Wine Chiller - SMPS issue - fluctuating voltages

[beetle1303]

My wine chiller, TECNO SW-126LCD, is semi-functional - it powers up, can set temperature, and chilled to the set temperature, and cuts off compressor, etc. It however runs very hot.

Upon taken out the PSU and did some basic check - 5V output to LCD panel buttons and display is stable, but there is no 12V output to LED lights, and fans.

Further checks found the secondary side voltage is fluctuating around 8-15V range, but the 7805 regulator seems ok and producing the stable 5V output.

Checking further on the primary side: Incoming line input to bridge rectifier to filter capacitor all ok and stable at ~330Vdc. However, the circuitry around the PWM IC is showing same fluctuating voltage around 8-15V range also.

I have pretty much taken out all the through-hole components - capacitor, transistors, diodes, resistors, photo-coupler, etc on both side. One component at a time, tested good and re-installed back.

Still same outcome - fluctuating voltages. All except when I pulled out and re-installed back this particular transistor, SBD20C150F, at the secondary output terminal of the transformer.

Since then there is no more voltage output at the secondary side, including the previously stable 5V. There is no power at the PWM circuitry also.

Seems like the PWM IC, AP8269, has stopped switching...

Any pointer on what to check further is greatly appreciated.

[redwire]

Re: Wine Chiller - SMPS issue - fluctuating voltages

How did you test the capacitors, value and ESR?

I'm suspicious of the big plastic film caps in sleeves. The one on the far left (primary side) looks like like an egg- it melted and spit out some goop on the top?

There are three small electrolytic capacitors.
CD7 is critical for the SMPS IC and I would outright replace it. There are two other small electrolytic caps.

[Th3_uN1Qu3]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Seconded. Caps look bad, replace them. Caps look good, replace them anyway. It's not like it's got too many of them.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

How did you test the capacitors, value and ESR?

I'm suspicious of the big plastic film caps in sleeves. The one on the far left (primary side) looks like like an egg- it melted and spit out some goop on the top?

There are three small electrolytic capacitors.
CD7 is critical for the SMPS IC and I would outright replace it. There are two other small electrolytic caps.

All the capacitors were test in- and off-circuit with a DMM and ESR meter - capacitance within the rated spec, and ESR well within the chart values.

The PSU is mounted inside the chiller control compartment, so those those capacitors are shielded heat resistant fabric with yellowed silicon on top.
* see top side without those shield.

I replace the CD7 (with another old but good capacitance and ESR), but same outcome..
I now noticed 1 of the 2 big capacitors at primary side has slight bulging top. Will replace those and all the rest of capacitors to try again.

[redwire]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Why do the board pics now have different capacitors?
I'm confused the primary caps are now electrolytic, one has a bulged top but tests OK?
I have not used a MESR-100 but its test voltage is given as only 40mVRMS which is called a flea fart. It's very little signal.
Anyone else used one?

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Why do the board pics now have different capacitors?
I'm confused the primary caps are now electrolytic, one has a bulged top but tests OK?
I have not used a MESR-100 but its test voltage is given as only 40mVRMS which is called a flea fart. It's very little signal.
Anyone else used one?

The board with capacitor shield/jacket removed. Yes, the top bulged one also tested good capacitance and ESR - both measured ESR 0.84ohm (33uF 400V).

Anyway - I will replace them all later and report back.

[CapLeaker]

Re: Wine Chiller - SMPS issue - fluctuating voltages

While an ESR meter is great for low voltage caps, it’s next to useless measuring high voltage caps with it. One of them looks bulged anyway, so it’s time to replace them all in your case, since this appliance ran many hours.
The not starting situation could have been that the ESR went up when the PSU cooled down. You could have tried to heat the PSU up with wifeys hair dryer and then plug it in. I guess fix what you know is bad and go from there.

[redwire]

Re: Wine Chiller - SMPS issue - fluctuating voltages

It's best if a defective component can be found. That's why I started to suspect the MESR-100 is not doing its job.

Kinda scary to put electrolytic capacitors glued inside a thermal sleeve - they're anticipating a fire or something. But the glue burns.
The primary fuse is huge at 8A and I can't see inrush PTC. RV2 seems to be a MOV.

These wine cooler power supplies run 24/7 and commonly eat their cheap capacitors.
OP check the PSU is OK with light load, it might just be unstable unless it has more load?

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

I have purchased the set of 7 capacitors and replaced all of them. Outcome is still the same - no voltage output on the secondary side, while the primary side filter capacitors has 335Vdc to the transformer. The CD7 capacitor to the PWM IC is still no voltage.

Seems like PWM IC is not powered up, and therefore not switching?

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

It's best if a defective component can be found. That's why I started to suspect the MESR-100 is not doing its job.

Kinda scary to put electrolytic capacitors glued inside a thermal sleeve - they're anticipating a fire or something. But the glue burns.
The primary fuse is huge at 8A and I can't see inrush PTC. RV2 seems to be a MOV.

These wine cooler power supplies run 24/7 and commonly eat their cheap capacitors.
OP check the PSU is OK with light load, it might just be unstable unless it has more load?

