• Please review our updated Terms and Rules here

Everex Step Mega Cube

Chuck(G) said:
If the capacitor is marked with a polarizing stripe, then it's a regular polarized electrolytic.

Hint: if the one that failed is rated for 85C, you might get a bit more life by switching to one rated at 105C. It's sitting in an isolated corner of the PCB, right next to a heat sink. (Why oh why do some design engineers put electrolytics right next to heat sinks? It's terrible practice.)
Click to expand...

Agreed. I am planning on getting a Rubycon 450V 10UF which should have a life of 12000 hours at 105C.

BTW: Any tips on cleaning the oily dirt. I've already blown the units with a compressor and got most of the dirt out but there is that residue left which looks like dirt and oil mixed together that I'd like to wipe up... If the system boots I am going to try and restore it to look as close to brand new as possible! :)
 
Last edited:
Finally, had a chance to replace the cap today. Put everything back together and tried booting up. No go! :bomb: I stuck a POST analyzer card in the one ISA slot and the lights for +5V and +12V do not come on. Are we still thinking bad PSU? If so what is the next diagnostic step? Thanks!
 
Unknown_K said:
Are there any fuses on the motherboard?
Click to expand...

None that I can see. There are two on the PSU but both seems good. I am still guessing the PSU is bad because when I connect to a load, w/o being connected to the motherboard, there is still no fan spin up on the PSU or the load. For whatever reason it is not supplying the DC power.

PS: Do you guys think the diodes could be bad? I am going to test them with DMM tomorrow and see if they are still working..
 
Last edited:
Is the fan still a no-go? Have you tried powering a couple of IDE drives with the PSU disconnected from the motherboard?

As I said before, the prudent thing is to replace all caps in the PSU.
 
Yes, under load w/ cap replaced the results are the same. I will look into it some more today and see if I can come up w/ anyhting else.
 
Getting out of my element here...

Getting out of my element here...

Okay. Did some testing w/ a DMM and looked a PSU connector. As someone already observed the PSU connector has the same number of pins as a std. AT PSU. In fact looking at it it seems as if the PSU has the same color coding as a std. AT PSU.

I looked at all the wires using the continuity setting and found a short in the red (+5V) wires at the 4 pin molex connectors as well as the MB connectors. I assume all the red wires go back to the same point in the circuit board on the PSU as all the RED wires on the MB connector showed a short. The ORANGE (+5V) wire also showed a short.

Now I need to find where the short is and see if I CAN fix it. To be honest though I am fast approaching my limits of electrical engineering. Somehow, all those BIO classes in undergrad did not prepare me for EE. Go figure! ;-) Any step by step help is appreciated.
 
It may not be a short. Returns are always made to the black wires.

Discharged capacitors in the decoupling and filtering sections of your motherboard and power supply look like shorts--initially. Set your DMM to its lowest resistance range, test the power terminal against ground (black) and see if the reading starts moving after a few seconds. If it does and gradually goes toward a resistance in the hundreds of ohms, then you don't have a short. If the darned thing stubbornly keeps reading .02 ohms or the like, then it really is a short.

Sometimes, on these low-resistance circuits, it's better to use a battery and a flashlight bulb as a continuity checker.
 
Okay some misdiagnosis on my part. The DMM was bad. Yes yes make cracks about the bio major guy...

Anyhow, I enlisted the help of a friend who as more knowledge in these matters then I do and here is what we found:

1. The blown capacitor was bad. So good thing we replaced it.
2. The PS supplies +5V power on the molex and MB connector.
3. The PS DOES NOT supply +12V or -12V Power on the molex or MB connector (i.e. the yellow wire on the connectors and the blue wire on MB connector)
4. The orange wire on the MB connector does not show 5V. I am assuming this is because not all the voltages are good.

We checked out all the diodes on the two circuit boards and thought we found the culprits. Checking the two diodes that seemed to be on the 12V circuit showed they passed current in both directions. However, when we desoldered the two diodes they worked fine. Put them back in the circuit and same results with two way passage of current.

At this point I am stumped and my friend wanted the circuit diagrams so that we were not bumbling about aimlessly...
 
At least you've got +5, that's a big step forward.

Looking at your photos, it appears that you really have two power supplies. The second, smaller board, looks like a single-voltage supply. Where do the red and black leads coming off of it go? Are the smaller blue and red leads attached to the fan? (Just guessing from what I can see)
 
Chuck(G) said:
At least you've got +5, that's a big step forward.

