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Old 01-26-2022, 03:26 AM   #1
momaka
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Default A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

More eBay specials: this time a Gigabyte GP-P450b 450W ATX PSU for $8 with free S&H. Listed “For part/not working”, as usual. Showed up in a beat up EVGA box without any padding… but that’s understandable given the total price. PSU made it out fine without damage. It’s a non-modular (yay!), pretty modern-day looking PSU with a black paint and all black cables (meh, not my favorite, but figure it’s good to keep a few of these in case I do need one for a more modern PC build, just so my old gray boxes don’t look too odd in there.)
Gigabyte GP-P450b (1).jpg

Gigabyte GP-P450b (2).jpg

And a shot of the label:
Gigabyte GP-P450b (3).jpg

Apparently its single 12V rail is supposedly capable of 36 Amps (432W), while the whole unit is rated for 450W. 3V3 and 5V have a combined power of 105W, so that suggests group regulation. UL number listed is E313928, which seems to go back to… Gigabyte?? Strange! I didn’t know Gigabyte made their own PSUs… and I was pretty sure they didn’t. I was that hoping the UL number would reveal a little more information about the real manufacturer, but no. Otherwise, looking up the model number online leads to Gigabyte’s page here:
https://www.gigabyte.com/Power-Supply/GP-P450B

Anyways, so I plugged the PSU in and… indeed it was DOA as the listing stated. According to the seller, the PSU came DOA to him due to shipping damage. I don’t see any indications on the PSU’s case to reaffirm this. But nevertheless, PSU was dead as promised, so I awarded the seller 5 stars for accurate description. So, time to crack it open and see what’s bad. But wait! The warranty sticker is still intact!
Gigabyte GP-P450b (4).jpg

Given this is a pretty new PSU, it probably still has warranty. I even amused the idea of sending it in for RMA for a few moments … but then, if Gigabyte really sent me a new PSU, this one would probably get land-filled, which doesn’t help anyone or the environment. And besides, what’s the fun in getting a working PSU anyways?!
So, here it goes, warranty VOID-ed and top removed with no regrets whatsoever.
Gigabyte GP-P450b (5).jpg

Gigabyte GP-P450b (6).jpg

Gigabyte GP-P450b (7).jpg

Well, there’s your Gigabyte 450W PSU. Honestly, I was a bit surprised at how mediocre it looks. What particularly struck me first are the two toroids on the output, confirming that this is a regular group-regulated PSU. And with that, I have a hard time believing the 12V rail output can be loaded all the way to 36 Amps (432W) without the 5V rail going out of whack with a low/no load. If it can, then I bet the 5V/12V/-12V common-mode output inductor would be running hell-a “over-clocked” to make up for the cross-loading.

Before looking for the problem, I decided to finish the photo-session and do a build quality “summary” here. So, let’s start with the primary side:
Gigabyte GP-P450b (8).jpg

Nothing crazy to see ^ there – the input filtering is complete (and I have to say, that 2nd common-mode choke looks quite interesting); bridge rectifier is “naked” without a heatsink, but looks capable for the rating of the PSU; APFC boost coil also looks interesting and well-made; primary cap is a *yawn* Teapo 400V, 270 uF, 85°C part, but that’s still better than some 3rd -grade dubious cap brand; all silicon on the primary heatsink consists of TO-220 parts (2x MOSFETs for APFC, 1x diode, 2x MOSFETs for main PS 2-transistor forward); and the MOV, thermistor, and fuse are all present, as they should be.

