Hi guys
Here's a brand I've not seen before, It is dead, no power at all.
The 2.5A mains fuse on the PSU board had blown (vapourised/blackened inside) but the 3.15A mains fuse near the IEC power connector is fine.
Had a poke round first with the Fluke - no obvious short circuits anywhere on power devices, rectifiers or PSU outputs. No distressed or visibly blown components other than teh 2.5A fuse
I fitted a new fuse and powered up via a light bulb current limiter
Nothing - dead - no power drawn (light bulb does not even flicker)
However the main electrolytic is charging up to about 320V. It slowly discharges on power off (there are high value bleed resistors across it)
Having had a look around the PSU it seems to have the following architecture/layout which has three main sections
I added some pretty clear pics of each of these sections so the description should be easy to follow
There is a PFC section controlled by an LD6562D (IC802)
The LD6562D has no Vcc supply on pin 8 so obviously it can't start up. The Vcc supply comes via a LM317 (IC828) - the LM317 input pin comes from the main electrolytic +ve and the adj pin is controlled via an opto-isolator. There is no voltage output from the LM317. My guess is it needs a signal from the isolated side of the PSU via the opto-isolator to turn on the power to the LD6562D and start up PFC but it's just a guess.
The main SMPS is controlled by IC807 which is an SG3525A https://cdn.badcaps-static.com/pdfs/...7c28cd62f5.pdf
Again the SG3525 has no Vcc power on Pin 15 so it can't start up. In this case pin 15 is connected via some low value resistors to what is probably the emitter of Q822. There also is an electrolytic from this pin to ground and it is not short. Q822 is part of a little circuit with three transistors and a diode D850. D850 gets power from the mains via D832 and 3x 1M0 resistors in series R913/R914/R915. I checked the circuit as far as D850 - the diodes and resistors all measure OK. Is this a 'startup' supply for the SG3525? I'm not sure. There is also another opto-isolator around here but I didn't trace out exactly how it connects.
Lastly there is a standby supply controlled by an NCP1014 (IC806).
In this case there is no output voltage from the secondary of the standby supply which powers some part of the isolated side of the PSU. There is no voltage on Pin 1 of IC806 (Vcc) though there is voltage on pin 5 (Drain) as it goes direct to the +ve end of the main smoothing cap. As I understand the datasheet the NCP1014 should just 'work' and generates it's own Vcc from the high voltage on pin 5 drain). There is no short or low resistance from Pin 1 to ground - in fact it reads several megohm. There is yet another optoisolator on pin 4 IC806 controlled from the isolated side of the supply
My best guess is either:
The IC806 chip has failed (though the is no sign of visible distress) which means there is no standby voltage therefore the PFC and main section of the SMPS can't power up?
Or alternatively there is some problem with what looks like it could be a startup supply for the SG3525A (R913/4/5, D850 and the three associated SMD transistors)?
But I have no experience with this type power supply, it seems a bit over complex to me.
Anyone have a schematic? (wouldn't that that nice!)
Or someone have some experience of this or similar PSU designs and know at how the three sections are dependant on each other and in what order the three sections should power up?
Cheers
Rich
Here's a brand I've not seen before, It is dead, no power at all.
The 2.5A mains fuse on the PSU board had blown (vapourised/blackened inside) but the 3.15A mains fuse near the IEC power connector is fine.
Had a poke round first with the Fluke - no obvious short circuits anywhere on power devices, rectifiers or PSU outputs. No distressed or visibly blown components other than teh 2.5A fuse
I fitted a new fuse and powered up via a light bulb current limiter
Nothing - dead - no power drawn (light bulb does not even flicker)
However the main electrolytic is charging up to about 320V. It slowly discharges on power off (there are high value bleed resistors across it)
Having had a look around the PSU it seems to have the following architecture/layout which has three main sections
I added some pretty clear pics of each of these sections so the description should be easy to follow
There is a PFC section controlled by an LD6562D (IC802)
The LD6562D has no Vcc supply on pin 8 so obviously it can't start up. The Vcc supply comes via a LM317 (IC828) - the LM317 input pin comes from the main electrolytic +ve and the adj pin is controlled via an opto-isolator. There is no voltage output from the LM317. My guess is it needs a signal from the isolated side of the PSU via the opto-isolator to turn on the power to the LD6562D and start up PFC but it's just a guess.
The main SMPS is controlled by IC807 which is an SG3525A https://cdn.badcaps-static.com/pdfs/...7c28cd62f5.pdf
Again the SG3525 has no Vcc power on Pin 15 so it can't start up. In this case pin 15 is connected via some low value resistors to what is probably the emitter of Q822. There also is an electrolytic from this pin to ground and it is not short. Q822 is part of a little circuit with three transistors and a diode D850. D850 gets power from the mains via D832 and 3x 1M0 resistors in series R913/R914/R915. I checked the circuit as far as D850 - the diodes and resistors all measure OK. Is this a 'startup' supply for the SG3525? I'm not sure. There is also another opto-isolator around here but I didn't trace out exactly how it connects.
Lastly there is a standby supply controlled by an NCP1014 (IC806).
In this case there is no output voltage from the secondary of the standby supply which powers some part of the isolated side of the PSU. There is no voltage on Pin 1 of IC806 (Vcc) though there is voltage on pin 5 (Drain) as it goes direct to the +ve end of the main smoothing cap. As I understand the datasheet the NCP1014 should just 'work' and generates it's own Vcc from the high voltage on pin 5 drain). There is no short or low resistance from Pin 1 to ground - in fact it reads several megohm. There is yet another optoisolator on pin 4 IC806 controlled from the isolated side of the supply
My best guess is either:
The IC806 chip has failed (though the is no sign of visible distress) which means there is no standby voltage therefore the PFC and main section of the SMPS can't power up?
Or alternatively there is some problem with what looks like it could be a startup supply for the SG3525A (R913/4/5, D850 and the three associated SMD transistors)?
But I have no experience with this type power supply, it seems a bit over complex to me.
Anyone have a schematic? (wouldn't that that nice!)
Or someone have some experience of this or similar PSU designs and know at how the three sections are dependant on each other and in what order the three sections should power up?
Cheers
Rich
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