Cuisinart wine cooler P/S board problems

[Jtroutt19]

Working on this wine cooler that keeps blowing the inrush current limiter. I found some diodes that were faulty and a cap thats was bad I replaced the pair. The original damage also toasted part of a trace which has been repaired as well. Could the choke filter be bad or am I looking at some other component that is causing this. Pictures included. I replaced fuse with a jumper for now. The burned spot on the filter choke is from the inrush blowout

[R_J]

Re: Cuisinart wine cooler P/S board problems

I suspect the fet's on the heatsink are shorted, try checking them first

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Good call. I was headed in the right direction so that is good to know. I started doubting myself though that was the reason for the post. Thanks for the assistance. I will report back once replacements arrive.

They were shorted.

[CapLeaker]

Re: Cuisinart wine cooler P/S board problems

when in doubt, change it out.

[momaka]

Re: Cuisinart wine cooler P/S board problems

As R_J said, you probably have a shorted main MOSFET on the primary side. Replace that, the input bridge rectifier/diodes, NTC thermistor, and primary-side caps if they were bad.

When all is done, connect power to the board in series with an incandescent light bulb to limit the current, should anything still be wrong with the PSU - this will prevent you from blowing fuses and other components. Here is more info how to connect the light bulb:
https://www.badcaps.net/forum/showpo...4&postcount=70

Note: when testing with the light bulb in series, you may need to have the PSU disconnected from the fridge. A heavy load on the PSU will cause the light bulb to drop a lot of voltage, and this may in turn make the PSU go into unver-voltage protection mode.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Hey guys so I have replaced the Two fets on that heatsink. Both of the large caps that are right by it the rectifying diodes and the Inrush current limiter.

As per recommendation I hooked light bulb up and the bulb burns bright. Which means that there is still something wrong correct?

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

I should also mention That the P/S board is out of the cooler at the moment. Nothing is hooked up to it.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

I believe the problem lies in one of the 2 transformers. I removed both and the incandescent no longer lights up.

[CapLeaker]

Re: Cuisinart wine cooler P/S board problems

I think we need better straight shot pictures of the PSU.

[momaka]

Re: Cuisinart wine cooler P/S board problems

As per recommendation I hooked light bulb up and the bulb burns bright. Which means that there is still something wrong correct?

Yes, most likely. For a PSU is good working order, the light bulb would typically go bright for a second (while the big caps on the primary side charge) and then extinguish or stay very very dim. Being bright means something is still conducting a lot of current on the primary, and that is not good.

That said, and excuse me if this sounds like a dumb question, but I would like to double-check something: was the light bulb you used incandescent (i.e. the oldschool type with Tungsten wire?). Just checking, as an LED or CFL bulb will not work here. Also, how many Watts was your bulb rated? 40W? If so, did you try a 100W light bulb? Again, these may seem like dumb questions, but I'm just trying to verify the results before we proceed further.

Another thought I had: if you disconnect the power supply from power and measure resistance across its input terminals, does it show a short circuit? If not, is there are short-circuit between the positive (+) and negative (-) legs of the bridge rectifier? (Be careful that the big caps are discharged before handling the PSU and also before measuring resistance.) I don't see an MOV or two across those big caps, so that can't be the problem. The only other thing I can think of is the protection diodes across the primary transistors - checked those? (You may have to remove them out of the board.)

As for the transformers - those almost never go bad (except for inverter transformers in LCD monitors with CFL backlights). Also, this is a half-bridge topology design, so one side of the main transformer is connected to the primary with a DC-blocking cap (that big dark red film cap). Thus, the short-circuit that you are observing on the primary with the light bulb cannot be due to the transformer being shorted. It would have to be somewhere before that. That's why I thought it might be worth checking the transistor's protection diodes again.

In any case, let us know what you find from the things I suggested above so we can try to further narrow it down.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

It is a 40watt incandescent bulb. No I have not tried a 100watt. No short across input terminals. I have checked both diodes that are right in front of the transistors. They are good. I've included some more pictures. The one with pink lines on it is stuff I've replaced. The one with blue is stuff I've tested and that is good.

[momaka]

Re: Cuisinart wine cooler P/S board problems

No short across input terminals.

What about the positive and negative sides of the primary bus?