Next, the secondary side:
Gigabyte GP-P450b (9).jpg

Ugh. This is getting too mediocre… maybe even bad. I would be surprised if the output filtering is enough to suppress ripple/noise adequately. Perhaps the 3.3V and 5V rails could be fine, as they aren’t rated very high and each one is filtered by a 2200 uF and a 1000 uF cap with a small PI coil in between. The 12V rail is the one I’m worried about, as it’s also filtered only by a 2200 uF and a 1000 uF cap (again, with a small PI coil). For 36 Amps worth of current, I’m skeptical it will hold up… but maybe it can? I haven’t looked up any reviews on this unit yet, so this is pure speculation based on visual observation on my part. On the same note, the main (5V/12V) output inductor is only a T106-45 part… which seems a bit on the small side, especially considering that a -45 core is actually inferior in terms of losses compared to a -52 core (at least at higher frequencies.) On the other hand, -45 material offers higher inductance per turn, and my guess is the manufacturer did this in order to keep the 5V and 12V rails balanced with the higher 12V rail cross-loading modern PSUs are expected to handle. Note, however, that the 3.3V rail still uses a -26 material core material. So this suggests the overall PS switching frequency is likely under 50 KHz.
Also visible on this picture is the likely PSU manufacturer: MEIC. Various info sources online suggest their website disappeared when Gigabyte had (has?) the scandal with their bundled Newegg PSUs (the ones that were blowing up or DOA frequently.) On that note, the reviews for this particular model on Newegg also show a disproportionately high number of DOAs. With that stated, I’m including the PCB m/n on mine, in case this happens to apply only to certain batch of PCBs / models. It’s P4502119-be04 and dated 2020/05/13. So yes, the PSU is definitely still under warranty!

Finally, here’s a shot of the solder side:
Gigabyte GP-P450b - PCB solder side [hi-res] rszd.jpg
The soldering is relatively good overall. I did notice a number of loose solder balls rolling around in the PSU case and a few stuck with flux on the PCB. But they were all really small and didn’t seem like they could cause any shorting. Nonetheless, if there are small solder balls, this means bigger ones can exist too. I probably just didn’t happen to run into any on my unit. But really MEIC just needs to tweak the temperature settings on their wave solder machine, it seems. If anyone is interested in high-resolution pictures of the solder side (say, to look up a resistor value for a blown unit), see the attached zip file at the end of the post.

Last but not least, the fan:
Gigabyte GP-P450b (10).jpg
Hmmm, now where have I seen that fan brand before?
Oh yes, that crappy KDMPower MIPC MI-X8775CD ATX PSU I showed a while back had the same BOK (or as I like to pronounce it: “Be OK?” ) fan brand. Not exactly inspiring any confidence here, is it? I didn’t open the fan to see if it really has a rifle-bearing, which the Gigabyte product page proudly advertises. But then again, it’s a budget, “cheap” PSU (or maybe not, given the $49.99 price tag on Newegg?), so I couldn’t care too much either way.

With that said, let me just finish the build summary here so that we can jump to the troubleshooting part afterwards:

Primary Side:
* EMI/RFI filtering: two 102M + three 222M(?) Y2-class caps; two 0.47 uF X2-class caps; two CM chokes
* Protection: T10AH250V fuse; NTC thermistor; MOV between L&N (not heatshrinked!)
* Other: 8-10 Amp (?) bridge rectifier (not heatsinked); 1N540x (1N5406?) APFC bypass diode
* APFC: 105j450V P.P. cap after B.R.; “MS30EQ-X02” APFC boost coil; 2x JCS18N50f MOSFETs (TO-220FP) + 1x SU860 diode (TO-220)
* Caps: 1x Teapo LH, 400V, 270 uF, 25x42 mm; 1x YC LE, 50V, 10 uF, 5x11 mm (5VSB startup?); 1x ChnCap TM, 50V, 47 uF, 6.3x13 mm (pri. aux. filter); 1x YC TH, 50V, 4.7 uF, 5x11 mm (main PS run/timing?)
* Main PS (2TF topology): 2x JCS18N50f MOSFETs (TO-220FP) + 2x SR308 diodes
* Transformers: “MS35ERL-X06” (35 mm) for main PS; “MS19ES-X30” (19 mm) for 5VSB; “MS10ES-X17” (10 mm) driver for main PS MOSFETs

ICs:
*PR6249 (PDIP-8) for 5VSB; CM6805bg (SSOP-10) for PWM+PFC; WT7525Y (PDIP-14) for supervision, PS-ON, and PG.

