IR3M02 from Sharp Corporation. Find the PDF Datasheet, Specifications and Distributor Information. IR3M02 Pulse Width Modulation Type Switching Regulator Contrl ic. Details, datasheet, quote on part number: IR3M Electronic component datasheet for IR3M02 manufacturer SHARP. Free doqnload!.

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The voltage selector switch actually reads ohms when in V, not sure if that’s by design or 20 years or corrosion. What if there is a short on the secondary of T1? The dagasheet doesn’t seem to have any markings on it indicating what it is. Looking at your photo, I’m guessing the back connector by the fuse is your AC input and the connector by the transformer is a voltage switch aka J1?

I get about 7V on the 12V and 3V on the 5V for a second and then it dies. We took a break and went out to a bar for a couple of beers, then the solution came to me and I went back to the shop and fixed it.

I tried to scan it to avoid perspective, but the capacitors are too high, which makes the PCB very dark.

IR3M02 Datasheet PDF

That kick is just from the start up circuit. I have looked through a few different diagrams of PSU design and not seen anything like this. I think your voltage doubler circuit is unbalanced due to an open main cap or maybe an open thermistor?

After you try Chuck’s suggestion with a step down, if you’re still thinking bad T1 you could unsolder the datashest and see if the voltage raises to VAC It was hard soldering when I was tipsy but I never told my boss Connect DC supply via a current limiting resistor eg ohms to SMPS IC – check voltage on each IC to determine that supply is within range, increase DC voltage until all ICs are powered up, check voltage drop across current limiting resistor for current drain.


Without a schematic, it will be hard to figure out which caps are bad but I would suspect the ones on the 5V supply used for a sample voltage. It’s probably the lighting but I circled what sure looks like a solder crack Yup some manufactures put the value on the cap as is, 2.

A project a long time ago. Or have i got this all wrong? I’m out of ideas but thinking you may be right that the primary of T1 is shorted.

If you’ve got a DMM with a capacitance scale, lift one ratasheet the legs from the board and verify the value. Thats a bit close to the 25V rating of C Datashete googling that IC brought up some diagrams that are quite similar but not the same. I have checked the voltages switch and it’s set correctly. That’s like an 80V loss which seems to be the increase you are getting across the datadheet so maybe the excess current is passing thru the rectifier bridge.

The outputs are taken from windings on the transformer, rectified and filtered. DMM’s are just not fast enough. I always get confused when DC is connected to AC. Connect J1 and measure AC across the red points. If not, check whatever the device is highlighted in blue. One thing i did notice is that the main filter caps that have VDC across each of or3m02 are rated as V uF?

One suspect is the cap labeled C4 the blue one –if I’m guessing right, it’s usually a non-polar one and ripple current can run very high and heat it.

IR3M02 Sharp, IR3M02 Datasheet

I’m guessing datawheet Vcc on pin 12 provides a 5V dattasheet on 14 which is compared to the sample. Retraction – looking further at it’s location it looks more like a tuning cap by the transformer.


The voltage selector switch is set as open. I haven’t been exhaustive, partly because its a bit beyond me and partly because it is only an AT PSU. One time a coworker and I were doing overtime work in the evening. I will have a look at it tomorrow.

dtasheet The datasheet i found for it is dreadful quality. If you’re running it on the V setting, the rectifier circuit is placed into a voltage-doubler configuration and output should be no higher than about V 1. That can’t be right. Your AC should be plugged into the other connector where the fuse is.

I have been looking for a startup resistor but I don’t seem to be able to find one. I will try to do a circuit diagram tomorrow of this part of the circuitand point them out. Ahh yes diodes, i will desolder and check. Here are his 1.

Datasehet anyone have an idea of how to do this? Its been a while since I read the values on a power resistor, is the placement of the ohm symbol supposed to indicate the if3m02

What is the AC across the blue? Most of the small caps i have replaced. You have J2 in the right place.

Some PSUs have a protective “crowbar” overvoltage circuit, but it’s been a long time since I’ve seen one of those fail. Most of my troubleshooting back in the day was using my scope as a DC meter also. The LM requires a power supply voltage of: In V mode it is open. The main caps are not bulged, yet V an allits just the light. I’m not sure if this is the circuit or just the multimeter, its very cheap.

It got me back out of bed.