Basic doubt regarding PCB component testing

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
Hi Guys,
I am a Finance professional however like to learn about electronics. I have been reading materials on PCB components, their function and how to test them.
I am trying to rescue a water damaged Nikon D610 camera which doesn't turn on at all. I opened the camera and found corrosion on DC power board. Very slight corrosion on Main PCB and Flash driver PCB too. DC power board was outputting only 3V to Main PCB with a 7V battery input. I cleaned all the boards with Isopropyl and DC power board now outputs 7V to Main PCB, Main Driver board and Flash drive board. It has total 6 voltage output points as shown in the attached pic. Main PCB, Main Driver board and Flash drive board connections where I am getting 7V is marked in Green. There are three other connectors marked in red colour where voltage output is in few mV because it's still shorted I guess. Connectors marked in red connects to front body, shutter and auto-focus motor. I am getting a low battery indicator sign on top LCD now and the camera loops through boot cycle when I try to switch it on. I guess main PCB and Flash drive board should be working fine as I am getting low battery indicator sign on top LCD which is connected to these two. The low battery indicator may be because other three parts not getting 7V providing this feedback to Main board.

DC-DC power board_LI.jpg

I disassembled the boards again and testing DC powerboard to locate the short. With multimeter switched to continuity testing mode, I am keeping black probe on GND and probing both side of capacitor with red one by one. I am getting continuity on both side of a capacitor marked in yellow in the attached picture. This was also the location of the corrosion.

Now my basic doubt. When testing continuity on both side of capacitors, shouldn't I always get "Open Loop" on one side and continuity on another? My assumption is that if I am getting some continuity on another side of the cap, it means either the cap is leaking or there are still remains of conductive particles on PCB traces connecting GND and VLC side of the cap. Pls correct me if my assumption is not valid.
 

dl324

Joined Mar 30, 2015
8,885
Welcome to AAC!
Now my basic doubt. When testing continuity on both side of capacitors, shouldn't I always get "Open Loop" on one side and continuity on another?
In general, you can't measure the resistance of components in-circuit; at least not without knowing what other components interact with the one you're trying to measure.

A more typical troubleshooting methodology is to power the circuit, take voltage measurements, and, from the measurements, determine whether they're as expected. If they're abnormal, you need to come up with failure modes that would account for the observed measurements.

Seeing that you don't have a background in electronics or electrical engineering, it's unlikely that anyone here can help you. The first thing most of us will ask for is a schematic. If you can't produce one, it's unlikely that we'll be able to help.
 
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Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
Hi dl324,
Thanks for your response and apologies for my vague question. I tried to search for Nikon D600/D610 schematic, however, seems it's not available online readily. Though there schematics for older models.

I am attaching another pic to show what I am trying to do, which is more of trying to find the location of the short than testing individual component.

DC-DC power board.jpg

As shown in the pic, I have dialed the multimeter on continuity/resistance check mode. Put the black probe on a GND location indicated by line 3 in black. When I put the red probe on via hole as indicated by line 1 in red, I get 0 Ohm resistance, which indicates continuity. However, when I put the red probe on another side of the cap, as shown by line 2 in red, I get around 5kOhm resistance. My assumption is that it should show "OL" as this side is connected to voltage line.
 

MrChips

Joined Oct 2, 2009
19,271
As you may well imagine, trying to revive a complex piece of electronics is not an easy thing to do, in fact quite formidable.

There are some basic steps we like to take with trying to diagnose a failure.

The first thing we consider is the history. Was the unit working? When did it first fail? What conditions caused the failure? Have others already attempted to rectify the situation?

Next we do the physical examination. Look, smell, touch. Are there obvious signs of damage? Can we smell heat stressed components? Are there bulging capacitors, discoloured components or circuit boards.

At some later stage we do the power up test. Again, look, smell, listen, touch. Are any components getting unusually hot? Are there any bubbling, hissing, banging noises? Are there any functional signs?

After we have done all of the above, we are confined to finding a circuit schematic. Without a road map of what to look for we are totally lost. The unit is scrap.

Sorry, that's the way it goes for 99% of most modern electronic equipment.
 

hp1729

Joined Nov 23, 2015
2,304
Hi dl324,
Thanks for your response and apologies for my vague question. I tried to search for Nikon D600/D610 schematic, however, seems it's not available online readily. Though there schematics for older models.

I am attaching another pic to show what I am trying to do, which is more of trying to find the location of the short than testing individual component.

View attachment 121665

As shown in the pic, I have dialed the multimeter on continuity/resistance check mode. Put the black probe on a GND location indicated by line 3 in black. When I put the red probe on via hole as indicated by line 1 in red, I get 0 Ohm resistance, which indicates continuity. However, when I put the red probe on another side of the cap, as shown by line 2 in red, I get around 5kOhm resistance. My assumption is that it should show "OL" as this side is connected to voltage line.
Well congrats on the progress you have made so far. Unless someone here has a similar camera to compare readings there isn't much we can do you.
 

dl324

Joined Mar 30, 2015
8,885
However, when I put the red probe on another side of the cap, as shown by line 2 in red, I get around 5kOhm resistance. My assumption is that it should show "OL" as this side is connected to voltage line.
A perfect capacitor would show as an open circuit to DC; a leaky capacitor wouldn't. Measuring the resistance (called ESR) of a cap is sometimes useful; sometimes not.

