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Thread: Who Is It in the So Cal Area that Fixes the Crown PSA-2XH?

  1. #1
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    Who Is It in the So Cal Area that Fixes the Crown PSA-2XH?

    The high speed fan on my Crown PSA-2XH had been coming on prematurely and perhaps the protection had been coming on, and I took the amp out of service a while ago. The other day I disassembled it and thoroughly cleaned it inside and out. The big capacitors checked out fine (measured at ~11,120 mfd, rated at 10,000 mfd). I removed the circuit boards and sprayed them clean with electronics cleaner, cleaned the pin contacts, cleaned the fan and filter, and used the shop vac and compressor to get all dust out. It really wasn't bad at all though.

    Anyway, I put it back in service and it was working perfectly. Then a couple minutes later it "garbled" the fan kicked up, the overload lights came on, and I instantly shut it off. I left the top unscrewed so I could check the temp at which the fan goes into high speed and the boards weren't even warm. It drives my JBL W15GTi sub wired at 12 ohms. I pulled the inputs and output off and tried to turn it on. The protection instantly came on.

    I seem to recall that someone local (maybe Pasadena area) fixed these and had even sent me a diode for it at one time in the past. Anyone know?

    Thanks,

    Todd

  2. #2
    RE: Member when? subwoof's Avatar
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    east coast dude...

    I think that was me - am in new york.

    if the fan goes on too soon the 20K 1% resistor ( light green ) on the main board is way outta whack - replace it with any resistor (tolerance) as long as it reads very close to 20K.

    betcha that when you cleaned it you *disturbed* the low voltage trim pots on the power supply board...

    install NEW LV caps - esp if those are 30 years old...! get 105C if possible.

    Remove all 4 main output cards ( label them first! ), use a real good pot cleaner and douse the trim pots then rotate them through most of their rotation a dozen times or so.



    Fire the amp up and set them to +/- 15V and make sure the +20v is there.

    Then re-install the output cards and see what happens.

    sub

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    Quote Originally Posted by subwoof View Post
    I think that was me - am in new york.

    if the fan goes on too soon the 20K 1% resistor ( light green ) on the main board is way outta whack - replace it with any resistor (tolerance) as long as it reads very close to 20K.

    betcha that when you cleaned it you *disturbed* the low voltage trim pots on the power supply board...

    install NEW LV caps - esp if those are 30 years old...! get 105C if possible.

    Remove all 4 main output cards ( label them first! ), use a real good pot cleaner and douse the trim pots then rotate them through most of their rotation a dozen times or so.



    Fire the amp up and set them to +/- 15V and make sure the +20v is there.

    Then re-install the output cards and see what happens.

    sub

    Thanks sub,

    My only cleaning was removing the six boards, spraying the four output boards and main board, air blowing the low voltage board (I ran out of spray), and cleaning all of the pin contacts with alcohol/rag and put it back together just as it was. I didn't touch any of the pots.

    20K would be R1.

    Any specific caps on the low voltage board I should be looking at?

    Thanks,

    Todd

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    RE: Member when? subwoof's Avatar
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    if it fits....

    1000uf at 35-40vdc, 105C axial leads if I remember right.

    Be sure to do those pots...and while at it, remember that these amps were touring workhorses and have a LOT of vibration / miles on them. The higher voltage mains put stress on the bypass and other small caps connected to them.

    On the "mother" board ( where the output module's power connectors mate ) there is an issue with the resistor leads and the voltage rating of those film caps. There should be a service bulletin online to see. This would cause oscillation and shut down sometimes.

    sub

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    Thanks again Sub.

    I was reviewing the schematics and found that the LV board puts out +-15 volts and C8 (100 mfd) and C9 (220 mfd) are only 16 volt rated volt caps. It is easy to see how voltage drift over time could over-voltage these leading to their demise. I'll have to replace them and I'll use the next higher voltage rating. I'll measure/replace the 1K mfd 40 volt caps (C5, C6) too.

    Regarding the 20K resistor. I went though my values and old circuit boards on hand and could not lay my hands on one. As you know, it is not a common value. I do have a new 22K that measures 21,640 ohms (within 10%). Is this close enough or should I piggyback a larger value to get closer to the 20K ohm shown in the schematic? Also, the 20k resistor only measured ~5.5k, but it was still in the circuit so this could be misleading. Some resistors on the board measure their displayed values on the multi-meter while other are less due to current transfer elsewhere.

    Thanks,

    Todd

  6. #6
    RE: Member when? subwoof's Avatar
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    cheating

    I recommend getting some quality 10K resistors and just put 2 in series...much easier to find..

    it has to be close for the voltage divider to properly work at the temp threshold.

    for some reson nearly every "showco" amp I've seen had this issue.

