Thermaltake Smart 750w Repair 12v unstable. no pwrgood - Page 1
Forum section: electronics / beginners

author: huehu3gg
author_rank: Contributor
timestamp: December 27, 2021, 06:15:52 pm
content: i trying to understand the value of this resistor. there 2 with the same colors.black violet green red black. can someone help? i attach the diagram, they are r6 and r6a.

author: mariush
author_rank: Super Contributor
timestamp: December 27, 2021, 06:25:52 pm
content: Usehttps://www.digikey.ro/ro/resources/conversion-calculators/conversion-calculator-resistor-color-codeMake sure there's no silver or gold circle between the red or orange and the last black or brown.Silver would indicate 10% tolerance.

author: huehu3gg
author_rank: Contributor
timestamp: December 27, 2021, 06:27:20 pm
content: there are no other color. only what u see! . maybe confuse by the Shadow in that part.the resistor its from thermaltake smart 750

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 27, 2021, 07:17:39 pm
content: Not sure exactly what the value of those is... But it's going to be a very low resistance because they are the current sense resistors for the AC side of the supply. 750 watt supply?I would guess they would be in the milliohms range... Those colors make no sense to me either.We can see from the schematic that the peak voltage across them will be less than 1.4V (D1 & D27 protection diodes) on the current sense input of U2... This will be the peak current through BD1 measured as a voltage across those mystery resistors.

author: BrokenYugo
author_rank: Super Contributor
timestamp: December 27, 2021, 07:47:42 pm
content: Have you tried looking at it under different light/angles? The colors shown work out to a nonsensical 7500 ohms 20% tolerance.Have you tried measuring it? Being what appears to be a current shunt they should be very low value, may even just look like a short to a DMM.

author: huehu3gg
author_rank: Contributor
timestamp: December 27, 2021, 07:56:43 pm
content: "Have you tried looking at it under different light/angles?" yes, that why i came here. no sense for me those colors too.measuring resistor give me 0 omhs. 00.1 omhs.i think r18 its the sense resistor, thats 47 omhs.what u suggest?

author: tooki
author_rank: Super Contributor
timestamp: December 27, 2021, 08:14:42 pm
content: Quote from: huehu3gg on December 27, 2021, 07:56:43 pm1. You need a special meter to measure very small resistance values. A regular multimeter will not do.2. No, R18 definitely isn’t the current sense resistor.3. Ohm. O-h-m, ohm.

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 27, 2021, 08:23:54 pm
content: QuoteIt looks OK to me then. I would put it back in circuit and look elsewhere for problems. The only way to measure these low resistances accurately is with a 4 wire ohmmeter. Your two lead VOM isn't going to show anything below 1ohm very accurately because of lead and contact resistance.QuoteR18 just limits the current through D1 & D27 if a really high current passes through R6 & R6A. D1 & D27 protect U2's Isense input against over voltage.

author: huehu3gg
author_rank: Contributor
timestamp: December 28, 2021, 02:48:34 am
content: i just put the resistors, and test de power supply with a light bulb in serie. so when the current flow via the bulb, this turn on for a moment, i think it happend while the capacitor get charged.after that, el bulb go off, and i have 5vsb.so a short PSON with GND to turn on the PSupply, with the bulb of course, and i get 12v but with variants, 9v 10v 10.5 11 12v, every time the value jump.so i try to connect the PS direct without the light bulb, and the 12v were stable, But the PSupply disarm itself... after few second. it reach the 12v but, turn off... so to turn on again, got to discharge the main cap i think. so i try again, and the same.with the bulb got Variable voltage, and without got stable but PS disarm...any suggest? Thx and sorry for my english, i hope you can understand me.

