Antec "Stupid" Power rebuild

[LDSisHere]

Re: Antec "Stupid" Power rebuild

The little cap that went bad did not show any outward signs of failure. Once I saw its' readings I figured bad things happened down stream. I had read so posts that discussed this flaw. The board that was attached to this supply when I got it was an ancient (266 DDR max) socket A board that I was not planning to test as I have better ones boxed up with no purpose already. I am now curious if it is fried, so I may have play with it if I ever get at chance. The board I plan on using is an Asus P4 that I recapped a while ago and have been wanting to put into service.

It is a pretty crappy design IMHO that when the cap goes bad, the voltage fails high vs. off. If I ever intend to hook it to an expensive setup I will probably do the mod that was described above, but a P4 board I am not going to loose any sleep over. I am going to do a little more testing of diodes and such before I order my parts but hopefully I have it in before Friday.

[c_hegge]

Re: Antec "Stupid" Power rebuild

You can mod it if you don't trust the 5vsb circuit. Either you can replace the circuit with one driven by a PWM chip, which wont overvolt, or you can put a 5.5V 1W zenner diode across the output. Then, if the 5vsb goes slightly over 5.5v, it will conduct the excess over to ground. If it goes way over, it will short internally and blow up the switching transistor but the motherboard will survive.

[retiredcaps]

Re: Antec "Stupid" Power rebuild

The little cap that went bad did not show any outward signs of failure.

Jetadm123, a regular in the computer display subforum here, puts it eloquently

https://www.badcaps.net/forum/showpo...96&postcount=8

[LDSisHere]

Re: Antec "Stupid" Power rebuild

^
Retiredcaps, you are correct that guy sums it up very well. I was just excited about that capacitor, since I have recently built my ESR tester it is the worst testing / best looking cap I have yet come across. The only others to show open had their tops ruptured

You can mod it if you don't trust the 5vsb circuit. Either you can replace the circuit with one driven by a PWM chip, which wont overvolt, or you can put a 5.5V 1W zenner diode across the output. Then, if the 5vsb goes slightly over 5.5v, it will conduct the excess over to ground. If it goes way over, it will short internally and blow up the switching transistor but the motherboard will survive.

I think I will go for your zener idea, keep it simple for this situation. It is quick, easy and hopefully never tested. I have been wanting some 5.5V zeners on hand for a while so now is my excuse, I will add them to my order. Thank you very much for the idea.

[c_hegge]

Re: Antec "Stupid" Power rebuild

Cool. Just remember that the zener should be rated for 1W or more, otherwise, it will just melt if a 5vsb overshoot occurs. The stripe (Cathode) on the diode should go to the +5sb output, and the other end (anode) should go to ground IIRC

EDIT: I should probably add that the idea was originally Th3_Un1qu3's

[momaka]

Re: Antec "Stupid" Power rebuild

I fixed his Antec power supply and it is still going good, but the Intel motherboard has been sitting in my basement for about 18 months now.

Probably needs a new Southbridge... unless you got lucky and only had a linear regulator or standby-power MOSFET die somewhere.

I have a few old dead boards as well. I'm saving them to experiment with when I build myself a reflow/rework machine sometime in the future. Would be fun trying to change the chipsets and other BGA chips on those.

The stripe (Cathode) on the diode should go to the +5sb output, and the other end (anode) should go to ground IIRC

Correct.
I've seen this used on a few older power supplies so it's not a new concept.

[LDSisHere]

Re: Antec "Stupid" Power rebuild

Well I got my caps in, and I have now replaced almost all the old caps with new ones. There were some 16V ones that I missed on my order but I replaced them with scavenged ones that tested good. (Good brand also). I also have not replaced the main caps yet until I am sure I can get it to work.

I have a problem and I do not know where I should start troubleshooting it, I am only used to replacing power supplies. When I apply power I get 5.03VSB (multimeter reading) which is great if my understanding is correct. When I try my ATX tester I get nothing other than a green LED for 5VSB . Pressing the button to turn on the supply does nothing that I can tell. The only other voltage I get is 2.46V on the PS_ON# wire. I do not know what this is even supposed to be so I am not sure if it is correct. I have not tried to force it on using a jumper wire as of yet, I thought it best to get some input before proceeding. How do I need to proceed from this point?

Thanks,
Lloyd

[momaka]

Re: Antec "Stupid" Power rebuild

Does the PSU fan twitch when you try to turn the PSU ON? If not, try attaching a bigger load to it - fans and old dead hard drives are really good for this. Or even better, an old spare motherboard. If the power supply still doesn't do anything, start checking the circuits attached the to secondary side of the 5VSB transformer. There's usually 2 circuits - one for providing power to the PWM/supervisory IC on the secondary and one for the 5VSB output. The circuit for providing power to the PWM/supervisory IC might have a fault in it. It usually outputs 12-25V.

