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Old 09-01-2005, 09:19 PM   #1
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Question Tyan Trinity KT S2390 - VRMs? Capacitors?

A friend of mine was going to toss out a Tyan Trinity KT S2390 board. It stopped booting up one day, and he later ended up buying a new motherboard and CPU. The computer store told him that his CPU had gone bad and they said it was likely that the board fried the CPU since the heatsink and fan were all properly installed.

I should say that I've successfully recapped 3 mainboards so far (with Rubycon MBZ's) - two Abit KT7A's and a Soyo 7VEM, which all seem to be working better than they did when brand new.

I've looked at this Tyan board, and none of the capacitors seem *visibly* bad. None of the capacitors are bulging, none are vented, none seem to be leaking beneath the capacitors either.

The biggest capacitors are 1500uf 10V, with a brand I cannot identify... the only branding on these caps seems to be the letters "LE" contained within a rectangle. The board is then littered with a bunch of Canicon caps - 1000uf 6.3V. The rest are 470uf Rubycons and other smaller value caps.

I'm really hesitant to put a good working CPU and RAM in this board to "test" it, if there is a good chance that the board could fry it. I'm also hesitant to spend the time replacing ALL the capacitors on the board, only to find out that the caps aren't the problem.

I powered up the board without any CPU and RAM installed. Of course, no beeps or anything, but it powers up.

The board has 6 VRMs near the CPU, sort of scattered about. I used a digital multimeter to check the voltages at both sides of the VRMs to ground. Out of the 6 FETs, I was able to measure 5 volts on one side only of two FETs. The other side read 0V, and the other 4 VRMs read 0V on both legs.

If no CPU or RAM is installed, should I expect to read no voltage on both sides of 4 of these VRMs?

Of the two VRMs that read 5V on 1 side, would I at least expect to read, for example, 3.3V or some other voltage on the other side?

Would capacitors that are leaky or otherwise faulty, cause the VRMs to not function at all?

Would it make sense as an initial diagnostic, to replace the capacitors near the CPU and then try testing the VRMs again?

Would it make sense to try replacing all 6 of the VRMs wholesale and test again? I am not familiar with VRM circuitry, so I don't have a clue if these VRMs are all supposed to be fed with 5V, or 3.3V or 12V or if they are cascaded or what.

I also tried checking the impedance between each side of the VRM and various ATX power supply pins (5V, 12V, etc). It was inconclusive because the impedance seemed to increase as if a capacitor were being charged up.
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Old 09-01-2005, 09:42 PM   #2
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Default Re: Tyan Trinity KT S2390 - VRMs? Capacitors?

fire it up and measure across the large caps nearest the cpu.are you sure the cpu is bad?i got a pile of so called bad cpu's here at a shop i recap to testing and found only 2 of the 17 were bad.
got a p4 ee and 2 1.4 tulatin-s in the lot.
a pic of those le caps would be nice.canicon is a known offender.
oh and a shorted cap on the vrm output will shut it down.
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Old 09-01-2005, 11:07 PM   #3
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Default Re: Tyan Trinity KT S2390 - VRMs? Capacitors?

Here are the pics...

No I'm not sure the CPU is toast, but it has been misplaced, or so my friend says.

I do recall trying to diagnose it months ago, that at one point I could swear I could smell a faint smell of something burning, and I did think at the time that the CPU heatsink, for a Duron 700, was unusually hot! So I would not be surprised if the CPU was in fact toast, and that's also why I am reluctant to pull off a good working CPU in one of my other machines to test it!

OK, I checked voltages across various caps around the motherboard.

All of the caps near the CPU report 0V, although this is with no cpu installed.

Caps near the AGP slot read 3.4V. Caps at various points around the motherboard e.g. near the RAM slots and between the PCI slots read 3.4V. Some caps read 5.1V, and some smaller size caps rated 16V and 25V read 11.95V as expected.

So basically no power to caps near CPU, but is this dependent on a CPU being present?

Attached Images
File Type: jpg LEcaps1.jpg (87.2 KB, 226 views)
File Type: jpg LEcaps2.jpg (87.8 KB, 225 views)

Last edited by willawake; 09-02-2005 at 04:53 PM..
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Old 09-02-2005, 11:09 AM   #4
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Default Re: Tyan Trinity KT S2390 - VRMs? Capacitors?

That's a reasonably good sign; the fets aren't a dead short.

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Old 09-02-2005, 12:43 PM   #5
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Default Re: Tyan Trinity KT S2390 - VRMs? Capacitors?

So... what does that mean... if they're not shorted... then it may be safe to plug a CPU in there?
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Old 09-03-2005, 04:04 PM   #6
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Default Re: Tyan Trinity KT S2390 - VRMs? Capacitors?

I took a chance and plugged in a known working CPU I had, a Duron 1.1 Morgan core. The Morgan core CPUs aren't officially supported on this board.

I was surprised when I powered it on and heard some error beeps - i.e. missing RAM! The voltage across the caps near the CPU read 1.78V which is not too far from the 1.75 spec of the Morgan core.

I put in a stick of RAM and an AGP video card and the board boots, recognizing this supposedly unsupported CPU as an Athlon 1.1GHz.

Three different sticks of PC133 RAM are giving memory errors in Memtest86... so perhaps the capacitors on the board may really be bad, so time for a recap and see!
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Old 09-03-2005, 11:23 PM   #7
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Default Re: Tyan Trinity KT S2390 - VRMs? Capacitors?

After a couple of hours of use, I heard "click click" and the machine froze, then I got that lovely burnt electronics smell.

I didn't see any components with any burn marks, so I decided to recap the board and try again. After recapping the board, the machine booted up fine, all the voltages seemed great. I was constantly monitoring the Vcore voltage, which was at 1.79V (even though BIOS says 1.83!). Then the machine froze again and I noticed at that moment that the Vcore dropped to 1.4V or so.

After resetting the machine, it booted up into Windows fine and even ran a single run of Sandra burn in successfully.

Then after a couple of minutes of surfing, the same thing happened, click click, Vcore dropped to 1.4V, and the machine froze.

This time I waited a bit, as I wanted to see if I could locate the component that was burning up.

Well one of the VRMs apparently got hot enough to scorch the board below, and caused the top layer of the board to separate...

So that seems to be the end of the story. The damage to the board is significant enough that I'm not bothering to attempt repair, on what is essentially a free motherboard.

I pulled off all the replacement Rubycons for future use. It's funny how quickly they come off the board when you're not concerned about preserving the foil lining and the traces of the board!!
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