Wine chiller actually working, and cut in and out the compressor when reaches set temperature. The 2 sides the the exterior walls were very hot, and I suspected fans are not running since the light also cannot be turn on..

I think the capacitors are all shielded from condensation/moisture probably, because this control board is mount upside-down inside the chiller compartment, with a non-airtight cover.

[Th3_uN1Qu3]

Re: Wine Chiller - SMPS issue - fluctuating voltages

So I take it the SMPS is just for the fans and light? I would replace the primary controller IC at this point, it is very possible that the bad primary side capacitor has taken it out.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

So I take it the SMPS is just for the fans and light? I would replace the primary controller IC at this point, it is very possible that the bad primary side capacitor has taken it out.

No.. this SMPS for everything - it has stable 2x 5V to each of the zone control panel for power-on, temperature setting, display, compressor relay, etc. And a bunch of 12V connectors for fans and lighting which with fluctuating voltages.

I was pulling out one component at a time to see which one could be the cause if the fluctuation and all seems the be ok as the fluctuation continues. Until I pulled out and in-inserted the SBD20C 150F Schottky Rectifier at the secondary winding side , then no output voltages completely.

The PWM IC is 8269, and I presumed AP8269 attached is the correct pinout.
What can I do to tests/checks to see if this IC is dead? Reason is this IC probably need time to order from online store, and pretty challenging for me to replace.
Thank you in advanced.

[R_J]

Re: Wine Chiller - SMPS issue - fluctuating voltages

What is the Vin voltage and the VCC voltage? The vcc needs to be about 16v to start and cant drop below 10v

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

What is the Vin voltage and the VCC voltage? The vcc needs to be about 16v to start and cant drop below 10v

Pin3 Vin: 3.5V
Pin7 Vcc: 0v - the diode and resistor in series to the capacitor feeding Pin also tested ok.

Also,
Pin2 CMP: 0V - there is no voltages on either side of the opto-coupler either. They were fluctuating voltages before, but now 0v since the re-insertion of the Schottky Rectifier in previous post.
* that rectifier test working in- and off-circuit though..

Also, power mosfet Drain-Source reads 335Vdc, same voltage as bridge rectifier output, indicating pwm ic not switching?

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

I was reading up further on a few causes on SMPS no output voltage on secondary side:
1) Faulty PWM IC
2) Fault power mosfet
3) short-circuit somewhere Son secondary side
4) Faulty opto-coupler
5) Faulty capacitors (which I have replaced all)
etc.

I pulled out the power mosfet, SVF12N65F, and did all permutation with DMM reading, and not sure if it help anyone to help me further:

Basically, measure all combinations of the 3 pins, in- and off-circuit. The results are somewhat different and I do not know if they are normal and expected.
Kindly enlighten me, thank you.

[stj]

Re: Wine Chiller - SMPS issue - fluctuating voltages

take the transformer out and check the windings and the soldering on the windings.
then check the resistors and diodes related to the chip while the transformer is off the board.

[R_J]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Pin3 Vin: 3.5V
Pin7 Vcc: 0v - the diode and resistor in series to the capacitor feeding Pin also tested ok.

Also,
Pin2 CMP: 0V - there is no voltages on either side of the opto-coupler either. They were fluctuating voltages before, but now 0v since the re-insertion of the Schottky Rectifier in previous post.
* that rectifier test working in- and off-circuit though..

Also, power mosfet Drain-Source reads 335Vdc, same voltage as bridge rectifier output, indicating pwm ic not switching?

The Vin should be supplied from the main B+ 335vdc through one ore more resistors, likely R17 and R18, either the resistor/s are open or the ic is bad. The vcc is developed internally from the Vin

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

take the transformer out and check the windings and the soldering on the windings.
then check the resistors and diodes related to the chip while the transformer is off the board.

Arha!!
After taken off the transformer, traced the diode and resistor and capacitor circuit to Vcc, found the culprit - R13 resistor is OPENED!!

*I don't have a SMD 220 resistor, plan to salvage a through hole 22ohm resistor from some power board on hand later.

Thank you very much @STJ

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

The Vin should be supplied from the main B+ 335vdc through one ore more resistors, likely R17 and R18, either the resistor/s are open or the ic is bad. The vcc is developed internally from the Vin

R17 and R18 are good at ~2.2Mohm and 0.6Mohm. As stated in previous post, R13 is open and thus capacitor not changed up to feed Vcc externally.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Arha!!
After taken off the transformer, traced the diode and resistor and capacitor circuit to Vcc, found the culprit - R13 resistor is OPENED!!

*I don't have a SMD 220 resistor, plan to salvage a through hole 22ohm resistor from some power board on hand later.

Thank you very much @STJ

My joy was short-lived unfortunately...
After soldered in a 22ohm resister, powered up - still exactly the same status: there is still 3.6v input to Pin #3 Vin, but still no voltage output at Pin#7 Vcc, and the CD7 capacitor still 0v...

Looks like PWM IC still not switching, probably dead..., and I've just placed online order the this replacement IC.

If anyone has any clue to possibility of secondary side shorted somewhere, I would be pleased to investigate fully.