Cuisinart wine cooler P/S board problems

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Those caps came from mouser. I would hope they wouldn't be bad...lol. I am going to start checking things today. I will let you guys know

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

OK So I got it!! The board is working now as far as not blowing anything when plugged in. I also here a very high pitch ringing coming from it. That being said the front display just flashes now. If I hit the power button The inside leds will flash then go out until I hit the power button again. So now I am assuming that we have an issue on the secondary side?

I did look at voltage going to the front panel. The little PCB up there says 12v and I read 11.6. But upon plugging the front board in the voltage drops very low. What is next.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Here is a picture of the secondary side.

[CapLeaker]

Re: Cuisinart wine cooler P/S board problems

So there are two choices:
A: The secondary on the PSU can't handle the current. - Do a load test.
B: There is something wrong with that front board (shorted?) and it loads the PSU down.
Personally I would go with B. Check the resistance between the positive and negative pin on the front board, unplugged from the PSU.
Is that high pitched ringing still there when the PSU is just powered up by itself without any boards connected to it?

[jazzie366]

Re: Cuisinart wine cooler P/S board problems

They look normal to me... at least from the pictures we are provided. A picture of the side of the cap with the text could reveal more, though (but I don't think it is necessary.)

But even if they are fake, that still wouldn't cause the issues the O/P is having, unless those Nichicon caps are both internally shorted (which wouldn't be the case, since they are not bulging.)

That's not true. A cap can be shorted and not bulge. There's a YT teardown of a cap that's not bloated, it's just got a .35 ohm short in it. Also even though that's likely not the issue, I was just pointing it out because Nichicon vents usually are very square, those look as if there was a worn machine that made the vent.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

So there are two choices:
A: The secondary on the PSU can't handle the current. - Do a load test.
B: There is something wrong with that front board (shorted?) and it loads the PSU down.
Personally I would go with B. Check the resistance between the positive and negative pin on the front board, unplugged from the PSU.
Is that high pitched ringing still there when the PSU is just powered up by itself without any boards connected to it?

I powered the front board by itself with a bench power supply. It works perfect. I did this to eliminate the front board.

Yes ringing is still there with everything unplugged from the board. So the issue has to be in the secondary side? To be honest with you guys I am not sure how I would load test this board. The two IC's on the secondary side are a PWM controller and an opamp just in case you are wanting to know.

[momaka]

Re: Cuisinart wine cooler P/S board problems

Yes ringing is still there with everything unplugged from the board. So the issue has to be in the secondary side? To be honest with you guys I am not sure how I would load test this board. The two IC's on the secondary side are a PWM controller and an opamp just in case you are wanting to know.

What is the PWM controller part number? KA7500? TL/DBL494?

Get datasheet and check voltage going to the Vcc pin of the PWM controller. If okay, check all of the small caps near the controller.

I did look at voltage going to the front panel. The little PCB up there says 12v and I read 11.6. But upon plugging the front board in the voltage drops very low. What is next.

Might want to load the PSU with something else rather than the wine cooler's main PCB. Some car bulbs or PC fans should do the trick to put a basic load on the PSU. See if it starts with a fan or two. If not, add more load (12V car bulbs are good for that). That said, are there any labels on the PSU that say how many Amps it can output on its 12V rail? If not, what's the power rating of the wine cooler? (If looking at that, see if there is something that is not powered from this PSU, as that could inflate the power rating.) Reason I ask all these details is because both under- and over-loading the PSU can cause it to shut down and oscillate. So we need to know in what power range can this PSU be expected to operate normally.

That's not true. A cap can be shorted and not bulge. There's a YT teardown of a cap that's not bloated, it's just got a .35 ohm short in it.

For small caps in a low voltage or low current circuit with protected outputs - yes.

But for primary cap, a short-circuit typically makes the cap bloat and shoot up crap everywhere. In rare cases, the fuse will blow quickly to save the cap from doing that.

[CapLeaker]

Re: Cuisinart wine cooler P/S board problems

Can you post a high resolution picture of the back side from the PSU?

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Ok pWm controller is a tl494l. VCC pin 12 is 4.5 volts. Only power rating I can find on the colors says .934a AC.


I will try and load the board and see what happens will report back

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Which the fans are 12v fans so something isn’t right. I am seeing 5v at the fan plugs

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Ok quick update guys I realized I didn’t have one of the chips soldered back in. Stupid me anyway. I got it soldered back in now I get a little over 7 volts on the fans. And the fans will come on. I can eve get the front panel to come on just fine. It’s when I plug in the cooling element that the board takes a shit.

[CapLeaker]

Re: Cuisinart wine cooler P/S board problems

Does the PSU still whine?

