No voltage reading on the secondary side of SMPS power supply

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
Hello all you good people.
As usual I am full of problems I have uncertainty with. It is what happens when one walks in the unknown.
I have this power supply, I am not sure what it was in that I took it out of.
There is no DC output at the plugs. Both of them got no voltage.

The larger one with multiple pins has (3) grounds, (2) 24V, (1) 5V, (1) 3 1/2 volts.
The smaller is a 3.7V

I read 167VDC all the way to the great partition. [ I DO NOT HAVE OSCILLOSCOPE]
I get no reading after the two coils. I don't know what kind of coils ( chopper coils?) they are but the wire in them look more like cable. Well, what do I know.
When I tested between its legs and the diodes, there are one diode for each side and I guess may couple of more diodes. No voltage reading.
Should I conclude that those coils are shot, whatever kind of coils they are called.
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Thread Starter

Alchemy One

Joined Oct 5, 2019
205
Good post!
Are there pulses on the primary side?
=========================
Good one. Meaningfull question.
There is no way anything will happen with just DC. In essence it must be high frequency AC that mimicks being DC, with small amplitudes ( up and down) I would think, just common sense or intuition or something.
I don't have osciloscope and if I had one first I have to learn how to use it, probably not a good idea hooking it up to check any oscillation. I don't know.
Well since I have bought everything else.......
 
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DickCappels

Joined Aug 21, 2008
8,708
You can make a simple AC detector that you can couple to the switching transistor's collector by holding a wire connected to the input of the detector close to the collector. The voltage on the output would change when the wire is brought close to the circuit if there is "stuff" on it.
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The transistor can probably be any small signal transistor. The battery voltage can be 1.5 volts and up.
Feel free to change the resistor and capacitor values.
 

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
You can make a simple AC detector that you can couple to the switching transistor's collector by holding a wire connected to the input of the detector close to the collector. The voltage on the output would change when the wire is brought close to the circuit if there is "stuff" on it.
View attachment 259619
The transistor can probably be any small signal transistor. The battery voltage can be 1.5 volts and up.
Feel free to change the resistor and capacitor values.
========================
I just want to make sure I have this right.
With board unplugged and capacitor discharged.
Testing the transistor in the circuit supplying power to it using a battery.
Do I have it right?
Editing:
There is one 20JL2C switching mode converter chopper [ I assume I check this one?]
There are two K3314 NPN DC to DC converters
and two NEC K2370 P Channel switching



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Attachments

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Thread Starter

Alchemy One

Joined Oct 5, 2019
205
You can make a simple AC detector that you can couple to the switching transistor's collector by holding a wire connected to the input of the detector close to the collector. The voltage on the output would change when the wire is brought close to the circuit if there is "stuff" on it.
View attachment 259619
The transistor can probably be any small signal transistor. The battery voltage can be 1.5 volts and up.
Feel free to change the resistor and capacitor values.
--------------------------
What a trip.
I see what you mean.
Except first I had the gate attached to the wire.
Well then I said maybe he means that that wire itself is antenna.
So I unhooked it and then approached the gate with it.
Just as it is like a 1/4-1/2 inch away, the voltage drops.
I used a lithium ion.
Well, It is a trip that even in the proximity things happen. However that works.... that is what I like to know. :)
The left front wire to the gate.
Okay. update:
I get how the whole charging and discharging capacitor plays the role. When the gate is open, no current goes through the transistor and the cap charges.
And when voltage/current is at the gate, the cap gets to discharge and current flow through, voltage dropping.
But how on earth it is sensed when the wire/antenna hardly even touches the gate? I don't understand that at all.
Although as I repeated it, it changed behavior. I had to get closer and closer to the gate and touching it for the meter to show voltage drop.
Come to think of it I never did ground everything to chasis if that will ad to the effect.
It looks like the emiter is grounded to the body of mosfet which is connected to the chasis.
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DickCappels

Joined Aug 21, 2008
8,708
The transistor just senses the changing of the electric field by capacitive coupling to the driver stage and the capacitor "saves" the peaks, which are negative on the collector.

