Hi. Finally managed to get some power onto this board with a 2a inline fuse.

So measuring the two caps mentioned. The first, under C19 (seems to have a different number covered) measures at 320VAC. I think you mentioned it will be 1.2% input voltage so is higher than.

The second one which you mentioned would be the main filter capacitor on the secondary side? C23. It has 2.3vdc across it. Am I correct this is the problem and the issue is now to fix this to get at least 4.7v?

What do you think? I do have a lot of questions in my head about this but will leave it simple.

 

I estimated the input cap voltage would typically be about 120% of AC line voltage, so if the latter is 240 V you would expect 288 ... but, it could be very close to the peak of line voltage which would be 336 for 240 VAC. 320 is just fine.

Yes, I would expect the secondary voltage to be at least 4.7 as you say, probably 5 or a bit more, or it might even be higher than that if there is a linear regulator for the processor. We are assuming the processor runs on 5 volts, which may not be true. That is typically the maximum, but some run at lower voltage. 2.3 V definitely seems too low (you said AC - I assume you meant DC). The relay coil voltage is probably marked and probably the same as the secondary voltage.

This is probably "good" since it means there may be hope of repair.

Can you read the marking on (IC6?) - the long one with the metal tab next to the single blue relay?

Sorry, I'll be away til about this time tomorrow - again (you have knack for catching me just before I do my Sunday cycle). Perhaps some others will jump in in the mean time.

 

Yep. I thought "good" too. I had a win a few years ago needing to bump up a board to 5v to drive some stepper drivers once.

Ok.IC6 is a motor driver. BA6222 the datasheet I read shows a 8-22v supply voltage. Its quite a driver at 2A.

The relays are 12vDC action relays and they are switching 230v or line voltage.

Yes I measured 2.3 DC off that cap. But now I am a little confused, the output of the TOP device I read on the datasheet to be 4.7 to 5.7VDC not enough to activate the 12v relays.

Am I correct, that the TOP device outputs say 5VDC on average, and that is bumped up further down the chain to get the 12VDC required for operating the relays? I see a transformer on the output. But am not seeing how a rectified DC can be bumped up. Perhaps the DC being pulsed by pwm is doing this?? Or a linear regulator but I would only recognise the conventional 3 leg ones.

Anyways. Its time to stop overthinking this.

Absolutely no problem on timing. I understand. Its good to find an anomaly. Keep thanking you for this. Might have to send you a bag of pineapple lumps. A sheep would probably be held up at customs....

 

Just double checked. 320VDC across the primary cap not AC

 

Just double checked. 320VDC across the primary cap not AC

Looking at the clear photos of each side of the PCB in your post #15, the primary circuit to the switch mode transformer is made up of rectified mains (circa 320Vdc), switched by a single device (TOP222G).

I’ve not encountered such a simple driver design – normally a switch mode power supply incorporates an IC which receives feedback (from the output) and generates the required ac signal to drive the fet transistor (driving the primary transformer winding).

Therefore I would think that there is a high probability that the TOP222G has failed – and/or the components surrounding it, used to generate the ac signal to drive it (have failed).

If you have access to a scope, you could take a look at the voltage traces of the pins of the TOP222G. The whole primary circuit surrounding the TOP222G only consists of half a dozen or so components – if you could identify them, you could replace them all.

Of course, the failure of the transformer to generate a secondary voltage of around 12Vdc could be due to a fault/overload in the secondary circuit.

In answer to your question (trying to clarify things) – the grey capacitor (C30) is across the mains (and so should have the ac mains voltage across it) 230Vac. The 10uF with the silver top (C20), adjacent to R47 should have about 320Vdc across it (it being after the rectifier diodes).

 

I'm back - well sort of.
I seem to have lost my ability to feel thirsty which leads me to get dehydrated when cycling. It was quite cool this morning, so I racked up a moderate distance without drinking enough. I was OK til I stopped, then realized what I'd done. I took about 40 minutes before I could feel my radial pulse. I do know better, but sometimes I'm just so #!&% dumb! Did get a very nice close look at a Wilson's snipe, and a sora (common here this time of year in the right places, but you hear them about a zillion times for every actual sighting).

Anyway, sob story aside, I'm still feeling a bit, shall we say, dull. I'd hate to offer ill thought advice at this point.

 

Ha. Totally understand. Sugar, salt and water will fix. Yep. I just got back from biking the Heaphy Track here in NZ. In the snow...... All good, I am at work so cant do much until this evening or tomorrow at earliest. Best regards

 

OK, back to the diagnosis.

