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And now for the dead Antec SP-400

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    And now for the dead Antec SP-400

    Well, actually I had two Antecs that died on me. The SP300 is now alive after replacing a bunch of caps and the toroid filter inductor. Now it's time for the SP400 to live once more.

    I see a lot of postings about replacing the +5VSB circuitry. Well it's dead on this unit, but is there a particular reason why? I don't mind any inefficiency but if it just is impossible to fix, then I'll understand.

    I found it weird that though the 5VSB uses the same 2-transistor topology (as far as I can tell) it actually uses an IGBT to pull down on the primary - this would be the first PSU I've seen an IGBT.

    Also it's weird, this PSU uses the TL494/KA7500 controller + TPS3510 monitor instead of the UC3842 the SP300 used, though I think both supplies were made by Channel Well Tech. And both are full of Fuhjyyu's. Surprisingly they aren't exploded or leaking just yet for the most part...except for the two 1mF +5VSB output caps whose ESR are off the chart as well as some small caps here and there.

    One unfortunate thing I did notice is that one resistor (R54, close to the +5VSB transformer, closer to the "tickler" (in the middle) and main transformers) is heating up and smoking when I plug it in. I'm not exactly sure why, anyone seen this resistor heat up? I measured 1.5K in-circuit (with caveats of course since it was measured in circuit) which means something is really wrong, if it's dissapating 1 watt (utter guess, because it's a 1/4W resistor and it'd take at least 1 watt or so to smoke) across a 1.5K resistor, there would be almost 40 volts across it.... Since it's across the mason-dixon line from the mains input this should be low voltage but I don't quite get why it's heating up... Anyone seen this failure mode before?

    (I'm in process attempting to get a photo without removing the heat sinks...)

    #2
    Re: And now for the dead Antec SP-400

    I found another capacitor that was well out of spec, and replaced it. I measured the voltage across that smoking resistor and now it's a reasonable 4.8 volts. In fact +5VSB is now around 4.8V and I'm getting a solid 9+ volts on the KA7500C PWM IC - should be enough to run the device. Alas still no power. out. Hmm... need to study this circuit more...

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      #3
      Re: And now for the dead Antec SP-400

      Check pin 14 on the KA7500, you should have 5V on this pin. If you do not most likely the KA7500 is bad. I had a SLP-450 that had the 5VSB go out of control and it took out a couple of transistors attached to pins 8 & 11 of the KA7500 in addition to the KA7500 itself.

      Comment


        #4
        Re: And now for the dead Antec SP-400

        Thank you LDSisHere. Yep you were right, the KA7500C was kind of messed up, I measured 100mV on the Vref-out pin. I desoldered it, put it on a protoboard and put in +power on pin 12, and GND on pin 7 (normal power pins for those joining in) ...
        At first I started with around +6 volts and noticed from my bench psu that it was drawing 100mA... curious, not quite right... I raised it to 18V and the current draw dropped to near 0 (!) and I measured 12V out from pin 14 (!).

        Well if I didn't fry it, it's dead now.

        I did the same experiment to a DBL494 I salvaged a while ago from another PSU, this chip was correctly sending 4.99 volts out from pin 14.

        I soldered this DBL494 in, and did a quick check for any seriously broken transistors - which I didn't see any - and...

        IT LIVES! The dead-for-years Antec SP400 once again can be put back to service. I tested it real quick with the same headlight bulb,... eh... crappy regulation (12.2V unloaded, 11.8V with 4A load, but then again the unloaded number does not meet minimum load requirement of 1A.)

        Thanks again!

        Comment


          #5
          Re: And now for the dead Antec SP-400

          I am very pleased that my advice was helpful and I want to thank you for posting back with your results. Good job on reviving your power supply.

          Comment


            #6
            Re: And now for the dead Antec SP-400

            Well done

            Comment


              #7
              Re: And now for the dead Antec SP-400

              Nice.
              By the way, when you put the DBL494 in place of the KA7500, did you have to do any rewiring or are the DBL494 and KA7500 pin-compatible?

              Comment


                #8
                Re: And now for the dead Antec SP-400

                You know, I went back and looked at the specs. The DBL494, TL494, KA7500B, KA7500C are all pin compatible and electrically compatible - mostly. I just realized that the KA7500C is higher binned however - these are +/- 1% on Vref compared to the others that are +/- 5%. So I sort of downgraded my PSU a bit with a bit of accuracy loss, but I didn't have any spare KA7500C's...

                Comment


                  #9
                  Re: And now for the dead Antec SP-400

                  Just wanted to post, 9 years later... I got to fix again.

                  The crap caps I put in for 5VSB blew up again (surprise surprise) and I replaced once again with the caps I had on hand.

