Enginuitor

Uh oh... Just got a quote from MicroSemi, the only known maker of the PIC647: o__0 Methinks it may be time to research an acceptable alternative to this IC! Here is the manufacturer's datasheet: http://www.microsemi.com/datasheets/WT7-12.PDF Below is a schematic of the PIC647. It is essentially a small transistor driving a bigger one. If I were to basically create a makeshift substitute for this part, can anyone reccomend values for the components?

Q1 base is about 12.6 volts. Q1 emitter is about 12.2 volts. Q9 base is about 3 volts with C5 disconnected from input side, and does the ramping thing (0 to 45 volts) when C5 is fully connected. Q9 emitter is of course the final voltage output, and also does "the ramping thing". Very curious. I am ordering replacements for Q9 and U9. Anything else I might want to replace?

Took some more measurements on U9. Its output with the cap disconnected reads on the meter at about 19VDC with voltage knobs turned all the way down, and 23VDC when turned all the way up. In addition, when switching the meter to AC, it reads from about 1.1 volt to 0.8 volts respectively, at approx. 15.5kHz. The current knobs appear to have no effect. Unfortunately, I don't think my oscilloscope can handle very high voltages on DC coupling, so I can't see exactly what is going on here. Any ideas?

Interesting. The U9 input is at about 65 volts (it's connected directly to the input) while the U9 output behaves exactly as the final voltage output; it ramps slowly up to about 45 volts before the OVP kicks in. Next, I will disconnect C5 on the input side so I can see exactly what's coming out of U9.

Desoldering is putting a soldering iron against the solder to re-melt it, then either using something to wick/suck it away, or just pulling the component out while it's still hot.

Why not just desolder them??

Thanks again Ante! After I get all my real-life duties taken care of today, I'll hunker down and start taking measurements. Updates to come...

Thanks for all your help. Since we're past the capacitor issue, let's move this discussion into my other thread (Electronics Chit-Chat -> "Help with power supply repair") so we don't have to jump back and forth.

Here is the schematic for those who don't want to deal with the PDF: Click here to enlarge

I was halfway through the calibration steps when a wispy trail of magic smoke lead me to R43 (see schematic). Perhaps something has gone wrong with U2 (MC1723CG) or the surrounding circuitry. I would appreciate anyone's input. I have posted the full schematic so people no longer have to download the PDF:

Long story short, I set up the back terminal strip according to the strapping diagram for local sensing and control. It miraculously worked!... For a short period of time. Everything was working fine, so to test the current output I put a small wire across the output. I started easing the current up, and it did fine up to about 3 amps, then suddenly the needles dropped to zero. I think I may have heard a small click, but I'm not sure. This is a 10-amp power supply -- What happened?? Now it's in a truly wierd state. When I turn it on, the voltage slowly rises, charging the output capacitor, until it hits the OVP cutoff point (set by a small potentiometer; I have it at about 46 volts) at which point the relay shuts down the output stage. This happens regardless of the voltage settings, though a higher setting seems to make it happen more quickly. Obviously the system is no longer regulating properly. Currently I am running the manufacturer's calibration procedure to see if that might catch the problem. By the way, there is a full schematic in the pdf I linked to. Any suggestions?

It miraculously worked!... For a short period of time. Everything was working fine, so to test the current output I put a small wire across the output. I started easing the current up, and it did fine up to about 3 amps, then suddenly the needles dropped to zero. I think I may have heard a small click, but I'm not sure. This is a 10-amp power supply -- What happened?? Now it's in a truly wierd state. When I turn it on, the voltage slowly rises, charging the output capacitor, until it hits the OVP cutoff point (set by a small potentiometer; I have it at about 46 volts) at which point the relay shuts down the output stage. This happens regardless of the voltage settings, though a higher setting seems to make it happen more quickly. Obviously the system is no longer regulating properly. By the way, there is a full schematic in the pdf I linked to. Any suggestions?