The TOP device regulates so that the voltage at its control pin is nominally 5.7 volts. The part is very unusual because that pin serves both as the power supply for the internals of the part and the control input for regulation - even on versions with more pins. The power for the IC, once the supply is up and running, comes from an extra winding on the the transformer. In most cases, there is feedback from the secondary (i.e. low-voltage main output(s)) to the primary (HV) side using an optocoupler. Where precise regulation isn't necessary, this is sometimes omitted and the circuit regulates that voltage on the control pin directly, "assuming" that the voltages on the main outputs remain in reasonably good proportion, based on turns ratio in the transformer. I can't see anything that looks like an optocoupler.

Since the relays are 12 volt, there is probably a linear regulator for the supply for the microcontroller and maybe some of the other circuitry.
There may be an additional winding on the transformer secondary - I really can't tell for sure.

It looks like C26 is the main capacitor on the TOP power/feedback. There is some chance that if this capacitor has "worn out" that the output voltage would be too low. The other possibility for low output voltage is that something is overloading it.

Often an overloaded SMPS will start up, get the output voltage up reasonably well and then shut down, either due to detected over-current, or in a supply like this, because the overload pulls the voltage so low that the supply for the IC also drops too low and it shuts down, only to try again. If that is happening, sometimes you can hear a "tick" each time, but not always.

Do you have a digital meter with a "bar graph" that will show you fast changes in voltage before the numeric display is able to? That can be helpful in detecting this sort of thing, but you need to set a fixed voltage range if the meter auto-ranges. If you don't have that, and your meter reads zero on the AC ranges if you connect it to a DC source (any handy battery would do to check), the you may see some significant AC voltage on that main DC output filter cap.

My suspicion is that the motor controller IC might be at fault and causing an overload. The reason for that thinking is that it has a failure mode that could more or less short-circuit its power supply. But other parts could also do that. If you can find a resistor in the position of R1 in Figure 15 of the motor driver datasheet, it would be worth measuring the voltage across it. With the motor not connected, the voltage across it should be zero. If it isn't then it supports the idea of an internal problem in the IC.

Do you have a power supply that could deliver 12 volts that has adjustable current limiting?

 

Hi. I have an icemaker in my kitchen that has popped the board twice. This is the second time and paying $350 for a new one is not cool, and infact these boards are so unreliable they are now unobtainable. But, I am kind of getting tired of digging into the box with my hands to get ice. Its winter in New Zealand....

Anyways, looking at this little board, there is no power getting past the control transformer. Closer inspection I see the little comets tail of dust shooting out of one of the little diodes coupled into the TOP222G subcircuit. Testing it shows me 154k Ohms both ways, compared to 8m Ohms one way on the others around it. There are no identification marks on the top of this cute little number.

Does anyone have the time please to point me in the correct direction where I can identify a replacement for this little check valve? Also, would you recommend I change out the TOP222G as well?

I am basic electronic. But soldering in something to get power back onto this board would be well into my skillbase and just plain nice.

Regards
Boyd

Its loud bang if you get it wrong territory.

https://www.power.com/sites/default/files/product-docs/top221-227.pdf

 

Given the potential problems in fixing this unit – plus the admission by the manufacturer of its poor reliability, I would give serious consideration to the following option.

Isolate the PCB switch mode power supply section from the mains supply by cutting a PCB track at suitable location (mains power is required on the PCB, switched by the relays). Then using a separate mains PSU (output rated at say 12Vdc, 1A), connect this PSU output (with the correct polarity) at the secondary electrolytic reservoir capacitor (C23).

Looking at the PCB, I believe that there is a diode providing rectification, preventing the secondary transformer windings shorting this 12Vdc (when connected across capacitor C23).

 

Given the potential problems in fixing this unit – plus the admission by the manufacturer of its poor reliability, I would give serious consideration to the following option.

....

The problem with that is that if the fault is not the power supply, and I suspect it is not, without using a current limited external supply something may burn up.

If I had the board on my bench, I'd probably move to a bench supply test after confirming a couple of things (notably, if the switcher was running continuously or hiccuping), but it would be with a current limited supply. If something is overloading the supply, a cautious finger dance around the board might quickly locate the offending part.

I'm not totally confident there are not two outputs from the secondary.

The other thing a bench supply does is remove the chance of electrical shock while trying to troubleshoot.

 

The problem with that is that if the fault is not the power supply, and I suspect it is not, without using a current limited external supply something may burn up.

If I had the board on my bench, I'd probably move to a bench supply test after confirming a couple of things (notably, if the switcher was running continuously or hiccuping), but it would be with a current limited supply. If something is overloading the supply, a cautious finger dance around the board might quickly locate the offending part.

