iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

[torgeson5kqs]

I have a 17" acbel imac G5 power supply API3PC94-290 that I've fully recapped, even the tiny capacitors, with panasonic FM and FC caps. Everything powers up except that pin 22 on the power connector reads about 14 volts. This should be about 20 volts when un-jumpered and about 24 volts when jumpered. Mine reads 14 volts either way. Any help would be appreciated to figure out what is causing this voltage drop.

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

M6 is bad.

Trace the line back from output to standby transformer.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

M6 is attached by screw to heatsink, has 3 pins and is next to 1000uf 35v cap. Looks like a fairchild ka78m.. (can't read the rest) this looks to be a line regulator according to mouser.com There are a couple different versions, which do you suggest?

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

Get the part number, then you'll know.

Now, why is it bad? What voltages do you see?

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

it's a KA7M24 (fairchild) the outer pins read 14.2v and 30v inner pin reads zero. When I take the voltage across the two outer pins it reads 18.3v. Also when I type in part number to mouser (same with digikey) it shows end of life and out of stock. Is there an equivilent?

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

sorry it's a KA78M24

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

So, again, why is it bad...?

You can answer that by reading its' description...

Look at (get) datasheet for pinout and voltages. Do this anytime you come across a new component you don't comprehend. Usually there's at least one application schematic in the datasheet also.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

Data sheet shows input,grnd,output. In this case the output needs to be at 24v which its not and the input appears to be about 30 volts. It can handle upto 40volts input. So I've found a couple that might work. The only really difference that I can see is the line regulation is 480mv vs. 100mv on the obsolete version and the output current is 1A vs. .7A on the old one. So it appears that part KA7824TU should work (TU shows that it comes in a tube, but case package is still the same TO-220

[Toasty]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

Yes!

KA7824TU will (and does!) work fine.

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

Most excellant.....

[torgeson5kqs]

Re: iMac G5 AcBel 17" API3PC94-290 Low Voltage on pin 22

Well what do you know it works know...... Thanks for the help on this Toasty, I really appreciate it.