If you found a defective component, would you be able to replace it? If the answer is no, what's the point? If the camera was on when it got wet, things probably got shorted and something got damaged. If it was off, it's possible that thorough drying would restore it to operating condition; but that isn't the case here.

I have 4 decades of experience and wouldn't bother with trying to fix something that probably has custom parts that aren't available to consumers.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
As you may well imagine, trying to revive a complex piece of electronics is not an easy thing to do, in fact quite formidable.

There are some basic steps we like to take with trying to diagnose a failure.

The first thing we consider is the history. Was the unit working? When did it first fail? What conditions caused the failure? Have others already attempted to rectify the situation?

Next we do the physical examination. Look, smell, touch. Are there obvious signs of damage? Can we smell heat stressed components? Are there bulging capacitors, discoloured components or circuit boards.

At some later stage we do the power up test. Again, look, smell, listen, touch. Are any components getting unusually hot? Are there any bubbling, hissing, banging noises? Are there any functional signs?

After, we have done all of the above, we are confined to finding a circuit schematic. Without a road map of what to look for we are totally lost. The unit is scrap.

Sorry, that's the way it goes for 99% of most modern electronic equipment.
Thanks MrChips,
The camera was working fine even after the splash. However, the owner kept on using it in this condition without getting the boards cleaned. Seems finally the corrosion reached from GND side of the track to voltage side and shorted something. I checked the board under microscope and everything looks clean now. There is no visible damage under 20X magnification or heating. There are no previous attempts to repair. Nikon service centre guys may have opened it for inspection though.

Now, coming back to my question and to add more clarity, No..I am not trying to fix this DC board. This question is more focused on a short term learning objective. My assumption is that the way I am testing it, I should always get OL on meter when testing voltage side of the cap. Are there circumstances when a working board would show resistance on voltage side of the trace and still not shorted?
 

MrChips

Joined Oct 2, 2009
19,271
Others have already answered your question. To be sure that you are testing the component correctly you have to remove the component from the circuit board. The only other way of validating your test is with a knowledge of how the component is connected to the rest of the circuit and that would require access to a circuit schematic.
 

dl324

Joined Mar 30, 2015
8,885
My assumption is that the way I am testing it, I should always get OL on meter when testing voltage side of the cap.
Measuring resistances on components in-circuit is an exercise in futility if you don't have a schematic so you can determine what you should measure.

You need to draw a schematic (either on paper or mentally), measure voltages, and troubleshoot anything that doesn't seem reasonable. This is one of the most important steps for troubleshooting. A good technician/engineer can troubleshoot a circuit only using a schematic with expected voltages. That's what we do when people ask for troubleshooting assistance. We ask for a schematic and then direct where measurements should be taken.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
A perfect capacitor would show as an open circuit to DC; a leaky capacitor wouldn't. Measuring the resistance (called ESR) of a cap is sometimes useful; sometimes not.

If you found a defective component, would you be able to replace it? If the answer is no, what's the point? If the camera was on when it got wet, things probably got shorted and something got damaged. If it was off, it's possible that thorough drying would restore it to operating condition; but that isn't the case here.

I have 4 decades of experience and wouldn't bother with trying to fix something that probably has custom parts that aren't available to consumers.
Something is definitely wrong with the DC power board. Though, I can do soldering, replacing such small caps is something very daunting, I have never tried. That's why I have already ordered a replacement DC power board.

Though fixing the camera is the ultimate objective, as of now, my question was focused on a generalized learning useful for other troubleshooting too.
 

dl324

Joined Mar 30, 2015
8,885
Though fixing the camera is the ultimate objective, as of now, my question was focused on a generalized learning useful for other troubleshooting too.
Some people can learn electronics on their own, but many of those who do eventually learn that their lack of fundamentals makes learning hard and things start looking like black magic.

I learned the traditional way. Went to school for years and spent years refining my skills and knowledge. I'm self-taught in most things I know, but electronics isn't one of them.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
Y
Measuring resistances on components in-circuit is an exercise in futility if you don't have a schematic so you can determine what you should measure.

