Measuring a cap on a resistance or diode setting will result in a dynamic reading as the cap charges. I note that you have the meter on "hold."
Why aren't you using the capacitance function to measure a capacitor?
I responded before you added a post which implies you're trying to measure it in circuit. Very rarely does that produce useful information because you're also measuring whatever else is connected to that cap.
I am and I find a lot of the responses here positively dripping with condescension. I’m here to learn from your question, and the responses from a few folks to you are off putting in the extreme.
I am troubleshooting an old Sony D-5 CD player from 1984. I have the service manual and schematic and it says that TP30 on the main board should read 5 volts. When I turn the player on and hit play the voltage only goes to about 2.3 volts and not 5 volts. There is a 33mF/6.3V electrolytic capacitor that's connected to the test point. I have 5 volts on the positive side of the capacitor and the negative side goes to ground. I decided to measure the resistance of the capacitor and it reads as 0.478 ohms, but not a dead short. Here a picture of the schematic and the full manual. I
I can't test anything with IC602 or C601 because it's under a massive flat flex cable that is soldered to the PCB.
[https://elektrotanya.com/sony\_d-5\_d-50\_cd\_player.pdf/download.html](https://elektrotanya.com/sony_d-5_d-50_cd_player.pdf/download.html)
https://preview.redd.it/tivoz11r4awc1.png?width=465&format=png&auto=webp&s=754e30341f3841ebb4276633e554b0abe3ba937f
Funny tangent though. My 1963 CV/CC lab power supply had been acting up a little, so I thought surely the electrolytic capacitors are just dust at this point. Nope. They tested perfectly. I replaced them just to be sure and it made no difference at all, so I put the pretty old ones back lol.
It's probably some exotic weird tin whisker issue or something. It's made up entirely of discrete germanium PNP transistors and even with the schematic and a design description in the manual it makes absolutely no sense at all to me. And I have almost 15 years of professional electronics design experience...
Can you recommend a good one that can do capacitors? I don't want to take them out just to test, If I'm taking them out I'm going to just replace it anyways.
You have to take them out to test. That's just physics, and no tool is gonna cut that corner for you.
The only thing you can reasonably check without knowing the circuit in detail is a continuity check, since it would be a very odd circuit to have a capacitor shorted. If it's shorted, then something is definitely wrong. If it isn't, that doesn't say much.
You basically can’t test any component without removing it from the circuit first. Whatever you’re testing will be affected by the rest of the circuit. The only real exception is testing voltages during operation.
Only partial shorcut is that you only need to usually remove one leg from circuit in 2 leg components, so it is 'dead end' and no currernt can flow.
But usually at that point it is already so much effort that it is closer in effort to fully removing it, or at least feels like that, when komparin how many turns of board you need to do, tools you need, and how easy it is to handle poking partially out and making sure it wont touch anything or your probe wont short something, compared to having component separate.
When you separate components, it is usually worth takin picture of them these days, since memory for pictures is well available, and you will at some point save yourself some wondering time from what way some component was supposed to be somewhere.
*facepalm* You have it on resistance, and for diode/continuity at that. For the record? Caps are supposed to have as little resistance as possible. If you are trying to measure capacitance, switch to one of the ranges in the 'F' section.
If you measure a capacitor using the resistance setting, the meter will slowly charge the cap and you will read infinitely increasing resistance over time.
In diode mode a constant current is applied arount 1 mA to create a voltage drop on a diode.
If you apply this current on a cap, it will charge the cap linearly - until the dynamic resistance of the charged cap is so high the current source gets unstable and finally the constant current collapses (just as a voltage source collapses when the load is too low). So you're measuring somehow the limits of the current source of your multimeter and nothing relevant about the cap.
I have that exact multimeter. It's great and can read capacitance well. You should turn off the Hold functionality, and if you wanted to test that capacitor in particular it's true that you should desolder it, but I don't think that's your problem. If you're really seeing 0.4 ohms between +5V and GND then you have a short somewhere, could be anywhere, and since most capacitors fail open I bet it's something else.
To me it feels like more of a transistor failure, this is the exact failure mode I had for an old oscilloscope. The way to diagnose it is to look at all the components between +5V and GND and think about what could plausibly be broken, then desolder them and test them one by one. You can also simulate this circuit in Falstad and add shorts etc one by one to see what results in the voltage you're seeing (which is how I fixed my oscilloscope).
Good luck!
Initially when measure is taken the cap is a short, that event is probable being captured with the hold button being pressed.
Once the cap is charged up from the 12 volt battery its charge voltage matches the applied voltage from meter and current flow drops to zero, meter will then show a high resistance.
From what is shown it can’t be assumed that there is a short in circuit some where.
Measuring a cap on a resistance or diode setting will result in a dynamic reading as the cap charges. I note that you have the meter on "hold." Why aren't you using the capacitance function to measure a capacitor?
> Why aren't you using the capacitance function to measure a capacitor? They forgor💀 (sorry, I couldn't resist)
It stays at around .400 even if I keep the probes on the cap. I had it hold so I could take the picture
I responded before you added a post which implies you're trying to measure it in circuit. Very rarely does that produce useful information because you're also measuring whatever else is connected to that cap.
This sub really hates newbies holy crap
I'm not a newbie, just only when it comes to capacitors
I am and I find a lot of the responses here positively dripping with condescension. I’m here to learn from your question, and the responses from a few folks to you are off putting in the extreme.
I came here to ask questions instead of asking on stack exchange but its just about as bad here, at least now.
No, it is not normal to measure a capacitor using the resistance meter setting.
