Protection Circuit &
Probes Connected & for
(disconnect, discharge cap, reconnect)
Dot Matrix LCD
Version 4.0 Dot Matrix LCD no longer
Inside Version 4.0
This is an Equivalent Series
Resistance (ESR) meter is made in Russia by Radio Devices (Google
Translation). It's primary use is to test
capacitors for series resistance while they are installed on
printed circuit boards. It uses the ATmega88
microcontroller. The 2x5 hole pattern to the right of
the uC is probably the JTAG programming header.
The key thing this meter does that other ESR meters do not
do is that this one measures BOTH Capacitance and ESR at the
same time. The version 3 ESR-micro had an alternating
C then R display, but the version 4 has a two line
display. This tester may give better results for some
caps than the prior ESR meters. Will be running some
tests shortly (Jan 2010). Also there are audio tones
that tell you about the resistance of the DUT as well as at
power up or down.
This ESR meter uses the same method as the Bob Parker unit
that is no longer sold by Dick Smith Electronics, but this
meter uses a shorter pulse and so does a better job of
measuring low value capacitors. For example it
measures a 2.2 uF cap to within +/- 0.1 uF.
Cap: 0.2 to
60,000 uF (Note: the meter will not measure low
ESR Supercaps, but may
work on the memory hold up type supercaps)
Res: 0.00 to 99
Ohm (note: can be used as an
Ohmmeter for values below 99 Ohms)
The cap in the photo ( 22uF 250V) is the same cap that was used
in the SR715 photos.
ESR = 1.71 Ohms
Cap = 26.3 uF
The DIP socket on the front
panel has three uses:
The left center sockets are a short (0 Ohm res).
When the meter is powered up with the probes on these
sockets a self calibration is done. This is much
easier than trying to hold the probes on a penny and
pressing a button (that's best done with three hands).
On the left topmost and bottommost sockets are three
resistors. The center resistor is 1.0 Ohms, then 10
Ohms and finally 100 Ohms to confirm a proper
calibration. For the 0, 1 & 10 Ohm resistors you
hear the beeper that's proportional to resistance.
On the right are two terminals for testing caps with
radial leads and the socket pitch varies from 0.1" to 0.7"
in 0.1" steps.
Two CR2032 3V coin cells are
connected in series for a nominal 6 V supply. When the
unit is powered up the battery voltage is displayed for a few
seconds (Vbat=5.8v) along with the firmware version.
There is an automatic power off if there's been no activity
for 40 seconds.
To change the batteries remove the four (-) screws on the
back. Remove the old batteries using a pointed tool to
push back the metal clip. Install new cells + side
up. When installing the four (-) screws turn them CCW
until you feel the screw drop a thread then turn CW.
This avoids cutting new threads in the plastic case.
Battery Internal Resistance
Warning: Reverse Polarity
will blow the protection diode and maybe some traces,
so this is not recommended for the faint of heart.
If a capacitor is installed in
the socket on the left where the zero Ohms calibration is done
and then the unit is powered up it will zero out the capacitor
if the ESR is below about 2 Ohms.
This means a 10 uF cap is too small, so something like a 470
uF cap will zero the meter. Note the 10 Volt rating of
the cap so this setup is good for batteries up to 9 Volts.
Now if the cap is placed in series with the black test lead
with it's negative terminal free and it's positive terminal to
the black test lead you're ready to test a battery.
Connect the red lead to the battery positive terminal and
connect the negate cap lead to the battery negative terminal
(to keep the polarity correct for the cap) and wait a couple
of seconds for the reading to stabilize. Read the
batteries internal resistance.
Using a test lead with alligator clips on each end makes this
Another way to measure battery internal resistance is to use
the HP 4328A milli
Ohmmeter. This works for higher voltage batteries.
Capacitor Test Results Table
Moved to it's own Capacitors web page (too many to
parts for this page)
Heathkit GC-1000 Most Accurate Clock
A used Heathkit GC-1000 Most
Accurate Clock is not working properly. The test
results when first tested differed from the results a few days
later (clock powered up in the mean time). The results
seemed difficult to troubleshoot. Testing the
electrolytic caps showed most of them to be bad.
The following are power supply or decoupling caps where low
ESR electrolytics would be good:
C102, C203, C205, C206, C208, C212, C213, C301, C354, C357,
C401, C404, C405, C424.
The following are caps where low leakage is important and so
either a plastic or low leakage electrolytic would be good:
C348, C353, C355, C359, C412, C414, C421, C422,C425.