Secondary Side:
*Output Inductors: T106-45 common-mode toroid for 5V/12/-12V; T80-26 (20 mm dia.) for 3.3V rail

* 5VSB
*** 1x ChnCap TP, 10/16(?)V, 1500(?) uF, 8x20 mm cap (in 10 mm dia. spot) before PI coil
*** 1x ChnCap TP, 16V, 1000 uF, 8x16 mm cap after PI coil
*** SR5T45 (5 Amp, 45V) Schottky rectifier
*** PI coil: 14-turn, 20 AWG, 2.5x16 mm rod core

* 12V Rail
*** 1x YC LE, 16V, 2200 uF, 10x20 mm cap before PI coil
*** 1x YC LE, 16V, 1000 uF, 10x16 mm cap after PI coil
*** 2x SBP30V60ct (30 Amp, 60V, TO-220) Schottky rectifiers in parallel
*** PI coil: 4.5-turn, 16 AWG, 4x20 mm rod core
*** 2x 1-KOhm SMD load resistors in parallel

* 5V Rail
*** 1x YC LE, 10V, 2200 uF, 10x20 mm cap before PI coil
*** 1x ChnCap TP, 16V, 1000 uF, 8x16 mm cap (in 10 mm dia. spot) after PI coil
*** 1x SR3045Lct (30 Amp, 45V, TO-220) Schottky rectifier
*** PI coil: 4.5-turn, 18 AWG, 4x20 mm rod core
*** 2x 30-Ohm SMD load resistors in parallel

* 3.3V Rail
*** same exact arrangement as 5V rail above

* -12V Rail
*** 1x ChnCap TP, 16V, 680 uF, 8x14 mm cap (in 10 mm dia. spot) & no PI coil
*** 2x 1.5 Amp (?) diodes
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Old 01-26-2022, 03:31 AM   #2
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Thumbs up A Dead/DOA Gigabyte GP-P450b 450W ATX PSU – troubleshooting & repair

Since the PSU was totally dead (no 5VSB present at all), I started from the primary side first. The fuse, bridge rectifier, and NTC thermistor (placed between APFC boost diode and primary cap’s + leg) all checked out OK. APFC current sense resistor (0.05 Ohms I think, 3W MOX type) was also good. Thus, I applied 120V AC on the input of the PSU and checked the DC voltage on the primary Teapo cap, which was around 165-170V – so all good there. Then I checked primary-side auxiliary supply winding on the 5VSB transformer, and that was also OK (not open, at least), along with its rectifying diode. After this, I don’t remember what prompted me to check the output rectifier for the 5VSB, but when I did, I found it was shorted:
Gigabyte GP-P450b - faulty 5VSB rectifier.jpg

Well, that explains the lack of 5VSB and any signs of life.
Unfortunately, no matter how many PSU parts (and part PSUs) I have, I couldn’t quite find a rectifier/diode that I felt comfortable using here. The diode really needs to be Schottky type with low V_f. Otherwise, at 3 Amps, the power dissipation can get a bit too high. And since most large diodes (>2A If_avg) I had were just regular fast-recovery type with V_f of 1V or more, I decided to try something a little more… “deviant”. I’ll let the pictures below do the talking.
Gigabyte GP-P450b - experimental 5VSB rectifier (1).jpg
Gigabyte GP-P450b - experimental 5VSB rectifier (2).jpg

^ Ghetto-mod-thread nominee of the week?
It’s simply an ON-semi 4813NGH MOSFET wired as a diode. According to its datasheet, it can withstand only 30V DC, which probably isn’t optimal, considering the original diode was rated for 45V. In terms of current, though, the body diode on this MOSFET can do up to 29 Amps - provided the junction is kept cool! I didn’t do any junction to case/tab calculations as I should have, but I figured the 14 AWG wire soldered to the MOSFET tab and the surface area of the PSU’s PCB may be able to provide enough cooling for an Amp or two. So if nothing else, I installed this “diode” contraption in the PSU to see how it would work out.
Gigabyte GP-P450b - experimental 5VSB rectifier (3).jpg
Gigabyte GP-P450b - experimental 5VSB rectifier (4).jpg

Surely enough, the PSU sprung back to life, even with this hackjob repair.