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

No I do not hear a whine. If I plug in one fan the fan runs and there is no noise. If I plug in just the front control panel. It comes on and there is no noise. If I plug in both the front panel and a fan. Front board does not function and the display flashes fast and there is a buzzing noise.

That is the best way to describe it. a kind of buzzing noise.

[momaka]

Re: Cuisinart wine cooler P/S board problems

Ok quick update guys I realized I didn’t have one of the chips soldered back in. Stupid me anyway. I got it soldered back in now I get a little over 7 volts on the fans. And the fans will come on. I can eve get the front panel to come on just fine. It’s when I plug in the cooling element that the board takes a shit.

Which chips?

Going by the symptoms and low output voltage, it sounds like only half of the h-bridge circuit is working. Those small diodes and TO-92 transistors you replaced near the small transformer are responsible for driving the BJTs on the primary. Since you forgot to solder something, you should re-check the small diodes and TO-92 transistors again. Also re-check the BJTs and their base-drive circuit on the primary again.

Also, I still see crap-cap brands on the output in this picture:
https://www.badcaps.net/forum/attach...7&d=1506030197
Definitely worth checking and/or replacing. The smaller cap below IC2 (the 358 dual op-amp) might be a filter for the PWM IC Vcc.

Ok pWm controller is a tl494l. VCC pin 12 is 4.5 volts. Only power rating I can find on the colors says .934a AC.

That's not right. The TL494 IC needs at least 7V to function correctly. Follow the souce of Vcc for the TL494 IC, and check which components generate it. Should be a diode, cap, and maybe a series resistor - all near the small transformer.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Hey guys SO I tested all caps Electrolytic and ceramic on the secondary side. all are showing correct capacitance. I am getting a little lost in following the VCC trace. Would love some help with that. I took a picture of secondary side of board and drew in the areas where components were.

Red is resistors. Green is DIODE's , Purple is Capacitors. I didn't do Transitors or jumpers or connectors. The BLACK scribbly mark is the ground plane.

I did measure voltage on the Schottkey Rectifier I believe I did it correct. Negative on center pin "K" as the data sheet calls it and then measure both sides. I get 8.7v for a1 and 8.7v a2. I don't have any experience with these so excuse my ignorance. The heat sink on the Primary side does get warm. Just felt I should include that.

I did double check the transistors and the diodes they test good. Doubled checked the BJT's and the diodes and caps again on the primary. all tests good as well.

[momaka]

Re: Cuisinart wine cooler P/S board problems

Hey guys SO I tested all caps Electrolytic and ceramic on the secondary side. all are showing correct capacitance.

Correct capacitance doesn't tell the full picture. For electrolytic capacitor, you can have correct capacitance and bad (high) ESR. This doesn't usually happen very often with the big caps but is a fairly common failure mode of small caps. So if you have no way to test the ESR, it's best to replace the caps. If you don't have any caps in stock with the same voltage/capacitance as the ones in the PSU, just add a few in parallel to the ones already in the PSU - particularly with the output filter caps: that is C28 and C10(?) (the cap next to the output inductor - I can't see its designator on the pictures).

Also, for ceramic caps, you can have high leakage current, especially when they heat up. That's why I suggested changing ceramic cap C17 as well (the snubber cap), as it looks a bit darkened from heat.

I am getting a little lost in following the VCC trace. Would love some help with that. I took a picture of secondary side of board and drew in the areas where components were.

Red is resistors. Green is DIODE's , Purple is Capacitors. I didn't do Transitors or jumpers or connectors. The BLACK scribbly mark is the ground plane.

No problems! Thanks for providing that marked image - made tracing just a bit easier for me.

So first off, it looks like you have Vcc mis-labeled on your image. It should be the pin to the left of the one you labeled "Vcc".

That said, half-bridge PSUs usually have two supplies for the Vcc, and hence two paths. But I only see one path... though that is probably due to the fact that this PSU doesn't have a stand-by transformer. Regardless, let's follow it and see: you have a rectified (but unfiltered) voltage coming straight from main rectifier DD1 and going into diode D5 anode. Electrolytic capacitor C8 is the filter after diode D5, and that is what feeds the PWM's Vcc pin *once the PSU is up and running*. Since your PSU does appear to run correctly without a load, we can safely assume that whatever is powering the PWM before the main PS has started, is working fine (otherwise the PSU wouldn't start at all). To remain functional, the TL494 PWM IC must have at least 7V for Vcc *at all times*.

