Wine Chiller - SMPS issue - fluctuating voltages

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

I am curious about this primary side of transformer pin - +329V from bridge rectifier to middle 2 pins, and -ve to ground pin on the right.
The left most pin has 0V - is this correct, and why if this is so?

[R_J]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Look at the schematic in post #17, the connections in your picture are from left to right:
feedback winding
Primary B+ supply
Primary mosfet Drain
Primary hot ground for feedback winding

You MUST HAVE about 30v VIN before the ic will operate, Once it starts it will produce its own 16v vcc from the feedback winding. The ic's internal vcc clamping circuit is likely damaged or shorted.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Look at the schematic in post #17, the connections in your picture are from left to right:
feedback winding
Primary B+ supply
Primary mosfet Drain
Primary hot ground for feedback winding

You MUST HAVE about 30v VIN before the ic will operate, Once it starts it will produce its own 16v vcc from the feedback winding. The ic's internal vcc clamping circuit is likely damaged or shorted.

Thank you for these information, it super helpful for my education.
And for my further education:
1) B+ and Drain both read 329v from the bridge rectifier. If the IC is working, how does the feedback winding gets its 16v?
2) Vin must be 30v: but the only feed I see is from B+ through R17 & R18, and reads 3.6v, is the 30v generated internally to get started?

In fact, I would extremely thankful if you could briefly describe the sequence of events leading to the startup and normal operations of this IC, so that I can see the complete big picture.

Thank you.

[redwire]

Re: Wine Chiller - SMPS issue - fluctuating voltages

R17, R18 are the startup resistors that power the IC on pin 3 only until it starts oscillating. Then only a few blips the transformer takes over powering the IC. The aux winding generates around 16VDC from D4/R13 to run the IC.

But pulling the SBD20C rectifier out, a BAD idea because the PSU would go to max. (PW) output, because it was getting no feedback voltage. OUCH! This would burn R13 and must have damaged the IC now.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

R17, R18 are the startup resistors that power the IC on pin 3 only until it starts oscillating. Then only a few blips the transformer takes over powering the IC. The aux winding generates around 16VDC from D4/R13 to run the IC.

But pulling the SBD20C rectifier out, a BAD idea because the PSU would go to max. (PW) output, because it was getting no feedback voltage. OUCH! This would burn R13 and must have damaged the IC now.

A small price for ignorance, but a very valuable knowledge gained! Now it clearly explained why pulling out all other components changes nothing, until this unfortunate SBD20C...

Hmm... after restoring R13, and eventually a new AP8269 IC, I would most likely be back to square one then - a fluctuating voltages on the secondary side?

[stj]

Re: Wine Chiller - SMPS issue - fluctuating voltages

maybe not - if the ic was failing

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

maybe not - if the ic was failing

Noted - eagerly waiting for online purchase delivery.

[R_J]

Re: Wine Chiller - SMPS issue - fluctuating voltages

It is very likely the power supply was working properly, the fluctuating voltage was likely due to a light or no load on the 12v. and the ic was in burst mode (green mode)

Green Mode Operation
At light load or no load condition, the switch loss become the major loss of the power supply, to reduce the
power wasted in light and no load condition, based on a special designed voltage controlled oscillator, green
mode operation of the power supply can be achieved by using AP8269. The controller will judge the load
condition base on the voltage of CMP pin. In light load the CMP voltage will decrease, when VCMP is lower
than a set threshold voltage, a CMP depending time (TR2) will be generated by the oscillator and decrease
the operating frequency of the power supply, the minimum frequency is set about 22KHZ.
When VCMP decrease further, the power supply will enter into burst mode operation to decrease the power
consumed at no load condition. Besides there is no audible noise in any load condition

I had a closer look at your picture and it looks like the vcc pin (solder splash) may be shorting to ground, or is that just a reflection of the light?

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

It is very likely the power supply was working properly, the fluctuating voltage was likely due to a light or no load on the 12v. and the ic was in burst mode (green mode)


I had a closer look at your picture and it looks like the vcc pin (solder splash) may be shorting to ground, or is that just a reflection of the light?

It is the reflection of camera light. To be sure I just tested with DMM and there's no short.

This chiller has dual zone. In its original operating condition:
- 5V supply to both zone control panel are good, but light button is not functional, and internal fans are not spinning either.
- Lights and Fans are all connected to 12v sockets on this board.

I am not knowledgeable about fluctuating voltages is the reason lights and fans are not functioning. Guess now it's no point to install it back to the chiller to check since there's no output completely..

[R_J]

Re: Wine Chiller - SMPS issue - fluctuating voltages

The lights and fans are also controlled by the large ic on the power supply board, This ic switches the small transistors Q303, Q304, Q305 etc. I would have checked base of the transistors to see if they were getting turned on, If they were getting turned on I would think the fan would have tried to spin and lights would have been pulsing to the fluctuating voltage.
I suspect the original problem may have been a weak CD7 capacitor, or maybe a weak secondary capacitor.
I hope you ordered a few AP8269's

[Th3_uN1Qu3]

Re: Wine Chiller - SMPS issue - fluctuating voltages

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.

Likely just failure of controller IC due to bad primary side HVDC capacitor. The resistor opened because of excess draw of the controller chip. You are unlikely to run into any other trouble once the replacement IC arrives.

[CapLeaker]

Re: Wine Chiller - SMPS issue - fluctuating voltages

likely just failure of controller ic due to bad primary side hvdc capacitor. The resistor opened because of excess draw of the controller chip. You are unlikely to run into any other trouble once the replacement ic arrives.

+1

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

The lights and fans are also controlled by the large ic on the power supply board, This ic switches the small transistors Q303, Q304, Q305 etc. I would have checked base of the transistors to see if they were getting turned on, If they were getting turned on I would think the fan would have tried to spin and lights would have been pulsing to the fluctuating voltage.
I suspect the original problem may have been a weak CD7 capacitor, or maybe a weak secondary capacitor.
I hope you ordered a few AP8269's

Yes, I have ordered 5pcs of AP8269, anticipating damages on for couple of attempts..
So yes, will follow the input and do test cases depending on the outcome of this IC replacement.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

Likely just failure of controller IC due to bad primary side HVDC capacitor. The resistor opened because of excess draw of the controller chip. You are unlikely to run into any other trouble once the replacement IC arrives.

I am now very optimistic with your confidence, knowing that all the capacitors are now replaced. Thank you.

[beetle1303]

Re: Wine Chiller - SMPS issue - fluctuating voltages

AP8269 pwm ic finally arrived after 2 weeks. Not very good at SMD component replacement, but managed to get it working after 2 tries.

Tested bare board - working!!! No more fluctuating voltages at both primary and secondary sides.

Installed beck to the chiller - fully functional with fans and lights, and chill to set temperatures much faster.

Here' the summary of this project:
1) Original fluctuating voltages must be due to 1 or more of the electrolytic capacitors bad/weak as mentioned by R_J. Replaced all of them works well now.
2) Removing the SBD20 Schottky Rectifier probably killed the R13 resistor and the pwm ic AP8269 as mentioned by Redwire. Lesson well learnt.
3) Replaced AP8269 and R13 resistor, everything in working order.

A big thank you to everyone shared your experience and advised the next steps. A great learning journey for me.

Thank you, thank you.