I'm not totally confident there are not two outputs from the secondary.

The other thing a bench supply does is remove the chance of electrical shock while trying to troubleshoot.

If my proposed fix did not work, you could simply remove the external PSU connection and re-make the cut track.

By trying it, you would see whether the circuit (connected to C23) had an overload fault.

I would agree that there may be two outputs on the secondary (which would prevent my solution from working), but I don’t think so, looking at the tracks in the location of the secondary windings terminations.

 

There should be no need to cut the track. It is a flyback converter so there is a diode that will block current through the transformer winding.

The only issue I have with an external supply is hooking up a non-current limited supply. I'm afraid it may fry something and make possible repair more difficult.

I don't think there are two secondary outputs, either. I just can't be sure from the photos. I think there is a possibility that the processor supply is reg'd by D10 (zener?) with R49 as the dropper.

 

Just double checked. 320VDC across the primary cap not AC

Not encountered much equipment using PI SMPSU chips - but there should still be a list of "usual suspects".

A factory schematic would be nice - but if you can hand trace immediately around the switcher chip.

If it didn't go bang - look for a high or open start up resistor, also check any secondary side rectifiers.

Live testing is a bad idea unless you *REALLY* know what you're doing.

 

The ice maker in my fridge actually broke yesterday. It started leaking and had to be disconnected. I still need to figure out what the problem is. No joke.

So regarding the board, make sure to test every component in a suspicious area or the components may get destroyed again, wasting time and money. You can disconnect all leads except one to do a reliable component test. It will give you a very different value if you test it in the board.

 

I have designed a TOP part into an industrial power supply used by a company with a German name pronounced as if it were French.

I have no reason to believe the TOP is defective or that it is failing to start. The startup circuit is internal to the IC. There is voltage on the secondary which can only get there if the TOP is driving the transformer. For me, the unknown that is critical is if the TOP is continuing to run or is hiccuping.

I can tell from looking at the parts on the board that the circuitry surrounding the TOP is very standard. There is an RCD snubber, already discussed. The parts associated with the power supply for the IC itself are as expected, with the exception of what may be a zener diode (diode closest to pin 1 of TOP). The purpose of this appears to be to cause regulation of the control power winding of the transformer to a voltage above what would otherwise be the case, which is a bit odd but perhaps has been done to improve the regulation at the secondary given that there is no feedback from the secondary used for regulation.

boydage: it is worth checking this diode to see if it might be shorted or open - shorted would allow the TOP to run but the output voltage would be low (assuming I'm correct about function); open the TOP would hiccup because it wouldn't get power to keep it going continuously. Also carefully inspect all the nearby small parts for signs of solder joint or other problems​

 

If you had to replace this board previously, I hope that you kept the failed ones because they would be easier to work with and possibly take parts from. Tracing out parts of the circuit will certainly help with diagnosing the fault. And even just comparing components on boards will assist in finding the failed ones. But the big question is always why do the parts fail??

 

Look for capacitors and other components being pushed to their limits. Replace them with components that can handle greater voltages, currents, etc but have the same characteristics otherwise. That will probably help a lot.

 

The ice maker in my fridge actually broke yesterday. It started leaking and had to be disconnected. I still need to figure out what the problem is. No joke.

So regarding the board, make sure to test every component in a suspicious area or the components may get destroyed again, wasting time and money. You can disconnect all leads except one to do a reliable component test. It will give you a very different value if you test it in the board.

Exactly right - its very risky to attempt live testing on these things.

 

Ok. Great thanks all. Its the weekend here in NZ and am back onto this board. Although EPB this is just prior to your shift?

I remember testing all the diodes around the TOP device to find they are good. Well thats with them installed they certainly acted like little check valves.

What I will do is inspect the datasheet for the motor driver and locate R1 to see.

My meter does not have a bar function. Actually, C26 did appear to charge up when I put a meter on it. I might just solder a new one in and see what happens. Yep will do that. Understand about the AC voltage on the C23 too and will check that. So that means it may be cycling on/overload/off/on/overload yes?

I do have a power supply. Current limited. But..... and the big but, it is a kit I bought to make myself to brush up on my soldering skills. Have never used it. It has no indicators so I need to plumb it in using my meter to set the amps and voltage (cool aye ha) But I do like this idea as dancing around the board looking for something hot with 230v pumping around some of the components would be the same as sticking my have in a box of snakes. Feels about the same - snake bite/shock - yep.

So. I will setup my power supply to 12vdc, put a load on it and set it to 1A. And connect it to the board and see what happens, see if we get anything warm. Sound good?