Antec SP500P "resurrection"

[everell]

Re: Antec SP500P "resurrection"

You can determine the amount of voltage generated from your APFC circuit by measuring on each side of the APFC diode. The difference between the two readings is what that circuit is doing. The negative side of that diode should have about 390 volts on it.

Oops! Not correct. Do not measure DC voltage on positive side of APFC diode .... it has the switching signal on it. Measure the DC voltage across the two mains caps, then measure the voltage on the negative side of APFC diode. The difference is what the APFC circuit is doing. The negative side of the APFC diode with respect to common should have about 390 volts on it.

[Khron]

Re: Antec SP500P "resurrection"

Actually yeah, i realised i "mis-counted", after i wrote that last post. (I guess i was just happy nothing on the board had "taken up smoking")

For some (strange) reason, from what i could trace on the pcb, it looks like there's the input filter, rectifier, then a fat poly cap, then the + goes through the PFC inductor, FET and diode; the - goes through a pair of paralleled resistors for the PFC current sense, and only after that, to the two big primary caps.

I'm taking the psu to school today, to finish the re-cap, and i'll "play around" with a scope, to see if and what's happening in there

[Khron]

Re: Antec SP500P "resurrection"

UPDATE: i got the psu to school today. Soldered another 22ohm in parallel to the replacement of the blown R, on the PFC Vcc line. I also replaced the cooked zener with a 12v+4.7v zeners in series.

I plugged the whole thing in, and the series lightbulb lit up and stayed lit up pretty bright for the 2-3 seconds that elapsed until i pulled the plug. Something tells me that shouldn't have happened.

I unsoldered a jumper on the way to the PFC Vcc, plugged the psu back in, just a small flash of the bulb, and i now have around 16v on the Vcc (as opposed to last night's 10.8v).

The fan loading the 5vsb turned on and worked normally, for the duration of the plug-in. Could the PFC be drawing such a considerable current, in idle? Come to think of it, it might, since it DOES have to make ~400v out of ~320v or so...

[Khron]

Re: Antec SP500P "resurrection"

Something's definitely not right. I soldered the PFC Vcc jumper back in, plugged the psu in, and i got about 30v across each of the big primary caps, and this with the bulb lit up bright...

[everell]

Re: Antec SP500P "resurrection"

What you have proven is that the PFC FET is drawing a lot of current.

With the Vcc to PFC open, it does not draw excessive current, so the FET is not shorted.

With Vcc to PFC open, install that TL494 and see if the psu will come up without PFC.

[Khron]

Re: Antec SP500P "resurrection"

Ok, i poked around the PFC with an oscilloscope and an office-mate here at school. Unsoldered the gate drive resistor (22ohm smd; there's a 10k gate-to-ground resistor already installed), and probed the PFC controller output, only to find it was at near-full-duty-cycle. Makes sense, since the voltage at the output was only the 320v rectified mains (lower than programmed). Then we probed the IC output, and then across the current-sense resistor while connecting and disconnecting a 60w lightbulb across the 320Vdc, which prompted a slight reduction of the duty cycle, but no "reaction" on the current side of things.

Me thinks the chip might still be part-fried... Ah well, back to re-capping...

[stj]

Re: Antec SP500P "resurrection"

a bad FET will usually take out the chip driving it.

damn it! something else i better add to the shopping list!

i'll verify the part number later - what resisters are unidentified? i'll check mine when i open it later.

[everell]

Re: Antec SP500P "resurrection"

Yes, I think your PFC chip is bad. Evidence is pointing toward a 5vsb overvoltage failure. My Antec SP350 had 5vsb measuring 12.15 volts. The KA7500, like yours was burned. One (not both) of the driver transistors was bad, just like yours. Mine did not have PFC.

If your 5vsb line more than doubled, that would mean the pwm chip (7500) was beyond spec and would give problems, and could have turned one driver transistor on and one off. That would account for the bad driver transistor and the burnt pwm chip. The PFC chip is powered from the primary feedback winding. It should have a voltage of about 18 volts. So if the 5vsb is doubled, the feedback winding would be doubled also, making it about 36 volts. That would explain the burnt zener, the burnt resistor, and a not so good PFC chip. The Vref on the PFC chip, pin 8, should measure 5.0 volts. Measure it and see what you get. If it is zero or equal to Vcc, then the chip is definitely fried. Since the output is turning the FET on full speed, the FET might be a little leaky from the abuse. To be on the safe side, I would replace it.

One nice thing, your VIPer pwm chip in the 5vsb circuit will stop the overvoltage nonsense. So that is one problem definitely solved!

[Khron]

Re: Antec SP500P "resurrection"

I currently have 15.8v on the PFC supply line, which is well above its 11.2v turn-on threshold.

The closest thing to Vref on the PFC IC i could find was its Vsense input (pin 6), taking its signal from a resistive divider between the output and "ground" (3x "394" smd's = 390k from V+ to pin 6, and a small 1/8w R with a 1nF cap in parallel with it, from pin 6 to "ground"). At pin 6 i'm measuring 4,35v or so. Datasheet says its reference voltage is 5V; since there's only about 320v across the two big primary caps, it makes sense, it's a bit lower than 5v, since 320v (present) < 380 ("programmed"). Not quite sure what to make of it, but i'll leave it be, for now (PFC FET still disconnected).

I'm almost done with the re-capping, just the voltage supervising board left to do. The 0.1u 'lytic on the 12Vsense line was replaced with a 0.1u film cap; it goes to ground through a 1,8k resistor, so i hope the ESR difference won't be of great significance.

I'll pop in the TL494 in a few mins and report back with the results (positive, i hope )

[Khron]

Re: Antec SP500P "resurrection"

The voltage divider is 3x 390k = 1.17meg, and then there's a 15k from pin 6 to "ground", so according to a quick calculation, it should put out around 395v (5v across 15k gives 390v across the other 1.17meg.

