Trouble removing Bios Password on Toshiba C655

[sparker1]

Hi, I have a board I bought that was supposed to be working but it isn't. It was said to have had a bios password on it that nobody knew. An attempt had been made by the person to remove the password by following this video https://www.youtube.com/watch?v=IkmKCFSt0pg. However, now the board is dead.
The jumper concerned is B500 as shown in the schematic. If the procedure was done properly I can't see how any damage could be done to anything else but google shows it's not an isolated case. Could this process when it goes bad for some reason damage the bios chip itself because it is the target for the process?

[Agent24]

Re: Trouble removing Bios Password on Toshiba C655

The first thing I would try is a full BIOS reset. Remove the BIOS battery (make sure to remove system battery and power also) or use the BIOS reset jumper\switch\pads if they exist.

Multiple people could still have done something wrong... it looks a little tricky if someone had never done it before and even that guy in the video took about 5 goes at it (I could hear the CD drive spin up each time he rebooted) so who knows what happened in each case?

When you say it's dead - what exactly happens now? Do you get any lights or anything or absolutely nothing?

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

Hi, no lights, no fan...dead as a dodo. I just found a buck controller getting really hot so the issue may not be related to the "B500" operation. This is the correct schematic and the buck controller is U6200 (a TPS51125).

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

Dam! other components in the area are even hotter - U6100 is the hottest - It's a G86/87 low voltage reset IC-whatever that is? I'll replace the buck controller and see if that fixes it.

[Agent24]

Re: Trouble removing Bios Password on Toshiba C655

U6100 just creates a control signal to enable or disable U6200, so U6100 should not get hot unless something is really wrong. Of course it may be getting heated up by other components nearby.

Possibly some rail is overvoltage or the chip has been damaged when someone tried to do the password reset, if the U6100 is indeed generating the heat itself.

Are any of these components near the B500 jumper? Have you checked in that area for damaged components?

You should probably check that the transistors U6200 drives and the +V5A rail are not shorted.

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

U6200 is on the other side of the board and diagonally opposite. There are lots of test pads in the area for me to check voltages. I'll post the results tomorrow. Thank you for the advice.

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

I tested voltages at the pads as follows:

No CPU, no Ram and not switched on:
Pad 6200=0 volts should be 5V
Pad 6201=1 volt should be 5V
Pad 6202=19+ volts should be +vbat (3.3v?)
Pad 6203=19+ volts should be +vbat (3.3v?)

Mosfet Q6206 has 1.4V on gate but no voltage on any other pin (I thought it would have 19v on drains). It's not hot
Mosfet Q6207 has 19V on gate. It's not hot either.
caps C6201, 3 and 4 all have 19V.

Is changing TPS51125 the best option?

[meritosari]

Re: Trouble removing Bios Password on Toshiba C655

I tested voltages at the pads as follows:

No CPU, no Ram and not switched on:
Pad 6200=0 volts should be 5V
Pad 6201=1 volt should be 3V ( you've mistyped)
Pad 6202=19+ volts should be +vbat (3.3v?)
Pad 6203=19+ volts should be +vbat (3.3v?)

Mosfet Q6206 has 1.4V on gate but no voltage on any other pin (I thought it would have 19v on drains). It's not hot
Mosfet Q6207 has 19V on gate. It's not hot either.
caps C6201, 3 and 4 all have 19V.

Is changing TPS51125 the best option?

-check resistance respect to ground on pad6201 & pad6200 (without adapter and battery)
-pad6202 & pad6203 should be 19v (if using adapter) and +12v (if using battery)

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

Hi Meritosari, You're right, pad 6201 should be 3v. I'll check those resistances without battery or adapter. Here they are: pad 6200 is shorted to ground according to the beep meter and about 3 ohms on the resistance scale. The mosfet Q6207 is shorted drain-source-drain and pad 6201 has about 13.04k ohms resistance.
Should I remove that mosfet first and test it off the board?

[meritosari]

Re: Trouble removing Bios Password on Toshiba C655

Hi Meritosari, You're right, pad 6201 should be 3v. I'll check those resistances without battery or adapter. Here they are: pad 6200 is shorted to ground according to the beep meter and about 3 ohms on the resistance scale. The mosfet Q6207 is shorted drain-source-drain and pad 6201 has about 13.04k ohms resistance.
Should I remove that mosfet first and test it off the board?

yes,if you test mosfet.
or you can remove pad6200 with solder wick and check the pad

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

There are too many shorts: C513, C6202, C6200, C6144, C6150, C509 are all shorted and so are Q6207 and Q6028. I removed TPS51125, Q2007, C6200, C509 and C513 and all the shorts were still present. Something is seriously wrong with this board and I've spent to much time on it already.

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

I'll try your pad 6200 suggestion. Thanks

[Agent24]

Re: Trouble removing Bios Password on Toshiba C655

Are all those capacitors really shorted or do they just show up as shorted because they're in parallel?

Did you re-test the capacitors after you took them out of circuit to see if they were really shorted?

[meritosari]

Re: Trouble removing Bios Password on Toshiba C655

try isolate with remove:
pad6201 (c6202/+v3LA rail)
pad6200 ((c6200/+v5A rail)
powerpad_2_0610 (c6150,c6144,c509/+v3S rail)
after you remove one by one, which side that shorted

my suspect: conex_cx20671 is the culprit

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

Are all those capacitors really shorted or do they just show up as shorted because they're in parallel?

Did you re-test the capacitors after you took them out of circuit to see if they were really shorted?

Yes I did the re-test. It was the pads that were still shorted and no, they weren't in parallel. However, I'm just a hobbyist with this stuff so appreciate the input.

[sparker1]

Re: Trouble removing Bios Password on Toshiba C655

I took off the conex and some of the shorts went away. However there were still many other ones. I think it needs someone with more expertise than I have. It's going to the bin. Thanks for the help from everyone.