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  • Allen USPS 3 Schematic

    Does anyone have a schematic of this board? Smelled something burning this morning......luckily I already had the back off the organ.....saw a small stream of smoke lofting upwards right over the cage PS board. Disconnected power, pulled PS from cage....plugged PS in at bench and 2, either breaker type switches, thermal limiters or ceramic caps started smoking right next to diodes. Not sure what they are.
    Attached Files

  • #2
    They're inrush current limiters. Or at least they were before they transformed into fine particulates.

    D304CS was the part number.
    PM me an email address for more info.

    td
    Servicing electronic organs since 1969.

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    • #3
      Thanks TD!
      I saw an identical board on ebay and noticed their limiters cracked and flaking too.

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      • #4
        Must be a common problem with the USPS-3. We recently repaired an ADC6000 in which the cage supply had gone down. Found the same two little devices had exploded. The church let us sell them a brand new USPS-3 from Allen, which was a wise choice considering that they are 3 hours away and couldn't afford multiple service calls had the repair turned out to be complicated. Besides, I'm not really sure why the little current limiters failed. I see some evidence on this board here in my shop that the filter capacitors may have started leaking juice. Perhaps a cap went bad and pulled a lot of current, causing the limiters to pop.

        So if you decide to fix the supply, check carefully for bad capacitors, and of course you should check all the diodes to see if one of them shorted out. Something must have caused the large inrush of current to pop the limiters.

        BTW, when I first got the supply into the shop, I looked up those little parts and they were quite cheap, seems like it was just a dollar or two each. On mouser.com or somewhere like that.

        Considering the high cost of Allen replacement assemblies, it will probably pay off to fix that unit if your can. In a pinch, you can use off-the-shelf 5 volt and 15 volt power supplies that are sold for computer systems and the like. I believe the 5 volt section of the USPS-3 is rated to put out well over 20 amps, possibly close to 30 amps. But good quality computer supplies with that kind of capacity are available, and they don't cost very much.

        I'm not 100% certain, but I think the + and - 15 volts in the cage can be served just as well by the more common + and - 12 volts available from ordinary AT or ATX style computer power supplies. I recently bought some low-cost computer supplies from Tiger Direct, for the express purpose of experimenting with using them in Allen ADC cages, but I haven't had time to try them out. They won't fit inside the cage, of course, but some simple wire-extending should make them work, and I know the 5 volt output of an ATX computer supply is plenty hefty enough for the Allen cage, capable of putting out something like 35 amps.
        John
        ----------
        *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

        https://www.facebook.com/pages/Birds...97551893588434

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        • #5
          Thanks John and Dave!
          Would either of you gentlemen know of what value limiter I should be looking for? The "D304CS" number comes up nowhere on a google search. Yet there are some electronic component supply shops that have numerous types....I just don't know which one is correct or that would work in my situation.
          John, I ended up buying a clean used USPS-3 board off the auction site so I will try that first but want to test/check mine out thoroughly and rebuild as necessary for a "spare" or swap back in as the operational board leaving said recent board as a spare.
          Thanks again for both of your help!

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          • #6
            For the current limiter I'd try GE CL-50 or CL-40 for a 400 W power supply. Check the fuse, the CL50 is 5 A max and the CL40 is 6. 400 is the wattage of a PCAT ATX supply that puts out about 25 amps 5 vDC. And put in a MDL fuse if Allen was too cheap to. MDL allows 11 x the nominal current for 5 or 10 seconds.
            The oriental limiters are not well supported among the suppliers I use.
            Switcher mains caps take a beating and run hot, the ATX's I buy last a couple of years max. I'm saying replace yours. The longest switcher performance I've seen is in Ishida packaging machines, where in a fleet of 18 we had one fail after about 8 years 16 hours a day 6 days a week. It had Nitsuk mains caps, a brand I don't think you can buy in onesies.
            city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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            • #7
              Indianajo, you are somewhat over my head....what are you calling "switchers"? I had already planned to replace both infeed E-Caps and diodes....as well as the limiters.

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              • #8
                By Switcher he means switched mode power supply. Your supply is of this design.
                https://en.wikipedia.org/wiki/Switch...e_power_supply
                -Admin

                Allen 965
                Zuma Group Midi Keyboard Encoder
                Zuma Group DM Midi Stop Controller
                Hauptwerk 4.2