I also noticed that C17 (a small ceramic cap on the primary) looks pretty dark. Check it out of circuit and if possibly verify capacitance.

Other things to check: diodes D8 and D9 on the secondary behind the small transformer as well as the two TO-92 transistors between them. Those transistors are the drive transistors for the BJTs. And while at it, also check the resistors around the BJTs on the primary side.

Finally, check the output rectifier on the heatsink - that is, DD1.

And try the 100W bulb too, if the PSU still does the same thing with the 40W one and all of the parts above have checked out fine.

In any case, report back what you find.

[jetadm123]

Re: Cuisinart wine cooler P/S board problems

I'm thinking that since the bulb goes out after you remove the transformers, then maybe something's shorted on the secondary side? Did you check single mosfet on the heatsink for shorts to the right of those transformers? Also try the 100w bulb as momaka suggested.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Thanks guys for all the help here I really appreciate it! I am still learning this stuff. Anyway


D8 and D9 are both bad diodes. The two transistors that are right next to those diodes. one is bad and the other is good. I am going to replace both. C1815 ordering them today.

Once they arrive I will update you guys on what happens. Thanks again!

C17 Test good tested with a BK precision Capacitance meter model 890b.

Forgot to also note that DD1 is good as well

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

alright guys I have test all remaining diodes and and transistors. I even tested the germanium diodes(glass with orange stripe) I am still getting the lightbulb glowing with both the 100w and 40w. Getting a little frustrated here. What am I missing?

[CapLeaker]

Re: Cuisinart wine cooler P/S board problems

Did you check the gate drive circuit on the primary? If the fet was shorted all the way around, chance is good that the gate drive circuit is bad.

[momaka]

Re: Cuisinart wine cooler P/S board problems

alright guys I have test all remaining diodes and and transistors. I even tested the germanium diodes(glass with orange stripe) I am still getting the lightbulb glowing with both the 100w and 40w. Getting a little frustrated here. What am I missing?

When you say the bulbs are glowing, for how long are you leaving the PSU connected to the bulbs?

It is okay if the bulb glows bright for a second or two. But then it should go dim after that.

If the bulb does stay lit no matter how long you leave it, then there is still something shorted on the primary side. In that case, there can only be a few things that can cause this. A shorted or malfunctioning component on the secondary cannot cause this, because this is an oldschool half-bridge design without 5VSB/standby circuit

So First, I suggest you check the orientation of the diodes in the bridge rectifier again as well as the actual diodes too. Next, check your BJTs again. And finally, although these are unlikely to fail, but feel free to remove any of the input EMI/RMI filtering components - that is, you can remove capacitor CX1 and coil LF1. If you remove LF1, your short-circuit on the primary will disappear because you will be disconnect the primary from power. Thus, if you remove LF1, install two jumpers in its place. If there is still a short-circuit (bulb glowing), then remove the primary or secondary transformer... or the two BJTs and check for proper voltage across the bulk caps on the primary. It should be about 160-170 Volts DC across each cap, or about 320-340 Volts DC total (since they are in series). If not, please note that down before continuing anything else.

Did you check the gate drive circuit on the primary? If the fet was shorted all the way around, chance is good that the gate drive circuit is bad.

There are no MOSFETs on the primary of this design. The switching devices are BJTs (Bipolar Transistors, NPN type). That said, you do make a valid point of checking the base-drive circuit (the resistors, diodes, and capacitors connected to the Base of each transistor), even though those won't cause a hard short-circuit like the O/P is seeing.

[Jtroutt19]

Re: Cuisinart wine cooler P/S board problems

Yes the bulb glows for longer than a second or two. I will double check everything and report back.

[jazzie366]

Re: Cuisinart wine cooler P/S board problems

It is a 40watt incandescent bulb. No I have not tried a 100watt. No short across input terminals. I have checked both diodes that are right in front of the transistors. They are good. I've included some more pictures. The one with pink lines on it is stuff I've replaced. The one with blue is stuff I've tested and that is good.

Those Nichicon caps look fake... Is it just me or does the vent look wrong?

[momaka]

Re: Cuisinart wine cooler P/S board problems

Those Nichicon caps look fake... Is it just me or does the vent look wrong?

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.)