But now to see if my theory would hold true with the power dissipation: run some load tests on the 5VSB and see how hot this “diode” would get. I put my K-type thermocouple on the tab and started applying a load (via NiCr wire element) on the 5VSB. With just 1.1 Amp of current, the tab of the MOSFET was already sitting at a toasty 75°C – and that’s with the PSU PCB completely out of the case and exposed to room temperature, which at the time of this experiment was a rather chilly 18°C (64°F.) In summer, I know my house can easily hit 30°C (86°F), which is a whole 12°C higher. Add to that 2-3°C with the PCB installed back into the case, and I guesstimated the resulting temperature could easily hit 90°C on the MOSFET’s case… which means I’ll probably be running close to the thermal limits of the device. Not good! Therefore, it was time to improve/revise (improvise? ) things. No point in trying out higher loads if 1.1 Amp already made the MOSFET/diode this hot.

I considered soldering a penny on the tab of the MOSFET for a lowly-low cost heatsink solution of $0.01 … but didn’t feel like removing the MOSFET to do that. So instead, I settled on a piece of copper sheet I already had cut out for something else that I didn’t end up using. Rather than it sitting and collecting dust in my scrap bins, I figured this was a better use… and it allowed me to solder it to the MOSFET without removing it from the PSU.
Gigabyte GP-P450b - experimental 5VSB rectifier v2.jpg

I then proceed to do the same 5VSB load tests again. With 1.1 Amps of load, this time the MOSFET’s tab only got up to 55-56°C at the same room temperature – almost a good 20°C lower than before. With 1.5 Amp load, the temperature rose to about 68°C. And with 2 Amps of load, the temperature was 80°C… which is still very high. But that’s to be expected. After all, the typical forward voltage of the body diode for the 1348NGH MOSFET, according to the datasheet, was given as about 0.9 to 0.95V. Thus, at 2 Amps of power draw, the MOSFET’s body diode was likely dissipating around 1.8 to 1.9 Watts… so it’s normal for it to run this hot. Although I could easily pull 2.5 and 3 Amps of current from the 5VSB, I didn’t try it for any extensive amount of time, because the P_d of the MOSFET’s diode would have been too great and likely caused it to overheat. Therefore, 2 Amps is all I could do with my hackjob – good enough for now!

Thermal dissipation aside, the 5VSB performed admirably well (IMO) in terms of efficiency. With the 1.1 Amp of load (@ 5.08V output), my Kill-A-Watt registered 7.5 Watts of draw from the wall. That puts the efficiency at a little under 75%. With 1.5 Amps, the K-A-W showed 10.3 W, dropping the efficiency to slightly under 74%. And with 2 Amps of load, the efficiency was back around 74.5% again… so overall, the 5VSB seemed to float very closely to 75% efficiency overall (as far as the K-A-W’s accuracy goes anyways), which is very good. In contrast, most 2-transistor self-oscillating circuits I’ve tested seem to do no better than 50%... and often times hover around 30-40% (i.e. about half of what the 5VSB circuit in this Gigabyte PSU got.) Imagine if I actually used a proper Schottky diode! Its lower V_f would probably improve the efficiency even further.

I guess that means I should probably also get some Schottky diodes/rectifiers on my next parts order. Since I don’t know when that will be (maybe soon maybe not), I decided to close up the PSU with this “temporary” repair. Of course, the label was also modified accordingly.
Gigabyte GP-P450b - experimental 5VSB rectifier label.jpg

Besides, the next time I open it again, I will probably upgrade/replace the output caps too. I don’t really trust those YC caps. And the “ChnCap” (China Cap? ) – who’s heard of that brand before? Definitely recommend a recapping to anyone who wants to use this PSU long term. In my case, since the PSU is still pretty new, I’ll just run it as-is with its original caps and kludged 5VSB. If the PSU proves to work reliably well over time, I’ll recap it and fix up that 5VSB “fix”. The (revised) warranty on these PSUs is 3 years, so I imagine the dubious output caps will probably make it at least that far – especially with lighter loads, which most of my PCs are.

