Indigo 2 Impact +5V standby

[Camiel]

My Indigo 2 Impact doesn’t work anymore. Thank you Elf for your information about the Indigo 2 power supply. I am measuring no voltage on pin 5 on the left hand connector (+5V standby) with the motherboard connected. When I disconnect the motherboard I measure 5V.
When I connect another 5V power supply to pin 1 and pin 5 of the motherboard I measure 5V. But the current is about 130 mA, it keeps changing between 120 and 135 mA. I think that’s too high.
Can anyone five me some advice?

 

[Elf]

Glad it was of use to you! I would have to measure standby draw on a working Indigo 2 to see what "normal" is, but that would certainly be within the nameplate rating of the power supplies (e.g. 1A for 5Vsb).

If you draw 100mA or so from +5V Standby on the power supply while it is out of the machine, does it drop down to 0V? If so, perhaps the power supply has gone bad.

 

[Camiel]

This is the nameplate of my power supply. I think '+5 AUX.' is the 5Vsb? If that is true it is 100 mA.

I connected pin 1 and 5 to a light bulb and it does drop down to 0V. Even without seeing light for second. I used a 6V light bulb that draws 73 mA on a 5V power supply.

I found out the power supply used a LM317T without heatsink for regulation of the 5Vsb. Changing the LM317T and some capacitors did not help.

Next I bought another ZYTEC Indigo 2 Power Supply. I bought it in working condition but I don't have another Indigo 2 to test it. The 'new' power supply can't light up the light bulb either...

 

[Elf]

Ah I see, I was looking at my old non-Impact supply that had a higher rating, my apologies! When I have some more time, I can try to see what the current limiting behavior of my +5Vsb (+5V AUX) rail does. Unfortunately however that doesn't seem to solve your original problem...

I could also see what my Indigo 2 draws on the standby power line, though given your (much lower 0.1A) nameplate rating and the second (presumably functioning) I2 power supply, I would guess then that you were right in your original conclusion it is drawing too much. I think it would be an exercise trying to trace the standby power circuitry on the motherboard to figure out where the problem lies.

 

[Camiel]

While tracing the standby power circuitry I found out C40 is connected and getting a bit hot when I connect the motherboard to a 5 Volt power supply. Do you think its save to power on the standby power with this capacitor removed? And can I find out the correct values for this capacitor?

 

[Elf]

If it is getting hot it has probably failed; sometimes MLCC capacitors like that crack and short out. Since a lot of them are just used as bypass capacitors, I would think it is safe to try without it (though it's hard to be 100% certain).

If it has failed you won't be able to find the value of it; capacitors need to be measured using an LCR meter while out of circuit. If it is a bypass capacitor, they are often a value like 0.1uF or similar and the exact value is not often important. If it is for some other usage (e.g. an oscillator or other analog circuit), then the value will be more important and the only way to tell would be to find someone with an identical board, have them remove it, and measure it. Unfortunately MLCCs like that are not marked with a value.

 

[Camiel]

Good news!
I desoldered C40 and tested it. The capacitor tester says 'in circuit or leaky'. But 0,1 uF is to little to measure for it.

The I tried the motherboard without HD or graphics card. It turns on and I heard the startup harp sound! Then I tried my other power supply and it also works!

C40 is indeed directly connected to pin 1 and pin 5. So the best I can do is replace it with a 0.1 uF MLCC ?

I think C40 can be important for more people with a 'dead' Indigo 2.

 

[Elf]

It's more likely than not that it is just a bypass capacitor (e.g. 0.1uF or similar); however, I'd be a little hesitant to give a specific recommendation of what to replace it with unless we know the original value. Still, for the adventurous, perhaps just putting your favorite value of MLCC bypass capacitor in there will work.

I'm glad to hear your Indigo2 works though!

 

[Camiel]

Thank you for your help! My Indigo2 is working fine with a 0.1 uF MLCC capacitor.

After a couple of ours an other problem appeared. On the audioboard capacitor C57 exploded. C54 exploded a couple of years ago and ripped off a solder pad hence the patch wire. I removed C57 and it is working fine again. The solder pads are okay, I will replace it soon.