Service manual and/or schematics for SOAR 3430 multimeter

[giosif]

Hi,

Does anyone happen to have the service manual and/or the schematics for the SOAR 3430 multimeter, please?
I am trying to mend one such meter.

Thanks!

[retiredcaps]

Sometimes we can fix meters without a manual.

Describe what is wrong.  Does DCV work?  Does ohms work?

Some info

https://www.radiomuseum.org/r/soar_true_rms_digital_multime.html

I also believe Soar meters are made by someone else.  Just can't recall right now.

[giosif]

Indeed, although I was hoping I might be able to obtain the manual, as I believe the meter will require calibration after it is repaired.

The symptoms I have observed so far are:
- with no leads connected, the meter measures around 26 MOhm in resistance mode (it autoranges and then slows down around the 26 MOhm figure).
- input impedance looks ok (around 10 MOhm) in all ranges except the 250 mV range, where I get 8 MOhm or even lower.

Otherwise, DCV seems to work, although I didn't test all ranges.
Also, measuring a 10 kOhm resistor was close enough.

[retiredcaps]

Suggestions.

1. Put the meter into manual 250 ohms mode.  Measure a 1k ohm resistor.  What does the lcd show?

On some of my meters, instead of displaying 0L, it shows the highest count mode.  I'm wondering when it displays 26M ohm, that is the way the meter indicates open circuit?  Your meter is a 25,000 count meter?

2. Take apart your meter.  Look at the main IC.  Search for its datasheet.  It might yield clues.

3. Tweaking the ohm trimmer POT (which one out of the 13) will unlikely have any affect on the 26M ohm reading with no leads attached.

4. If you haven't given the pcb a good IPA bath, give it a try?  Any contamination may be affecting the ohms reading?

5. Post clear focused pictures of your pcb.  The one at radio musuem is too blurry and small to see any components for testing.  I think I see two green PTCs?  Measure them and report the readings.

[giosif]

Thank you for the suggestions!

Last night, I was going through the checks you mention, but then decided to continue today.
And I'm glad I did, since today, in daylight, I spotted the issue in the attached pictures (nothing beats natural daylight for providing proper illumination).
So, that's at least part of the problem.
I've ordered a replacement 100 Ohm trim pot and will report once it has arrived and it's been installed.

Until then, I am posting higher res pictures of the boards in the hope they might help someone in the future.

[giosif]

And the high-res pictures, as promised.

[giosif]

More photos...

[giosif]

And the last set...

[giosif]

And, as suspected, that trim pot was not the only issue.
In fact, I am not sure replacing that trim pot resulted in any observable change (that's not to say it shouldn't have been replaced, though).

So, the troubleshooting continues and am I trying to answer some of the questions below.

1. Put the meter into manual 250 ohms mode.  Measure a 1k ohm resistor.  What does the lcd show?
On some of my meters, instead of displaying 0L, it shows the highest count mode.  I'm wondering when it displays 26M ohm, that is the way the meter indicates open circuit?  Your meter is a 25,000 count meter?

It shows OL when connecting a 1 kOhm resistor and the range is manual on 250 Ohms.

2. Take apart your meter.  Look at the main IC.  Search for its datasheet.  It might yield clues.

Judging by the fewer markings on the IC (you can see in the pictures I uploaded earlier), I am guessing it is a custom IC.
Also, a quick search for what I think is the IC model doesn't seem to come up with anything useful.

3. Tweaking the ohm trimmer POT (which one out of the 13) will unlikely have any affect on the 26M ohm reading with no leads attached.

Not sure what this means and what I'd be supposed to do here.

4. If you haven't given the pcb a good IPA bath, give it a try?  Any contamination may be affecting the ohms reading?

Possibly, but two observations/questions here:
- wouldn't IPA get inside the relays and possibly damage them?
- could contamination also explain the low impedance reading in 250 mV range?

5. Post clear focused pictures of your pcb.  The one at radio musuem is too blurry and small to see any components for testing.  I think I see two green PTCs?  Measure them and report the readings.

There are indeed two PTC's:
TDK 5005 - 821 Ohms
TDK 501Y - 467 Ohms
I tried to look for the data sheet for these PTC's, but came up empty handed.
Any help with identifying the specs would be appreciated.

[retiredcaps]

Possibly, but two observations/questions here:
- wouldn't IPA get inside the relays and possibly damage them?
- could contamination also explain the low impedance reading in 250 mV range?

Maybe desolder the relays before an IPA bath or ultrasonic bath.

I don't know what the input impedance should be on the 250mV range.

On my Fluke 87, for example, DCV is 11.11M ohm and mV is 10M ohm.  That is, mV range has lower input impedance.

There are indeed two PTC's:
TDK 5005 - 821 Ohms
TDK 501Y - 467 Ohms

Those values are within the range of what I expected (500 to 1500 ohms).  If the readings were 8K or 80K ohms, then I would suspect they are bad.

