Bad oscons in notebook?

[Rainbow]

My DTK FortisPro TOP-5A notebook has some problems recently. When I turn it on, it boots fine. But if I run firefox and click through the menus, it hangs with screen turning white (LCD panel powered off). If I boot Linux and run OpenOffice.org, it reboots. But after if I leave it for a minute or two to "warm-up", it works fine - no hangs, no reboots, everything stable.
First I thought that it's caused by CPU voltage too low - I was running P166MMX at 1.8V only. So I increased the voltage to 2.5V (there are DIP switches for this and DTK sent me the settings) and the problem appeared to be solved. But today, it hanged again. So I increased the voltage to 2.8V (the default for Pentium MMX CPUs) - and it did not solve the problem. It hanged in Firefox with white screen. After it warmed up, it works fine again (even running prime95).
I also remember that sometimes, the LCD was not initialised properly on power on - screen was dark gray but it booted. Suspend/resume fixed that. The weird thing is that this problem disappeared recently.

There are many tantalum caps on the board and also some oscons. I wonder if those oscons are bad? And what can be used as replacement?

[Rainbow]

Re: Bad oscons in notebook?

The big OSCONs 220uF/10V are used for TV-output only. VCore regulator is tantalum-only except for one OSCON 15uF/25V on input...

[gg1978]

Re: Bad oscons in notebook?

What brand are the Oscons?? I know kc8adu had a picture of a board with a blown one out of a laptop, but it was obviously blown.. I doubt the Oscon's are the problem though, but you could check by unsoldering them and putting them on a capacitance/LCR meter, that would show the capacitance, dissipation, and ESR.

As for the CPU, is it a desktop chip or an actual notebook CPU?? I suppose a P55C is low power enough to go in a laptop with no thermal issues. It was my impression that Intel had a special notebook revision of the P55C that went all the way to 266Mhz.


You can check Vcore with an oscilloscope to see if the Vcore is being filtered correctly.


I think it's probably a memory/motherboard issue.

[Rainbow]

Re: Bad oscons in notebook?

They're Sanyo. They're connected to the TV-out port and nowhere else so they're not a problem.
CPU is standard desktop one. If I had an oscilloscope, it would be great. I added Rubycon 2200uF/6.3V cap to the VCore and it did not change anything - it still hanged after a while.

And now I know what's wrong. A transistor in CPU VCore regulator blew after a couple of power cycles (quiet pop and only black screen). Again. It's third one. When I bought the machine, that transistor was bad - so the VCore was absent and there was non-MMX Pentium (P54C) installed - it runs from 3.3V so it worked fine. Then I replaced the transistor (and also one bad diode) and replaced CPU with this P166MMX. It worked great about year and a half until the transistor and diode blew again. The last days before that, it was unstable like this. Then I replaced the transistor and diode and now it failed again after about a month (only the transistor this time, the diode seems to be OK).
The transistor is SMD, marked 1P - MMBT2222A. Maybe there's something other wrong that causes the transistors to fail or it's a bad design. I'll probably replace it with something higher-rated or put 2 of them in parallel.

[Rainbow]

Re: Bad oscons in notebook?

And some more bad news. Replaced the transistor and it works again. But the instability persists.
I've tried P233MMX at 166 - no change. Then K6-2/200 at 166 - it rebooted instead of hanging. And there was some interference on the LCD when the CPU was loaded - and also the 3.3V was only about 3V! So maybe there's something wrong with the 3.3V supply.
I wish I had a scope...

[Rainbow]

Re: Bad oscons in notebook?

I have to use the notebook again and it drives me crazy.
It boots just fine. It can even run prime95 without any problems! But the moment I unpack tar.gz archive in Linux, it crashes after a while. It also crashes when updating or installing Firefox in Windows.

[gonzo0815]

Re: Bad oscons in notebook?

Tantalum caps are prone to fail after some years, not only eleectrolytic ones. In the inputfiltersection there are mostly elektrolytics or oscons due to the high ripple current tantalums can`t sustain. The tantalums are probably used as outputfilter, that means on the cpu side. And the descripton of the symptoms are sounding for a bad outputfilter.

[Rainbow]

Re: Bad oscons in notebook?

I hooked a meter to 3.3V line and ran Firefox setup. It was around 3.3 - 3.37 all the time, jumping to 3.39V when it crashed - I think it should be more stable (it's probably even worse as the multimeter is too slow). The weird thing is that the moment it crashes, the battery charging LED turns off.

[Per Hansson]

Re: Bad oscons in notebook?

Well, 3.5v would be the highest the spec allows for the 3.3v line, and 3.17 the lowest, So I think you are fine... It would help to have a look on the board with a scope though... Maybe you have excess ripple current...

[Rainbow]

Re: Bad oscons in notebook?

Too bad I don't have a scope. I'll try to add another Rubycon to 3.3V line.

[Rainbow]

Re: Bad oscons in notebook?

So it's probably 5V line. Figured out that heavy disk usage resulted in reboot. Turning off DMA helped for a while - as it slowed down the transfer rate and thus consumption. However, it's getting worse and yesterday I had problems to boot it up even without DMA.
I remember that there is a silver SMD electrolytic cap on the power board - so I'll test if it's on 5V line and maybe add new cap in parallel.

[kc8adu]

Re: Bad oscons in notebook?

check those smd lytics too.
been seeing lots of them bad lately.
been getting samsung touch lcd's from strongarm robots with every last smd cap open.
using tants to replace them.these are a little over 1 year old!