That being all said, the only two other things that worry me about this PSU are 1) the big primary Teapo cap being rated for 400V and 2) the PSU not shutting down with a low line AC input. With the former, a new good quality primary cap would probably cost at least $4-5. As for point 2) above, I performed the same type of low AC line tests / abuse as I do on all my other PSUs now. The Gigabyte GP-P450b here didn’t want to shut down, even when the AC line dropped to 75V AC. Instead, the output on the 12V rail dropped to 11.3V, which is out of spec. I didn’t check if the PG signal dropped, but I suspect it likely did, which is how that should be at least. Nonetheless, I’d rather see the primary-side APFC and main PS circuitry shut down when the AC dips below 85-90V. I didn’t run the PSU long enough with this low AC line to see if something will blow up or overheat on the primary. It surely would be an interesting experiment! But on the other hand, I’m also trying to keep things out of the landfill, so I’d rather keep this PSU operational for the time being. And that’s where it ends with this one so far – another dead PSU saved (for now.)

As time goes on, I’ll try to update the thread if anything happens/changes to this PSU.
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Old 01-26-2022, 06:32 AM   #3
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

It's the same series but a completely different platform so not related to your issues.
Still the failure to shutdown with low mains is a bit "how you're doing"
https://www.youtube.com/watch?v=aACtT_rzToI
https://www.youtube.com/watch?v=Xts3pvbcFos
https://www.youtube.com/watch?v=7JmPUr-BeEM
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Old 01-26-2022, 06:40 PM   #4
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

The CM6805 switch frequency is fixed, 67.5KHz. It uses pulse width modulation rather than phase modulation.

My very first impression from the pix was, "Where's the beef?!" The heatsinks, main transformer, coupled output inductor, and output caps all seem marginal or under-sized. I don't think I'd run that more than 350W-400W continuous.
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Old 01-29-2022, 06:00 AM   #5
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

Quote:
Originally Posted by momaka View Post
Repairing computer switching power supply
Very nice repair I have one question for you and that is this what do you think cause this to fail

“ After this, I don’t remember what prompted me to check the output rectifier for the 5VSB, but when I did, I found it was shorted:”
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These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

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All of these had CAPs POOF
All of the mosfet that are taken out by bad caps

Last edited by sam_sam_sam; 01-29-2022 at 06:04 AM..
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Old 01-30-2022, 01:35 AM   #6
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

Quote:
Originally Posted by Per Hansson View Post
It's the same series but a completely different platform so not related to your issues.
Still the failure to shutdown with low mains is a bit "how you're doing"
https://www.youtube.com/watch?v=aACtT_rzToI
https://www.youtube.com/watch?v=Xts3pvbcFos
https://www.youtube.com/watch?v=7JmPUr-BeEM
Yeah, I saw these way back this summer/spring, when the issue cropped up. In fact, this was probably the other big reason to buy this Gigabyte PSU, despite being a lower-end model and possibly quite different.

But it's interesting how they blow up - usually after shutting down properly from an over-load. FWIW, I think MEIC just set the over-power protection too far for all of their PSUs, and that's what might be causing the issue here. In fact, after watching some of the above videos and following a few links and whatnot in the comments, I stumbled upon a video by another popular tech reviewer who even showed the component changes Gigabyte (or rather MEIC) made on the newer revisions of the PSUs to stop them from blowing up - and it worked.

So it may be possible to actually fix this by changing the OPP level (likely with a few SMD resistors for the PWM controller on the primary side.)

Sorry I don't have a link to the video now. It's on my other PC that I use for YT. If anyone is interested, I'll dig it out and post it. In fact, I might do that anyways, once I open the PSU again for a recap sometime down the road.

Quote:
Originally Posted by PeteS in CA View Post
The CM6805 switch frequency is fixed, 67.5KHz. It uses pulse width modulation rather than phase modulation.
Cool, thanks for posting that.
I was too lazy to download and open the CM680 data sheet to see what's going on.

Quote:
Originally Posted by PeteS in CA View Post
My very first impression from the pix was, "Where's the beef?!" The heatsinks, main transformer, coupled output inductor, and output caps all seem marginal or under-sized. I don't think I'd run that more than 350W-400W continuous.