[LDSisHere]

Re: Antec "Stupid" Power rebuild

Thanks for helping. I have 11.5V on my PWM chip pin 12. I am attaching the pwm datasheet and the supervisor chip datasheet. I figure the problem may be in that area. I have no idea how they work together. I get no fan twitch. Any ideas on what to check next?

Thanks,
Lloyd

[LDSisHere]

Re: Antec "Stupid" Power rebuild

Well I still am not sure as to why this supply is not working. I have done a lot of searching and reading but I have not found very much that is helpful to me. I am suspecting the problem may be the TPS3510 supervisor chip. I am not sure as I am not getting much out of its' datasheet or the one for the KA7500, especially how they interact. I took some voltage readings in standby for both chips then I did the TPS3510 while trying to power on the supply with a load. The only reading that changed on the TPS3510 was the PSON going from 2.6 to ~0V

Here are the readings by pin number:

TPS3510

1 0V
2 0V
3 0V
4 2.6V
5 0V
6 0V
7 4.5V
8 1.5


KA7500

1 0V
2 0V
3 0V
4 0V
5 0V
6 0V
7 0V
8 2.1V
9 0V
10 0V
11 1.6V
12 12.1V
13 0V
14 0V
15 0V
16 0.1V

Other than the Vdd for both chips I do not know what these should be in standby mode. Any input would be much appreciated as I have no idea what to do next besides replacing these two chips and see if that helps.

Thanks,
Lloyd

[momaka]

Re: Antec "Stupid" Power rebuild

Although the supply voltage on pin 7 for the TPS3510 is still in spec (more than 4V), I find it a bit low. It may be okay after all, but considering that the supply voltage for the KA7500 is 12V, I think you should look into it. Do you think you can trace the circuit that provides power to the TPS3510 on pin 7?

Also, if I'm not mistaken, pin 4 (PSON) should be close to 5V. It's still in spec as well, but not by much (just 0.2V).

Any chance you can post a few pictures (top and bottom side of PCB) of the controller area?
These ICs usually don't go bad, but it's possible that the out-of-control 5VSB pushed the auxiliary supply too high and killed one of them.

[LDSisHere]

Re: Antec "Stupid" Power rebuild

I could easily be mistaken but it looks like the according to the datasheet that pin 7 TPS3510 should be connected to 5VSB and the 12V that is generated off the supply for OV protection on 12V. They both are supposed to feed pin 7 across separate diodes. (5.03VSB - .5V diode drop = ~4.5V until the supply starts) I agree that pin 4 PSON seems low voltage wise, but best as I can tell it is only connected to pin 4 through a resistor so the low voltage is caused by the TPS3510. I am sure this supply had a 5VSB over-voltage situation as the capacitor that was supposed to control it was hammer dead. I suppose it could have easily have gone high enough to damage this chip. It gives no response to its' weak PSON signal. I think this chip may be my problem. Based on this information what do think? I already ordered one of each chip from Digikey last week just in case there was a problem with one of them. I had to place an order and they were cheap compared to time and parts already spent on this project. Should I just wait until they arrive then replace the TPS3510, then the KA7500 if the TPS3510 does not solve the problem? Or do I need to investigate more before replacing parts?


I should be able to post pictures, I may need to wait until tomorrow morning so I will have good light. Bad light will equal bad images. Thanks for taking the time out to respond.

Lloyd

[BigTroll]

Re: Antec "Stupid" Power rebuild

Throughout the years of tearing stuff down i rarely if only a couple of times found a bad teapo.

[everell]

Re: Antec "Stupid" Power rebuild

The reference voltage (internally generated) on pin 14 of the KA7500 should be 5 volts. Since you have 0 volts on this pin, this chip has been toasted. Anyone else agree?

The TL494 chip can be used as a substitute for the KA7500 chip

[LDSisHere]

Re: Antec "Stupid" Power rebuild

I apologize for not posting any pictures. It was raining all day and my parts came in so I was hoping to have this unit working but it did not happen. I did see some improvements but it still will not start.

The KA7500 and TPS3510 have both been replaced with new identical replacements. During voltage testing I intermittently tried to start the supply with a load. After testing I noticed that the 5VSB transformer was warm to the touch. Upon farther investigation I noticed the heat sink between the transformers and the main caps was even warmer than the transformer. I think the only three devices connected to this heat sink is a transistor (Fairchild FQPF 5N606 is what I could make out.) and two diodes. I think the transistor is for the 5VSB and the diodes are for the other two transformers but I have not confirmed this. It seems strange that the heat sink and transformer would get this warm from what I was doing as I would not think it would be a lot of load to be in standby and do some intermittent attempts to start but for all I know this could be normal.

Here are the voltage readings I took after installing the new components. The first number is standby and the second is the reading while attempting to start the supply with a load.

