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Linn Axis PSU

Discussion in 'd.i.y.' started by les50in4, Jan 21, 2004.

  1. les50in4

    les50in4 Member

    I have obtained a faulty Axis PSU and Motor, I found this info about faults.

    Check the resistor that is is series with the input. If it's over 27 ohms replace it Early units were 47 ohms.

    I did not get the IEC connector or wiring so I do not have this serial resistance.

    Anyone know where this resistor goes or what the spec is for it. I need to power up the board to be able to fix it.

    I am going to build an offboard supply (lesgo) for my LP12 to see if it is better then the valhalla. FYI I have checked the motor spindle with calipers and although it is a different design the major diameter is exactly the same as the LP12.

    Also does anyone have any good ideas as to how to unglue the motor from the circuit board.
     
  2. redart

    redart Member

    Hi All,
    Am searching for info on the Linn Axis PSU and found this old post. I'm trying to fix a dead Axis for a friend - motor has 240 on each of it's three legs but doesn't turn. No LED's lit on the switch. If I apply 240 ac directly to two of the motor legs it spins fine. I've tried dropping the value of R1 as below but no difference. Is anyone familiar with the Axis?. Is it similar to the Valhalla / Lingo PSU ?. Anyone know where I can get a circuit diagram (Linn would only advise to take it to a dealer for service due to the 240 V nature of the board). Any advice on troubleshooting?.
    Thanks.
     
  3. Mullardman

    Mullardman Moderately extreme...

    If you know what you're doing with electricity, I'd look for an S/h Valhalla and stick it in an outboard box. Don't ask me how though...

    Mull
     
  4. redart

    redart Member

    Thanks Mull....replacement may be the only (best?) option. I know a bit about electricity, and I guess I'm on a 'repair high' after fixing a Cyrus Two amp (still sounds pretty good after 20 odd years). Would like to have a go at fixing the Axis PSU before chucking it, but not having much luck finding a schematic for it. Somebody out there must have one!?.
     
  5. Albertb

    Albertb pfm Member

    Got one here! Have PMd you on it. ;)
     
  6. Jiiim

    Jiiim bodger extraordinaire

    Hey Albert,

    Did you say you have the schematic for the Axis? Could you send it to me too?

    Thanks,

    Jim.
     
  7. Albertb

    Albertb pfm Member

    I do have a pukka .pdf of the Linn original but I can't see a way to post it in the thread, (would that be allowed on the site)? Unless I am missing something simple, (not the first time and definitely not the last), if anyone wants it they will have to PM me with an e-mail address and I will send it on.
     
  8. Albertb

    Albertb pfm Member

    Thanks Tony L for the advice on posting the PDF in the forum. I can see now that it can't be done. Looks like anyone who wants a copy will just have to contact me with an e-mail address and I will post it on to you.
     
  9. hacker

    hacker Delicious and nutritious

    If you send it to me, I'll put it up on my website for all to download. carllivitt at yahoo dot com.

    Cheers,
    Carl
     
  10. hacker

    hacker Delicious and nutritious

  11. Albertb

    Albertb pfm Member

    Great Hacker, thanks. Does this mean I can break my vigil at the keyboard and get some sleep now? :D
     
  12. redart

    redart Member

    Have just downloaded the schematic and circuit diagram for the PCAS011. Thanks to Albert for making them available and to Hacker for posting them on his website. Albert - I've replied to your PM (I think - can't see how to view my reply). Has anyone ever fixed one of these PSU's ?. There seems to be quite a few threads in various forums concerning the PCAS011, but I've yet to read of anyone having success in bring one back to life.
    Thanks again guys.
     
  13. Albertb

    Albertb pfm Member

    So let's have a look at the schematic then. I'm no expert on this but if I offer a few thoughts someone more knowledgeable will probably be tempted to continue or correct.

    Top left is the basic PSU function, 320v direct from mains and a simple 13.5v regulator.

    Mid left are U1 & U2, D type flip flops. These get the logic gating to turn on and off, and to select 33/45 by holding switch on for longer period via the delay caused by components around C12.

    Lower mid left, note that C14 and C15, though marked, seem to be missing as components! The 2 op-amps are acting as integrators with time constants dictated by the resistor networks around solid state switch elements U6-6,8,9 and U6-3,4,5. U3-5,6,7 is controlled by the 45rpm output of U2 and switches in this resistor network to make the change. This setup is the quadrature oscillator and produces 2 outputs at points O1 and O2, linked to the motor control section in the top right, which are hopefully exactly 90deg out of phase. Part way there! (Have a look here for better info, http://www.inesc-id.pt/ficheiros/publicacoes/2840.pdf.)

    Top right is the motor drive itself. The out of phase signals from the previous section are amplified and fed to the motor windings. Each of the pairs U4-1,2,3/Q5 and U4-12,13,14/Q8 are switched off when the marked ON point is held low. When this is raised to about 13.5v by the U1/U2 gating, the 2 amplifiers are actived and O1 and O2 are transferred to the motor windings.

    Below right is U5, again missing the components C18 and C20. Each of the first 3 amps is acting as a comparator and the very right is an integrator. The 2 right amps make up an oscillator through their control of the action of solid state switch U7-10,11,12. This affects the voltage on C19 which in turn affects the switching of the first comparator of the pair. Otherwise C19 will charge up and stop any switching action. The left 2 amps are set up to affect this action in 2 ways. If the OFF point is held high then the first comparator output is low and presumably C17 cannot charge up high enough under its link to the motor drive section enough to reverse this. If the switch U7-6,8,9 is open it will also be inactive. If these 2 allow it to be active then it will pass pulses to the next comparator based on the voltage across C17 which in turn reflects the current passing through the motor and R14.

