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ASTEC AA11040C repair

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    ASTEC AA11040C repair

    Hi All,
    I'm in a apple II repair month
    I have this Astec AA11040C supply that had the usual smoked rifa X2 capacitor. Other than that, it's outputting about 5.5V on the +5V line and 13V on the +12V line. However, with a 7 ohm load on +5V, the rail goes to 5.0V. I'll check the ESR of all electrolytics, but I was curious to know what's the minimum load (if any) to start regulating correctly the +5V rail?
    Is there a schematic of this power supply floating around?
    Thanks in advance.
    Frank IZ8DWF

    #2
    Originally posted by iz8dwf View Post
    Is there a schematic of this power supply floating around?
    http://bitsavers.org/pdf/apple/power...lies_Aug82.pdf

    Comment


      #3
      Hi Al!
      Of course I had already downloaded that, but it covers the AA11040 and AA11040-B only. I don't know yet if the -C that I'm repairing is too much different from -B (so far it looks almost identical), that's why I asked if this 1983 version is documented separately maybe.
      Did anyone try that minimum regulation load? By a quick look at the schematic, it shouldn't have regulation problems with light loads, but I may be wrong on this.

      Frank IZ8DWF

      Comment


        #4
        But you'd expect it to drop to the regulated level once you put some sort of load on it wouldn't you? So long as it doesn't suddenly start putting out 3.75 and 10 instead of 5 and 12 it should be pretty happy I would've thought.
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          #5
          Originally posted by Anthony Adverse View Post
          But you'd expect it to drop to the regulated level once you put some sort of load on it wouldn't you? So long as it doesn't suddenly start putting out 3.75 and 10 instead of 5 and 12 it should be pretty happy I would've thought.
          I don't expect it to regulate that "poorly". With about 10mA load, its output voltage is 5.5V, with 160mA load, it's 5.2V, with 730mA load, it goes at 5.0V.
          My question since the beginning is: is this supply supposed to need any sort of minimum loading on the 5V rail, and if yes, what is that load, in everyone elses experience?
          It is my first encounter with Apple II SMPS, so maybe it's just poor design from 1980's era, I just don't know.
          Thanks

          Frank IZ8DWF

          Comment


            #6
            I don't have a direct answer to the question at hand. In my experience with IBM "AT" power supplies, the +5VDC rail required a minimum of 2 to 4 amps. And I anticipate the same goes with the Apple II power supplies, since both it and the AT switching power supplies are around the same era (i.e. pre-ATX.)

            You might be complicating things when the answer could be staring right at you. I'd simply connect the PS to the Apple II logic board, measure the current draw, and the result should be your answer. Run the test with no cards and keyboard. This may not be the exact calculated minimum you maybe shooting for. But, in the words of the great ozzie bloak Dave Jones, physical measurements are better than theoretical.

            Comment


              #7
              Originally posted by groink View Post
              I don't have a direct answer to the question at hand. In my experience with IBM "AT" power supplies, the +5VDC rail required a minimum of 2 to 4 amps. And I anticipate the same goes with the Apple II power supplies, since both it and the AT switching power supplies are around the same era (i.e. pre-ATX.)

              You might be complicating things when the answer could be staring right at you. I'd simply connect the PS to the Apple II logic board, measure the current draw, and the result should be your answer. Run the test with no cards and keyboard. This may not be the exact calculated minimum you maybe shooting for. But, in the words of the great ozzie bloak Dave Jones, physical measurements are better than theoretical.
              Well, surely I'll try the "real" load, once I make some more tests.
              However in my experience, "AT" type SMPS have a fairly good regulation circuit. I've never seen a 10% variation of the +5V rail even at zero load on all the ones I've repaired and used in many years.

              Frank

              Comment


                #8
                I know that some claim the PSU will switch off without sufficient load, but mine runs fine no load to full load, but yes, the regulation is quite 'loose'. Regulation from 5.5 down to 5.0 seems fine to me. There are no IC comparitors in this PSU, its an analog switching circuit.
                Current fleet
                TRS80 Model 4 - BBC B - Tatung Einstein - PCW9512 - PET 3032 - C64 - ZX81 - Spectrum 48K - Amiga A500 - Apple II europlus - Apple iMAC G3. Sharp MZ-80K. - IBM 5160 XT - Multibus 286/10 - Micro PDP 11/73 - Rainbow PC100A - MicroVax II - MicroVAX 3100, 3300, VAX 4000 VLC & 4000 Model 96 - AlphaStation 225 Apricot PC - Apple Performa 6200 - Apple Mac IIcx - Osborne 1 - ACT Sirius 1