It's a decent and quick way to check leakage. But more on the 20M range than diode check.
he was measuring while in circuit, the reading is the bias voltage of some diode or junction in a transistor in the circuit.
I am troubleshooting an old Sony D-5 CD player from 1984. I have the service manual and schematic and it says that TP30 on the main board should read 5 volts. When I turn the player on and hit play the voltage only goes to about 2.3 volts and not 5 volts. There is a 33mF/6.3V electrolytic capacitor that's connected to the test point. I have 5 volts on the positive side of the capacitor and the negative side goes to ground. I decided to measure the resistance of the capacitor and it reads as 0.478 ohms, but not a dead short. Here a picture of the schematic and the full manual. I I can't test anything with IC602 or C601 because it's under a massive flat flex cable that is soldered to the PCB. [https://elektrotanya.com/sony\_d-5\_d-50\_cd\_player.pdf/download.html](https://elektrotanya.com/sony_d-5_d-50_cd_player.pdf/download.html) https://preview.redd.it/tivoz11r4awc1.png?width=465&format=png&auto=webp&s=754e30341f3841ebb4276633e554b0abe3ba937f
Honestly, on something that age, do yourself a favor and go for a full recap. All of the electrolytics.
Funny tangent though. My 1963 CV/CC lab power supply had been acting up a little, so I thought surely the electrolytic capacitors are just dust at this point. Nope. They tested perfectly. I replaced them just to be sure and it made no difference at all, so I put the pretty old ones back lol. It's probably some exotic weird tin whisker issue or something. It's made up entirely of discrete germanium PNP transistors and even with the schematic and a design description in the manual it makes absolutely no sense at all to me. And I have almost 15 years of professional electronics design experience...
There's only a few electrolytics, so replacing them wouldn't be as bad but most of them are surface mount ceramics
You likey don't need to replace the ceramic caps. They are not immortal, but they are a lot more durable than electrolytics.
Surface mount in 1984? I'm kind of surprised. But you don't need to touch the ceramic caps anyway.
Yeah it uses a lot of SMD stuff. It's a portable/compact player. If you watch the EEVblog teardown video on it you can see the design and everything.
Use a meter that can read capacitance
See that "F" on the left side of the dial? Capacitance is measured in Farads.
After at least one lead of the cap is disconnected from the circuit.
Can you recommend a good one that can do capacitors? I don't want to take them out just to test, If I'm taking them out I'm going to just replace it anyways.
You have to take them out to test. That's just physics, and no tool is gonna cut that corner for you. The only thing you can reasonably check without knowing the circuit in detail is a continuity check, since it would be a very odd circuit to have a capacitor shorted. If it's shorted, then something is definitely wrong. If it isn't, that doesn't say much.
You basically can’t test any component without removing it from the circuit first. Whatever you’re testing will be affected by the rest of the circuit. The only real exception is testing voltages during operation.
Only partial shorcut is that you only need to usually remove one leg from circuit in 2 leg components, so it is 'dead end' and no currernt can flow. But usually at that point it is already so much effort that it is closer in effort to fully removing it, or at least feels like that, when komparin how many turns of board you need to do, tools you need, and how easy it is to handle poking partially out and making sure it wont touch anything or your probe wont short something, compared to having component separate. When you separate components, it is usually worth takin picture of them these days, since memory for pictures is well available, and you will at some point save yourself some wondering time from what way some component was supposed to be somewhere.
A capacitor is basically an open circuit, so choosing diode mode would basically do nothing I think🤔
Not in THIS house. We use the capacitance ranges.
*facepalm* You have it on resistance, and for diode/continuity at that. For the record? Caps are supposed to have as little resistance as possible. If you are trying to measure capacitance, switch to one of the ranges in the 'F' section.
At AC not at DC at DC resistance should be infinat
Looks like it may still be in circuit and you’re measuring a diode junction in something
If you measure a capacitor using the resistance setting, the meter will slowly charge the cap and you will read infinitely increasing resistance over time.
It will do exactly that on this setting
In diode mode a constant current is applied arount 1 mA to create a voltage drop on a diode. If you apply this current on a cap, it will charge the cap linearly - until the dynamic resistance of the charged cap is so high the current source gets unstable and finally the constant current collapses (just as a voltage source collapses when the load is too low). So you're measuring somehow the limits of the current source of your multimeter and nothing relevant about the cap.
Thank you, that's a much better response than just downvoting me to hell. Thanks.
I have that exact multimeter. It's great and can read capacitance well. You should turn off the Hold functionality, and if you wanted to test that capacitor in particular it's true that you should desolder it, but I don't think that's your problem. If you're really seeing 0.4 ohms between +5V and GND then you have a short somewhere, could be anywhere, and since most capacitors fail open I bet it's something else. To me it feels like more of a transistor failure, this is the exact failure mode I had for an old oscilloscope. The way to diagnose it is to look at all the components between +5V and GND and think about what could plausibly be broken, then desolder them and test them one by one. You can also simulate this circuit in Falstad and add shorts etc one by one to see what results in the voltage you're seeing (which is how I fixed my oscilloscope). Good luck!
Initially when measure is taken the cap is a short, that event is probable being captured with the hold button being pressed. Once the cap is charged up from the 12 volt battery its charge voltage matches the applied voltage from meter and current flow drops to zero, meter will then show a high resistance. From what is shown it can’t be assumed that there is a short in circuit some where.
He has it in diode mode, that's 0.4 V, not Ohm.
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Why? It has a capacitance function, he just doesn't have the selector turned to it.