bad caps preventing video output?

[tukidid]

on older mobo will not output display no more ,but cpu,fan seems to be working-
does this sound like a caps around the graphics chip problem or some solder gone bad

[Dgtech]

Re: bad caps preventing video output?

You have to explain more first. Do you have a mobo with the integrated video? or is it a separate card?

If it's built in, try to disable it and add a separate card. If not built in, just swap the card to see if that fixes it.

[kaboom]

Re: bad caps preventing video output?

I assume you have a keyboard hooked up to it. Look at the numlock, capslock and scroll lock LEDs when turning the system on.

Do they light up for half a second and go out? Or do they stay on? Former would be if the board came out of reset, latter would be if the system were frozen.

If your keyboard LEDs stay lit and you have no video, check the following: power good signal from PS (gray wire) should read 5v; neither north/south bridge should be too hot nor any MOSFETs in the VRM/buckverter for CPU; if you have one, make sure the reset switch or its wires are not shorting.

But if those keyboard lights flash and go out, just try swapping the video card, like DG suggested. Don't forget that you may have to move a jumper or remove/replace the CMOS battery to 'force' the BIOS to default back to 'Automatic' selection between onboard GFX and a card.

Sometimes, you have to remove battery/reset CMOS to get onboard video, set video option to 'EXT CARD' while connected to onboard GFX, then kill power and install card and finally, your card works.

What caps do you have or suspect? Do you have a meter?

Good luck,
-Paul

[tukidid]

Re: bad caps preventing video output?

no video without/with external graphics card ,what are you supposed to get ohming into pwr/gnd pins of good mobo (when off) and is VRM a chip close to cpu(which gets warm)
Caps are LICON throughout but suspect ones are 2 1000mF close to mobo integrated video out(but then again they look visually ok and if external card did not help than that is not it)

[kaboom]

Re: bad caps preventing video output?

VRM- Voltage Regulator Module

Your CPU does not run right from the 12 or 5v from the PS. The VRM is in fact a small buck converter, a switching power supply, that takes the 12 or 5v and converts it to the voltage the CPU requires- 1 to 1.3v for current CPUs.

On anything remotely recent, the VRM is that group of inductors, MOSFETS, and electrolytic capacitors for this purpose in the immediate vicinity of the CPU. Not all caps by the CPU skt are for it though. Sometimes there's a small cap, like 100u/16 or 25v for the fan. Or even several 1000u/6.3 or 10v for the keyboard, mouse and USB connectors.

On something like a Pentium MMX 233 or older, the VRM is diminutive. One high side MOSFET, sometimes just a large schottky diode in lieu of a low side MOSFET for synchronous rectification, one toroidal inductor for the buckverter proper, and a little ferrite bead-on-a-lead for the isolation choke. Only three or four caps.

Ohming out the various pins on the power connector can be misleading- you may have several tens to several thousands of ohms from various power pins to various ground pins on a functioning system. Things like pullup and biasing resistors can give you a false indication of a fault. What I suggest is checking all supply pins on your board's ATX connector to a ground on the board- be it the mouse/kb shield or the ground pins on the ATX connector.

What you'd do is stick the black probe to one of the commons in the diagram, then touch the red probe to all others except common/gnd.

In other words (20 pin as example) test from:
Use 'continuity check'

Black: 3
Red (move from):1, 2, 4, 6, 8, 9, 10, 11, 12, 14, 18, 19, 20

You are only looking for a dead short- 0 ohms. Touch your test leads together, the reading should be very close to 0. If you get something like 2.4 ohms with test leads shorted and the reading varies when you flex the leads, they may be starting to break inside their insulation. Sometimes, just the jacks get dirty- a shot of DeOxIt or CRC's 2-26 will take care of that.

Once you have determined that your meter will read 0 or even .2-.3 ohms with leads shorted, go ahead and test those pins as in my example.

Be aware that if anything was shorted to ground, the power supply will shut down if it's a good one or blow up if it's not so good.

What brand/type of power supply are you using? What are the voltages under load?

I was serious with the whole bit about the keyboard LEDs- hook a keyboard up and tell me what the lights do. Remove the memory and see if you get beeps out of the system speaker. This would be the 'speaker' header on the board near the front panel connections, not the onboard audio, if any.

Would you happen to have a model number for this board? How about a manufacturer's brand? A picture of the board would go great lengths to help you out here. It wouldn't happen to be an NForce chipset would it? What type of CPU does this board take, P4, P3, P2? Just how old is it?

Was the board sitting around not being used, or was it used everyday? What do you mean by "external graphics card?" I guess you meant a PCIe, AGP or PCI card, not one of those USB things.

Any signs of leakage by any caps? (Probably)

Sorry for all the questions

[tukidid]

Re: bad caps preventing video output?

no shorts on power connector,
swapping 2 other power units,ram or cmos battery makes no difference -no beeps,keyboard flashes, cpu worms up but no video with on board agp or external pci graphics

[kaboom]

Re: bad caps preventing video output?

Chipset, specifically northbridge, not working or initializing completely. Get rid of those Licons. Use Nichicon HE, HM after 2006, PJ, PW, PM, Panasonic FC or FM. Any of those will work. No fleebay junk.

Any 1000 mikes in the vicinity of the northbridge should go- no need to make extra work for yourself by only changing a few now, only to have others go. Usually, there are small caps, 100u/16v, even 22-47u/10 or 16v. Don't believe 'small caps aren't important.' Those little caps around the northbridge can be for such things as filtering for internal reference voltages or supply/stage decoupling. In other words, they _are_ important.

Did you have this system off for a while and try to bring it up, only to have no video? Or was it running and the video quit outright?

Take a hair dryer and warm the board up. Kill power to the system and bathe warm air from the dryer over the entire board for a minute or so. Get it to about 120 degrees Fahrenheit. This will warm the caps and make what electrolyte they may have more active and can marginally improve their characteristics. Possibly to the point that the board's behavior changes. You might even get it to give video or at least beep codes.

This is exactly what I did with a certain nightmare 5EH5 board back in 2001. In this case, it was the caps in the VRM- nasty green 'wendell' things. I'd go try turn it on and fans ran, chipset and cpu got warm, keyboard lights stayed on. No video, no beeps, no nothing. Leaving it on for a while then hitting the reset button would sometimes help it along. So I heated the board and got the caps warm. Hit the reset again and it came right up. Would stay running till it was off for a while and the caps cooled. Replaced caps and it was fixed, at least until the internal traces in the cheap board started breaking.

Hope it helps,
-Paul