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|03-08-2012, 01:05 PM||#1|
Join Date: Apr 2011
City & State: University of Leeds (MEng ElecEng undergrad)
My Country: UK
Line Voltage: 230Vac 50Hz
I'm a: Student Tech
Cheapo PSU recapped
Found this PSU in the junk pile.
Plugged it in, 5VSB measured ~1.8V and rails were dead when the paper clip power on was used. Checked with scope - nice 50kHz ripple from 1V to 4V on 5VSB.
Pulled the case open and unsurprisingly found a three bulged Teapos. One on 5VSB and two on the 3.3V.
Checked the 5VSB cap (470u 16V) for ESR - about 3 ohms. Replaced that (Panasonic FC - 680u 16V), as well as some other caps. The output LC cap for 5VSB measured >20 ohms & leaky, so replaced that with a Rubycon ZLH 1000u 16V. (Originally a pathetic 100u.) Checked power for PWM controller - 100u 35V, replaced with Chemicon KMG 100u 50V. (Checked this cap later on ESR meter - measured 0.5 ohms, probably out of spec.) Checked the 3.3V caps (2200u 6.3V) - both had ESR about 5 ohms(!) Replaced them with Chemicon KZE 3300u 16V.
I also fixed some cold solder joints around the main switching transistors.
All these caps I had lying around as spares left over from TV repairs. PSU now works 5.2Vstby, but still main rails don't fire up.
It seems like the 12V is shorted to 5Vstby as the rails measure the same... exactly. I'm not sure how that could happen!
If I can't repair it I'll probably take my caps out of it and throw it in the trash - it would just be nice to see if it can be fixed. Even if it's just a piece of crap, I have distant plans to use it for a reflow plate (high current 12V supply... for a custom engineered 100W heating element.)
It's actually got a decent passive PFC choke, a proper EMI filter (two coils, 3 X caps and some Y caps) and a real bridge rectifier. 470u 200V primaries, better that most but still a bit lackluster (should really be 680u+.) I think it's a 250W model.
** Begin Signature **
I fix TVs and electronics as a hobby and to save nice things from the dump. 40 LCD TVs, 4 monitors, 13 plasma TVs, and a 6.1 system!
Free service manuals database: http://www.tgohome.com/ServiceManuals - Have a manual? Need a manual? Please PM me.
I have successfully fixed (from best --> worst build quality):
3 Panasonic Plasmas, 1 Yamaha HTS, 1 NEC Plasma, 2 Sharp LCDs, 2 Toshiba LCDs, 5 Philips Plasma/LCD, 1 Hitachi Plasma, 5 LG LCD/Plasma, 10 Samsung LCD/Plasma, 1 Thomson Plasma, 1 Atec LCD, 1 Hanspree LCD, 1 Xerox LCD, 1 Harwa LCD, 2 Proview LCD, 2 Hyundai LCD, 1 "Onn" LCD, 1 Dell LCD, 1 iiyama LCD, 1 Logik LCD, 5 Bush LCD, 9 Vestel LCDs
[Please do not PM me for help: I am a busy student, and we prefer input from all sides on this forum.]
Last edited by tom66; 03-08-2012 at 01:08 PM..