| zebelkhan |
I am trying to isolate a problem. I want to find out if my wires are too thin, or I have a bad power supply.
Problem: My carputer sometimes does not post on startup (the fans and the lights come on but no boot or drive activity). But if I hit the power button 4 or five times in rapid succession, it boots right up and runs normally from that point on. There are no issues when I restart the machine and it will run for hours without a hiccup. But if I turn it off, it usually will not boot again unless I do what I described above. The machine seems to be doing the same thing when I run it outside the car. There, I use a 60W AC-DC brick to power the built in power supply.
I have narrowed down the cause of the problem to not enough power at startup. Now I need to decide if the size of the wire that feeds power to my carputer is too small, thereby not letting enough amps through, or something is wrong with my built in power supply.
Set-up: Total current draw of the machine is about 50 Watts. Inside the case I have a 90W DC-DC power supply that doubles as a voltage regulator and startup and shutdown controller. Power runs directly from the battery to the carputer using a 10 ft long 18 or 16 gage wire. Ground wire is 2 ft long and is also 18 or 16 gage. When I was installing it, I thought this size was going to be good enough because it was just as thick, if not thicker, than the wires that fed the 100 watt / 8.3 amp fog lamps. Carputer uses only half as much power (50 watts-4.2 amps and the wires inside of it are thin too.
My question is: Considering the lenght of the positive wire, is it possible that it is simply too thin for its lenght and current draw? The wire does not get warm at all so if it was insufficient, wouldn't it get warm? Also, then why would it run perfectly once it gets going?
I really hope the wire is good enough. I installed it so well and so "OEM looking" that I hate to touch it! I prefer for the power supply unit to be bad as it would be easier to replace! :)
Any ideas? Thanks in advance....:) |
|
|
| mgthe3 |
I would think what you have is fine.
I have had problems with things like old VHS video cams not liking very tiny wire (I bet it was like 24), but I would think their startup amps are a whole lot more than ur carputer. I bet the strongest draw is ur hdd and fans spinning up, and that can't be much.
What's it sound like to you jaak? Anyone? A cap maybe croaked in the PSU?
You could always try a thicker wire jumped around for test couldn't you? |
|
|
| zebelkhan |
quote:
Originally posted by mgthe3
You could always try a thicker wire jumped around for test couldn't you?
Thanks for the input. The problem is that it is intermittent so I really can't tell if the fix was caused by the jumped wire or if it is simply one of those times that it decided to work! |
|
|
| mgthe3 |
ahhh intermittant things drive me nuts.......like my exch 2k3 server I was fighting a few weeks ago.....
I would think a substantial jumper would be a sure fire way to rule out the wire gauge guess though....at least the wire itself.
How intermittant is it? If you can simulate the problem in 1 in 10 powerups, you should be able to rule it out with the jumper.
orrrrr
Connections on the power feed?
Connections in the PSU to carputer?
Connections in general within the carputer?
Hell, maybe even the on switch. |
|
|
| zebelkhan |
quote:
Originally posted by mgthe3
Connections on the power feed?
Connections in the PSU to carputer?
Connections in general within the carputer?
Hell, maybe even the on switch.
Connections on the power feed? - Checked
Connections in the PSU to carputer? - Checked
Connections in general within the carputer? - Checked
Hell, maybe even the on switch. - PSU sends an on signal to the motherboard to turn on and boot. The board obviously gets the signal as the fans and the lights come on. So I would say this is checked too.
I can almost predict when it does not boot. It usually happens if the PC has been turned off for a little while, between 30 minutes to a couple of hours. In this case, it will NOT boot about 90% of the time. If the PC has been off for an extended period, such as overnight, it WILL boot about 90% of the time! |
|
|
| mgthe3 |
So, it doesn't post.
(rereading your initial post is always a good idea, I tend to sped read lately)
Does the hda spin up?
Your power wire seems substantial enough IMHO.
It could be the psu, especially since it doesn't like the ac/dc brick either. I would have to see a schematic of the psu and the motherboard to see how the fans spin up yet the boot prom doesn't do it's thing.....or the hda doesn't spin up.
The first thing should be to see if the hda is actually spinning up, it should do that blindly without the boot prom. If it does, then you are looking at the hdd controller asic. Why isn't the asic telling the hda to read into memory?
If it doesn't spin up, it is the psu--it does sound like a connection being thermal doesn't it. The repetitive button pushing getting it to boot sounds like something isn't getting a signal long enough to turn on the 12v to the hda.
Why can't jaak bring over an O-scope to chase the signals? :D
You have a tuffy for sure.
Good luck! |
|
|
| zebelkhan |
quote:
Originally posted by mgthe3
Does the hda spin up? If it does, then you are looking at the hdd controller asic. Why isn't the asic telling the hda to read into memory?
You have a tuffy for sure.
Does the hda spin up? Unfortunately yes! I opend the case and disconnected the ribbon cable to HD and I could hear it wind down.
If it does, then you are looking at the hdd controller asic. Oh boy!
You have a tuffy for sure. I know... :3:
I have heard others with the same PSU having a similar issue. I suppose it is possible that it does not power the 5 volt or 3 volt rails properly, and the reason the fans and the light come on are because that rail is only a regulated pass through. I tried to do this once but it is possible I missed something so I am going to take the PC apart again and messure the 5 and 3 volt rails right when it fails to boot to see if I have anything. Hopefully it will tell me something!
Thanks for your help. |
|
|
|