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 28, 2021, 06:49:59 am
content: I assume you put the light bulb in series with the AC input as a means to protect against over current while troubleshooting?Without the bulb in series, try loading the 3.3v, 5v, & 12V outputs with some resistors. Maybe 5-10 watts for each rail. It may be shutting down because it is unloaded.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: December 28, 2021, 12:24:52 pm
content: About the resistorIt is 5 bandsThe fifth band is usually the tolerance, BUT:If the fifth band is black, the resistor is a winding resistor, (very high tolerance), usually very small ohmsIf the fifth band is white, it is a fuse resistor.Here is something about a wirewound resistor:https://eepower.com/resistor-guide/resistor-materials/wirewound-resistor/#The conclusions here that the resistor is a very low value, are entirely correct.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 28, 2021, 01:33:32 pm
content: My guess would be 0R075, 2%Looks like a bigger gap between the green and red band

author: huehu3gg
author_rank: Contributor
timestamp: December 28, 2021, 02:23:31 pm
content: Thanks to all !! as i say, i used them. but my trouble now its the PSU disarm when it connect direct to 220v!. as long i keep in the bulb it no disarm.mmm its about load?? or could be anything else?and yes, the bulb for protectionedit: i try with a fan 12v as load. and same result when its direct to 220v. fan spin, i got read of 12v in multimeter for a 2 second, and then disarm and all drop to 0v.the only way i can turn on again, its waiting for the caps to be discharged.

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 28, 2021, 08:35:50 pm
content: QuoteThe bulb trick is OK for a linear power supply because it's input current tends to decrease when it's input voltage decreases. The bulb's resistance decreases as the current through the bulb decreases which makes for a relatively stable situation: Negative feedback.The problem with using the bulb trick on a switching power supply is that it's input currentincreaseswhen the input voltage decreases. So it would tend to be unstable when a bulb is put in series with the AC supply line: Positive feedback.QuoteA common fault with switch mode power supplies is that the output capacitors (The ones on the 3.3, 5, 12V lines) tend to fail and go high ESR. Sometimes it's obvious because their tops tend to bulge a bit in really bad cases. Older supplies needed a minimum load, but I think newer ATX supplies are more tolerant of a no load situation.What output is the LED end of U7 connected to? (Post full schematic if you can) I think this is the voltage feedback loop, so you may want to try loading that output. (The output of the supply,notU7 directly) I don't think a single 12V fan is enough.QuoteYou could try your meter on the other lines and see if any go unusually high before shutdown.

author: huehu3gg
author_rank: Contributor
timestamp: December 28, 2021, 09:05:33 pm
content: i post the diagram. i got the bulb with a switch, to make it direct to 220v. first i test with bulb, then i press the switch and override the bulb.something i see its the Q3 and Q2 GS give me 10 ohms in the Board, without mosfet solder. of course with mosfet solder-in give me 10 ohms too...edit: adding this. the resistor r36 i think its cap discharge right? its about 00.1 ohms that what mi multi reads... should fine? its a 2 o 3w resistor metal oxide. i attach the pictore of that resistor.edit 2 : i try the 5v output of molex, and it reach 5v without the bulb, but protect itself , and with 12v fan connected too.another edit: i replace Q8 , Q9 and Q10 . they blown up.

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 28, 2021, 11:04:35 pm
content: QuoteGate to Source you'll see the value of R17 when measuring Q2 since they're in parallel. Same for R38 & Q3.QuoteIt's another current measuring resistor... It'll be a really low resistance, so 0.1ohm on a multi shows it's probably fine.Poor man's 4 wire ohmmeter:If you have a small bench power supply with current limiting, you can set it to 1A and put 1A through the resistor (out of circuit). Place the leads from the power supply at the very ends of the resistor leads. Next, take your multi-meter and set it to read millivolts DC. Then measure across the resistor, but not at the same physical points as the power supply connection, and read how many millivolts are across the resistor. 1mV = 1milliOhm. ie: If you read 75mVdc then the resistor is 0.075ohms (75 milliOhms) because 1 amp is going through it. (Only use 1A for resistors less than 1 ohm and rated for more than 1 Watt. ie: Estimate the wattage 1st)QuoteNice. Yup, it looks like U7 is the voltage feedback and they are monitoring the DC voltages on the 5V and 12V lines and respond to transients on the 3.3V line.QuoteQ1 also might be damaged since it is in parallel with Q10.How is it operating now?

author: huehu3gg
author_rank: Contributor
timestamp: December 28, 2021, 11:15:21 pm
content: Quotei measure out of the board, and he is fine. as long i can see! my bad to not buy 2 and change both. i dont have the schematic by that time. so i doesnt know that was in paralel. BUT the measuring its a little low than the replace i put. but no big diference, so i think its fine. \edit: znr1 varistor? TH1 termistor??edit: Th1 i took off, and measure. give me 1ohm / 1.5 ohms, SCK 015 . when i heat up outside of the board it goes up to 0 omhs, but in board i heat with hot air and Ohms raise to 8 ohms... mmmmmmmabout 10 ohms GS Q2 Q3 . r38 & r17= 10k / r16 & r37 = 10ohms.

