Abit ST6E "Casper" fix

[bartx]

Hi,

I have an Abit ST6E board aka "Casper", which is unfortunately not working. Because it's very rare board, I'd like to repair it, not matter the cost or how hard it will be. It's in 95% identical with ST6, only difference which I saw is that ST6E has different NB and SB (ST6E uses 815, while ST6 uses 815EP without IGP). I've already bought working ST6 for diagnostics, and maybe a part donor if needed.

Here is what I've found out already about this board:
- hangs on 00 code using PCI Diagnostic card, no matter what CPU
- reports the lack of CPU or RAM (by C1 code)
- came with Tualatin CPU which was dead I think, there was a two tone siren from beeper on this CPU
- I switched the bios chips between boards, bios chip from ST6E is working on ST6
- no physical damaged, no broken components or damaged traces, no badcaps
- voltages are present, there are also no shorts on main componenets (CPU, RAM, NB and SB).

Can anyone help me with diagnostics? I can handle all the replacements by myself, even the BGA.

Thanks,
Bartek

[dicky96]

Re: Abit ST6E "Casper" fix

Do you have CPU CLK?
What's happening on the CPU RESET pin?

Are you sure the BIOS revision/version is compatible with your CPU type?

[piernov]

Re: Abit ST6E "Casper" fix

I'm a bit confused by those 2 statements as they seem conflicting:

- hangs on 00 code using PCI Diagnostic card, no matter what CPU
- reports the lack of CPU or RAM (by C1 code)

Anyway, what are the symptoms? No POST, no display, beeps, something else…? Caps lock key triggers caps lock LED on keyboard? CMOS reset done?

[bartx]

Re: Abit ST6E "Casper" fix

I have two type of CPU, confirmed working - Celeron 800MHz Coppermine and Celeron 1000MHz Tualatin.

I've checked once again the codes:

- no CPU, no RAM - 00 code, no beep
- CPU present, no RAM - ends on C1 code, before that C0 and AF are present, all 4 LED on PCI card are on (RST, FRAME, IRDY, CLK), long beep
- CPU present, RAM present - hangs on 00 code, IRDY is off in this case, no beep

No post, no display, new cmos battery - that's basic. I tried also with bios IC from ST6 - no luck.

Looks like it hangs when RAM is present, I have also two SDRAM which are not working, placing them in the slots also causes 00. I have to look at CPU reset signal later, I've found the pinout already.

[dicky96]

Re: Abit ST6E "Casper" fix

I was also confused by the original description/ If it is doing that (C1 and long beep with no RAM) then the CPU will be running, not held in reset

[piernov]

Re: Abit ST6E "Casper" fix

- CPU present, no RAM - ends on C1 code, before that C0 and AF are present, all 4 LED on PCI card are on (RST, FRAME, IRDY, CLK), long beep

Indeed that's fine and means CPU is running and executing BIOS instructions properly.

- CPU present, RAM present - hangs on 00 code, IRDY is off in this case, no beep

Does it show some other POST codes before showing 00?
Did you try to connect a known good graphics card and a display to it?

[bartx]

Re: Abit ST6E "Casper" fix

Indeed that's fine and means CPU is running and executing BIOS instructions properly.

Does it show some other POST codes before showing 00?
Did you try to connect a known good graphics card and a display to it?

Placing the RAM in the board leads to exact the same situation as the board will be without the CPU - instant 00 code. No other codes before that.

It doesn't even come to this moment, when board checks if the GPU is present or not. Anyway, it has the IGP so GPU is always present.

I've checked on working Abit ST6:

- without the CPU - on both boards 00
- with CPU, no RAM - on both boards C1 and long beep
- with CPU and RAM - Abit ST6 moves further with testing, display other codes and hangs on GPU check with other beep code, on non working board instant 00 code after placing the RAM, I tested various modules 128-256MB, single and dual rank

EDIT: I went further with diagnostics, looks like there is an issue with RAM voltage. Good board have 3,4V on capacitors near the RAM slot, no matter if the RAM is present or not. Bad board have 2,2V with no RAM and about 1,4V with one RAM stick present.

EDIT2: I measured the voltages on Mosfets on both boards. Those two voltages written in red are on good board, on bad board it's different. Should I replace this element or look for any possible shorts?

[dicky96]

Re: Abit ST6E "Casper" fix

Is that device marked D114 351? It's a bit obscured by the red text

But yes there does seem to be a problem there. It seems a bit odd you also have 5V on the left hand pin, I would expect you to have something else on that pin as it probably controls the output voltage

I can't see it being a short - looks more like D114 351 is acting as a high impedance source and leaking some current to the RAM, because when you put a load (fit RAM) then the voltage drops

[bartx]

Re: Abit ST6E "Casper" fix

That's Fairchild component, marked D114 G51, on other board it's marked D139 G51 - unfortunately I was not able to identify it by SMD code.

I also noticed difference between capacity measured on the legs on the capacitor just below this componenent mentioned above. Good board have 2700uf, bad board 1800uf. Could one of the RAM capacitor cause such issue?

[dicky96]

Re: Abit ST6E "Casper" fix

Possible I guess but I doubt it.

I dont' see any inductors around there so I would think that is acting as a series regulator

The thing looks something like a 1117 regulator to me, though I couldn't find a datasheet either

Some linear voltage regulators don't work well without a capacitor from the output pin to ground, so it would be worth just tagging a 1000uF 6.3V or greater from the Vram pin of the regulator to ground to see what happens. I can't see that would do any harm.

I would suspect that having 5V on both pin 1 and the centre pin is not correct, so the regulator is kinda disabled maybe?