Is there much of a signal on the drain?

If you want to check the transisors, I would first just do a quick check for shorts between the drain and source, keeping in mind that the drain should be connected to the positive lead of the ohmmeter. Also collector and emitter of the bipolar transistors. If you see what you think is a short reverse the ohmmeter connections and see whether the short looks the same (near 0 ohms) in both directions.

You may have to remove the parts from the circuit to do a thorough check.
 

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
The transistor just senses the changing of the electric field by capacitive coupling to the driver stage and the capacitor "saves" the peaks, which are negative on the collector.

Is there much of a signal on the drain?

If you want to check the transisors, I would first just do a quick check for shorts between the drain and source, keeping in mind that the drain should be connected to the positive lead of the ohmmeter. Also collector and emitter of the bipolar transistors. If you see what you think is a short reverse the ohmmeter connections and see whether the short looks the same (near 0 ohms) in both directions.

You may have to remove the parts from the circuit to do a thorough check.
=========================
It is easily possible that I may have tested the voltage on the primary side where I could read voltage and not where it counts.
I have this feeling that the ceramic capacitor by the tranformers are shot. They read for capacitance in terms of value but I don't believe they acutally hold charge.
I took two of them that was next to each other before one of the transformers because when the circuit board was turned on I measured no voltage across either one.
I said to myself to charge it. I have actually never charged a capacitor before. I figured 4 or 12 volt won't kill anyone or anything or cause any explosion.
I hooked up both of the and held my voltmeter connected to the two pins. Of course it read 12 volts. After 20 seconds I unhooked one of the wire from the battery and the voltmeter immediately read 0. I did this two other ceramics capacitors in my collection and all behaved the same. No voltage retention. I just threw them out at least in the garbage can next to my desk.
I figured maybe this is not how they are charged. So I went on the internet and googled it.
There was not a single place anywhere ( unless google just can't take it anymore with me prying into everything and just make sure their algorithm is stacked against me.... yea talk about conspiracy :) ) that I could find, just how you charge them and specially how long it would take.
So I grabbed an electrolyte one and absolutely no problem. Held charge perfect at 12 volts and wont give it up with my bad breathing or dancing stupid.
So, obviously either these ceramic capacitors are some other wierd breed that charges in some other way, I care less since no one tells it. Probably because there is nothing to say. You just plug that sucker and be done with it Mr. Do you also want to tell you how to breath... just give it up. Aside from that dry humor, that is where it stands.
I am concluding bad capacitors and perhaps among other things.
And if this correct, I will never trust the farad readings again. And especially in the circuit that everybody just test it as business as usual. If what I am seeing is correct then everybody is full of it. At least the people I have been watching.
That electrolyte capacitor is still charged by the way after 20 minutes.
I guess them electrolytes are better than ceramics after all. Or maybe they just like me... you know just for reason that can not be known in this side of whatever universe this is.
So either bad capacitors or these ceramics are charged in some way that is something else.
If this be the case, I better replace them before I can figure out what else is happening.
I have to see if I have these in all them circuit boards I have hoarded.
123J. 1.25KVDC. [ just found out that these are what is called film capacitors]. I guess they withstand high voltage. So any capacitor won't do.

I should replace the 3 of them and see what happens. The only way I know for sure they are shot if I can find just one ceramic that will hold charge like the electrolyte. Oh I know what. I grab a new one and charge it. That is right. Hang on.
Oh yea, mystery solved.
The new one charged within a second. I noticed it was discharging fast. Just a small thing. Nonetheless, there I have it.
Long lasting ceramics... wrong. At least for now.
Untill next time...
 
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Thread Starter

Alchemy One

Joined Oct 5, 2019
205
The transistor just senses the changing of the electric field by capacitive coupling to the driver stage and the capacitor "saves" the peaks, which are negative on the collector.

Is there much of a signal on the drain?

If you want to check the transisors, I would first just do a quick check for shorts between the drain and source, keeping in mind that the drain should be connected to the positive lead of the ohmmeter. Also collector and emitter of the bipolar transistors. If you see what you think is a short reverse the ohmmeter connections and see whether the short looks the same (near 0 ohms) in both directions.

