Author Topic: Broken IC on old Pentium 2 motherboard  (Read 6170 times)

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Offline spilihps

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Broken IC on old Pentium 2 motherboard
« on: October 16, 2019, 07:06:48 pm »
Hello!

So i have had an old P2 pc to play around with some old software. And tonight when i went on and started it up, i could hear a loud pop from inside the PC.
First i thought it was the PSU, but it was still running and all voltages checked out fine. Took it apart to investigate the motherboard, and found this IC that had a chunk blown away.
Please see the attached image.

There is not much info that i could find with a quick google search. It seems to be a over-current protection IC.
Got any ideas why this happened? Could it be just the IC itself or some other problem?
I did replace all electrolytic capacitors on the board when i took it out of storage. Been running fine for about 2 months now..

Possible replacement chips?
 

Offline fzabkar

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Re: Broken IC on old Pentium 2 motherboard
« Reply #1 on: October 16, 2019, 07:22:52 pm »
www.electroscheme.ru/datasheet/AIC/AIC1569.PDF

Check the +12V supply from your PSU, and the two nearby MOSFETs.
 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #2 on: October 16, 2019, 08:08:14 pm »
Thank you very much for your input.

The two MOSFETs are not a dead short when i measure them in circuit at least. Have to pull them to be sure they are okey though.

The +12v rail measures fine, however i cannot be sure if it had a "spike" of some sort?

It seems that the AIC1569 is not available for purchase anywhere, however the one that is referred as compatible "HIP6004" is on ebay.
Seems like its a drop in replacement?
 

Offline Rasz

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Re: Broken IC on old Pentium 2 motherboard
« Reply #3 on: October 16, 2019, 08:59:12 pm »
this chip blowing up can mean 5V went into CPU
Id triple check those power transistors, and the diode, and measure if CPU is not a dead short now
HIP6004 will be fine
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Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #4 on: October 16, 2019, 09:27:21 pm »
this chip blowing up can mean 5V went into CPU
Id triple check those power transistors, and the diode, and measure if CPU is not a dead short now
HIP6004 will be fine

Thanks for your help!

well thats no good. especially if its designed to protect it  :-//

I can remove the transistors tomorrow to check their functionality, however, as they sit right now in circuit, they are not shorted atleast.
Will also check the diode. Not really sure were to check if the CPU is dead short though?

The question is if these chips fail by themself or if there were something else that made it pop?
 

Offline fzabkar

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Re: Broken IC on old Pentium 2 motherboard
« Reply #5 on: October 16, 2019, 10:01:11 pm »
The junction of the two MOSFETs connects to a coil, and this coil would connect to the CPU's core. So measuring the resistance between the coil and ground should tell you if the core is shorted.

See the application circuit on page 2 of the datasheet. Vout is Vcore.
 

Offline amyk

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Re: Broken IC on old Pentium 2 motherboard
« Reply #6 on: October 17, 2019, 01:17:55 am »
 

Offline Rasz

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Re: Broken IC on old Pentium 2 motherboard
« Reply #7 on: October 17, 2019, 02:56:44 am »
especially if its designed to protect it

its not, primary function is variable voltage buck converter controller/driver, secondary is monitoring
Quote
PGOOD and OVP comparator circuits use this signal to report output voltage status
there are no protections without outside circuity like
Quote
Built-in over-voltage protection triggers an external SCR to crowbar the input supply.

The question is if these chips fail by themself or if there were something else that made it pop?

Sometimes things just die, but external cause is more likely. Either big spike on 12V rail, or maybe one of the mosfet gates blown/leaking back to the driver (pins 14 and 17).

