Question PSU tests out OK but doesn't power mobo?

[huesmann]

Gotta PC with a Thermaltake TR2 RX-550 PSU powering an 11-year old mobo and CPU. Yesterday, the computer wouldn't turn on. I pulled the PSU connectors (24- and 4-pin), jumpered the 24-pin, and tested the voltage across the various pins. Everything tested out as expected—12V, 5V, 3.3V.

So, I assumed a mobo failure and went to MicroCenter and picked up a new mobo/CPU/RAM. But those didn't power up. I found an old case with a generic PSU and pulled it to test with the new mobo—it turned on. So clearly the Thermaltake PSU has gone bad and I'm gonna have to make another trip to MicroCenter.

Good opportunity to upgrade the ancient (but still working well) hardware anyway, but I'm just curious how the Thermaltake can test good but not work. Any ideas?

TIA.

 

[fralexandr]

Just because the voltages are fine doesn't mean it can put out enough current/Amps. The voltage test is a relatively easy test, but it only tests half of it. Sure, it can do those voltages at the <<1 Amp the meter tests it at. To get a better picture you'd have to also do a load test, like what the PSU reviewers do to determine efficiency, ripple, etc. That requires either a separate computer or expensive specialized equipment that most people won't have access to.

The multimeter voltage test is an alternative for people without spare parts to quickly determine if the psu is completely dead.

Fyi, the TR2s were not quality power supplies. Hardwaresecrets tested two 750w units and neither were able to output the rated load. They both failed with excessive ripple at 75% load (voltage off by >10%).

Thermaltake TR2 RX 750 W Power Supply Review - Hardware Secrets

TR2 series from Thermaltake is targeted to users on budget. Let’s see if the 750 W model from this series is a good option.

hardwaresecrets.com

 

[mindless1]

Yes it's about load, or could be that your 5VSB rail has failed. Did you measure it while hooked up to the system?

What I'd do next is (unplug it first ) pop the PSU open and inspect for vented capacitors, domed tops or leaking residue, primarily the caps at the output wire area and the 5VSB area. If the big primary side cap looks domed but has a plastic sheet on top, that can be normal and those caps tend to far outlast the others on the output side.

 

[maluckey1]

I recently had a Corsair TX-750 that was running my gaming rig during a lightning storm (dumb...I know). The power browned, blinked a few times, then went out for a second or two. Lights came back on and everything seemed fine. I went to bed. In the morning, I noticed my overclock wasn't at all stable, so I bought a Dr.Power II, to test the PSU, and found that it was bad.

I'm just sharing to show that a bad PSU can start and run a system. In your case, likely a bad PSU, so it's time for a new one.

FWIW, Corsair sells from their website, and shipping is FAST! I got my RM 850X v2 in just three days.

M

 

[huesmann]

Yup, already replaced it. Got one from Amazon with same-day shipping, which was really about 4-hour shipping!

 

[mindless1]

You kids and your disposable society mind-set.

If you have a soldering iron and a multimeter, and the will to use them, there is no need to trash an entire PSU for some discrete component failure.

Putting it in context, do you send a car to the junkyard if the water pump fails, or replace your refrigerator if the light bulb goes out, or trash your bike if it needs new tires?

Yes you have to learn how to repair electronics, same as learning to screw in a light bulb. It's a very handy skill in this era, electronics aren't going away, more like being integrated into things that didn't really need them, then becoming the early failure point.

You can pay a premium (x2 in the covid era) for a high quality PSU, or when yours fails, you can spend about $15 and have it last longer for the 2nd tour of duty than the first, even 3X as long if you pick parts wisely. This ignores AC mains power surges, they are an unpredictable variable.

I'm just sayin', I can take a dead PSU, put $15 worth of parts into it, and make it last more than twice as long as a brand new $60 PSU. Of course there are outliers but my success doing this has been pretty rewarding.

 

[VirtualLarry]

You kids and your disposable society mind-set.

If you have a soldering iron and a multimeter, and the will to use them, there is no need to trash an entire PSU for some discrete component failure.

Putting it in context, do you send a car to the junkyard if the water pump fails, or replace your refrigerator if the light bulb goes out, or trash your bike if it needs new tires?

Yes you have to learn how to repair electronics, same as learning to screw in a light bulb. It's a very handy skill in this era, electronics aren't going away, more like being integrated into things that didn't really need them, then becoming the early failure point.

You can pay a premium (x2 in the covid era) for a high quality PSU, or when yours fails, you can spend about $15 and have it last longer for the 2nd tour of duty than the first, even 3X as long if you pick parts wisely. This ignores AC mains power surges, they are an unpredictable variable.

I'm just sayin', I can take a dead PSU, put $15 worth of parts into it, and make it last more than twice as long as a brand new $60 PSU. Of course there are outliers but my success doing this has been pretty rewarding.

You do "cap fixes" on monitors? I have an Acer Nitro 4K UHD 28" (27"?) monitor, bought it refurbished from AcerCertified on ebay.