While your pictures are clear, the pcb layout is crowded and despite my best efforts, I could not see any MOVs or spark gaps.  Since you have the board, try to see if there are any of these components.

[retiredcaps]

I forgot to suggest also to check your range switch for any contamination, dirt, debris, spilled battery juice, carbon tracks, etc.

http://mrmodemhead.com/blog/ideal-carbon-footprint/

[retiredcaps]

I forgot to ask what the lcd shows in the following situations.  Meter with no probes.  Set meter to manual range ohms mode.

1. 250 ohms
2. 2500 ohms
3. 25 k ohms
4. 250k ohms
5. 2500k ohms
6. 25M ohms

Do all manual modes above show 0L?

Also if you desolder the relays for cleaning, mark them left and right.  After cleaning put them back in the same position.  If 26M ohm problem still exists, desolder the relays and switch them around to see if that makes a difference?

[giosif]

Maybe desolder the relays before an IPA bath or ultrasonic bath.

I don't know what the input impedance should be on the 250mV range.

On my Fluke 87, for example, DCV is 11.11M ohm and mV is 10M ohm.  That is, mV range has lower input impedance.

I was trying to avoid having to desolder the relays, since there is some comformal coating in the area where they are soldered.
But, unless I find any other leads, I will probably end up doing just that.

I don't know what the input impedance should be either, although I wouldn't think it cannot be 8 MOhm, like I am measuring.
I was hoping I could find at least some data sheet for this meter to get at least input impedance info, but there doesn't appear to be anything on it on the net.
Maybe there is someone here with a working 3040 that could measure that and please let us know?

Those values are within the range of what I expected (500 to 1500 ohms).  If the readings were 8K or 80K ohms, then I would suspect they are bad.

Ok. Thanks for the confirmation.

While your pictures are clear, the pcb layout is crowded and despite my best efforts, I could not see any MOVs or spark gaps.  Since you have the board, try to see if there are any of these components.

There are no MOV's or spark gaps.
There is, though, this thing that I can only describe as a resistor inside a glass body - the component identified as Z1 or ZI in the picture below.
In-circuit measurement of the component gave a resistance of about 15 MOhm.

I forgot to suggest also to check your range switch for any contamination, dirt, debris, spilled battery juice, carbon tracks, etc.

This meter doesn't have a range switch - ranges seem to be controlled via the two relays.
Another reason I've been thinking of desoldering them, but they checked ok in circuit (I can operate them by applying external power to their coils) and, as mentioned before, I didn't want to disturb the conformal coating unless I was sure the problem was located there.

[giosif]

I forgot to ask what the lcd shows in the following situations.  Meter with no probes.  Set meter to manual range ohms mode.

1. 250 ohms
2. 2500 ohms
3. 25 k ohms
4. 250k ohms
5. 2500k ohms
6. 25M ohms

Do all manual modes above show 0L?

Also if you desolder the relays for cleaning, mark them left and right.  After cleaning put them back in the same position.  If 26M ohm problem still exists, desolder the relays and switch them around to see if that makes a difference?

Thanks for continuing to help!
I will look into the displayed values tomorrow (it's 1 am over here) and report my observations.

[retiredcaps]

There is, though, this thing that I can only describe as a resistor inside a glass body - the component identified as Z1 or ZI in the picture below.
In-circuit measurement of the component gave a resistance of about 15 MOhm.

Z usually denotes a zener diode.  I don't know what the function of that component is in the circuit though.  I don't know if 15M ohm is good or bad.

It might also be a gas discharge tube?  GDT is another form of input protection.  GDT is used in some Agilent and Hioki meters.

If it is a GDT, I *think* it should measure 0L ohms.  I don't have an Agilent or Hioki meter to verify.  If it is a GDT used for input protection and it measures 15M ohm, then I would desolder it to see if Auto ohms without leads shows 0L.

[giosif]

Z usually denotes a zener diode.  I don't know what the function of that component is in the circuit though.  I don't know if 15M ohm is good or bad.

It might also be a gas discharge tube?  GDT is another form of input protection.  GDT is used in some Agilent and Hioki meters.

If it is a GDT, I *think* it should measure 0L ohms.  I don't have an Agilent or Hioki meter to verify.  If it is a GDT used for input protection and it measures 15M ohm, then I would desolder it to see if Auto ohms without leads shows 0L.

Yes, I too would normally read Z as standing for zener diode.
However, this is not the case here, as there are actual zener diodes on the board and they are marked with ZD (e.g. ZD1, ZD2, etc.).

I also know of GDT's being used in some meters for a similar purpose as MOV's and, while I can't claim I know much of GDT's, I personally very much doubt the item we're discussing here is one such component.
Two reasons I think this:
- so far, all GDT's I've seen have a specific physical construction which doesn't match with what we're looking at here (i.e. normally a ceramic body, much thicker and much shorter than our component).
- inside a GDT, I expect there to be physical separation between the two ends/leads of the component, with that gap being filled with a gas which probably has a specific breakdown voltage. OTOH, if you look at our component, you will see there is something looking like a resistor connecting the two leads. So, not much of a "discharge" that can happen there, IMHO (as in "sudden discharge").