Now if cap C8 is bad (which I suspect it is), a sudden demanding load on the output of the PSU can cause a the voltage at rectifier output DD1 to drop quite a bit before that coil. If C8 is bad, the Vcc voltage for the PWM IC could drop below the minimum threshold and cause it to shut down, followed by a restarting of the initial power-cycle. But if the heavy load on the output of the PSU is not removed, it will cause the same condition to re-occur again shortly after the PSU starts - hence why the PSU may be stuck at 7-8V on the output when it is loaded.

Of course, we can't know for sure if that is what is happening now, unless you have an oscilloscope and can scope out the PSU output and PWM Vcc rail. So the better solution is to replace C8 and the rest of the caps on the output of the PSU.

Or alternatively, there is another test you can perform to verify if that is the problem, but this test is a bit dangerous and can blow up your PSU again. Essentially, you connect a 10-15V power adapter to the output of D5 / positive leg of C8 / Vcc pin of the PWM IC. This will keep the PWM IC operational even if the voltage on the output of the PSU drops. However, as this is a very simple h-bridge PSU probably without any protections, it likely relies on the output dropping low (and consecutively the PWM IC's Vcc) to make the PSU shut down in case of a short-circuit or overload on the output. So with the power adapter, the PWM IC can continue to drive the PSU even with a fault, and thus make the primary transistors blow up again.

So I don't advise you try that test. Or if you do, put a 800-1200 Watt appliance (toaster / mini oven / sandwich grill / hair drier / heat gun) in series with the PSU's mains. That should allow enough current to flow to the PSU even under load, but limit the current quickly in case of PSU fault so that nothing blows up.

But better yet, just replace those damn caps on the output so we know they are not at fault for sure. Otherwise, I'm not sure what else to suggest for you to test if you say there are no other bad parts and everything checks out fine.

I did measure voltage on the Schottkey Rectifier I believe I did it correct. Negative on center pin "K" as the data sheet calls it and then measure both sides. I get 8.7v for a1 and 8.7v a2. I don't have any experience with these so excuse my ignorance.

Though not exactly a correct way to check a diode... given the voltages you measured (8.7V would probably be AC, which multiplied by the square root of 2 gives approx. 12.3V for the output), that schottky diode should be okay.

Now, the correct way to measure a schottky diode/rectifier like that:
Put negative/black (-) multimeter probe on the cathode (K - typically the middle pin for standard rectifiers) and the positive/red (+) multimeter probe one one of the outer legs of the rectifier. With the multimeter set to "diode test" (should have a little diode symbol on your multimeter's dial), you should see a voltage drop of 200 to 800 mV (on some multimeters, it will display as 0.200 to 0.800), depending on if the rectifier is schottky or regular fast rectifier (fast rectifiers have higher voltage drop.) Now do repeat the same procedure for the other leg.

Once done, repeat that entire procedure again with the multimeter probes reversed. If the diode/rectifier is okay, you will get nothing/no reading on your multimeter's screen (i.e. either an "OL" for auto-range meters or a "1" on the left side of the screen for manual-range meters).

Of course, all of that above is how a rectifier will measure **outside** of a circuit. Inside a circuit, you may have various loads give you a reading no matter which way you place the probes. So do beware of that. But typically you will still get a normal diode reading in the forward directions (i.e. black probe on cathode and red probe on anode). A shorted diode/rectifier will show 0 or near 0 voltage drop regardless of the orientations of the probes.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

OK I am making an order currently. Having an issue finding the correct ceramic caps.

I'm ordering on mouser Found all the electrolytics could I get some help with the ceramics.

The only imprints on them are
102
222
and one is a little bigger and imprinted with 102 1kv

So I know the values of these but cant seem to navigate mouser to find the correct ones.

[momaka]

Re: Cuisinart wine cooler P/S board problems

I'm ordering on mouser Found all the electrolytics could I get some help with the ceramics.

The only imprints on them are
102
222
and one is a little bigger and imprinted with 102 1kv

I wouldn't worry about replacing the ceramic caps except for that snubber ceramic cap, which I presume is the one with "102 1kV" written on it.

In any case, here's how the value designators go to make it easier for you:
105 = 1.0 uF (or 1000 nF)
104 = 0.1 uF (or 100 nF)
103 = 0.01 uF (or 10 nF)
102 = 0.001uF (or 1 nF)
101 = 0.0001 uF (or 0.1 nF)

.... so 222 = 0.0022 uF = 2.2 nF

And 1kV = 1 kiloVolt... i.e. the voltage rating of the cap.
Probably not necessary, but it's never a bad idea to increase the voltage rating of the snubber caps to 2 kV.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Ok so new caps are installed. Still having same issues. I am obviously missing something here.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

OK I found a 10ohms and 2 ohms resistor that is bad next to the NPN transistors on the primary side. I must of missed them before.......