Looking at your photos, it appears that you really have two power supplies. The second, smaller board, looks like a single-voltage supply. Where do the red and black leads coming off of it go? Are the smaller blue and red leads attached to the fan? (Just guessing from what I can see)
Click to expand...

Chuck(G),

I think they used a european std for color coding. Here is what I think is happening:

1. Power comes in through the system into the white PCB of the PSU to the contact points right underneath the white fuse. There it is converted to DC (you can see the four diodes in the center). I did not measure what comes out of this part but I am guessing it is 12V.
2. The power is then distributed to the Green PCB via the black and red wire to the contact points in the lower right hand corner.
3. In the green PCB the voltage is further regulated/manipulated into 5V and 12V. I am GUESSING the section with the smaller solenoid (in between the two heatsinks) is for 5V.
4. In the bottom left hand corner of the green PCB there is a rubber covered solenoid. Right above that (very hard to see) next to the grey resistor there is two diodes. These wer ethe ones that passed current in both directions. We thought they were bad. So we unsoldered one leg and re-tested and they worked correctly. re-soldered the leg and again the same problem.
5. The RED and BLUE wires connect to the green PCB on the connector at top. The fan has another connector in the middle of the green PCB.

Thanks for the help.
 
Okay, I could see the photos, but didn't have any idea of how the boards went together.

So, with the power off and everything disconnected, how much of a short (using the lowest range on your DMM and allowing 10 seconds for settling) is there on the +12 side? In other words, does that side show any sort of charging?

Check the diodes again, while they're still attached. If they still appear to be shorted, try reversing your probe leads.
 
Chuck(G) said:
Check the diodes again, while they're still attached. If they still appear to be shorted, try reversing your probe leads.
Click to expand...

I am not sure what you mean by this? Are you saying to just flip the probe leads from one end of the diode to the other? If so, I have already done that and that is why I can say the current goes both ways. W/ the other diodes the current flows only in one direction. But with those two in the circuit I get current flow no matter the orientation of the probes.

On the 12V end of things with the PS plugged in I get a reading of 46 on the + (yellow) and -7.9 on the blue wire. W/out the PS plugged in I get no readings.
 
Right now, it's almost impossible for me to figure out how your +/-12 supply is wired without some sort of a circuit diagram. Can you trace out that side, from the transformer secondary on out to the yellow leads? In particular, what is that component with the gray wires attached to the heatsink and connected to the board near the fan connector?
 
Chuck(G) said:
Right now, it's almost impossible for me to figure out how your +/-12 supply is wired without some sort of a circuit diagram. Can you trace out that side, from the transformer secondary on out to the yellow leads? In particular, what is that component with the gray wires attached to the heatsink and connected to the board near the fan connector?
Click to expand...

Thats about where we got stuck as well. As for the Grey wires I think it is a temperature sensor. I found a refurbished unit for order and placed an order for it. However, after talking to them they don't even know if they have it in stock. I'll know by Friday. Assuming I can get a PSU, power up the machine then the real fun begins. I have not been able to find the EISA cfg file for the board yet and need to replace the batteries for the board. But one thing at a time... First need to POST!
 
Is there continuity across the temperature sensor? Any labeling on the part? Where do the ends of the wires connect? (Note that I do not have a photo of the fail side of the PCB, so it's impossible to say).
 
I have to check on continuity. There is no labeling on the part and it is my "guess" that it is a temp sensor. I can provide a picture of the backside of the PCBs if that helps.
 
Well, let's see what a continuity test says (lift one end from the board if you're not certain of a good reading). A photo would help.

Usually, the +12 and -12V supplies on a PC PSU are pretty simple. Usually just a couple of diodes, some inductors (for filtering) and capacitors. Maybe a pass transistor for regulation.
 
Chuck(G) said:
Well, let's see what a continuity test says (lift one end from the board if you're not certain of a good reading). A photo would help.

Usually, the +12 and -12V supplies on a PC PSU are pretty simple. Usually just a couple of diodes, some inductors (for filtering) and capacitors. Maybe a pass transistor for regulation.
Click to expand...

Sorry for the long delay in response but real life keeps popping its ugly head in! :) I did the continuity test on the "temp sensor" and there is continuity. I will post pictures of the underside of the board as well as a closeup of the upright standing PCB.

The refurbished PSU fell through. The place never had it. I thought it was to good to be true. I found another Asian Micro Sources PSU with almost the same power characteristics as this one. However, the physical PSU shape is different. It is my hope that AMS went the cheap route and used the same PCB layouts and just mounted the PCBs differently for a different physical form factor. At the very least I can power test the MB and see if there is any point to continuing this...
 
You must log in or register to reply here.
Back
Top