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

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View

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

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.

DaveC (in the USA.)
We've slightly trimmed the long signature. Click to see the full one.
Re: Help with Bob's (DS) ESR meter kit?

Schematic of the meter circuit is in the manual (p4), here:

The manual is in 2 parts; part "b" is here, but contains no schematic:

We've slightly trimmed the long signature. Click to see the full one.

Site Timeline