TC electronic D.Two PSU problems

[redmojosteve]

I have recently acquired a TC Electronic D.Two which has a PSU problem and it keeps on blowing fuses. Having built a lot of gear from this superb forum I was happy enough to open the enclosure to see what is or was going on. The switching FET 2SK1637 has blown but whether it finally gave up in its own right, or something else pushed it over the edge I don't know yet.
Generally the other components appear visually fine with no obvious signs of overheating and the PCB tracks are not damaged either. In any case it would seem sensible for me to replace some of the caps with new ones. I have looked to buy the FET but there is more than one variant (2 ohm or 3,3 ohm being one of the parameters that spring to mind).
If anyone could advise me which FET it is, it would be helpful. If anyone has any experience of these PSU's and can offer any other advice I would be most grateful.
Thanks
Steve

 

[pvision]

Join my D-Two Power Supply Resuscitation Society! The D2PSRS pulls apart pieces of switchmode crap and reassembles them in the hope of salvation

http://groupdiy.com/index.php?topic=63922.msg809204#msg809204

I just recapped an M2000 power supply and it's just the same. The 5 Volt rail drifts about from 2 to 7 volts with no apparent rhyme or reason

I am OK with ordinary power supplies as they are so simple. Now it's above my pay grade

There are two +5V outputs to the PCB. I am not sure why but have a theory that one powers the standby circuitry and the other wakes up and powers the unit when it's switched on from the front panel

Something pulses the front panel power LED - I wonder what does this?

Nick Froome

 

[moamps]

Maybe you can find here

http://groupdiy.com/index.php?topic=20801.60

some new ideas what to check.

 

[redmojosteve]

Thanks for the responses. Like pvision, I am quite happy with conventional power supplies but the switching ones need some expertise that I don't have yet.
I'll let you know how I get on
Cheers
Steve

 

[radardoug]

At least one TC supply I have seen has no current monitoring on the fet, and so the fet can blow easily. You can add current limit reasonably easily. As to fets, buy something with the same or higher voltage and current ratings. Look for a low value resistor in the bottom end of the fet to ground. If its not there you have no current limiting.
To add it, put the resistor in . Then put an npn transistor with emitter to ground, base to top of resistor, collector to fet gate.
The resistor value is worked out by ohms law, working on .5 volts turnon voltage for the transistor.
So V = I * R
.5V = I * R
I = .5/R
If R is .5 ohm, current is 1A
If R is 1 ohm, current is .5A.