IBM 5155 PSU testing with minimum load (free magic smoke and exploding caps included)

Testing an IBM power supply from an old IBM PC (51510 / 5160 / 5155) without it being connected to the motherboard is not trivial.
I had read online that the IBM PSU won't start if there is insufficient load on it, and adding a hard drive or a fan is simply not enough.
I decided to put this to the test, and see what was needed in order to start the IBM PSU.

[@edward_grabczewski]

Great tip. I'll be doing this next week!

[@lelandclayton5462]

220 ohm resistor on the five volt rail will kick start it. However you would want to use a high wattage rated resistor.

[@justsheeeps134]

What of we connect some resistor in series but each of them is just 1 or 2 watts ?

[@Romanon26]

Nice, I tried two 3.5" drives but it wasn't enough so I am using old 5,25" FHT disk drive, which is enough to start IBM XT/AT power supplies

[@Inject0r]

Very informative. Thanks!

[@Inject0r]

Darn those low powered peripherals! 😋

[@AntonFetzer]

What resistor do I have to put into a Molex terminator to jump-start a PSU ? Would be cool to have a little terminator so I can test my PSUs, because I have a cupboard full of them and would like to sell them, but I don't want to risk my mainboards or hard drives when testing them.

[@pipschannel1222]

One mainboard will be enough too ;-)

[@drakethedragon457]

Any switch mode PSU requires a minimum load in order to start for whatever reason

[@pipschannel1222]

Not all of them. I have 3 AT SMPSs that do start without a load. I wouldn't recommend it though as some of the IC's will get very hot

[@Ramdileo_sys]

come on @ RetroSpector78 .. this makes no sense ... the PSU run fine without HDD ... and without Floppy ... just with 1 MotherBoard ........ so what you need to recreate... is the load that a motherboard put to the PSU .. and in the pins where the motherboard it puts that load...

[@Stoney3K]

This is hardly specific to IBM supplies, it applies to pretty much *any* switch mode PC supply.

[@pipschannel1222]

Negative. A lot of them do indeed but I own 3 AT PSU's that start up fine without any load. It isn't healthy but they do start..

[@maurice2vd6]

Ah you made a video of starting up Power supply. Good thing Alway startup Power Supply without any thing attached of your precious computer parts. Better to reform the main 400V/450V Capacitors. How? With slowely turning up the voltage and watch the current. Look up "Reform Capacitor". Capacitor is a pure chemical device, a bit equal to a car battery. After long stay without power the have to reform. If you suddenly put full power on them they will break down due to very high current. Old ones at start up are just like a full shortage. Alway's replace capacitors in especially PWM -PSU's with the Low-ESR variants. Then look at the datasheets for Life-Time, often only 1000h or 2000h, Better to look for the highest Life-Time app. 10.000 up. Old electronic device ,Never just put in the mains Plug and power up. ALWAY's inspect the power supply first and other visual problems. Look around electrolyte Capacitors for leakadge marks around the case, corroded pcb's. Or at the top if they already are buling up. due to gas and heat inside, thats why there are those grooves to make weak point so it can blow. Especially Computer logic ICs can not handle over voltage. Its done in milli seconds. To check your secondary DC output for a AC voltage component. Just put your V-meter on AC. That is also a marker for the condition of the secondary capacitors.