                  LOL... I bet in another 9 years (or sooner) I will need to change them again...

                  Comment


                    #10
                    Re: And now for the dead Antec SP-400

                    Originally posted by eccerr0r View Post
                    Just wanted to post, 9 years later... I got to fix again.

                    The crap caps I put in for 5VSB blew up again (surprise surprise) and I replaced once again with the caps I had on hand.

                    LOL... I bet in another 9 years (or sooner) I will need to change them again...
                    You like to live dangerously you could run out of luck doing this

                    But seriously this is a nice write up on this repair

                    Thanks for posting it
                    9 PC LCD Monitor
                    6 LCD Flat Screen TV
                    30 Desk Top Switching Power Supply
                    10 Battery Charger Switching Power Supply for Power Tool
                    6 18v Lithium Battery Power Boards for Tool Battery Packs
                    1 XBox 360 Switching Power Supply and M Board
                    25 Servo Drives 220/460 3 Phase
                    6 De-soldering Station Switching Power Supply 1 Power Supply
                    1 Dell Mother Board
                    15 Computer Power Supply
                    1 HP Printer Supply & Control Board * lighting finished it *


                    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

                    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
                    2 Hem Saw Computer Stack Board

                    All of these had CAPs POOF
                    All of the mosfet that are taken out by bad caps

                    Comment


                      #11
                      Re: And now for the dead Antec SP-400

                      Originally posted by eccerr0r View Post
                      Just wanted to post, 9 years later... I got to fix again.

                      The crap caps I put in for 5VSB blew up again (surprise surprise) and I replaced once again with the caps I had on hand.

                      LOL... I bet in another 9 years (or sooner) I will need to change them again...
                      It's called Job security

                      Comment


                        #12
                        Re: And now for the dead Antec SP-400

                        fortunately I knew exactly what to check when I noticed the 5vsb line was oscillating thanks to LEDs on the motherboard I was working on... as well as the keyboard LEDs. definitely improper behavior, ESR meter and instantly knew what was bad without opening the psu.

                        now need to mark on the psu case that it had been fixed again. Just that 8mm 1mF caps are hard to find, had to use a 1cm cap extended off the board

                        Comment


                          #13
                          Re: And now for the dead Antec SP-400

                          Originally posted by eccerr0r View Post
                          Just wanted to post, 9 years later...
                          Well, no wonder I couldn't recall replying to a thread about someone fixing an Antec SP-400.
                          Holy ancient thread revival, lol. Just look at the post I made back then - I didn't even know that KA/TL7500 and TL/DBL494 were pin-compatible.

                          Originally posted by eccerr0r View Post
                          The crap caps I put in for 5VSB blew up again (surprise surprise) and I replaced once again with the caps I had on hand.
                          I swear, those fixes will give me anxiety one day.

                          Originally posted by eccerr0r View Post
                          LOL... I bet in another 9 years (or sooner) I will need to change them again...
                          Sure. If you're lucky.
                          Get a lottery ticket too if you feel extra lucky.

                          Originally posted by R_J View Post
                          It's called Job security
                          LOL, exactly!

                          Originally posted by eccerr0r View Post
                          fortunately I knew exactly what to check when I noticed the 5vsb line was oscillating thanks to LEDs on the motherboard I was working on... as well as the keyboard LEDs.
                          You know, those 2-transistor 5VSB designs don't really have much in the way of over-voltage protection. So when the output caps go bad, you are literally relying on the motherboard to just hold up and not croak when the 5VSB starts going crazy. Unfortunately, not all motherboards are designed well. The FIC AM-37 that was often paired with the Bestec ATX-250-12E "mobo killer" PSU in those infacmous eMachines PCs had a bunch of TTL logic gates specced to 5.25V max Vcc... and these were directly connected on the 5VSB without any protections. So what happened? - A lot of these mobos died as soon as the 5VSB started going even slightly out of spec.... let alone the Bestec ATX-250-12E, which sometimes wouldn't stop until the KB and MS wires melted (and yes, I've seen one like that.)

                          So I honestly don't think it's a good idea to rely on your motherboard to tell when the 5VSB is starting to act up again. Next time, however soon that may be, might end up with something in smoke / biting the dust. Of course, it is your hardware after all, so your call how you want to play it. But like Sam x3 said, maybe it's more fun to live "dangerously" like that.
                          Last edited by momaka; 02-23-2021, 09:46 PM.

                          Comment


                            #14
                            Re: And now for the dead Antec SP-400

                            True, luckily I usually have this psu powered off so it didn't have much time to do any damage, and this board was already toast pretty much -- unsure why it's so unstable now, works for a few minutes perfectly and then freezes solid regardless of what PSU I connect to it... sigh.

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