Help me repair the PC Power Supply - Page 1
Forum section: electronics / repair

author: toli
author_rank: Frequent Contributor
timestamp: August 11, 2012, 08:52:38 am
content: The PS is a Tagan (480W if I remember correctly) - I will check the model later, it's not in front of me at the moment. The fuse burnt, I open it up, and see a couple of low voltage cap + one of the 200V caps with the lead slightly bent. I assumed they were all fried. Took them out of the circuit, measured them (with both the DMM, and by putting a voltage on them) and they work fine.Kept on searching, found 2 transistors (2SC3320) which are shorted. Next to them is a PFF6N60 which has a diode between two pins, and an open circuit to the 3rd pin.So the questions at the moment are:1 - Is there anything else I should check? The rectifier is mounted on a small PCB next to it and it check fine.2 - What replacement transistors would you recommend for the 2SC3320?3 - I could not find the datasheet for the PFF6N60. I found some data sheet with the same part number but it isn't the same part. This one is in a TO-220 package, and the one I found is actually for some sort of DO-XX package. Can someone tell me what this part is, and what commonly available part I can use in its place?Thank you.

author: amyk
author_rank: Super Contributor
timestamp: August 11, 2012, 09:09:30 am
content: 1. Check for bulging caps and burnt resistors.2. 2SC33203.http://www.chinaeds.com/zl/201012112032415509_PFD2500PDF.pdfMade by what seems to be now-defunct Pyramis. It's an N-channel 600V 6.2A MOSFET with 1R2 Rds. Replace with any other 6N60 MOSFET.

author: toli
author_rank: Frequent Contributor
timestamp: August 11, 2012, 09:17:01 am
content: Thank you for the reply.1. Did that, could not find anything so far.2. I can't get it locally, and since at the moment my little brother has no PC to spend his time I must fix it ASAP or my head will explodeAre there any similar devices you can recommend? I can simply look for something with similar spec's but if there's any recommendations it would be best.3. Thank you very much for that, I couldn't find that one. If that's the case then this one is fine (the D/S have a diode between them, and the gate is disconnected from both so seems it's still alive).

author: Rerouter
author_rank: Super Contributor
timestamp: August 11, 2012, 09:32:43 am
content: its gain is between 10 and 30, its a power transistor, rated for 400V, CEperhapshttp://au.element14.com/nte-electronics/nte2333/bipolar-transistor-npn-450v-to/dp/1383712

author: Unclegummers
author_rank: Contributor
timestamp: August 13, 2012, 02:03:12 am
content: Sounds like an waste of time?Aren't computer supplies cheap nowadays?I'll retract my first statement if you learn lotsPost pics, more measurements.

author: David_AVD
author_rank: Super Contributor
timestamp: August 13, 2012, 03:58:12 am
content: I find that once a switchmode power supply goes bang (shorted chopper, etc) they are often not worth repairing, not even for the hobbyist.Simple repairs (bad caps, etc) are ok as they usually haven't taken out a whole bunch of stuff.

author: Kremmen
author_rank: Super Contributor
timestamp: August 13, 2012, 06:33:03 am
content: Generally not worth the effort if your only aim is to get a functional power supply. Especially not worth it if the unit is done with a passive PFC, recognizable from a big transformer-like inductor usually fastened separately in the metal housing. Such vintage units are best committed to the scrap heap, or salvaged for parts if you can use the components / experience.The cheapest PSUs - like so many other cheapo things - are often underdimensioned, always implemented with bad / cheap components and generally fragile designs. You can fix it now only to have it blow from the next seam in a short order.

author: toli
author_rank: Frequent Contributor
timestamp: August 13, 2012, 07:12:38 am
content: Thank you for the replies.BTW, the model is TG480-U22 if anyone is interested.I've already purchased another PS. I got one from a friend at a good price and it should be able to power my brother's PC with no problems.I will probably repair the Tagan PS anyway. Seems like a couple of transistors + a couple of capacitors will get it up and running again. If it won't work I can always pull it apart for parts (lots of HS's, transistors, high-current diodes, caps, inductors, etc).

author: Kremmen
author_rank: Super Contributor
timestamp: August 13, 2012, 08:30:27 am
content: OK, i quickly googled the type and for a change that particular PSU may be worth something. It is a bit on the old side already and not very powerful viz current PC power needs, but otherwise may actually be worth fixing if the fault is an easy one.

author: T4P
author_rank: Super Contributor
timestamp: August 13, 2012, 01:36:00 pm
content: Actually if it is 480W then it's okay.Mind you i don't really think you can draw 100W with a Radeon HD 7770 GPU ... not even 90W with a 100W TDP CPU you aren't getting anywhere near 300W, more like 200W and you reached every SMPS Peak efficiency areafirst of all first of all, it looks REALLY high quality

author: toli
author_rank: Frequent Contributor
timestamp: August 13, 2012, 07:10:52 pm
content: Now that I have a new PS for my little brother's PC, repairing this one is just a matter of fun (and I'm sure it might be useful someday). I've looked for these transistors and found them on eBay. However, I've seen a few for very low prices compared to most sellers. For example this one:http://www.ebay.com/itm/4pcs-2SC3320-C3320-TO-3P-Transistor-A74-/170611814548?pt=LH_DefaultDomain_0&hash=item27b941b094Do you think there's any reason to be suspicious? I know there are some fake stuff on eBay, the question is if this is the case here as well?

author: T4P
author_rank: Super Contributor
timestamp: August 14, 2012, 01:31:00 am
content: ... you have every reason to be suspicious especially when they come from SZ, china

author: toli
author_rank: Frequent Contributor
timestamp: August 14, 2012, 05:19:26 am
content: How can I lower the odds of purchasing a fake item? I could not find this transistor at any major parts supplier (Mouser, Digikey, Farnell).

author: ju1ce
author_rank: Regular Contributor
timestamp: August 14, 2012, 06:17:40 am
content: Look for another transistor that is close enough. STW2040 may be suitable, it can be found on Digikey.

author: Rerouter
author_rank: Super Contributor
timestamp: August 14, 2012, 10:59:18 am
content: or the transistor i linked for you half way down the page :/

author: toli
author_rank: Frequent Contributor
timestamp: August 14, 2012, 11:01:34 am
content: I didn't forget about it. It's just that it is TO-220 while the 2SC3320 is TO-3PN (similar to the TO-247 from what I can see). I was also hoping to use the same transistor that was originally there, but I guess that ship has sailed.