I was active in pc parts around 1998-2006, dead motherboards were very rare. We (national Euro Asus distributor) had literally single bad Asus motherboard in over a year of bulk sales (P2L97), we did get tens of pcchips garbage back every month, but almost all "just" crashed/had bad drivers/compatibility/were outright scams with fake features like non existent 3d acceleration/agp.
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Online NiHaoMike

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Re: Broken IC on old Pentium 2 motherboard
« Reply #8 on: October 17, 2019, 03:13:53 am »
Unless you need ISA slots, wouldn't it be easier to just replace the machine with a somewhat newer old machine? You could even underclock/undervolt to dramatically reduce the heat output.
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Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #9 on: October 17, 2019, 07:20:55 am »
especially if its designed to protect it

its not, primary function is variable voltage buck converter controller/driver, secondary is monitoring
Quote
PGOOD and OVP comparator circuits use this signal to report output voltage status
there are no protections without outside circuity like
Quote
Built-in over-voltage protection triggers an external SCR to crowbar the input supply.

The question is if these chips fail by themself or if there were something else that made it pop?

Sometimes things just die, but external cause is more likely. Either big spike on 12V rail, or maybe one of the mosfet gates blown/leaking back to the driver (pins 14 and 17).

I was active in pc parts around 1998-2006, dead motherboards were very rare. We (national Euro Asus distributor) had literally single bad Asus motherboard in over a year of bulk sales (P2L97), we did get tens of pcchips garbage back every month, but almost all "just" crashed/had bad drivers/compatibility/were outright scams with fake features like non existent 3d acceleration/agp.

Thats cool, i thought that were the high times for the capacitors that leaked? Remember several boards doing that at those times.

Thank you for all your help!

I did a quick check this morning and Vout is not shorted to ground. Will pull the diode and the transistors tonight to properly test them out. If they check out i will drop in a replacement and see what happens? 
 

Offline Rasz

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Re: Broken IC on old Pentium 2 motherboard
« Reply #10 on: October 17, 2019, 05:59:26 pm »
Thats cool, i thought that were the high times for the capacitors that leaked? Remember several boards doing that at those times.

That was mainly Abit, MSI, Gigabyte, ECS and fleet brands like HP and DELL. Afaik Asus switched to Taiwanese caps after 2006 when it came out everyone else was screwed and capacitor vendors started claiming fixes.

I did a quick check this morning and Vout is not shorted to ground. Will pull the diode and the transistors tonight to properly test them out. If they check out i will drop in a replacement and see what happens?

means diode is also fine
how is AIC1569 powered on your board? is it single 12V or dual supply setup? might be prudent cutting 12V and powering it from external limited current supply when testing.
« Last Edit: October 17, 2019, 06:01:34 pm by Rasz »
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Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #11 on: October 18, 2019, 08:40:52 pm »
Quote
means diode is also fine
how is AIC1569 powered on your board? is it single 12V or dual supply setup? might be prudent cutting 12V and powering it from external limited current supply when testing.

Yes! i see, thats good! I leave the diode in then.
The thing left to pull and test out of circuit is the transistors?

About the supply for the chip, from what i can gather, the VCC is directly connected to +12v of the PSU connector on the board, if that is what you meant?
As you can tell, iam a bit out of my league here  :-DD



I have ordered replacement chips from china, so it will be a couple of weeks.
 
 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #12 on: October 20, 2019, 04:06:09 pm »
A small update on this.

So i pulled both of the transistors out. And a simple switch test with my multimeter shows they are operating normal.
May replace them just in case anyway?

 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #13 on: November 21, 2019, 05:03:29 pm »
So, finally today i received the control ICs. So i soldered that one in place, also re-used the old FETs, since they at least passed the switch test.
But no go.

Nothing bad happened though, (as in exploding), the cpu fan turns on, and nothing more.  I was giving up, but just for a quickie i hooked my scope up, and i could see signals on all pins on the second FET, (the one furthest from the cpu), and signals on Gate and drain on the first one, but a total flat-line on the source.
What could this indicate? Now, it was just a super quick check, so didnt take note on the levels or frequency, but if that might help i can hook it up once more.
 

Offline magic

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Re: Broken IC on old Pentium 2 motherboard
« Reply #14 on: November 21, 2019, 05:55:44 pm »
It could mean it's synchronous rectification and the source is hard-wired to ground ;)

Better check what's the voltage on the CPU side of the coil and if there is significant ripple.
 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #15 on: November 21, 2019, 11:13:25 pm »
It could mean it's synchronous rectification and the source is hard-wired to ground ;)

Better check what's the voltage on the CPU side of the coil and if there is significant ripple.

