Problem with a 30 volt 20 amp variable power supply. Repair help.

[Ylli]

So when it is operating, you have about 20 volts across R414. That indicates that this section is drawing 20/.82 = 24 mA. - that is not excessive.

If it runs for 5-10 minutes, it might be something thermal. Does anything seem to be getting hot? If you power it up, and find it shuts down in 5 minutes, then turn it off and turn it right back on, does it go again run for 5 minutes or does it shut down much quicker?

 

[mramos1]

Ahh! I do have to let it sit for 5 minutes are more to get it to turn back on. I figured a cap slow discharging. I did hook back up the 105 on last test. I have a laser/thermometer I can check it for hot parts..

 

[mramos1]

OK. So I solder in the R105 (last change). Just went for laser temp reader.

Now, the thing has not cut off for more than 2 hours and still going (normal run and die is about 5 minute range). I have a .6 amp 12 volt load for that time.

Looks like I will dig out some power resistors and see. It is 60 degrees and the cover's off. Normally it was 90 degrees. in that room.

Cold solder joint? It was a zener diode and cap across it, both legs in the same though hole.

Any ideas? I also now hear a buzz/chirpping sounds, very faint when I play with the voltage knob.

 

[Ylli]

OK. So I solder in the R105 (last change).

Just to confirm we are on the same page.... You mean D105, correct? D105 is not a Zener, it is a fast recovery rectifier diode.
The chirp/buzz may be normal depending on the units switching frequencies - you might be hearing some singing of the magnetics.

 

[mramos1]

You are correct. For some reason I thought they were Zeners (my old eyes.). We are on the right track.

Both back in and it started working for hours today (never seen that). I added more load and it stayed on.. I flipped off and later flipped it on and it's back to the same 5 min or so and off with switch on.

I saw 128 degrees F on the cop223, rest of the parts were around 80.F. It's staying on again, if it drops out I will hit with light freeze mist and see if it will restart faster. What do you think.

 

[Ylli]

if it drops out I will hit with light freeze mist and see if it will restart faster. What do you think.

Sounds like a good idea, although the TOP223 might be shutting itself down because it is getting too hot, but it might be getting too hot because it is being overloaded. I assume the TOP223 is on some form of heat sink. Sometimes the thermal grease dries out and becomes less effective, you might try lifting it, cleaning the old grease off and using new stuff.

You indicated with D105 and D108 removed, the TOP223 section continued to operate, correct? With D108 reinstalled and D105 still out, then it would shut down, correct? With the thought that the section powered by H2 is drawing excess current when it gets hot, you might want to check the operating temperature of D108, C106, & C105.

 

[mramos1]

It is taking a lot longer to drop out now for some reason.

But it did, cop223 was 130F and I cooled it and other heatsinked items. Did not bring it right back. It has to sit to recover. Also, the top223 is the only TO-x device in there that does not have a heatsink.

When it shuts down next time, I could power off and unplug and short a couple of the larger caps?

I see you are online. There is a chat and start conversation. Never try either, but this pace if fine for me too. I'm US EST.

 

[Ylli]

I'm kind of running out of ideas. Maybe someone else has something to suggest.

 

[mramos1]

Ylli, Thanks for the help. I might order cop223 and opto and wait for them to get here and change them. Cheap and can not hurt.

Thanks again for the help.