Astec LPT63 switched mode psu circuit diagram

[Michaelhohara]

i have an astec switched mode psu that will not start up , It uses a UC3848 ic

[momaka]

Re: Astec LPT63 switched mode psu circuit diagram

So what have you checked so far? Any output voltage on the PSU, even if partial or very small? Primary-side electrolytic cap charges to ~340V DC? If not, check input fuse. If yes, try heating up the adapter with a hair drier. Sometimes (actually more often than not), the small "startup" cap on the primary side dries up and then the PSU cannot startup. Heating things in the PSU with a hair drier (heat only until hot to the touch, but not too hot where you can't keep your fingers on it) will make the ESR of the electrolytic caps go down, and that is sometimes enough to make the PSU work again. If PSU seems to work OK while hot after the hair drier "trick", then the adapter probably needs a recap only - most likely just the small startup cap... but do the whole PSU if it uses cheaper brands of capacitor and not first-grade caps like Rubycon, Panasonic, Nichicon, or United Chemicon. Given it's made by Astec, I suspect it should come with good Japanese caps already. Of course, that's not always the case with their latter-made PSUs.

Most of all, share some pictures of your PS if you could. Helps us to see what you're seeing so we can make more suggestions.

[CapLeaker]

Re: Astec LPT63 switched mode psu circuit diagram

Not to sound like an @$$, but with real sparse info, sounds like:
I drive an Audi that doesn’t want to start. It uses a 2l turbo.
There isn’t much to chew on to narrow down what the problem could be.

[stj]

Re: Astec LPT63 switched mode psu circuit diagram

post pictures, but 99% chance it's the startup capacitor
https://cdn.badcaps-static.com/pdfs/...f38b1092e0.pdf

c3 in the example on page 9
also if it has current limitting on the supply - check the resistor(s) between pin 4 and the rectified mains.
r12 on the example, but in real life it's often 2 resistors in series for safety

[Michaelhohara]

Re: Astec LPT63 switched mode psu circuit diagram

Thank you very much for your reply. Hi
I am very new to this forum, I retired 12 years ago but i am gradually being drawn back into electronics again.When i worked my speciality was audio equipment and radio studio, and transmission equip.
My problem with the psu is that it just will not start to switch, it usesa UC3848 ic the start up voltage supplied is 13 Volts (min seems to be 16V). It looks to be a simple problem b but it is not , the switching board works when supplier by a psu when removed from the unit .
Regards
Michael

[Michaelhohara]

Re: Astec LPT63 switched mode psu circuit diagram

Just now i found the replies to my query. I have attached a pic of the psu and the sub board that has the switching ic, I have replaced all the mentioned caps,
I have looked on line for a circuit , but without any success

[stj]

Re: Astec LPT63 switched mode psu circuit diagram

did you check how pin4 gets fed from the rectifier?

long ago i repaired dozens of sat recievers using these chips,
every one had a bad pair of resistors that wherent rated for the voltage being used to feed pin4