gateway desktop no post

[everell]

Re: gateway desktop no post

First, lets clear up some questions about the Bestec power supply. The last photo you posted showed the output side of the power supply. There are two semiconductor devices screwed to the heat sink, both are diodes. I also see some crud on the top of one of the capacitors. Check this closely as it is probably a bad capacitor leaking.

What I am looking for is to see if there are two transistors on the other heat sink - on the other side of the pc board. See if you can get pictures of what is on the other heat sink.

[davg]

Re: gateway desktop no post

First, lets clear up some questions about the Bestec power supply. The last photo you posted showed the output side of the power supply. There are two semiconductor devices screwed to the heat sink, both are diodes. I also see some crud on the top of one of the capacitors. Check this closely as it is probably a bad capacitor leaking.

What I am looking for is to see if there are two transistors on the other heat sink - on the other side of the pc board. See if you can get pictures of what is on the other heat sink.

Thanks I tried to get pic between the heat sink but what I posted is the best I can do but yes there are two (what looks like transistors) screwed to the other heat sink? one larger than the other. I can't get a pic nor can I read the numbers on them. The crud you see was added at the factory I checked all caps none seem to be leaking.

[everell]

Re: gateway desktop no post

The two numbers you gave earlier to identify the two "chips" are the numbers on the two transformers. Since there are two transistors on that heat sink (I don't need to know part numbers), there should be only one chip (integrated circuit) located between the two heat sinks with part number UC3842 written on it. It is a very small device having eight pins, four on each side, soldered to the pc board. See if you can find it.

There are four optocouplers on this power supply, giving added protection which the killer Bestec ATX-250-12E does not have. But the 5vsb now looks to be the two transistor circuit design which at this point is very questionable. Until your electronics experience increases, I HIGHLY recommend that you set the Bestec aside to play with later. The consequences could be killing a perfectly good mother board. So far, looks like it did NOT kill the board it was originally powering, but no sense in taking chances. Don't toss it, just don't use it for now. Do you have another power supply that you can use for testing the other bad mother board?

[davg]

Re: gateway desktop no post

The two numbers you gave earlier to identify the two "chips" are the numbers on the two transformers. Since there are two transistors on that heat sink (I don't need to know part numbers), there should be only one chip (integrated circuit) located between the two heat sinks with part number UC3842 written on it. It is a very small device having eight pins, four on each side, soldered to the pc board. See if you can find it.

There are four optocouplers on this power supply, giving added protection which the killer Bestec ATX-250-12E does not have. But the 5vsb now looks to be the two transistor circuit design which at this point is very questionable. Until your electronics experience increases, I HIGHLY recommend that you set the Bestec aside to play with later. The consequences could be killing a perfectly good mother board. So far, looks like it did NOT kill the board it was originally powering, but no sense in taking chances. Don't toss it, just don't use it for now. Do you have another power supply that you can use for testing the other bad mother board?

Sorry for my lack of knowledge but there are two of these 8 pin chips near the heat sink one that you saw at first is UC38420 and the one right between the heat sink is a A6351A. Yes I do have an extra power supply that I can use to test the other board.

[davg]

Re: gateway desktop no post

First, lets clear up some questions about the Bestec power supply. The last photo you posted showed the output side of the power supply. There are two semiconductor devices screwed to the heat sink, both are diodes. I also see some crud on the top of one of the capacitors. Check this closely as it is probably a bad capacitor leaking.

What I am looking for is to see if there are two transistors on the other heat sink - on the other side of the pc board. See if you can get pictures of what is on the other heat sink.

Maybe these will help? On closer look at that cap that appeared to be leaking It do look like some leaking but it is not a regular cap it looks like the one in the last pic?

[everell]

Re: gateway desktop no post

You are doing a good job and learning quickly. Now you can identify what the chips (integrated circuits or ICs) look like and what the part numbers are. This is very important to know how to do.

The pictures were great and showed what I needed to know. Identifying those two chips helped to verify that the Bestec power supply you have is OK to use. It has the PWM chip in the 5vsb circuit along with the four optoisolator chips for added protection. You can go ahead and use this power supply without worry about the "Bestec spike of death" you will hear mentioned so often on this website. You have the good one, not the mother board killer.

Next post I will try to give some ideas on troubleshooting the bad mother board.

Keep a sharp eye out for any bulging or leaking capacitors.