                Comment


                  #9
                  This may be of use:
                  http://www.vcfed.org/forum/archive/i...p/t-44160.html

                  Comment


                    #10
                    Originally posted by Gary C View Post
                    I know that some claim the PSU will switch off without sufficient load, but mine runs fine no load to full load, but yes, the regulation is quite 'loose'. Regulation from 5.5 down to 5.0 seems fine to me. There are no IC comparitors in this PSU, its an analog switching circuit.
                    Well, unfortunately 5.5V is a bit on the edge. This particular PSU was sent to me because it seems the only thing that could have damaged two "FloppyEMU" boards. Unfortunately I haven't yet found a schematic of this FloppyEMU, but it uses a Xilinx XC9572XL CPLD directly connected to 5V I/O. This is usually fine since this part is rated up to 5.5V
                    You see the problem here?
                    Both FloppyEMU boards have a shorted CPLD

                    I think I better tweak somehow the voltage regulation of this PSU if I can... I still can't believe they made a thing that regulate so poorly, even with all analog regulation, it should be better than 5% easily.
                    Frank

                    Comment


                      #11
                      Seeing you mentioned the Floppy Emu, did you run across this article: https://www.bigmessowires.com/2014/0...damaged-chips/

                      Comment


                        #12
                        Originally posted by groink View Post
                        Seeing you mentioned the Floppy Emu, did you run across this article: https://www.bigmessowires.com/2014/0...damaged-chips/
                        Yes I've read it and sincerely it doesn't add any clue at least to what I know.
                        My totally unproven theory is that those CPLDs have a bit of "datasheet confusion". I mean, if absolute maximum rating for inputs is 5.5V, how would it be safe to list the same 5.5V as the allowed range? If you check any good old TTL/CMOS datasheet, you'll notice something like absolute maximum rating of, say, 6V and allowed max input of, say, 5.5V. These differences exist to account for production tolerances etc.

                        Frank IZ8DWF

                        Comment


                          #13
                          Originally posted by iz8dwf View Post
                          Well, unfortunately 5.5V is a bit on the edge. This particular PSU was sent to me because it seems the only thing that could have damaged two "FloppyEMU" boards. Unfortunately I haven't yet found a schematic of this FloppyEMU, but it uses a Xilinx XC9572XL CPLD directly connected to 5V I/O. This is usually fine since this part is rated up to 5.5V
                          You see the problem here?
                          Both FloppyEMU boards have a shorted CPLD

                          I think I better tweak somehow the voltage regulation of this PSU if I can... I still can't believe they made a thing that regulate so poorly, even with all analog regulation, it should be better than 5% easily.


                          Frank
                          Different times with different requirements.

                          I believe a C supply is basically a B, the +5V can be adjusted by altering R32 & R25 ratio.

                          Failing that, an old style PC PSU with the -5V can still be bought 'new' and runs an Apple II easily, so you could always try one of these (I have one on my spare motherboard for testing and it works well, with the added advantage of having a soft switch to turn the PSU on & off)
                          Current fleet
                          TRS80 Model 4 - BBC B - Tatung Einstein - PCW9512 - PET 3032 - C64 - ZX81 - Spectrum 48K - Amiga A500 - Apple II europlus - Apple iMAC G3. Sharp MZ-80K. - IBM 5160 XT - Multibus 286/10 - Micro PDP 11/73 - Rainbow PC100A - MicroVax II - MicroVAX 3100, 3300, VAX 4000 VLC & 4000 Model 96 - AlphaStation 225 Apricot PC - Apple Performa 6200 - Apple Mac IIcx - Osborne 1 - ACT Sirius 1

                          Comment


                            #14
                            Originally posted by iz8dwf View Post
                            Yes I've read it and sincerely it doesn't add any clue at least to what I know.
                            My totally unproven theory is that those CPLDs have a bit of "datasheet confusion". I mean, if absolute maximum rating for inputs is 5.5V, how would it be safe to list the same 5.5V as the allowed range? If you check any good old TTL/CMOS datasheet, you'll notice something like absolute maximum rating of, say, 6V and allowed max input of, say, 5.5V. These differences exist to account for production tolerances etc.

                            Frank IZ8DWF
                            One more "hint" from the datasheet: The 3.3V VCCINT power supply must be at least 1.5V before 5V signals are applied to the I/Os.
                            Now, imagine a connected device to an Apple II where the 5V is raising, and the CPLD supply depends on the local 3V3 regulator capacitance decoupling (both input and output decoupling...). Do you believe the designer paid attention to this?
                            That's one of the reasons I never use "tolerant 5V" devices in my retro-designs. Real 5V parts are still around (mostly Atmel and Altera), so why take these risks?

                            Frank

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