Instead, I am guessing our Z component might be a high value resistor (100's of MOhm).
And the 15 MOhm in-circuit measurement is probably the total resistance of the circuit the resistor is connected to.
But all this is guesswork at this stage and, in the absence of any schematics or other data, there is only one way to find out.
I just need to muster some courage (for some reason, I'm always afraid of being too invasive with my troubleshooting)...

[giosif]

I forgot to ask what the lcd shows in the following situations.  Meter with no probes.  Set meter to manual range ohms mode.

1. 250 ohms
2. 2500 ohms
3. 25 k ohms
4. 250k ohms
5. 2500k ohms
6. 25M ohms

Do all manual modes above show 0L?

All ranges show OL except for the 25 MOhm one.

Also if you desolder the relays for cleaning, mark them left and right.  After cleaning put them back in the same position.  If 26M ohm problem still exists, desolder the relays and switch them around to see if that makes a difference?

I will keep this in mind in case I do desolder the relays.

[retiredcaps]

All ranges show OL except for the 25 MOhm one.

I wondering if there is something in the path of that 25Mohm that is affecting the readings?  Dirt, debris, spilled battery juice, bad/cold solder joint.

Or the main IC has a suspect solder flow, or internally only the 25M ohm range has a problem?

I like to start with the simple stuff like a thorough IPA bath/cleaning/tooth brush scrub, close examination of the components and soldering using jewelers loupe and then work up to the harder stuff.

Another question or data point.  Does the 10A work on the shared 25M ohm/10A button?  Are the 10A readings somewhat accurate?  If there is a problem with 25M ohm, maybe there is a problem with the 10A since they share a button?

One other idea from helping in this thread. 

https://www.eevblog.com/forum/repair/fluke-87-dc-reading-very-slow/

What is the input impedance of a Fluke 83/85/87 when you use the Soar 3430?

https://www.eevblog.com/forum/repair/fluke-87-i-repair/msg390462/#msg390462

The Soar should read 11.11M ohm.  Is a solid and stable reading?

[retiredcaps]

Wrt to IPA bath, I just remembered ...

- with no leads connected, the meter measures around 26 MOhm in resistance mode (it autoranges and then slows down around the 26 MOhm figure).

From

https://www.eevblog.com/forum/repair/fluke-189-strange-readings/?all

- In terms of resistance measurements, the initial readings were about 60 MOhm with the leads open and 0 Ohm with the probes shorted.

Update: after yesterday's post, I decided to "grow a pair" and clean the PCB with IPA and a toothbrush.
And, lo and behold, we have an improvement in the situation:
- in resistance mode, with no probes attached, we now measure OL, which is normal vs. the initial 60 MOhm.

[giosif]

So, today, I decided to follow retiredcaps' advice and give the board a scrub with IPA and a toothbrush.
In preparation for that, I also desoldered the two relays.
After doing this and re-installing the relays, I am happy to report the meter is working properly.   

Thank you, retiredcaps, for helping me once again get a multimeter back to working state!
I owe you a beer or two. 

In terms of what might have caused the initial issue, I am not 100% sure, but it might have been residue of some kind on the PCB, porbably in the gap between the relays and the PCB.
When desoldering the realys, I could see there was some of the conformal coating material that had sipped in that gap at the time the coating was applied.
After that, I suspect some other substances got trapped between that conformal coating and the PCB or the relay body, something that was somewhat conductive.

In any case, now that the meter is working, I measured the input impedance for the 250 mV range and it seems to be around 0.03 nS / 33 GOhm.
Also, the 25 MOhm range is now showing OL with the leads open.
If I short the leads, the meter gradually goes to 0.xxx Ohms - not as fast a a modern meter, but much faster than it did before.

[retiredcaps]

In terms of what might have caused the initial issue, I am not 100% sure, but it might have been residue of some kind on the PCB, porbably in the gap between the relays and the PCB.
When desoldering the realys, I could see there was some of the conformal coating material that had sipped in that gap at the time the coating was applied.
After that, I suspect some other substances got trapped between that conformal coating and the PCB or the relay body, something that was somewhat conductive.

Any sort of contamination will affect the readings especially when the current is around 0.5uA in the 50M ohm range.  See picture of Fluke 87V and typical current in the different ranges.  Its 1mA in the 600 ohm range.

In your Fluke 189, it displayed 60M ohm instead of 0L.  Very similar case here with the Soar 3430.  In the highest ohms, you are dealing with less than 1 microamp.

[giosif]

I understand.
What threw me off was the fact the rest of board and components looked clean.
And I guess some contamination is hard to see with the naked eye.