Yeah, haha, as stated before, im a bit way over my head here!
By the coil, do you refer to Vout after L2 or 5V after L1 as in the typical application circuit of the datasheet?

Will hook it up to a more "permanent" test bench, the one before was dodgy to say the least.

 

Offline magic

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Re: Broken IC on old Pentium 2 motherboard
« Reply #16 on: November 22, 2019, 08:09:54 am »
By the coil, do you refer to Vout after L2 or 5V after L1
Whatever is the power output to the CPU; Vout sounds like it might be it, 5V not so much.

typical application circuit of the datasheet?
Wait, if you have the datasheet you should know how the FETs are connected :P
I bet one is meant to go to ground and there is nothing wrong with it.
 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #17 on: November 28, 2019, 06:45:06 pm »
Yes your right!
So i took some measurements on the Vout, and i get a mean value of 1.263v.

I attach a screenshot from the scope
The bet is that the cpu also died i guess?
 

Offline james_s

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Re: Broken IC on old Pentium 2 motherboard
« Reply #18 on: November 28, 2019, 06:49:18 pm »
Unless you need ISA slots, wouldn't it be easier to just replace the machine with a somewhat newer old machine? You could even underclock/undervolt to dramatically reduce the heat output.

That's completely missing the point of playing with retro hardware. If one just wants to run certain software, virtually any old PC can be emulated but that's nowhere near the same.
 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #19 on: November 28, 2019, 06:53:15 pm »
Unless you need ISA slots, wouldn't it be easier to just replace the machine with a somewhat newer old machine? You could even underclock/undervolt to dramatically reduce the heat output.

That's completely missing the point of playing with retro hardware. If one just wants to run certain software, virtually any old PC can be emulated but that's nowhere near the same.

Yeah exactly my point! Thanks for understanding. Also, i am the original owner of this board, that has to account for some sentimental value, right? ;)
Best of all, trying to fix it, one might learn something.
 

Offline Rasz

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Re: Broken IC on old Pentium 2 motherboard
« Reply #20 on: November 28, 2019, 08:36:16 pm »
So i took some measurements on the Vout, and i get a mean value of 1.263v.

thats too low. You didnt mention exact model of your processor, Ill wager a guess its something popular like 333, those need 2V
Measure resistance on Vcore rail with CPU in the slot. Check VID[4:0] setup, pinout of SLOT1 is at https://web.archive.org/web/20060622200013/http://developer.intel.com/design/pentiumiii/datashts/24445209.pdf

You could hardwire VID pins without the CPU and recheck generated voltage.
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Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #21 on: November 28, 2019, 08:42:48 pm »
Oh okey. This is a p2 350mhz. And now I see it is marked with 2.0v on the case itself.

Will try what you suggested, thanks!
 

Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #22 on: November 28, 2019, 09:38:40 pm »
So the resistance is 340ohm with the cpu in the slot.

By "check VID4 setup" do you mean how it is connected on this specific board, or how its signal is when powering the board? Sorry for not catching that.
 

Offline Rasz

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Re: Broken IC on old Pentium 2 motherboard
« Reply #23 on: November 29, 2019, 12:33:35 am »
VID pins in the cpu slot program hip6004 voltage
there is a table in linked pdf explaining how
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Offline spilihps

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Re: Broken IC on old Pentium 2 motherboard
« Reply #24 on: November 29, 2019, 07:15:04 pm »
VID pins in the cpu slot program hip6004 voltage
there is a table in linked pdf explaining how

Ah i see!

So firstly, i checked VID0..4 when CPU in slot and it gets 10000, this corresponds to 2.0v as stated in the datasheet.
Removed the CPU, and then all gets to 11111.

Did as you said and hardwired them so they get 10000, still the same output voltage.

The strange thing is though, when they are 11111 they get that same voltage also. According to the datasheet i think it should be no output?
 


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