Yesterday, when probing the gate drive output, it was switching at around 64-65KHz, which is in tune with its frequency setting resistor (just measured and calculated that).

All that's left might indeed be a bad FET. I'll have to see if i have any "compatible" ones in the psu's i have in the closet at home. There might still be some hope left

[everell]

Re: Antec SP500P "resurrection"

Is the PFC chip KA3844? If so, pin 8 is Vref. It should measure 5 volts. The chip takes Vcc, runs it thru an internal voltage regulator, and puts 5.0 volts on pin 8. If this voltage is wrong, then something inside the chip is fried.

[Khron]

Re: Antec SP500P "resurrection"

No, the chip's an Infineon ICE1PCS01.

I mistakenly thought it was an XX3844 when i first mentioned it, because i had poked in another psu with one of those, and something "melted together" in my head or something

[Khron]

Re: Antec SP500P "resurrection"

Anyway, moving on:

The TL494's in, nothing blew up upon plug-in, but when i short PS_ON to ground, there's just a short "blip" on the 12v line (monitoring that via a LED), and nothing else. I've also got a fan hooked up to the CPU 12v line, and it tries to start to move, but can't even make it over one "bump".

Hmmm... Max voltage for the TPS3510 supervisor IC is spec'ed at 16v. There's a GREAT chance that this is cooked as well, i reckon

[Khron]

Re: Antec SP500P "resurrection"

UPDATE



Good news: upon de-soldering a diode going from the FPO (pin 3) of the TPS3510, to the dead-time control (pin 4) of the TL494, the psu is ALIIIIIVE!!! True, unprotected, but it's great news so far

Guess i'm gonna order some free samples from TI, and replace the TPS, then put back the diode and see if it (still) turns on...

5vsb = 5.05v
+12v = 12.18v
+5v = 5.00v
+3.3v = 3.34v
-12v = -10.8v

I also soldered back the 22ohm gate drive R for the PFC, and the series bulb did NOT light up this time Getting only around +300v according to the multimeter, but that's with a fan loading the +12v and a few leds on the other voltages. Guess the PFC FET is still kickin'

[everell]

Re: Antec SP500P "resurrection"

Great job. Now all you need to do is put the finishing touches to it.

I still wonder about that PFC circuit. On the negative side of the PFC diode you should be getting around 390 volts instead of just 300 volts. I am still suspicious that the PFC chip might have been damaged.

Keep us posted. I was very pleased that you were able to successfully complete one of the 5vsb mods. I think you will be very pleased with the results - no more overvoltage problems!

[Khron]

Re: Antec SP500P "resurrection"

SUCCEEEEEEEEEESSSSSSSSSS!!!!!!!!

I finally pulled out an oscilloscope and probed each leg of the TPS, and the main voltages. In the ~80ms that the FPO pin was low (enabling the TL494), the 12v rail didn't have time to get higher than about 4v, the 5v reached around 1.5v, and the 3.3v around 1v, before plummetting back down to 0.

The waveform was similar on the pin4 of the TL494, so i ended up putting in a 4.7u soft-start cap instead of the 10u in the original, and IT LIIIIIIIIVES!!! Dad quite sanely suggested that the original 10u Fuhk-yoo might've had something around 5u actually, so the REAL 10u i replaced it with might've been too much

Seems the TPS is ok after all A workmate said he'd get me some car bulbs to use as loads, next week, so i'll report back some voltages under "real" loads next week.

Oh, and the PFC's putting out around 375v, so that seems to be still ok as well

Once again, everell , i extend my enormous gratitude for the advice, pointers and time you've given me I owe ya one If you're ever passing through Finland...

[Khron]

Re: Antec SP500P "resurrection"

Hmm... Dad just said there was a post from everell earlier this morning, but it's now gone. Something wrong?

[everell]

Re: Antec SP500P "resurrection"

Everything I posted on this thread is still there - the post he might be talking about is on another thread - titled "Computer power supply: ST P3NB80FP". Someone looking for a replacement FET.

I hoped you noticed my thread titled "Handy power supply tester". Mine gets used a lot!

As for power supply design, I have an idea. Between the voltage source and the Vcc of the PFC chip, you have a resistor (burnt one replaced) and a zener diode (also burnt) to bring voltage down to some value for Vcc to PFC chip. You might try removing the resistor and zener. In its place put a 7815 voltage regulator. My reasoning is that this chip will handle one amp of current. On the other hand, if voltage ever goes high again, the zener will conduct current to regulate voltage, but if the current rating of the zener is exceeded, it gets cooked, as the earlier one did. Compare the maximum current rating of the zener you are using with the one amp capability of the 7815 and I think you will see the difference. If you do use the 7815 regulator, be sure to put a .1 uF disk ceramic cap (or equivalent) across the input and output of the 7815 to take out any spikes.

[Khron]

Re: Antec SP500P "resurrection"

As you said before, now that i've replaced the 5vsb switcher, the chance of over-voltage should be reduced to nearly-none But anyway, the PFC chip seems to have survived regardless; i'm getting something over 370v over the two big smoothing caps (with next to no load), so it must be doing something (right).

Looking forward to next week's load tests, to see how it's behaving

[Khron]

Re: Antec SP500P "resurrection"

Ok, load-test day today

All good news

Test 1: two 6v / 40w bulbs in parallel on the 5v rail, and two 24v / 100w bulbs in parallel on the 12v rail. Voltages: 12.28v, 4.70v

Test 2: same, but with a 12v / 55w bulb added on the 3.3v line. Voltages: 12.23v, 4.95v, 3.34v

WOOHOO!!! I almost feel like a young Dr. Frankenstein