Need help with photo of Silverstone power supply - Page 1
Forum section: electronics / repair

author: giosif
author_rank: Frequent Contributor
timestamp: August 16, 2020, 05:08:25 pm
content: Hi,I am trying to repair a Silverstone ZM1350 computer power supply for which the PWM controller for the main switching MOSFETs has failed, along with a few other components (the PWM IC is located on a separate smaller board, mounted vertically next to the MOSFETs).Luckily, I could read the PN of the actual controller IC (it's an ISL6752), so I can find a replacement for that.That said, there is one SMD resistor which was blown and two more for which I cannot read the markings and I was wondering if there is someone here on the forum who might have the same supply and could take a picture of said board with the PWM controller.I am aware this is a long shot, but I thought I'd ask.Thanks!

author: giosif
author_rank: Frequent Contributor
timestamp: August 21, 2020, 08:58:28 pm
content: That was lucky: I found a picture with the board in question on a review web site - please see below photo (courtesy ofwww.xoer.cc).The only thing I'm not sure of is the resistor in the top-left corner: is that an 5R0, 6R0, or something else?

author: garrettm
author_rank: Frequent Contributor
timestamp: August 22, 2020, 04:21:36 am
content: Looks like 6R0 to me. Using that as a baseline, the one on your board looks like 6R1.Best of luck on the repair!

author: sean0118
author_rank: Frequent Contributor
timestamp: August 22, 2020, 07:48:20 am
content: You might already know, but R159 is 2k on the original but 120k on yours.

author: giosif
author_rank: Frequent Contributor
timestamp: August 22, 2020, 10:26:25 am
content: Thank you, both!Those are good observations.One last question, if I may: are those black diodes with white stripe any special type, or it's just aesthetics?Forward voltage drop measures around 0.6V.And they are definitely not Zener diodes (those are marked with ZDx on the board and the rest of the power supply).

author: garrettm
author_rank: Frequent Contributor
timestamp: August 22, 2020, 09:21:28 pm
content: A forward voltage of approx. 0.6V suggests a silicon diode. However, the diodes may need to have a particular reverse recovery characteristic. Looking over the datasheet for the ISL6752, I found them talking about a Schottky diode for the soft start circuit--but I don't know if that is implemented on this board. I also couldn't find them talking about the reverse recovery characteristics of any of the diodes, so maybe it's not important here...Hopefully someone more knowledgeable about switching power supplies can help you with selecting the diodes. But at the moment, it looks like normal silicon rectifiers should be fine.

author: wraper
author_rank: Unknown
timestamp: August 22, 2020, 09:32:31 pm
content: 6R8 IMHO, though on faulty board it likely had a different nominal.

author: giosif
author_rank: Frequent Contributor
timestamp: August 23, 2020, 10:38:45 am
content: Thank you!I'm aware my board had resistors with different markings, but I cannot reconstruct those markings in their entirety and, taking them out of circuit, they proved to be blown/broken (i.e. measuring OL).So, I'm thinking of going with the resistor values in the picture I found on the Internet.