bob

 

[Bob Parker]

Thanks, Bob. See my private e-mails.

I sent you a reply to what I hope is your correct real address. If
you get it, can you please hit the Return Receipt or tell me here?
Thanks!