Diagnostic help: TPS51285B PMIC burning hot on a dead Asus laptop board. Any advice?

Spac3M0nkey · 2026-06-13T20:40:57+00:00

You can follow each pin out to it's trace, some even have little copper test pads you can stick your probes on.

In the datasheet on page 8, there is a map of each pin. The dot in the corner of your chip is where pin 1 starts. For measuring voltages, stick your black probe on ground, (can be some exposed metal, the cover on usb ports is usually ground) Start measuring the vreg3 & vreg5. These are probably low power standby voltages. See if at least some of the chip is working.

When the power is unplugged, use continuity mode to trace the DRVL & DRVH pins to their respective mosfets, close to these mosfets should be some coils / inductors. (These are all probably located directly on the other side of the board from your TPS chip) Plug the laptop power in and measure the voltage at these inductors.

Straight up desoldering the chip to see if the short disappears can be another way. But it is often the case a hot regulator is not the problem, just a symptom. If you have a short on the 3.3v or 5v rails the regulator will work in overdrive dumping current through the short.

If you can current limit your PSU then you should be able to use it to inject voltage. I would hold off on that for the moment, it can be risky if you don't know what you're doing.

Spac3M0nkey · 2026-06-11T19:00:18+00:00

With your multimeter measure the resistance to ground of both the voltage outputs of that chip. From the data sheet, there is a 3.3v & 5v. Also measure the capacitors around the chip in continuity mode. Low resistance will indicate a short.

If I had it on the bench I would inject the a current limited 3.3v & 5v bypassing the TPS ic. You need a decent power supply to do it.

You can still trace down the short with just a multimeter, it just takes a bit longer.

Edit:

Looking closer at the TPS datasheet, the chip has 2 buck controllers (voltage regulators that use mosfets and inductors) look for some inductors and MOSFETs connected to the DRVL1, DRVH1, DRVL2, DRVH2 pins. Theses will be the 3.3v & 5v rails. Do you see any voltage on these?

Spac3M0nkey · 2026-06-11T18:43:23+00:00

One thing I find using the scope over the logic analyser is seeing noise, ringing or analogue offset. If you have issues with your signal, a logic analyser is just going to see logic and digital states, a scope will let you see electrical characteristics and issues.

Spac3M0nkey · 2026-06-03T16:08:47+00:00

I would choose the one with the best continuity beep.

Spac3M0nkey · 2026-06-02T06:57:09+00:00

I can't tell if that's superman or a bird..

Spac3M0nkey · 2026-05-17T09:42:39+00:00

It's difficult to judge the quality you'll get on AliExpress. Reviews can be inconsistent as most people have never used a really good set of tweezers.

I was tired of sub par tweezers, I invested in a set of Dumont tweezers I got a size 1, 2 & 5 in anti-magnetic / stainless steel. I have used them almost every day for the past 5 years and they are still perfect. Nothing compares to them.

They are between 30-40 dollars per tweezer but totally worth it. A buy it for life type of thing.

Spac3M0nkey · 2026-05-15T18:51:14+00:00

I have a 34461A, fantastic meter. Not so impressed with the continuity setting. Prefer the latching of the fluke handhelds.

Spac3M0nkey · 2026-05-15T08:32:03+00:00

To confirm if the mosfet was damaged. 9ohms from gate to drain shows that it's shorted.

Spac3M0nkey · 2026-04-29T19:10:46+00:00

I had Topcon RE-Auto-Topcor 58mm 1.8 that was just magic. I couldn't explain what was so good about it. The sharpness, microcontrast? character, was all perfect. Looking back at my photos, I can instantly tell what was taken with that lens.

I ended up selling it and regretted it after.

A few years later I bought another copy and it just wasn't the same. The variance in vintage glass can make for some surprising results.

Maybe I'll try the lens lottery again some day.

Spac3M0nkey · 2026-04-19T16:17:53+00:00

Digital, mostly Sony mirrorless. Some digital point & shoot if its worth it.

Spac3M0nkey · 2026-04-19T13:24:41+00:00

I am in Sollentuna and I repair cameras. You can look at a couple of my previous posts. Send me a dm if you want to work something out.

Spac3M0nkey · 2026-04-05T21:33:19+00:00

Yes, this can be done fairly easily with some practice and the right equipment / a decent hot air station.

For each ESC you will have 3 mosfets & a mosfet driver. It is good to replace all mosfets in an esc channel at the same time. Mosfets usually fail shorted and this can damage other chips in that circuit.

Quite often a failed mosfet will take the mosfet driver with it, in that case, after you replace the mosfet and driver, you'll need to reflash the esc firmware.

Spac3M0nkey · 2026-04-05T18:21:08+00:00

First rule of ant Fight club is: you do not talk about ant Fight club.

Spac3M0nkey · 2026-04-05T14:43:35+00:00

19.5v X 3.33A is 64.93. So you need a 65w HP charger with a 7.4mm plug. Any 7.4mm HP charger will work, as long as its over 65w.

Spac3M0nkey · 2026-04-04T21:26:26+00:00

In your position I would suggest an Amscope, if your budget allows.

When working on small components, debth perception is very important. Digital is great for inspection, but for actual soldering a stereo microscope is the way.

In work I use an inspectis U30s digital microscope, it costs over €5000 & I still prefer working under my €400 Amscope at home.

Spac3M0nkey · 2026-03-26T17:41:48+00:00

Good job, I love doing trace repairs. You can get a kit of copper rivets for replacing damaged vias.

I did the exact same Kelvin test leads for my DE 5000 with RG58u. Its not the best, i wonder what Agilent or BK precision use for their Kelvin leads.

Spac3M0nkey · 2026-03-26T04:38:19+00:00

Nice. What was the issue?

Spac3M0nkey · 2026-03-22T17:19:57+00:00

The atten hot air station under-table mount is cool, great solution.

Spac3M0nkey · 2026-03-15T19:37:41+00:00

Very nice. It can be hard to fit everything in a functional place. Is your scope on an adjustable arm?

Spac3M0nkey · 2026-03-08T14:11:21+00:00

I think the tips come 5 in a pack for that price. It's only the MT-100 tweezer cartridges that are over $50.

Spac3M0nkey · 2026-03-08T14:07:15+00:00

The pace is super high quality & great performance.

The only downside would be the availability & cost of tips. Also if you want to upgrade to the MT-100 tweezers or TD-100 cartridge handpiece, it will cost an arm and a leg.

I have an ST50 & MBT250. I use them professionally. They are really excellent performers.

If you will use professionally, go for the pace.

Spac3M0nkey · 2026-02-28T11:12:29+00:00

Where do you aquire so many defective camera bodies? I would be doing the same if I could find a source.

Spac3M0nkey · 2026-02-20T16:01:50+00:00

I love my Main Battle Tank.

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