Probably even 400W continuous would be pushing it with those heatsinks and secondary-side components. I think 350 Watts is about right.

Quote:
Originally Posted by sam_sam_sam View Post
Very nice repair I have one question for you and that is this what do you think cause this to fail
Thanks!

Good question. I am not entirely sure, TBH.
The seller said he got the PSU non-working. So it must have been like that from whoever had it before him... or perhaps that's how it came new, even.
Given the substantial number of negative reviews on NewEgg that said they got a DOA unit also... I can only assume that either this happened at the factory (perhaps during Hi-Pot/Burn-in testing) or there's something inherently wrong with the 5VSB's rectifier. In case of the former, it could be that the factory was testing their PSUs a little too hard, and that's what damaged the 5VSB's rectifier. And in case of the latter, it could be that the rectifier itself is a bad part. Actually, I'm more inclined to think this is the issue here. Everywhere I looked for an "SR5t45" diode/rectifier datasheet, I couldn't find one. The closest I came to was one of those Chinese IC online order websites, which is how I found out the SR5t45 is supposed to be a 5 Amp, 45V Schottky rectifier.
SR5t45 (5 Amp, 45V, schottky diode).jpg

^ And while the above image (screenshot of the website) would have you believe they have a link to the data sheet, clicking on the link lead to the wrong datasheet on a different website.

Thus, it could be that this rectifier's manufacturer is making shoddy parts.

In any case, I imagine something like an SB540 Schottky rectifier (5A, 40V) should work fine as a replacement (a rather common/standard part even, for most PSUs that have a 5VSB rated at >2.5 Amps.) Even SB340 might be OK... and probably less lossy than my fix. Thus, I'll probably end up getting an SB540 or something very similar when I feel like fixing this properly again next time.
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Old 01-30-2022, 04:19 PM   #7
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

Excellent presentation and repair momaka.

This psu reminds me of the Coorsair VS platform (the CWT based one, not the newer, that they switched OEM).

Everything is tiny and it is obvious they tried to save every penny they could before the unit was considered gutless and could not do its rated current, even for some minutes.

On the other hand, the APFC coil is much bigger than the VS platform and also on the VS-450W unit, the primary cap is even smaller than the primary here: 1x Teapo LH, 400V, 270 uF and it's not Teapo but total crap brand, if I remember correct Aishi or something like that.

Anyway, enough with the off topic about the CWT platform.


Quote:
Originally Posted by momaka View Post
But it's interesting how they blow up - usually after shutting down properly from an over-load. FWIW, I think MEIC just set the over-power protection too far for all of their PSUs, and that's what might be causing the issue here. In fact, after watching some of the above videos and following a few links and whatnot in the comments, I stumbled upon a video by another popular tech reviewer who even showed the component changes Gigabyte (or rather MEIC) made on the newer revisions of the PSUs to stop them from blowing up - and it worked.

So it may be possible to actually fix this by changing the OPP level (likely with a few SMD resistors for the PWM controller on the primary side.)

Sorry I don't have a link to the video now. It's on my other PC that I use for YT. If anyone is interested, I'll dig it out and post it. In fact, I might do that anyways, once I open the PSU again for a recap sometime down the road.
This is the video with the changes in the protection circuit:

https://www.youtube.com/watch?v=Edv3UcJw0nk
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Old 02-05-2022, 12:18 AM   #8
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

Quote:
Originally Posted by goodpsusearch View Post
This is the video with the changes in the protection circuit:

https://www.youtube.com/watch?v=Edv3UcJw0nk
Thank you!

Yes, this is the exact video I was talking about. Good reference for anyone who has one of these PSUs and wants to thinker with the configuration resistors on the PWM controller. I'll probably look into mine the next time I have it open.
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Old 04-09-2022, 04:12 PM   #9
virgiliodc
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Default Re: A Dead/DOA Gigabyte GP-P450b 450W ATX PSU

Hi, i have successfully repaired my Gigabyte GP-P450b thanks to your post. It have had the same demaged schottky diode, i have replaced with a 5A 100v schotty diode. Thank you!!
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