Trying to repair some clamp meters

[Nigel Goodwin]

What were the readings on the clamp meter display?.

 

[KeepItSimpleStupid]

The other question I have is can you manually range the AC range? If you can, select an appropriate range for each input and repeat the measurements.

The output appears saturated, but we really don't know what the power rails are. The voltage from +Vs to COM would help a little.

 

[BGAmodz]

OK i will check with other ranges , this one i got has auto-ranging and also a button for manual ranging .
And BTW the test I've done before were in auto range mode

Those are the ranges i got :
0.000 V ; 00.00 V ; 000.0 V ; 0000 V ; 000.0 mV .
i get the same high reading on every range.

Actually i just realized that the checks i was doing before were not on the output but on V+
I will do the checks on output and get back with the results .

 

[BGAmodz]

What were the readings on the clamp meter display?.

Hi
I dont have readig on the screen , neither on auto range nor on manual range , i get high reading on screen without even checking anything

 

[BGAmodz]

The output appears saturated, but we really don't know what the power rails are. The voltage from +Vs to COM would help a little.

Sorry did a mistake , the output results actually were the V+ results .

Here is a summary of my tests on both modes for the IC :

 

[KeepItSimpleStupid]

Confirm the units of (In AC). Is this AC or DC volts?

In any event, out seems to be stuck at 1.8 give or take. It's midscle, which could mean something.

When in manual range is the display basically 0.000 or 1 like an overload?

What does 0V AC give as well?

 

[BGAmodz]

Confirm the units of (In AC). Is this AC or DC volts?

In any event, out seems to be stuck at 1.8 give or take. It's midscle, which could mean something.

When in manual range is the display basically 0.000 or 1 like an overload?

What does 0V AC give as well?

No these numbers 0.000 /00.00 ............... are the ranges .
In AC is in AC not DC , the unit is Volt

So what do think ?? should i change the IC ?? na dwhat midscale could mean btw ??

 

[KeepItSimpleStupid]

Let's take one of your rows for the 6 VAC measurement:

6 VAC, In AC (Pin for IN), 1.8 (units ?) 1.8 (Units?), 0.4 (Units?), 0.4 (Units?). 0.4 (Units?)

This is supposedly the voltage at the IN pin of the AD726, but I'm not sure if this is an AC or a DC voltage.
What I'd like to see is:


A: 6 VAC, In AC (Pin for IN), A VDC, A VDC, , B VDC, B VDC. B VDC
and

B: 6 VAC, In AC (Pin for IN), A VAC, A VAC, B VAC, B VAC. B VAC

A is a variable 1.8 in what you measured. B is 0.4 Just don't know if it is AC or DC volts.

and both lines (IN, OUT) for nothing connected to the meter. e.g 0V and with all of the ranges.

My thought is that the attenuator has to be before the IN of the Chip, so we should see something like 0.1 VAC, 1 VAC 0.001 AC as you change the range.

Do, you know if the range is 1999 or 2999 or 3999 counts for full scale. My guess is 1999 counts full scale.

Units are important. For all I know, your measuring the values in "potatoes".

Be prepared to figure out where the Input of the IC comes from or the output goes to, but we're not ready for that.

There is no question that the output is stuck, but the input is stuck too except for the lowest range. I'm just not sure if your measuring the input to the AD736 in AC volts or DC volts?

Post a link to the manual of the clamp meter too.

 

[BGAmodz]

Ok to make things clear :
The measurements on the AD736 pins when i apply 24 volts AC and 6 volts AC on the probes .
For the IN pin , measurement is in volts AC
For the Out and V+ pins , units are volts DC

here is a picture of the area where the IC is soldered . pin 1 is top left of the AD736

I will see the pins and tell you whats before and after the IC

 

[KeepItSimpleStupid]

The input is 200 mV RMS full scale, so anything above that (400 mV that you measured) would result in an overload.

So, I would start looking at stuff before the input to the RMS chip. The measurements don't rule out the possibility that the chip is bad. The only thing we can infer is that the voltage at the inputs are too high. Shorted protection diodes is a possibility. Let's look at the DC value at the input with 0 volts input and mode set to AC on a manual range (one that read 0.4 VAC).

It is a pricey chip. Around $10.00 USD depending on suffix. Removing the chip and making the same measurements is an option, but not quite yet.

 

[BGAmodz]

You are right , we are not sure if the problem comes from that IC , so i will take a look at what comes before its IN connection .

But the problem is that this card is a recto verso card , and there is a large number of ICs around , it going to be really challenging to see where every pin goes and witch IC could be responsible for the dysfunction .

 

[KeepItSimpleStupid]

First look at the DC value of the input to the TRMS chip at 0 V in. Something near 3 VDC or - 3 VDC would be a problem.
Then find out where that input comes from.

 

[BGAmodz]

OK , i got 0.4 v DC at input , 3 v dc at output , 5 v dc at V+

 

[KeepItSimpleStupid]

Why do you get +5 VDC on V+? Kinda thought the power supply was +- 3 VDC and you got 4 V the last time.

Pins are usually numbered counter clockwise from the marked pin #1,

Measure the resistance from Vin of the RMS chip to ground with the battery pulled in both directions. Also use the diode test in both directions.

Also do resistances and the diode test in both directions from Vin of the RMS chip to V+ of the RMS chip.

So a total of 8 measurements. 4 diode, 4 resistance. Battery removed.

 

[BGAmodz]

Well i got +- 3 VDC when i was applying AC voltage on the probes the 6 and 24 ac voltages ; i got 5 VDC on IN input with no voltages applyed to the probes .
Don't worry about the pins i got them right .

Will do the 8 measurements and get back to you


I really appreciate you assistance , thanks a lot

 

[BGAmodz]

OK here is the results :

( ==> means + to - )

Vin ==> GND : 5 Mohm / no continuity
GND ==> Vin : 2.86 Mohm / 1.240 v for a sec and then no continuity
Vin ==> V+ : 5 Mohm / no continuity
V+ ==> Vin : 2.83 Mohm / 1.240 v

 

[KeepItSimpleStupid]

Check R48.

 

[BGAmodz]

Really weaird ; that resistor normally has 10 Mohms ( 106 written on it) but i only read 2.6 Mohms on my meter

 

[Nigel Goodwin]

Really weaird ; that resistor normally has 10 Mohms ( 106 written on it) but i only read 2.6 Mohms on my meter

Are you measuring in or out of circuit?, you can't generally make ohms measurements in circuit.

 

[BGAmodz]

I removed that resistor and it gives 10 Mohms , so its good .

Now whats interesting , i followed the COM probe port and its connected in series with that R48 resistor and then to the pin #2 of the IC .
I checked the other '+' probe port to see were its branching out and its in series with a thin resistor ( on picture ) and another resistor (1001) and then to the Microcontroller's 24 th pin ( VI ' voltage input terminal ), now i checked this resistor out of circuit and its marked on it 10M witch is 10 mega ohms , but when i test it with the meter the resistance goes high till 15 Meg then decreases till 10 Megs stays that way for a while then decreases more till 5 Megs .
Any ideas ???