    AND the multiple fractured solder connections on the rear panel switch board that has the 1/4 jacks.

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    Thanks sub.

    Two 10Ks it is. I found two precision 10Ks in an old RS digital meter that no longer works. In series I'm reading 19.96K ohms, so these should do the trick.

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    Thanks again sub.

    At this point, the high speed fan comes on instantly on power up and only the right IOP light stays on. Like I said, it was working fine, for a while, before this occurred. It is in bridged mono.

    I pulled the amp four boards, the main board, and removed the 20k resistor. Out of the circuit, it has a measured value of 19.95k, so is there really any reason to replace it with the two 10Ks?

    Should I just put it back and check the voltages with the amp board removed or move on to the LV caps first?

    Thanks

  9. #9
    RE: Member when? subwoof's Avatar
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    debug

    debug in stereo mode first of all.

    sounds like the 20K is fine.

    the LM339 next to it takes the ref voltage from the LM334 on each heatsink and if any of them tells it, the fan goes to high. One of them is screwing up somehow...?

    pull that chip, resolder the IC socket and scrape corrosion off the leads and/or get a new chip. They are not the most robust IC around.

    IOC light comes on when there's DC on the outputs, and tells that channel's relay to cycle off. You can defeat this on the back panel BUT do NOT connect any loads..!!

    See what the voltage is.

    The output cards should have +/- 95VDC to them - if one is lower then you have an open main cap or bad connection.

    those molex power connectors burn out sometimes and the solder connections crack - resolder them at the least. need a decent iron to do it right.

    Check for cracked solder connections on all 16 and all 4 large to-3's on the output cards.


    fixing these is like a rusty old car - you cannot just remove one thing without making something else mess up.

  10. #10
    RE: Member when? subwoof's Avatar
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    if one works...

    if one channel orks then all the LV stuff is fine - look elsewhere.

    the IOC light will go on / and maybe others if the display board has issues. the 1.2K 1/2 watt resistors open up all the time and the transistors ( 2961 ) pop open too.

    have one of those amps right here...wanna buy another??


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    Smiles for the moment. I flipped the mono/stereo, and other two switches below and they seemed gritty. Flipping them a bunch of times smoothed them out.

    With the main board and four amp boards still dismounted, I checked the + and - voltage on the LV power supply. I got +15.05 and -10.94. I touched the "- pot" with a screwdriver to give it a twist, and it instantly jumped down to -15.05 volts.

    Mains are 94.8-9 / 95.0 volts.

    So I guess that I need to still replace the the boards and give it a try. (Should have checked this first.) When I removed the resistor, I did remove the two adjoining ICs so as not to overheat them. Re-seating them should clean any corrosion from their contacts.

    It is interesting that without the five boards mounted, when you turn on the unit the 6 LEDs on the face still cycle and the low speed fan stays on.

    Update! I put it all back together and it went through its start-up routine and the IOP light is no longer lit and the fan is in low speed mode, both in stereo and bridged mono.

  12. #12
    RE: Member when? subwoof's Avatar
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    tank

    properly tweaked and configured it's a real solid workhorse...and easy to work on.

    those adj pots for the LV get dirty and are the rarest thing on earth so be sure to clean them carefully.

    99% of repairs consist of cleaning and repairing connections - NOT components...

    sub

    PS - it's IOC

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    Regarding the 95 volts on the rails (with 100 volt capacitors used), the schematic only shows this at 75 volts with 90 volt capacitors. Why the difference? Is this what makes it an "XH." The difference between 95 and 75 volts is 60% more power or 2 dB.

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    RE: Member when? subwoof's Avatar
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    long story.

    Way back in the late 70's / early 80's the sound company in dallas ( showco ) bought HUNDREDS of these for touring rigs. Madonna, zepplin, bob seger, the who and many others. Because they can be rewired for 100V ( japan ) entire racks ( 5 amps plus I/O) could be reconfigured when going overseas. Now the "legend" ONE day, a system ( or one rack, accounts vary ) came back from japan and *didn't* get rewired to 120V before going out with a US ( 120V ) tour. On the first show they powered it up ( and all the amps behaved ) and suddenly they had 60% more "punch" and were amazed..! The techs figured out what happened and the showco engineers made the required changes to the bias and fan circuits to keep them safe and the HX amp was born. Crown, in their usual "duh" mode did NOT offer this variation to the general public ( otherwise could of made a killing ) and when the macrotech amps came along, 4 rack space amps were doomed. BUT this has the best overall thump and sound character of any of the crowns...and are still prized today. IF the correct output transistors are installed, the older consumer SA2's and first gen PSA2's ( white fan guard frame ) can be modded. sub

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    Way cool.

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