Well, it has a "rolling grey bar" that floats around on the screen, kind of like a sync signal issue. But it only pops up once the monitor has been on for 5 minutes.

I think *maybe* a cap is failing, or something is overheating.

 

[mindless1]

^ Sadly, I have replaced the caps on at least 70% of TVs and monitors I've owned, it's the #1 failure point, BUT I buy value priced gear... sometimes... I've got a nice Sammy TV that has outlived two other less prestigous brands but this was back when 1080p was expensive. Prices dropped and component quality had to necessarily follow.

However, I don't know anything about a rolling grey bar, usually when the caps go it fails to turn on, or shuts off within seconds once the capacitor decay progresses.

If it is out of warranty, time to pop it open and see. Almost always a bad cap will be domed, if not leaking electrolyte too. However in some cases, a cap failing bad enough before you notice it, in a SMPS regulation subcircuit (where they most often fail) can damage an IC downstream of it. Best to always check at the first sign of a problem.

 

[huesmann]

You kids and your disposable society mind-set.

If you have a soldering iron and a multimeter, and the will to use them, there is no need to trash an entire PSU for some discrete component failure.

Putting it in context, do you send a car to the junkyard if the water pump fails, or replace your refrigerator if the light bulb goes out, or trash your bike if it needs new tires?

Yes you have to learn how to repair electronics, same as learning to screw in a light bulb. It's a very handy skill in this era, electronics aren't going away, more like being integrated into things that didn't really need them, then becoming the early failure point.

You can pay a premium (x2 in the covid era) for a high quality PSU, or when yours fails, you can spend about $15 and have it last longer for the 2nd tour of duty than the first, even 3X as long if you pick parts wisely. This ignores AC mains power surges, they are an unpredictable variable.

I'm just sayin', I can take a dead PSU, put $15 worth of parts into it, and make it last more than twice as long as a brand new $60 PSU. Of course there are outliers but my success doing this has been pretty rewarding.

If a car cost under a hundred bucks, I guarantee people would trash them if the water pump failed.

That said, I'm happy to have you direct me in repairing the PSU—it has been replaced, but not yet discarded. A cursory glance did not indicate any burst caps.

 

[maluckey1]

If a car cost under a hundred bucks, I guarantee people would trash them if the water pump failed.

That said, I'm happy to have you direct me in repairing the PSU—it has been replaced, but not yet discarded. A cursory glance did not indicate any burst caps.

Great attitude It's true that PSU's aren't expensive compared to televisions and the like.

It's never a bad thing to take a poke at learning. I diagnosed and repaired several Adcom amps and preamps over the years. I also built several guitars and repaired two guitar amps (1962 stuff with germanium transistors). The hard part for me was understanding how to read schematics. Once learning that, I branched out into automotive electronics, which comes in handy with my Volvo (notoriously picky electronics).

If nothing else, you spend the time doing something interesting, that may someday pay you back.

 

[mikeymikec]

nvm

 

[huesmann]

That said, I'm happy to have you direct me in repairing the PSU—it has been replaced, but not yet discarded. A cursory glance did not indicate any burst caps.

A caveat: note that in my original post I indicate that the voltages all tested out as expected. I do not have the test equipment that fralexandr mentions for more detailed analysis. Pretty much the only way to test it would be to connect it to the old mobo and see if the CPU fan powers up.

 

[mindless1]

Considering lethal voltages inside a PSU, I'd suggest it be more of a long term goal. I started learning electronics working with low voltage projects and that's the better way to start, if a visual examination with it unplugged does not indicate anything.

Besides basic electronics principles, there are youtube videos about PSU diagnosis and repair, which are far more comprehensive than is reasonable for a forum post.

However with it producing voltage the areas of most interest would be capacitors, transistors, diodes, and cold/broken solder joints, but outside a shotgun approach that replaces on odds, it does take a load and measuring where the voltages drop, since in this case it does power on.

 

[Iron Woode]

Yes it's about load, or could be that your 5VSB rail has failed. Did you measure it while hooked up to the system?

What I'd do next is (unplug it first ) pop the PSU open and inspect for vented capacitors, domed tops or leaking residue, primarily the caps at the output wire area and the 5VSB area. If the big primary side cap looks domed but has a plastic sheet on top, that can be normal and those caps tend to far outlast the others on the output side.

Bad advice.

do not open up a PSU. You can get a shock big enough to kill you.

Just through the PSU away.

 

[mindless1]

^ Lots of ways someone can die... don't drive, might wreck, don't eat, it might be poison, etc.

Once unplugged from mains AC there are two separate mechanisms at work to drain the PSU to save levels. One is the bleeder resistor(s), and the other is the 5VSB circuit on ATX era and newer.

You do have to be mindful of what you're doing if probing live circuits, just like you have to be mindful not to stick your fingers in a blender when making a smoothie.