TPS3510

1 0V / 0V
2 4.5V / 4.5V
3 0V / 0.19V
4 2.6V / 0.10V
5 0V / 0.17V
6 0V / 0.08V
7 4.5V / 4.5V
8 0V / 0V


KA7500

1 0V / 0.14V
2 2.48V / 2.48V
3 0.08V / 0.08V
4 4.12V / 0.02V
5 1.57V / 1.57V
6 3.51V / 3.51V
7 0V / 0V
8 2.16V / 1.45V
9 0V / 0V
10 0V / 0V
11 2.15V / 1.44V
12 12.35V / 12.35V
13 4.96V / 4.96V
14 4.96V / 4.96V
15 4.96V / 4.96V
16 0.13V / 0.5V

Pins 9-10 are tied together.
Pins 13,14, and 15 are tied together.

I will try to get some shots posted in the morning, hopefully the sun will be out. I do appreciate the help on trying to figure this out. It is really turning into a good learning experience, but I have no idea where to go from here. Do I have a bad transistor but one that is not shorted? I did not have a fan attached, will this keep the supply from starting?

Thanks,
Lloyd

[everell]

Re: Antec "Stupid" Power rebuild

Pins 8 and 11 are the output from the 7500 chip. Notice that before changing the 7500 chip you had a noticeable difference in voltage. They should have been the same. After replacing the 7500 you still have a slight difference. It is common that when the 7500 goes bad one or both of the driver transistors also goes bad. I recommend replacing both driver transistors AND the small (usually glass) diodes in the driver circuit. There should be 3 or 4 of them. Also check resistor values in this circuit - sometimes a resistor has changed value due to burn damage.

From your voltage readings, it looks like your psu is trying to come back to life. If you still don't get a twitch of the fan when attempting to turn it on, I would look at that driver circuit between the 7500 chip and the small driver transformer. Two transistors, 3 or 4 diodes, and a few resistors.

[LDSisHere]

Re: Antec "Stupid" Power rebuild

Thanks, I will see if I can find the components you are talking about and test/replace them. If I am lucky I will get it going, if not I will post back with some pictures shortly.

[LDSisHere]

Re: Antec "Stupid" Power rebuild

I finally have pictures. I removed the two transistors attached to pins 8 & 11. They and the diodes all test good with the DMM diode test. The transistors are H945 and I do not have any on hand with that pin-out so I decided to check the voltages with them out. I put the voltage readings directly on the first image by the pin location.

Pin 16 on the KA7500 came up to 0.73V and pins 8 & 11 went to 3.3V. I still do not understand what all the pins on this chip are supposed to do so I do not know what the voltages should be on them. The datasheet says the typical voltage on 8 & 11 is supposed to be 30V. Is this supposed to come from a transformer or does this chip generate that voltage somehow?

If I need to take pictures of something else or differently let me know and I will do my best to take them as directed. Any guidance on what I should do next would be appreciated very much.

Thanks,
Lloyd

[LDSisHere]

Re: Antec "Stupid" Power rebuild

I found a couple of C1815 that I was going to use in place of the H945, unless there is a reason I should not. Would BAT85 diodes work to replace the hole mount glass ones (D18, D19,..) tied to the two transistors I am replacing? Should I also replace that vertical resistor next to the burnt spot and transformer, D18 is pointing up at it. It seems to test good with a DMM but I am not 100% of its' value.

Thanks

[LDSisHere]

Re: Antec "Stupid" Power rebuild

I am sure that those of you that are tired of seeing this thread pop up will be glad to know that this supply is back alive. I am not sure which part was the magic part exactly. I replaced the two H945's with scavenged C1815. The diodes turned out to be 4148's and I had those on hand so they were replaced. The thing I did that I feel uncomfortable with is replacing R51 which looked burnt and had a tested value of 1500 Ohms. I did a search on SmartPowers and "R51" and it came up with Everell saying he replaced R51 with 270 Ohm resistor. Thinking my burnt one had a higher than rated resistance I put in a 1/2W 330 Ohm resistor. I do not know what this resistor is for so I am playing with fire in a way, but it works. If anyone knows the real value for this resistor (R51) I would be grateful if they would share it and the life of my power supply may depend on it.

The Fan now runs a decent speed with the resistor mod. I have to change out the main caps for the new Chemicon's that I have for it. I also still have to do the 5.6V Zener / 5VSB mod and I thought I should use two 1 watt Zener's instead of one.

I did notice that my -12V was only slightly above -10.xxV, I do not have the exact numbers with me but they were closer to -10 than -11. Is this normal for these supplies or do I still have a problem?

I want to thank everyone for their input, it was priceless as I was really lost. This has been an excellent learning experience. I still have a lot of power supply gray or just plain black areas but at least bad supplies do not have to be instant garbage fodder for me any longer.