Hi, I have got a Seventeam ST-200W AT PSU that I'm trying to repair. Its the original Full AT style like in the 5170.
When i connect the PSU to a HDD, for a load, the fan spins, and then the whole thing shuts down. It doesn't try to restart.
I have in the past just put an ATX sized, AT PSU inside and hooked everything together but I would like to fix it if possible.
I'm reading http://www.repairfaq.org/sam/smpsfaq.htm, and have identified that the primary side seems to be working, I get 240V at the rectifier, ~480VDC across both the filter caps, ~240VDC between the center of the two filter caps, and either side of the caps, and ~240V at the input to the main transformer.
I'm using a DMM so I'm not entirely sure if the power transistors are switching to pulse through the transformer. In fact I think this is the problem.
From the source above I have narrowed it down to the control section. The PSU is based on the IR3MO2. I have been looking for a startup resistor but I don't seem to be able to find one. I'm looking for a large one with the third band as blue or green, in the Mohm range.
There are 2 ceramic power resistors. one is labeled 5W 1[ohm symbol]K and is connected between the AC input and one leg of the AC pin on the main rectifier. The other, 3W 51[ohm symbol]K, has one leg connected to one side of the main transformer T5, and via a ceramic capacitor to a tiny transformer T4. Its been a while since I read the values on a power resistor, is the placement of the ohm symbol supposed to indicate the multiplier?
The IR3MO2 is getting 7V at its VCC pin, which is the minimum voltage it is supposed to operate at.
The secondary from T4 goes back into the control circuitry, as does the secondary from T1. Each of T2 and T3 is connected to a power transistor, and the other side of T2 and T3 lead back to the control circuitry.
Photos: Sorry they are a bit grainy.
Does anyone have any ideas? Any help appreciated
Oh and BTW, yes, i know how to discharge caps
When i connect the PSU to a HDD, for a load, the fan spins, and then the whole thing shuts down. It doesn't try to restart.
I have in the past just put an ATX sized, AT PSU inside and hooked everything together but I would like to fix it if possible.
I'm reading http://www.repairfaq.org/sam/smpsfaq.htm, and have identified that the primary side seems to be working, I get 240V at the rectifier, ~480VDC across both the filter caps, ~240VDC between the center of the two filter caps, and either side of the caps, and ~240V at the input to the main transformer.
I'm using a DMM so I'm not entirely sure if the power transistors are switching to pulse through the transformer. In fact I think this is the problem.
From the source above I have narrowed it down to the control section. The PSU is based on the IR3MO2. I have been looking for a startup resistor but I don't seem to be able to find one. I'm looking for a large one with the third band as blue or green, in the Mohm range.
There are 2 ceramic power resistors. one is labeled 5W 1[ohm symbol]K and is connected between the AC input and one leg of the AC pin on the main rectifier. The other, 3W 51[ohm symbol]K, has one leg connected to one side of the main transformer T5, and via a ceramic capacitor to a tiny transformer T4. Its been a while since I read the values on a power resistor, is the placement of the ohm symbol supposed to indicate the multiplier?
The IR3MO2 is getting 7V at its VCC pin, which is the minimum voltage it is supposed to operate at.
The secondary from T4 goes back into the control circuitry, as does the secondary from T1. Each of T2 and T3 is connected to a power transistor, and the other side of T2 and T3 lead back to the control circuitry.
Photos: Sorry they are a bit grainy.
Does anyone have any ideas? Any help appreciated
Oh and BTW, yes, i know how to discharge caps