L'alimentatore del 5155 IBM

IBM 5155 Power supply

Yes, and the control chip is on the 'output' side of the PSU, the drive to the bases of the chopper transistors is transformer-coupled. There are 3 little daughterboards in there. One is an inrush limiter and contains a relay that shorts out a power resistor once the smoothing capacitors have charged. Another contains the overcurrent protection circuit, and, IIRC, a 12V regulator. The last contains the overvoltage protection circuit (the chips on that board are LM339 quad comparators).

There are 2 protection circuits. One is a current sensor, there's a current transformer in series with the chopper transformer primary winding. The other is a set of voltage sensors. Whatever you do, don't disable any of the trips. If there really is something wrong, the results would be spectacular!.

(Tony Duell)

One thing that I've seen on some switchers is something that watches to see if the transformer/coil core saturates. It is a simple coil that picks up the stray magnetic fields when the coil is overloaded( that often causes the blowout current in the switching transistor ). One has this detection circuit clamp the gate voltage to the switching transistor when it see excess leakage flux. It works better than a simple current detect because it self compensates for the cores temperature. If there is a current overload, it will keep the circuit from powering up. One could put a LED on it to visually detect the condition.

(Dwight K. Elvey)

Troubleshooting procedure

Check you're getting about 350V DC across the mains smoothing capacitors (2 electrolytics in series)

CHeck you're getting power to the 3524 (if not, troubleshoot the circuit round that little transformer you mentioned)

Check that the 3524 is oscillating.

OK, I've looked at mu schemaitcs. I am asusming this supply is the same

as the one you have.

The 3524 supply, at least at startup comes from the mains transformer T5

on the mainboard. C21 (470uF) is the smoothing capacitor for that.

Now, the 3524 is oscillating, but I assume it's producing no output to

the the driver transsitors Q5 and Q6, right? There seem to be 3 possibilites

1) The 3524 is defective

2) It's shut down. The shutdown pin is driven from the SCR CR11 on the 1144-01E PCB. That takes inputs from the current sense circuit and the overvoltage shutdown. Since you say that the shutdown pin is not asserted (do check this at the 'other' side of R11, 6k8), I think this is not the problem weeither.

3) The other way to shut down a 3524 is via the comp pin (compensation).

This is actually the output of the error amplifier, of course. In this supply, IC2a (LM339) can clamp this pin to ground. It appears this occurs if the startup voltage is not high enough (the inputs to this chip are the reference voltage form the 3524 and a potted-down version of the supply to that chip).

Data sheet del controller SG3524 della SGS Thomson

Piccolo corso per riparare questo alimentatore

	The main controller, SG3524 of SGS Data sheet del controller SG3524 della SGS Thomson
	This is the auxiliary power supply. T5 il a little transformer from 220V to about 6Vac. The bridge maked by CR24 to CR27 rectifier and the capacitor C21 is the filter. The voltage measured along C21 is about 8V. C21 = 470uF 16V CR24 .. CR27 = R 142 (I have substitute with normal 1N4007)
	The main rectifier and the main voltage connector
	The main filter capacitors
	The inrush current limiter. The relais shortcut the 4 ohm resistor after a short delay, during power up.
	Questa e' la piccola scheda del limitatore di corrente. La corrente viene misurata tramite un toroide, nel cavo di colore nero che potete vedere nella figura accanto, che e' in serie al trasformatore principale. The current limiter board. The current is picked prom the black conductor, you can see in the picture, via the litte toroidal transformer.
	The voltage limiter board
	The switching transistors
	The switching transformer




	The output of the voltage protection board is pin 9, that receive signals from CR3001 and CR3002 diodes. Pin 8 is the power supply for the board. IC3001, IC3002 = LM339 C3001 = 47uF 16V
	La piastra di controllo tensioni si inserisce sulla scheda principale in questa posizione.