You may have to remove the parts from the circuit to do a thorough check.
==================================
I also think I may have checked the wrong transistor assuming that my checking of it meant that transistor is working.
Should I not check the other two, the DC to DC chopper transistors and there are two of them? One for each driver coil and they are the ones I think that goes to them ceramic capacitors that I need to replace legs.
And if I don't have them capacitors, what equivalent one I can use just to test the board temporarily?
Thanks for your time and patience.
 

DickCappels

Joined Aug 21, 2008
8,708
When capacitors fail they usually look "failed", and failure of ceramic capacitors is rare. Be sure you don't have any dead semiconductors. Most often they fail with an internal short.

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An aside: I had a circuit that did not start up the way I expected it to. It turned out that a ceramic capacitor which was used to couple a signal to a MOSFET (High input impedance) was charging up during operation and not discharging after being switched off. The capacitor was holding its charge over night and had to discharged with a jumper before starting up the circuit. Ceramic capacitors can hold a charge for a long time.
 

bassbindevil

Joined Jan 23, 2014
422
There's a possibility that the power supply needs some kind of signal to tell it to turn on. ATX computer supplies are like that.
But, if the caps aren't obviously bad, I'd check the big semiconductors, starting with the rectifiers. And inspect the board carefully for cold or broken solder joints. And then I'd probably give up and chuck it in the scrap board box or strip it for parts, if there isn't a compelling need for that particular power supply.
 

Thread Starter

Alchemy One

Joined Oct 5, 2019
205
When capacitors fail they usually look "failed", and failure of ceramic capacitors is rare. Be sure you don't have any dead semiconductors. Most often they fail with an internal short.

View attachment 259812View attachment 259813View attachment 259814View attachment 259815View attachment 259816

An aside: I had a circuit that did not start up the way I expected it to. It turned out that a ceramic capacitor which was used to couple a signal to a MOSFET (High input impedance) was charging up during operation and not discharging after being switched off. The capacitor was holding its charge over night and had to discharged with a jumper before starting up the circuit. Ceramic capacitors can hold a charge for a long time.
===============================================

When the spirit moves me I will check this opamp ic or whatever they want to call it. I don't know if this thing tells the transistors what to do and which pins goes where and or if IC sends voltage to them caps or what is what.
Them capacitors were bad. How do I know that? Because the ones I installed was clearly a game changer and they have voltage across them when I turned the board on while the other ones had nothing. These ones I installed also held charge when I hooked to the battery. They weren't holding charge that long as in just holding charge and staying charged but slowely losing it. While the ones that were there, the instant I unhooked the battery, they were zero. So they were holding no charge in the first place period. I checked lots of other ones and they were bad.
Maybe it is spookey action of some sort between me and ceramic caps. Lots of them are not good and all them electrolytes, not one is bad. That is all I have to say about that.

Down below the ONLY ONE that suppose to be bad is the good one. STRANGE? But true.

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Thread Starter

Alchemy One

Joined Oct 5, 2019
205
There's a possibility that the power supply needs some kind of signal to tell it to turn on. ATX computer supplies are like that.
But, if the caps aren't obviously bad, I'd check the big semiconductors, starting with the rectifiers. And inspect the board carefully for cold or broken solder joints. And then I'd probably give up and chuck it in the scrap board box or strip it for parts, if there isn't a compelling need for that particular power supply.
==============================
Yea I thought about that.
I did think about that yesterday. See picture:
You can see two pins coming out of it right above it. But inside there are 4 or 5 conectors.
[ Well but of course, a trash can is a good place for it after I skin this smoke wagon :)]
It came out of HP laser printer. You can get them at Ebay for like $40
I like acquired around 20 or so HP government abandoned laser printers and big beast copiers and a bunch of other what nots couple of years ago. Most of them are still taking up space.
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bassbindevil

Joined Jan 23, 2014
422
If you know the model number of the HP printer, there could be a service manual on the internet with schematics. If you don't know the model number, maybe there's an HP part number on a sticker that will point to the model(s) it was used on.
 
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