author: huehu3gg
author_rank: Contributor
timestamp: December 29, 2021, 04:01:28 pm
content: i got an update. i Found a jumper doing bad conection, doesnt give continuity . so a resolder and now the PSU doesnt Protect itself.5vsb Stable3.3v stable after 2 o 3 second of psu ON.5v almost stable.but 12v flip between 9 10 11.4 12. doesnt get stable... im only trying with the 12v Fan connected and a Multimeter un the Molex 24 pin.maybe stil an issue in the 12v side...edit: New update. i Try in a 775 motherboard, and all voltage are stable! BUT the mother dont post with this psu. i try another psu and mother post... so i think its low in current... any suggest? i will investigate.

author: strawberry
author_rank: Super Contributor
timestamp: December 30, 2021, 07:16:43 am
content: for 230V grid, C2 must read 400V if not then PFC is not working

author: huehu3gg
author_rank: Contributor
timestamp: December 30, 2021, 03:00:35 pm
content: Quote from: strawberry on December 30, 2021, 07:16:43 amhow can i test this?? its active or pasive pfc? i post diagram few post above. i know 320v should be fine in 220v line. maybe something in the way can cause that and not particular the pfc?

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 30, 2021, 06:41:55 pm
content: QuoteHave you checked the ripple on all outputs with a scope with the motherboard connected? Compare with the good PSU.What is the powersupply's GP (Power Good) output level?

author: strawberry
author_rank: Super Contributor
timestamp: December 30, 2021, 09:47:20 pm
content: it must be above 320V

author: huehu3gg
author_rank: Contributor
timestamp: December 30, 2021, 10:05:03 pm
content: Quote from: Kim Christensen on December 30, 2021, 06:41:55 pmno scope here yet:(Pwrgood 4.7v . but connecting PSU to ATX tester those do you connect 24pin and autostart . show me 12v and -12 variables. and sometimes 3.3v variable.5.1vsb strong stable. so aux psu discard.now i found like a BUG sound, like and insect moving his clamp, that what i hear when i turn it on. it not like a buzzzz. its more like and insect sound.. i dont know how to describe better.i refresh memory. the Q8. Q9 and Q10 was replace cause they were blown. can i suspect malfuntion of the PWM chip? suppect in the 12v variable, and supect for the 300v in the C2 ?PFCout is conect directly to the Q9 and Q10 Base.thx for all answer!edit:Quote from: strawberry on December 30, 2021, 09:47:20 pmsorry i never post it, but i got 300v in C2

author: huehu3gg
author_rank: Contributor
timestamp: January 03, 2022, 04:26:40 am
content: after investigate. i found the pwm chip pin 13 is not getting the power supply. i do not understand if to supply the PWM, need the PSON be shorted to ground.pwm cm6800xt and the regulator or feedback ST9S429 or the s3515.cause in the u5a i got 5vsb in the pin1 , and in the pin2 i got 4.4v (diode)in the u5b i got 15.8v in the pin 4, and 1/2v in the pin 3... so the Q7 isnt switching, so the 15v does not reach the pin 13 vcc of the pwm. Q7 colector = 15v . emisor 0.4v . base same as pin3 u5b.BUT my question now is.... need to Start the Psu to activate the pin3 of the u5b.pin4 FPO of the U4 it an output. so if i trigger the PSON, will shorted to ground the u5a pin 2? that what im not understanding well.will replace the optos just in case.i read you. thxs

author: Kim Christensen
author_rank: Super Contributor
timestamp: January 03, 2022, 11:32:30 pm
content: QuoteYou should have more than 0.6V across pins 1 & 2 of the LED in U5a...QuoteYea, I'd think that pin3 (FPO) of U4 should be low (less than +0.5V above pin2 of U4) if things are operating properly. Do you have a part number for U4?

author: huehu3gg
author_rank: Contributor
timestamp: January 05, 2022, 03:51:52 am
content: Quote from: Kim Christensen on January 03, 2022, 11:32:30 pm0.6 across the diode i see normal.QuoteST9S429 or the s3515.but if a short pson, the psu goes down after few seconds...