Look at the tables on the right side of the page where Red is
out of spec and notice that some of the out of spec conditions
are for capacitance and some for ESR.
Robertshaw Controller in GE Oven
My electric oven was running too cold last year ago (see: Recipes: 5 Minute Bread)
and a couple of weeks ago my stepson baked a pie where the
bottom was raw dough. I had pulled the oven and started
shopping for a new one then had sticker shock so decided to
see of this one could be repaired. It turneded out that
a couple of caps (C1 & C17 in the analog section of the
controller board were bad. The repair saved $1,000 to
$2,000 for a new oven. See: Hints
and Tips: Cold Oven
This came DOA with a DC short at the 24 Volt Input.
After removing the rear finned high power assembly that
included the J3 input connector it was clear using a Fluke
87V DMM that the problem was not in
the finned high power assembly but in the main
chassis. Two large blue caps were tested with the
ESR-Cap meter with these results:
C1= 0.24 Ohms - 1530 uF [s.b. 01132U050AK - 1300uF 50V] so
C2= 0.00 Ohms - 1720 uF (Fluke 87V DMM shows
falling resistance not short) ESR meter now reads 0.40 Ohms
- 1720 uF [s.b. 101172U100AJ2A - 1720 uF 100V] so OK
After taking the chassis apart to gain access to the Input
DC Power Supply Filter assembly is was looking like there
may be something wrong with the SCR, but none of the DMM
measurements made sense, so the ESR meter was used.
The following circuit diagram was drawn:
At first I thought that the SCR was the
problem (and was thinking that the L1 choke terminal
"1" was the input and "2" was the output, but when I
came back to the drawing noticed the ESR readings that
I've highlighted in red. The L1 coke measures
0.43 Ohms and it's input terminal "2" shows 1710 uF
& 0.48 Ohms to ground. The L1 choke output
terminal "1" shows 0.00 Ohms to ground and 1720
uF. That means the problem is either with the A1
9V battery charging circuit or with C2. But C2
is showing 1720 uF which is exactly the label
value. What's going on????
After removing the bracket and unscrewing the negative
terminal on C2 (see photo on AM-7176A web page Fig 15)
both C2 and the rest of the circuit tested OK.
What's going on??
When reassembling C2 the answer came. When the
screw holding the terminal lug was tightened the
terminal rotated to the right causing the many black
wires attached to push into the other terminal.
While there was not a metal to metal short the
insulation on maybe a couple of wires was heavily
deformed, not enough to make a hard short, but enough
to cause a short when a voltage over maybe 10 Volts
was applied. By using the shank of a pocket
Phillips screwdriver to reform the black wires they
were moved away from the positive terminal and the
problem is solved.
A minor concern is the 1k resistor that is between the
2N685 SCR gate and cathode (ground) which measures 37
Ohms in either polarity using the DMM and ESR-Cap
meter. It looks like the only way the SCR can
turn on is if the input voltage goes over 200 so this
may be part of the EMP (wiki)
protection scheme. This is similar to the
crowbar protection circuit used to short the output of
a power supply when it's voltage exceeds some
threshold, but in this case the gate voltage will
never be as high (or higher) than the anode and so
will never turn on by the gate. That only leaves
the breakdown voltage as a turn on mechanism.
There has been some discussion of where to place surge
and the answer seems to be as close to the input as
possible. In this case it's just after the
Thoughts on Replacement Caps
It turns out that more than half
of the electrolytic and Tantalum caps in the GC-1000 are bad
(either low capactiance or very high ESR or both).
Rather than use new plain electrolytics I'd like to use better
1. Where there is an available replacement
(radial, adaquate DC working voltage) using Aluminum Organic
Polymer caps adds a whole lot of reliability.
It turns out that these
are only available in a very limited number of physical and
electrical values and are 10 to 100 times more
A better choice may be
either the Low ESR electrolytic or the Low Leakage
electrolytic, a plastic or ceramic cap depending on the
2 Using low loss electrolytics for things
like the NE567 PLL or op amps would be good or plastic.
3. Low ESR electrolytics would be better for
power supply decoupling.
The Fly Back Tester works by looking for the ringing of an
inductor. It's use is not limited to fly back
transformers. For example in the second photo below
it's connected to a loop antenna
and the right hand LED is green (Good).
If interested let me know.
on the back side of
the PCB is the CR2032 coin cell and on the front
side (shown at left) is the AT Tiny microcontroller.
Showing good (right
hand LED is green)
when connected to Loop antenna.
(high Q at 60 kHz)
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