Need help determining Ohm value of resistor.

[CAS]

By the look from the picture, it looks like the led is in parallel with the diode or resistor. This would give you same reading both ways. Bit hard to say exactly without seeing the other side of the board and knowing how its all connected.

[ToddB66]

Questio about testing diode.

CAS....Thanks for your last reply !

Here's the top-side view of the PCB, showing the LED, resistor and diode.

Does this help you make a determination of what could be causing the 027 meter reading to be the same, regardless of whether the meter test leads are touching the diode leads the correct way and then reversing the test leads ?

In reference to the picture of the underside of the PCB in my previous post #15, I assume you can see the circuit tracks plainly enough when you double-click the attachment.

Thanks,

ToddB66

[CAS]

This is the circuit as I see it.



So the resistor and diode are in parallel. You are just measuring the resistor.

[ToddB66]

CAS,

As near as I can determine, it appears your circuit schematic agrees with the PCB circuit at my end.

So I guess you are indicating that when I'm testing the diode with the meter set in the diode position and the meter leads touching the diode leads positive to anode and then switching the positive test lead to cathode, that the 027 meter reading is a false reading....right ?

If you agree with the above statement, then do you also agree that I would have to clip one of the diode leads and re-test to get a true diode test, i.e. current flow blocked in one direction, but not in the other direction ?

Bottom line, for my "testing diodes project", me thinks I'll just go buy an assortment of diodes to play with, rather than clip a diode lead on my PCB. As mentioned previously, the LED is working, so I'm going to assume that the rectifier diode is good.

I really appreciate the time you are spending to help me unravel this.

Looking forward to your reply to my two questions above and any other comments you decide to make.

Best regards,

ToddB66

[ToddB66]

Question about testing diode (Continued)

CAS,

(This supplements my post #19)

One more thought; since the rectifier-type diode and resister are on the PCB solely as requirements for the LED and the LED is working fine, I'm just going to assume that the rectifier-diode and resistor are soldered correctly in the circuit in a manner that's functionally correct for the LED. Therefore, I've decided to assemble the air freshener unit back together and forget about using any of the PCB components for experimental testing. I'll just buy a mixed bag of components for experimental purposes, as was suggested to me earlier in this thread.

At least my interest in the PCB components has been time well spent for me, as I have studied my electronics books again, conversed with you and Qiaozhi and got a better understanding of how diodes and resistors work together.

Again, thanks for helps on this.

ToddB66

[Qiaozhi]

The only puzzling thing here is the 027 reading, and appears to be a resistance value (close to 33Ω). However, in the diode test mode, I would have expected to see a voltage reading on the meter of around 0.7V. Perhaps this a feature of the meter. i.e. if it cannot detect a diode, it shows the resistance value.

[Qiaozhi]

On the subject of ALT CODES, I found this useful reference for entering Greek characters).
https://rotkel.de/Infothek/Tastaturk...-Alphabet.html

It's in German, but the table is self-explanatory, and lists the correct codes to use for Windows, Mac, Linux and Latex.
That's how I inserted the omega character (for Ohms) in my previous post.

[CAS]

The 33 ohm resistor is i parallel with the diode. If you measure a 33 resistor with the diode range thats the figure I would expect. A lot of SMPS seem to have resistors in parallel with diodes and fets etc which make it a pain when trying to fault find.

[Qiaozhi]

The 33 ohm resistor is i parallel with the diode. If you measure a 33 resistor with the diode range thats the figure I would expect. A lot of SMPS seem to have resistors in parallel with diodes and fets etc which make it a pain when trying to fault find.

I was intrigued to know what the result would be on my own meter, so I took a 1N4148 diode and a 33Ω resistor and put them in parallel. The displayed result was .032V.

ToddB66 - Can you confirm the reading on your meter was 027, or was it actually .027 (which would make more sense)?

[green]

I was intrigued to know what the result would be on my own meter, so I took a 1N4148 diode and a 33Ω resistor and put them in parallel. The displayed result was .032V.

ToddB66 - Can you confirm the reading on your meter was 027, or was it actually .027 (which would make more sense)?

Wondered what my meters would read. Used a 1N4148 diode and two 1 percent resistors, 30 and 500 ohms. One meter has an extra digit resolution. Diode (.549v, .5948v)
30 ohm resistor (30.2 ohms, .022v, 30.24 ohms,.0222v) 500 ohm resistor (497 ohms, .321v, 497.5 ohms, .3122v). Based on your readings I was thinking the meter displayed the voltage with 1 ma current. (E=IR) It appears my meters use less than 1 ma and it's not constant. The diode reading changes with temperature.