You could just try removing the FET or whatever it is and apply VRAM 3.3V from an external bench supply then powering up the ATX and see if the board will boot up

[ChaosLegionnaire]

Re: Abit ST6E "Casper" fix

aha! i see u got a boardful of teapos around the critical areas like the cpu vrm and around the dimm slots! teapos are no good on motherboards. i replace them on sight. bad teapos could have also damaged the other solid state components on the board like the mosfets and regulator ICs. replace the bad caps first before testing and using the board any further!

[bartx]

Re: Abit ST6E "Casper" fix

I've found a datasheet on FAN5063 controller, which contains application circuit.

Looks like Q3 is directly responsible for delivering voltage for SDRAM. There is no voltage control, output voltage is simply controlled by formula using R1 and R2 values (it's 2,5V for RDRAM and 3,3V for SDRAM). Q3 is the transistor where I found difference in voltages.

I measured both boards, both controllers, high/low states on PWR_OK, SLP_S5 and SLP_S3 and I haven't found anything different except voltage on Q3.

My qustion is - should I replace it? How can I check this component after unsoldering? I have this chinese electronic testing device with LCD, it's actually quite useful for other components.

From the datasheet:
Adjustable Dual Output

The adjustable dual output is intended to provide power to
RAMBUS or SDRAM memory.

Adjustable dual is generated by one external NPN bipolar
acting as a linear regulator from +5V main, and one linear
regulator internal to the FAN5063 from +5V standby, as
shown in Figure 4, and in the block diagram on the front
page. When main power is present, the NPN Q3 linear regulates,
and when main power is absent, the internal linear regulator
is on. Q3 cannot be substituted with a MOSFET. If
used in one direction, the MOSFET's body diode would permit
back-feed; if used in the other direction, it would shortcircuit
the linear regulator action.

The state of the external MOSFET and the internal linear
regulator is controlled by the SLP_S3 and PWROK lines,
and additionally the SLP_S5 line, as shown in Figure 3.
When SLP_S5 is de-asserted, both the external MOSFET
and the internal linear regulator are off, and there is no output
voltage on the 3.3V SDRAM line.

[dicky96]

Re: Abit ST6E "Casper" fix

You lost me.
Where is FAN5063, you didn't mention it before. Is it the 16 pin chip mounted horizontally near the transistors in your pics?

If so, which pin of FAN5063 goes to the base (pin 1) of the transistor D114 G51?

If it is pin 14, then D114 G51 is an NPN transistor connected as a series regulator, which makes sense, and it must be open circuit BASE-EMITTER. It has 5.0V-2.2V= 2.8V Base-Emitter! It's probably 'leaky" collector-emitter as well hence you get some voltage on Vram.

On the good board you have 4.1V-3.4V =0.7V Base Emitter which is correct for a Silicon Transistor that is turned on

Change D114 G51. Take the same transistor (with slightly different part number ) from the good board and fit it on Casper

If that works we can find some equivalent for your other board

[bartx]

Re: Abit ST6E "Casper" fix

You lost me.
Where is FAN5063, you didn't mention it before. Is it the 16 pin chip mounted horizontally near the transistors in your pics?

If so, which pin of FAN5063 goes to the base (pin 1) of the transistor D114 G51?

If it is pin 14, then D114 G51 is an NPN transistor connected as a series regulator, which makes sense, and it must be open circuit BASE-EMITTER. It has 5.0V-2.2V= 2.8V Base-Emitter! It's probably 'leaky" collector-emitter as well hence you get some voltage on Vram.

On the good board you have 4.1V-3.4V =0.7V Base Emitter which is correct for a Silicon Transistor that is turned on

Change D114 G51. Take the same transistor (with slightly different part number ) from the good board and fit it on Casper

If that works we can find some equivalent for your other board

Yes, exactly it's 16 pin chip next to the transistors. And from pin 14 voltage is supplied to the base (5V).

Q3 is descibed in this datasheet as Fairchild TIP41A (it has different case, but it should have the same paremeters I guess).

Sorry, electronics is not my profession, so I don't know on which details I have to pay the attention I have some experience in reading the datasheets though, I used them quite a lot vmodding the boards and GPU.

[dicky96]

Re: Abit ST6E "Casper" fix

TIP41A was quite a common NPN TO-220 package power transistor back in the day.

If B-E is open circuit (which it will be) you can expect pin 14 FAN5063 to go to 5V

Change the transistor for the one off your other board. I am confident that will fix your problem

After that we can find some alternative for your other motherboard if you want it have it working

[bartx]

Re: Abit ST6E "Casper" fix

Replaced this transistor and it's working Thanks dicky96 for help.

This tester which I have show the same values for both component, looks like this transistor was leaking after putting some load on it.

[dicky96]

Re: Abit ST6E "Casper" fix

Wasn't just me here.... but I thought that would be the answer once you put the datasheet up

I have a similar semiconductor analyser to that one - they are very useful

It's nice to see Casper back in the land of the living :-)

[bartx]

Re: Abit ST6E "Casper" fix

Ok. How can I find the replacement for this transistor? On what parameterers I have to look?

I already know that it's NPN transistor in SOT223 case.

[dicky96]

Re: Abit ST6E "Casper" fix

It's not going to be critical, it's just acting as a series regulator

FZT651 is a cheap easy to find SOT223 NPN Bipolar transistor. 6V 3A 2W - that should do the job nicely

The transistor has 1.6V voltage drop across it so 1.25A would hit the maximum rated wattage of 2W and I would be suprised if your RAM draws more than that. I don't know though it's just a guess - how much power does PC100/PC133 Ram consume? Someone here will know.

Rich

[dicky96]

Re: Abit ST6E "Casper" fix

That should say 60V 3A 2W