Capacitor Lab - Failed Capacitor Replacement

_Failed Recapping



	What to do if Replacement of Capacitors was not a success?

	Here are some tips to help you if you have recapped a motherboard and it does not post or is unstable. The most important thing is to stay calm and check carefully not start doing the recapping job again. If you are tired or upset then leave it for tomorrow.

	Did you do a Full Recapping?

	A full recapping consists of replacement of all bad capacitor brands on the motherboard that are 1000uf and above. Preferably also the capacitors which are smaller uf but reasonably large voltage (say 300uf 25v and 470uf 16v) should also be replaced. Replacement should be done with new Low ESR capacitors from a quality manufacturer. Using old capacitors from another board is not recommended. Using capacitors which are not Low ESR will cause instability and bad capacitor type symptoms.

	Leaving Bad Caps is Not OK

	Leaving capacitors from bad brands on the motherboard may cause instability even if you have replaced the worse looking ones with new caps. This is because the new caps will struggle to cope with the excessive ripple introduced to the circuit by the bad caps. Even if a capacitor is looking OK but is from a bad brand it is recommended to replace.

	Was the board POSTing before the Recapping?

	If the board did not POST when you received it then there are probably other problems with the board that capacitor replacement did not solve. If the CPU fan only twitches when you apply power then there can be damage to traces or a Mosfet can be shorted or the VRM chip is toast.

	PSU may have Bad Caps also

	While you have attended to the caps on the motherboard, there may be also bad capacitors inside the PSU. This is to be usually expected if the PSU is of the same age as the motherboard. Bad caps in the PSU can cause instability as the motherboard caps struggle to cope with the excessive ripple in the power supplied to them. They can also cause power on problems where many tries are needed to start the computer. Check the PSU for bad caps and replace them or get a new PSU.

	Memory may be Bad

	A motherboard with bad caps may actually also have bad memory. Whether this is from the bad caps or whether this is just a coincidence is unknown. Check the memory using memtest86+ preferably on a known good motherboard. It should have zero errors after many passes otherwise the computer will be unstable even if the caps are ok.

	If you have done a full recapping and the board was POSTing before you did the recapping and you have checked the memory and PSU then we can look into further problems :

	Have the board on your workbench

	Proper troubleshooting is done on the workbench and not in the case with only the minimum components connected that are required to get the board to post.

	Clear CMOS

	For some reason a board may fail to post after recapping until you clear the CMOS. Troubleshooting should anyway be done at default settings and then after the board is checked to be stable then overclocking and memory settings can be tweaked.

	Check cables again

	In your hurry to see if the recapping was a success you may have mistakenly forgotten to connect a power cable or monitor cable, something silly like that. Check carefully before you mistakenly decide the recapping was bad.

	Check compatibility of hardware

	Is the processor, ram etc actually compatible with the motherboard you have recapped? Especially when working on other people's hardware you may be testing with incompatible processor or ram.

	Then check for damages or mistakes during the recapping :

	Damaged Traces due to Heat

	Check for damaged traces (the many tiny thin wire lines on the board) particularly around the thru holes where you installed the new capacitors. Excessive long heating can lift the traces. This can be repairable but it is not easy.

	Damaged Traces due to Bad Handling

	During removal and reinstallation of the board in the case you may have scratched some traces. This can also happen during heatsink installation or just the screwdriver or iron slipping. This can be repairable but it is not easy.

	Metal Debris causing a Short

	Check carefully for pieces of solder, solder splatter or cut capacitor leads which are stuck on the board and shorting out two contact points. Remove these. If there is a short the power supply usually clicks and goes off immediately.

	Soldered Short

	Check that you have not soldered two thru-holes or other points together by mistake. Remove the short using the soldering iron, solder sucker or solder wick.

	Damaged Thru-hole

	Due to excessive heat you may have damaged a thru-hole during removal of a capacitor. This is rather difficult to repair.

	Check Soldering was Good

	Examine the soldering that you have made with a magnifying glass. Perhaps you have made some poor looking connections. Resolder them.

	A beginner looking at this list may think that the task is rather difficult but it is not. Damages are usually caused by carelessness or a poor soldering iron that requires very long heating (the kind that may result in the "paint" coming off the pcb) and therefore damages traces or thru holes. A careful beginner with decent equipment and after some practice on a trash board will most probably succeed with their first recapping.