Hi all, Related, is there a generally recommended guide for bringing up old PSUs? Cheers Alex On 7 Aug 2012, at 16:55, "Rod Smallwood" <rodsmallwood at btconnect.com> wrote:

Some swear by it, some swear at it :-). In particular (for old-time radios) if the rectifier is a valve (vacuum tube), it'll not do much with a low mains input voltage because the heater will be runnign at a low voltage too. So you are not doing a lot of good by 'running things up slowly' My methd is to check for shorts first. Check the capactiors and rectifier diodes. Then, woth the scrondary windings disconencted fro mthe rectifiers (if this is easilly possible), power up the trnasoformer with a seires light bulb. The bulb should be dark, the secodnary voltags should all be what you expect. If the bulb is glowing, supect shorted turns i nthe transformer. Then conenct the rectifiers, etc and try again. The bulb might 'flash' at switch-on (due to the charign of said capacitors), but if it continues to glow brightly, there's a short somewhere. If all's OK, power up withotu the seiries light bulb nad check the output voltages. Oh yes. Make sure the mains input fuse (and any other fuses) are correct. They are there for a reason!. In particualr the mains fuse will often protect hte transformer if somethign is shorted. Well, uless soem idiot has fitted a nail or something! if you want to reform electrolytics, it's better to do it separately with the capacitors out of the PSU using a bench suply and series resistor. SMPSUs approximat a constat _power_ load to the mains. What this means is that they draw more current as the mains input voltage decreases (the chopper transitor is turned on for logner, basically). So low mains input voltages can resuylt in overcurrnet damage. For SMPUSs, I always assume the previous owner has used the thing. So I check the fuse, if it's shattered or blackened, I tread carefully becuase there is likely to be a major problem on the mains side. If the fuse is OK, and nothing obvious is shorted, I conenct a dummy load and fire it up. -tony