[CAS]

I have found over the years that when using the 'diode' mode on any meter that I only use it as an indication if the component is faulty or not. As you have seen for yourselves, that actually reading you get varies depending on the meter.

[ToddB66]

Question about testing a diode (Continued).

CAS and Thomas,

Attached are pictures of my fan, showing top and underside of the circuit board and the motor for your reference while reading the following.

To work with attachments, left-click once on each individually. To enlarge a specific area of the picture, use your mouse to hover the little enlargement dot over the area and left-click once. To turn off the picture, left-click the red button with white X in the upper-right corner of screen and when the pop-up dialog box comes up, click on the right-hand button that says "Close current tab".

I just noticed that my Lutron Fan Speed Control, model FS-5F with analog control dial has a warning stamped on the aluminum face plate that says "To reduce risk of fire or shock use only with fans rated 5 Amps max 120 VAC ", whereas my True Air Fan apparently draws only 0,14 Amps (read 14/100) as embossed on the back of the plastic Fan housing.

Since the speed control device is analog type (continuously variable ) with a 5 Amp max. rating , I assume that when the rotary dial is first clicked ON it is outputting less than 5 Amps, but likely more than the 0,14 A (read 14/100) embossed on the back of the Fan housing.

Hypothetically speaking, even if my Fan Speed Control outputs within safe running amps when the dial is at the low end just after clicking ON, I would need to put a safety- stop on the dial. Bottom line, I don’t think the 5 Amp max. Lutron Speed Control is a good match for my Fan. So, I’m going to use the FAN “as is” (without any speed control device) and see if it draws soldering fumes satisfactorily at normal speed, which I’m guessing it will.


Thanks to everyone who gave help in this thread.


ToddB66

[ToddB66]

Wondered what my meters would read. Used a 1N4148 diode and two 1 percent resistors, 30 and 500 ohms. One meter has an extra digit resolution. Diode (.549v, .5948v)
30 ohm resistor (30.2 ohms, .022v, 30.24 ohms,.0222v) 500 ohm resistor (497 ohms, .321v, 497.5 ohms, .3122v). Based on your readings I was thinking the meter displayed the voltage with 1 ma current. (E=IR) It appears my meters use less than 1 ma and it's not constant. The diode reading changes with temperature.

Qiaozhi and green,

Just discovered I forgot to include you both in my post #27 when I thanked Thomas and CAS for their help.

Thanks much for your help too !

ToddB66

[CAS]

You havent quite got that right. The controller will handle a max. of 5A. Your fan will only draw what it needs. The controller doesnt 'pump' extra current into the fan. The controller should be ok.

[ToddB66]

Using a 5 Amp Max 120VAC, 60Hz analog Fan Speed Control with a 120VAC, 0,14 Amp 60Hz Fan

You havent quite got that right. The controller will handle a max. of 5A. Your fan will only draw what it needs. The controller doesnt 'pump' extra current into the fan. The controller should be ok.

Hi CAS !

Attached is a photo of my LUTRON analog Fan Speed Control. You may have to use your magnifier to see up close and then drag left-right, etc. to see what you want.

You know, I remember that " Your fan will only draw what it needs" from a Home-Study course in Electricity and Appliance Repair I took years ago from NRI (National Radio Institute), but I wasn't certain if the warning (pasted in-part below in quotes.) applied to analog type continuously-variable Fan Speed Controls. My rationale for this was mentioned in paragraphs #4, 5 and 6 of my previous post, but from your reply in quotes at the top of the page, apparently the warning doesn't apply in this case.

" To reduce risk of fire or shock use only with fans rated 5 Amps max 120 VAC and marked suitable for use with solid state fan speed controls.".

I'm happy that you say my Fan Speed Control will work, but I need answers to the following questions if you don't mind, to bolster my "electronic newbie" confidence before going ahead.

Questions follow :

#1) I guess it goes without saying that I'm going to have to cut the white Fan Motor wires to splice-in the black Speed Control wires.........agree ?

#2) Since the wires from my Speed Controller are both black and the Fan wires are both white I would assume there are no polarity considerations when making these connections........am I correct ?

#3) After connecting the Fan wires to the Speed Control wires, can I twist the Speed Control knob all the way up (to the far-right) without burning out any of the Motor armature or coil wires ?

Thanks for your continued help.
ToddB66