SMPS MeanWell AD-155c - Buffer PSU - no voltage on output - Page 1
Forum section: electronics / repair

author: K4masz
author_rank: Newbie
timestamp: June 01, 2019, 08:50:34 am
content: Hello everyone, recently I have received this old power supply from my friend. I decided to repair it, not for the money but mainly in order to gain some knowledge and maybe a working deviceOK, The main symptom is a fact that there is no output voltage.The things I managed to determinate so far:The bulk electrolytic capacitor  - charges.PWM&PFC IC receives voltage (output not tested).Two optocouplers are working properly.Two fuses are not blownFriend gave me piece of advice to change one of the fuses with light bulb - its behavior told me that there might be short on cold sideI am very open to suggestions about where to look for point of failure.The PWM&PFC Combo IC is FAN4803 - it is located right above main transformerIC on the right of the main is Dual OpAmp - AHA17358 B

author: PKTKS
author_rank: Super Contributor
timestamp: June 02, 2019, 11:01:28 am
content: Well this is not just a simple thing...First 2 cents of rant:- I have just overlooked that not very common supervisor- In the present days PFC has become kinda BUZ market thing - yet another one- That PSU is just barely 150W if that much - PFC is nonsense thing with that power- PFC puts a long list of complicated things to check in something (SMPS) already complicated- With 2 optocouplers I will expect more than 2 error amps and independent FB loops- sum that with a fairly complicated soft start required by that PFC chip what you have?You have a somewhat complicated (and patented) CURRENT MODE (ISENSE pin) softstart (very low power) SMPS **WITH** PFC bundled...just for the sake of patent incomes and that PFC BUZ thing.After the rant the advice or steps I would "try" ..- to have a clear view of what sort of messy topology that 2 optocouplersare driving back to the supervisor..- if that supervisor is able to soft start something... or notIt looks a rather complicated setup to a rather humble power class of less than 200W.In cost x time issues I would ditch that for a far more capable PSUand probably much cheaper..**ANY** S-360-60 based on 494 clones is below U$30 tagthat almost double rated 360W with true 10A output.30box? I would not bother that crappy PFC patented and probably expensive chip...I would ditch that for an s-360W or better.. and save the hasslePaul

author: magic
author_rank: Super Contributor
timestamp: June 02, 2019, 12:53:48 pm
content: What's that "battery low protection: 39V"?

author: mikerj
author_rank: Super Contributor
timestamp: June 02, 2019, 01:02:31 pm
content: Quote from: magic on June 02, 2019, 12:53:48 pmThis unit appears to have some kind of UPS function, and has a secondary output for battery charging. Thedatasheetis pretty vague on the operation of this however.

author: magic
author_rank: Super Contributor
timestamp: June 02, 2019, 01:14:12 pm
content: Yes, I'm reading the same datasheetThe question is of course could it be causing the unit to shut down in absence of a battery.Other than that, main capacitor charging indicates that the PFC works and the primary switching FET isn't shorted. Most likely the driver is OK too because it's part of the same chip as PFC. So probably the secondary is commanding a shutdown for some reason or malfunctions.

author: PKTKS
author_rank: Super Contributor
timestamp: June 02, 2019, 01:48:31 pm
content: if they follow that diagram published the 2 optocouplersare just for the over protections unless you have somesort of TL431 near those..in case the supervisor is unable to soft start thoseprotections or would be faulty or they have nothing to protectWith the PFC being CURRENT MODE driven and highlydependent on that "patented" soft start "single pin"..I would guess that the PFC is not able to start ..Geezzzz this unit costs U$85 deliveredAn s-600-60 cost U$ 35 (delivered) an s-360-48 or s-360-36 not even thisand they all can charge any battery the same way...and you can fix any S-xxx-xx series very cheap either...the parts are easily foundhmmm that PFC chip seems a hasslePaul

author: K4masz
author_rank: Newbie
timestamp: June 08, 2019, 08:00:56 pm
content: I actually have a second unit which seems to work properly.The diode is alive, and the output voltage on standard output and battery one can be manipulated in range 45V-61V. I haven't tested the current.Can I use this working one to somehow determine what may failed in the broken one?

author: PKTKS
author_rank: Super Contributor
timestamp: June 09, 2019, 04:30:53 pm
content: Quote from: K4masz on June 08, 2019, 08:00:56 pmYes you candraw a concise list os parts with locations and referencesMeasure the voltages at proper KEY POINTS(deciding what is a key point is your great challenge)BE VERY CAREFUL BECAUSE SOME POINTS MAY HAVE about 1KV (spikes)** DO NOT MEASURE THE SWITCH or FLYBACK PRIMARY DIRECTLY **it will damage your instrument quite easilythat said you have the secondary and the IC voltagesw/ care about the primary pulses...take note and dup the procedure on the failed unitwith some luck you may have a very good start point clue or directionPaul