You need to draw a schematic (either on paper or mentally), measure voltages, and troubleshoot anything that doesn't seem reasonable. This is one of the most important steps for troubleshooting. A good technician/engineer can troubleshoot a circuit only using a schematic with expected voltages. That's what we do when people ask for troubleshooting assistance. We ask for a schematic and then direct where measurements should be taken.
@dl324.. yes, you are right. Unfortunately, I was not able to find schematics for this or any newer Nikon DSLR model even after extensive online searching.
Requesting other forum members to help if they have access to D600/D610 schematic by any chance.
The replacement DC power board is already on the way which I should receive in couple of weeks time.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
Others have already answered your question. To be sure that you are testing the component correctly you have to remove the component from the circuit board. The only other way of validating your test is with a knowledge of how the component is connected to the rest of the circuit and that would require access to a circuit schematic.
Thanks, you guys have been really helpful. One more question on same line. If I put black probe on GND and Red on voltage line trace on a working board under resistance test mode, under what circumstance I may get resistance instead of OL?
 

dl324

Joined Mar 30, 2015
8,885
If I put black probe on GND and Red on voltage line trace on a working board under resistance test mode, under what circumstance I may get resistance instead of OL?
When the resistance being measured exceeds the meter range.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
When the resistance being measured exceeds the meter range.
You mean it's possible for a working board to have resistance between GND and voltage line? My understanding of resistor was that it's connected only between V to V, not between GND to V. Other components like caps, diodes or ICs which are connected between GND and V would put resistance in V line only when it's On. Whereas, I am doing the continuity test when the circuit is off.
Pls excuse my lack of knowledge on this.
 

dl324

Joined Mar 30, 2015
8,885
You mean it's possible for a working board to have resistance between GND and voltage line?
Yes.
My understanding of resistor was that it's connected only between V to V, not between GND to V. Other components like caps, diodes or ICs which are connected between GND and V would put resistance in V line only when it's On.
Your understanding is woefully inadequate.

This site has educational materials, but I don't know how useful they'll be if you try to pick and choose what you want to learn.

If you think you could teach yourself physics or calculus or differential equations, you might be able to teach yourself electronics. Like I said, the number of people who have done that successfully is a small number. There are probably a large number of people who are self-taught think they're competent; until they come across a problem that makes them realize they're not.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
Yes.
Your understanding is woefully inadequate.

This site has educational materials, but I don't know how useful they'll be if you try to pick and choose what you want to learn.

If you think you could teach yourself physics or calculus or differential equations, you might be able to teach yourself electronics. Like I said, the number of people who have done that successfully is a small number. There are probably a large number of people who are self-taught think they're competent; until they come across a problem that makes them realize they're not.
Thanks for your pointer. You have been very helpful. I am good with Physics and Calculus be it integration or differentiation. That's what I read till college, before moving to Finance.

I'll go through more materials on electronics. Unfortunately, I'll have to pick and choose materials relating to area I am concerned with. Don't want to end up learning quantum physics trying a DSLR repair :D
 

BR-549

Joined Sep 22, 2013
4,936
Troubleshooting an un-documented broad. First of all, you're lucky. Even tho you don't have a print...you have known function and the I/O.

I used to repair orphan boards. Neither function nor I/O was known.

1. do not clean board. inspect all board and component surfaces. note possible problems.

2. brush with dry soft paintbrush. blow with low pressure dry air. a small spot of corrosion can be stopped.....but a corrosion of a trace is almost always a future failure. An experienced tech can preform a bypass. if corrosion is thru-out ...crap can the board.

3. the first thing to check is function.....not value. We don't know the function of the board.....but we know the functions of the components.

4. construct and study an oscilloscope "octopus". cost 10 bucks. or spend multi k $ on network analyzer.

5. check function of each component while on un-powered board. This will get you in the area.

6. value test. one can super very easily see a defective active component, on an un-powered board, without removal. The hard ones are the resistor values and the cap values. you have to pull one lead. only for value.....you can see function without pulling lead.

7. a good tech can replace all board components a lot quicker than trying to understand it.


If course.....this was in a time=money environment. I didn't hesitate to charge 500 to 1000 bucks per board.......and that was almost 2 decades ago.

Edit....sorry.....I have repaired two SLR boards that I know of. Both were bad electrolytic caps.
 
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Kermit2

Joined Feb 5, 2010
4,158
Do more close up, visual inspections.

Use a magnifying lens, or (my favorite) a 5X jewelers loupe.

Look inside connectors. Look at soldered joints on components to spot hairline cracks around the fillet where surfaces meet.

Many times a quick re-heat with a small soldering iron will cure a faulty joint.

Moisture will creep into the crevice and corrosion will quickly separate the rest of the joint.

If you don't know theory, knowing the cure for basic problems and applying them where your "eye" says to, can often serve to fix problems that you don't understand.
 

Thread Starter

amitksingh2003

Joined Mar 2, 2017
10
Troubleshooting an un-documented broad. First of all, you're lucky. Even tho you don't have a print...you have known function and the I/O.

7. a good tech can replace all board components a lot quicker than trying to understand it.

Edit....sorry.....I have repaired two SLR boards that I know of. Both were bad electrolytic caps.
Thanks @BR-549. I would have preferred to do the same, provided, components were available.

As @dl324 suggested, I started this with very little theoretical or practical knowledge. So obviously I took lot more time.

I was wrong in assuming a short on the board. I replaced the two caps I was doubting for shorts, and problem remained same. After further checking, I found it was a bad voltage regulator bus (WLA126, part-TC7WBL126AFK) on DC power distribution PCB. I couldn't source it locally. 2.8V of voltage was going into this from battery, however, the output voltage was 0V. As per the data sheet, operating range is 2V to 5V. I guess it might have received 8V from the main battery when water went inside and it gone bad.
 
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