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1. What is the volts/div and the sweep speed for each scope trace. I tried to enlarge the image, but I cannot read it from the screen.
2. What type of power supply is it? Is it a linear supply with a large transformer connected to the AC main? Or is it a switching power supply?
3. Are these waveforms with the supply connected to the receiver or with it disconnected?
4. What is the manufacturer and model number? Do you have a schematic that you could post or link to?
With so very little to go on, my only guess is that this is a switching power supply that is trying to regulate the +3V supply. The +3V supply has some fault, like a shorted diode and the supply is going into overcurrent shutdown and then attempting to restart. Of course, this is only a guess because I know so little about the particular system.
bottom looks like you have too little capacitcance...or the capacitance has too much esr.
maybe your caps are damaged.....maybe whirling around up their in space with bad temperature...maybe they get damaged.
maybe you waveforms are at cold temperature and esr is bigger there?
but it looks like is it discontinuous mode flyback?
please tell more, do not worry , you will not be giving away company secrets as every converter is known these days....even the "secret" ones that our companies tell us they only have.
My dear Friends,
This is switching PS and woltages are open circuit(The PS is not conected to satellite).
Inout signal is OK, the signal after T1 is OK too, BUT after the bridge diods and checking voltage at two pins of the big CAP after bridge diodes, the signal is not rectified, because I could see minus signals too.
and the funnt thing is I could here a ticking sound each time these repels happens.
Added after 1 minutes:
besides, for the first post: they're all voltages. 12VDC Volt/Dev=5
5 VDC Volt/Dev=2
3 VDC Volt/Dev=2
It's hard to see from the fuzzy image,but it looks like your cap failed by the puddle around it marked bridge diodes. The big cap likely the input filter cap. I would try and swap this out. Change the bridge diodes they may have gotten fried from the leaking cap or one failed causing the cap to fail.
siavashhn said:
the signal is not rectified, because I could see minus signals too.
that is bad news as you say your input DC bus has the negative mains cycles on it.So those electrolytic caps will be fried up bad with the wrong polarity voltage having been on them.
was it a big iinrush that fried those input diodes.
i say i reckon your pwm controller is fried by all those wrong polarity signals in there.
So what it looks like is you've shorted FWB and the mains has wreaked havoc within.
The puddle around the electrolytic capacitor looks like glue. This is fairly common in automated assembly to glue down large components before wave soldering.
The ticking sound is one of two causes. Either the supply is going into shutdown because there is no load. Or the supply is going into shutdown due to an overcurrent condition. Does the ticking sound also exist when hooked to the rest of the circuit? If so, then its probably and overcurrent condition. If the ticking only occurs with the supply disconnected, then it is a no load overvoltage shutdown. You will have to provide a minimum load to get the power supply to run on the bench.
The load can be regular old power resistors. Usually, you just need a load on the supply section that is being tightly regulated. My guess would be the 3.3V section.
With the power supply disconnected and the power off, I would suggest measuring the resistance with an ohmmeter across all the electrolytics. If any capacitor shows an incircuit resistance of less than 200 ohms, unsolder it to determine whether it is the capacitor or a diode that is at fault.
Capacitors that fail often give some visual clues. The cases become swollen. (If the swelling is extreme, they may vent. The pattern on the top of the capacitor that looks like a pie cut into thirds, is on purpose to make them vent out the top rather than the side or bottom.) They ooze out the electrolyte. They overheat and their plastic wrapper changes color. Inspect all the capacitors for any that look different than the others. If one or more capacitors look different in color, shape, etc it is possible that its the bad one.
Added after 6 minutes:
Also, open capacitors can be checked out of circuit using a battery and a resistor to form an RC circuit. Place a voltmeter across the capacitor and then charge it through a resistor. Use a large value resistor and note the amount of time required to charge. You can compare this to a known good capacitor of similar value to get an estimate of the suspect capacitor's value. This gives a quick check before purchasing replacement capacitors. Electrolytic capacitors have large tolerances and most circuits work fine with capacitors that are slightly above or below the value on the label. Therefore, you are looking for gross errors. Failed capacitors will either be shorted, or have a value less than 50% of the label.
Yes My friends, that puddle thing IS glue. And all CAP appearance is just fine.
I've cut the connection between the Input filter cap and the other part of PS. So Just I had inout signal till rectifing part, and at the end of rectifying part, I had 290 VDC just fine... that negative signal was a mistake of me not connecting ground signal to correct ground which is the ground after the bridge diods.
any how, the input circuit is fine. now I have to check the switching part and the 5L0365R.
P.S. Voltage at input-filter-CAP will start to have some repples with that fu... ticking sound. each time I hear that sound, this voltage, drops down.
you have ticking sound...i had that once, it was sue to both poor layout and also a badly selected RCD flyback snubber cap, which was resonating with the primary leakage inductance.
i once worked in a high voltage switcher place, and finished products that had to be shipped in a few days time used to sometimes tick like hell......not a periodic thing, but just now and again the output volts would just splurge about.
youve gotta suspect noise in the circut due to "something"...maybe poor layout?....maybe somthing else...maybe subharmonic oscillation...did u use slope compensation if you need it.
is your transformer saturating
Added after 2 minutes:
i'll bet my bottom cent its a resonant power supply (most sat ones are)
resonant ones can be more trouble that they are worth......there is often certian conditions which freak them out and make them unstable...........is you loop compensation ok.....what about getting a network analyser..................do other similar power supplys do this ticking.
Sometimes you can get a clue by placing an ammeter in series with the fuse. Then the ticking sound should correspond to jumps in the ammeter reading. If the readings droop with the tick, then its probably and over voltage shutdown. If the readings spike higher with the ticks, then its probably overcurrent shutdown.
Due to the multiple windings and multiple output voltages of these switchers, the brute force troubleshooting approach often is the fastest. Check all external MOSFETs and BJTs. Check the impedance or resistance across all capacitors and diodes. Any showing low resistance lift one end to determine if the low resistance path is the component or the rest of the circuit. Next check all diodes with the diode test feature of most DVMs, conducts in only one direction. Next start looking at the low value resistors. These often contain fuse links and are called fusible resistors. They blow open during surges. Finally, start looking at the high value resistors. These often provide startup bias. If they increase in value, weird stuff happens. Shorted turns in transformers or coils and bad ceramic capacitors do occur, but they are much more rare. If this device was hit by a power surge, it is much more likely to be a shorted or leaky diode and perhaps an associated fusible resistor.
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