[davg]

Re: gateway desktop no post

Thanks everell I look forward to your next post I am excited that we were able to get one up and running and it is still doing well. The environment will be that much better!! I already have a charity for it if it holds out, plus the knowledge and satisfaction that I have gotten, don't get much better than that?? Happy Fathers Day if that is appropriate.

[everell]

Re: gateway desktop no post

And a happy Father's day to you also. I have one boy - he is currently with the 82nd airborne somewhere.

Well, lets get started. The thing to understand is that something is shorting or loading down the power supply. When the power supply detects the problem, it shuts down to protect both the power supply and the mother board. So just play detective and find the short.

First, make sure all fans are unplugged, and remove the cpu, heatsink, and fan. Place the cpu in a piece of aluminum foil to protect it from static electricity. Also remove the stick of memory, also placing it in a piece of aluminum foil to protect it from static electricity. Plug the power supply connector into the mother board. Don't worry about plugging monitor into video connector, this test will NOT give any video response. Make sure all ribbon cables, and any other cables are unplugged from mother board. The power supply should not be plugged into hard drive, cdrom, or anything else. Just the mother board. Plug power supply cord into wall outlet and measure voltages. You should get 5 volts on the 5vsb and that's all.

Next, plug the Power-On cable from the case into its proper place on the mother board. Press Power-On button. Now measure the +12, +5, and +3.3 volt on the power supply connector attached to the mother board. Voltages should now be present. If they are, hold the Power-On button in for 4 or 5 seconds, and these voltages should go back to zero. Try getting this far.

[davg]

Re: gateway desktop no post

Thanks with all unplugged I am reading 4.97vsb with the power-on cable connected the front panel light is on but I am not reading any voltages on yellow red and orange? The power on cable is a single connector with six wires red/white, blue/white and black/white and it will only connect one way. If I hold the power on button in for 2-3 seconds the light goes out.

[everell]

Re: gateway desktop no post

With power supply plugged in, push Power-On button in. Measure voltage at +12, +5, and +3.3. Light should come on. Now push Power-On button and hold for 4 to 5 seconds. Light should go off. Measure +12, +5, and +3.3. These voltages should return to zero when the light goes off. We need to know what each of these three voltages are doing. All three should have a voltage when light is on. All three should have zero when light goes off.

[PCBONEZ]

Re: gateway desktop no post

+5vsb comes off a different transformer than the other voltages. That xfmr is called a "Fly Back Transformer". It's one of the small ones in there.
It is not part of the main SMPS but a small separate PSU off to the side.
-
Your 'switchers' may be OOC which means the main xfmr isn't getting any power..
.

[davg]

Re: gateway desktop no post

With power supply plugged in, push Power-On button in. Measure voltage at +12, +5, and +3.3. Light should come on. Now push Power-On button and hold for 4 to 5 seconds. Light should go off. Measure +12, +5, and +3.3. These voltages should return to zero when the light goes off. We need to know what each of these three voltages are doing. All three should have a voltage when light is on. All three should have zero when light goes off.

sorry but when I push the power on button the light comes on but I do not have any voltages at +12 +5 or +3.5 on the main connection on the mother board (or the yellow red or orange at any of the connectors). It would appear that the switch is turning on the light but not putting power to the board? There is 4.95 v at the plugin on the board where the power-on switch connects?

[davg]

Re: gateway desktop no post

+5vsb comes off a different transformer than the other voltages. That xfmr is called a "Fly Back Transformer". It's one of the small ones in there.
It is not part of the main SMPS but a small separate PSU off to the side.
-
Your 'switchers' may be OOC which means the main xfmr isn't getting any power..
.

Thanks PCBONZ When I test the power supply the voltages are in spec.and whei i conect to the mb I get 5vsb and that is present at the power switch connector but when I push the power switch the power light comes on but there is no voltage present at +12 +5 +3.3. so the switches you refer to are the switching transistors?? What is ment by OOC?

[everell]

Re: gateway desktop no post

One more test to try. Be sure power is disconnected from wall socket. Remove the bios chip from its socket and place the chip in a protective piece of aluminum foil. Now plug power cord back into wall socket. Power supply still connected to mother board, power supply not connected to anything else, cpu and its heat sink off, memory stick removed. Now push the Power-On button. Light should come on and measure the +12, +5, and +3.3 volts. Voltages should be there. Push and hold Power-On button for 4 to 5 seconds. Light should go off and voltages should drop to zero.