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                • #9
                  diodes you can check with one lead lifted. 0.55 to 0.74 v forwards, 1999 or ---- or OL backwards, they are probably good. Diode scale of some meters or 2000 ohms scale on my sears craftsman dvm.
                  Those toriod choikes or transformers in your picture, mostly are associated with switcher supplies post 1988. If the main cap is 200 V or higher, that confirms it. If the main caps are 35-80 volts, it is a transformer diode capacitor supply.
                  On switchers, FET's often blow up too. With gate to source shorted (left two pins) the drain should be 1999 ohms. If it is lower, the FET is blown. I bought some Fairchild FDP52n20's last year that should be tough enough to replace most older FET's. They get tougher every year. Don't forget the insulator.
                  I haven't successfully repaired a switcher. The first one I worked on, the fet had melted some lands off the board and I couldn't draw out the schematic diagram. The ATX ones have a lot of import parts you can't get datasheets on or find anything about.
                  Last edited by indianajo; 02-08-2016, 05:16 PM.
                  city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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                  • #10
                    Originally posted by indianajo View Post
                    I'm saying replace yours. The longest switcher performance I've seen is in Ishida packaging machines, where in a fleet of 18 we had one fail after about 8 years 16 hours a day 6 days a week. It had Nitsuk mains caps, a brand I don't think you can buy in onesies.
                    The capture power supply in my Allen MOS-2 is a switcher and still going strong after 35 years with the original components.
                    -Admin

                    Allen 965
                    Zuma Group Midi Keyboard Encoder
                    Zuma Group DM Midi Stop Controller
                    Hauptwerk 4.2

                    Comment


                    • #11
                      Okay looked at the 5300 usps diagram. It is a very early switcher supply.
                      There are no fuses, so there is no easy way to tell what size inrush limiter is appropriate. Start off with the CL50 and if that takes too long to power up, change to the CL40. Once in permanently be sure to wrap heat shrink insulation around the inrush limiters, you don't want them to get cold during the sermon and then limit current available at the start of the next hymn.
                      I wouldn't install limiters until the TO3 fet transistors had been checked that they are not shorted across. Forget what I said about the FDP52n50, those are TO220 package and won't fit the heat sink. I would update from an IRF440 though to something with more SOA, there has been a lot of progress on FET's in 20 years.
                      When removing fets be sure to wear a grounded wrist band. These apparently don't have protection gate zener diodes. Notice they have a backwards diode, so .7 v backwards between d & s is normal. Should be infinity with the gate shorted the other way though. Datasheet will be on datasheetcatalog.com to tell you which pin is d,s,and gate.
                      If the fets are shorted q3 - q6 are likely shorted or blown, and if those are blown, Z1. You do the double diode test on bjt transistors like q3-q6. I'm not sure about availability of z1, fashions change in switcher design a lot and this is so old fashioned it probably has leads.
                      Watch the heat sink compound is poisonous, don't get on mouth eyes nose etc.
                      city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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                      • #12
                        That all sounds like Greek to me, I-Jo! You are more into board-level repair that I have ever been, especially on switching power supplies. I've never successfully repaired one of these, and just feel they are too spooky for me to work on. Even when I've revived one by re-flowing all the solder, it still failed again before long. I have two or three of these old Allen cage supplies on the shelf in the shop, having died in other organs, but I'll probably never get around to fixing any of them.

                        Not sure how Allen put together the later revisions of the USPS-3, but the corresponding parts in the Rodgers PDI cage, which outputs a very high current +5 along with lower current +12 and -12, are built with commercially available supplies mounted into a frame that fits into the cage.

                        Right now, the Allen MDS45 at my church is operating with a makeshift power supply for the cage. The USPS-3 failed and I didn't have the time or the money to order a new one. I happened to have a pair of the old original cage supplies that Allen used at the beginning of the ADC era. This was a two-part design, with the 5 volt supply on one frame and the +/- 15 on a separate assemblage. One was mounted in each end of the ADC cage. After a year or two of production, they decided to put all the supplies into one assembly, making the old two-parters obsolete. But I still had a pair in an old kit, so when the USPS-3 gave up the ghost in the MDS, I plugged them into a power strip, laid them down beside the cage, and ran the wires out the cage to them. Works great, but looks ugly.

                        So I've been thinking of getting something better to put in there without spending the several hundred dollars for the Allen assembly. I believe I read somewhere that the 5 volt supply leg of the USPS-3 has to provide 20-something amps, so it has to be a hefty replacement unit. The 15 volt legs are only rated at one amp each, I believe, so any garden variety supply should work for that. I suspect that they could be 12 volts instead of 15, as they are used only for some op-amps and the muting relays on the USAP board.

                        A solid 5 volt supply like this one might be made to fit into the cage, and leave room for a small 12 or 15 volt supply.

                        http://www.mouser.com/ProductDetail/...dHKBoCVNbw_wcB
                        John
                        ----------
                        *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

                        https://www.facebook.com/pages/Birds...97551893588434

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                        • #13
                          Good news the 2526 swticher pulse width modulator IC is available from TI for $3.50 and Mouser stocks the DIP version. Newark has the IRF440 for $16. So if the transformer is not melted (unlikely) Allen switcher supply usps-3 appears to be repairable.
                          city Hammond H-182 organ (2 ea),A100,10-82 TC, Wurlitzer 4500, Schober Recital Organ, Steinway 40" console , Sohmer 39" pianos, Ensoniq EPS, ; country Hammond H112

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