[davg]

Re: gateway desktop no post

One more test to try. Be sure power is disconnected from wall socket. Remove the bios chip from its socket and place the chip in a protective piece of aluminum foil. Now plug power cord back into wall socket. Power supply still connected to mother board, power supply not connected to anything else, cpu and its heat sink off, memory stick removed. Now push the Power-On button. Light should come on and measure the +12, +5, and +3.3 volts. Voltages should be there. Push and hold Power-On button for 4 to 5 seconds. Light should go off and voltages should drop to zero.

Thanks pal Still no go bios chip removed, power light on. 0 voltage at +12 +5 and +3.3???

[everell]

Re: gateway desktop no post

OK - now looks like good power supply and probably bad mother board. If you are a gambling man - I would predict that you have probably a one in three chance that the bios chip needs to be reflashed. As for any other problem, I think it beyond the scope of what you can do at this time. So you can try a reflash of the bios chip or chunk the mother board. You can often find a mother board to replace it by letting friends know what you are looking for, and by looking at thrift stores. The second hand stores are often a good place to look for used parts. There might be a computer shop willing to work with you and provide a low cost mother board. So you still have lots of options.

If you trash the mother board, you should save the cpu, heat sink and fan, memory, and even the bios chip might come in handy later. Store these items in aluminum foil to protect against static electricity.

As for the working computer, it probably has Windows as operating system. The operating system software is licensed only to original owner. To stay safe and LEGAL, I highly recommend that you load a Linux operating system - it is open source (free) so you can stay out of legal trouble. The most popular version at the moment is Ubuntu. Not that hard to learn and lots of fun. If you should give the computer to someone else, it will also keep them out of legal trouble with Microsoft. If you need help getting a copy of Ubuntu, let me know.

I noticed from your last post that you are from Canada. What part?

[davg]

Re: gateway desktop no post

OK - now looks like good power supply and probably bad mother board. If you are a gambling man - I would predict that you have probably a one in three chance that the bios chip needs to be reflashed. As for any other problem, I think it beyond the scope of what you can do at this time. So you can try a reflash of the bios chip or chunk the mother board. You can often find a mother board to replace it by letting friends know what you are looking for, and by looking at thrift stores. The second hand stores are often a good place to look for used parts. There might be a computer shop willing to work with you and provide a low cost mother board. So you still have lots of options.

If you trash the mother board, you should save the cpu, heat sink and fan, memory, and even the bios chip might come in handy later. Store these items in aluminum foil to protect against static electricity.

As for the working computer, it probably has Windows as operating system. The operating system software is licensed only to original owner. To stay safe and LEGAL, I highly recommend that you load a Linux operating system - it is open source (free) so you can stay out of legal trouble. The most popular version at the moment is Ubuntu. Not that hard to learn and lots of fun. If you should give the computer to someone else, it will also keep them out of legal trouble with Microsoft. If you need help getting a copy of Ubuntu, let me know.

I noticed from your last post that you are from Canada. What part?

Thanks again pal appreciate all your help I have no problem trashing this board I came by a number of them for free and I am still anxious in learning how to troubleshoot them. I have another board that is not posting but do have voltage at +12 +5 and +3.3 when I push the power switch to on and 0 volts when it is off. I have taken this one up to the same test point as the last one except for removing the bios. With the help of this forum I am hoping to learn. I truly appreciate your expertise. Yea Eastern Canada NFLD
Thanks again and I am not familiar with the Linux OS although I have been reading some on it. Would appreciate help on getting a copy.

[davg]

Re: gateway desktop no post

I found a download for Linux Ubuntu thanks everell

[davg]

Re: gateway desktop no post

If you are a gambling man - I would predict that you have probably a one in three chance that the bios chip needs to be reflashed.
Just curious what would you suggest are the other two possibilities?

[everell]

Re: gateway desktop no post

Three possibilities I predict:
1. Easiest to fix: reflash bios chip
2. Next, harder, but not too tough, bad capacitors. Recap the board. There may yet be a bad cap causing the trouble.
3. Toughest to fix: anything else, such as bad chips or other semiconductors, or defective passive components. Few technicians take repairs to this level, the labor cost outweighs replacing the board. Also, the mother boards are multilayer. I have not done much in this area - so far I have been working mostly with bad power supplies. The Bestec I am familiar with, see my thread in the power supply forum under the thread "Bestec up and running". I also started the thread "Bestec revisited" which drew lots of interesting comments.

Glad you found Ubuntu. Hope to see you around on this website as you make more posts.