    There is a lot of interplay in which area is on at any time, and each area is obviously set up to trim the action of others. This will be the interesting area for discussion I think. Maybe a new Pink Fish Valhalla could come out of this?

    Anyone want to comment on the bits I have not touched on or have wrong?
     
  14. redart

    redart Member

    Albert,
    Being an electronics dilettante I can't comment on your analysis of the circuit - only learn from it, so thanks for that. At present my focus is on getting the circuit to work. Here's where I'm at:- top left.....I have no 320 and no 0 volt, they measure as +120 and -120, referenced to earth. Also there is no 13.5v across C5. This measures at 1.2v. So something is amiss with this input stage. I've tried replacing the bridge rectifier (it's a W04M) but it didn't seem to help. Also my board does not have V1 and V2. Instead it has R1 (47ohms) between the fuse and neutral(3), as per the 'Changes' notes in the lower right dated 25/4/88. I can see how V1 and V2 would have made a voltage divider, but as I say, they're not there. Could this explain why I have +120 and -120 ?. Also what would the purpose of R1 be?. Without the 13.5v the rest of the board obviously can't work, but it seems to have 240vac 'everywhere'. Any thoughts on what's going on?
     
  15. Paul R

    Paul R pfm Member

    'Earth' is not relevant. Take huge care with all this, the voltages are potentially lethal and the board is directly connected to the mains...

    Anyway you need to measure wrt 0v as marked on the diagram. Take all the DC volts around the PSU components, the broken bit may become obvious.

    Paul
     
  16. Albertb

    Albertb pfm Member

    BE CAREFUL WITH INVESTIGATING THIS CIRCUIT! BE AFRAID, BE VERY AFRAID!!!

    As Paul has said, the reference to Earth is meaningless and will give completely erroneous readings. This can give the impression that there is no voltage around, when it is a matter of the voltages simply floating. Take voltages with reference to what is marked as 0V or across components directly and I suspect it will be a totally different matter.

    If it stays the same when you measure with the 0V as a reference then you probably have a simple repair to do. If yours is an American setup then the +-120V could be completely correct. You are effectively just measuring the mains voltage with respect to its earth after V1 or V2.

    Take a couple of simple voltage readings across the components themselves, directly across C5 for example, or CAREFULLY across C1 and C2. Remember that the voltages you measure across components like C1 or C2 are in reality bouncing around on the mains supply. So do not make the mistake of thinking that, just because your meter reads 13.5V it is safe to touch. You either learn very quickly or very finally with that way of thinking.

    If you were measuring directly across C5 when you read your 1.2V then there is certainly something wrong. V1 and V2 are varistors. These are meant to break down at a certain voltage and prevent over-voltage conditions occuring, spikes on the mains sort of thing.

    If you feel safe doing it without touching anything on the boards with your hands, what is the voltage directly across C1 and C2? Then, what is across D1? Then R5//C4, which should have about 14V across them. The Vbe of Q1 should be about 0.6V, (top of C4 to top of C5), but if it has significantly more than that your problem is at least that Q1 and possibly Q2 are blown.

    Assuming you feel safe doing this, post a couple of readings thinking of measuring direct across components or with respect to the 0V line not the mains earth and we can see where they go.

    The advice still stands, MAINS BITES! If at all in doubt as to your ability to do this safely then simply - DON'T! This board is directly connected to the mains with no working earth reference point, it is floating around carrying extreme voltages even on the points marked 0V, hard to accept but true, and what is more there is NO isolation in the form of a mains transformer!!!!! Who needs extreme sports when you can have this?
     
  17. hacker

    hacker Delicious and nutritious

    If you've every been bitten by mains, you'll heed the above. If you got bitten by touching both hands on a mains connection, then you probably wouldn't be reading this because the current would have travelled through your heart and you would, in all probability, be dead. Scaremongering? Yes, certainly! Music sounds much better when you're alive!!!
     
  18. redart

    redart Member

    Thanks for the warnings guys.....good to know there are still some people out there who care!. Wether by destiny or design, I've never been bitten by mains voltage, and I don't intend to start anytime soon....I'm too much of a chicken to poke anything that looks as scary as this board with my fingers !.:D
    Think I may have found the problem anyway. Zener diode D1 is toast. Haven't had the chance to replace it yet, but it looks like it would certainly explain why C5 only has about 1v across it. Wether it explains the rest of the board I don't know. Will let you know how I get on.
     
  19. redart

    redart Member

    IT'S ALIVE....!!! And possibly equally as important, so am I.
    The Axis is up and running once again. Turns out that Zener diode D1 was the culprit as suspected. How a 17 cent component can bring down a thousand dollar turntable!. Anyway, now that it's spinning again, I need to adjust the speed, as it's running fast on both 33 and 45. I'm guessing that VR35-1 and VR37-2 are the pots I need to tweak (I inadvertedly adjusted them whilst troublseshooting the supply). Would I be right in saying I need to reduce the resistance of these pots in order to increase the voltage at U3-13, thereby reducing the output to O2 ?.
     
  20. Albertb

    Albertb pfm Member

    Great news Redart. Looks from the schematic as if the best way is to first set the deck to 33. This will remove VR35 from the circuit via U6-3,4,5. Then trim VR37 for correct 33V speed. I suspect that you will simply have to check which way affects speed up or down as you go, unless someone else knows this unit's workings in practice.

    When you have this right, change to 45 and do NOT touch VR35 again! U6-3,4,5 has now brought in VR33 in parallel and it is used alone to trim the 45 speed.

    A quick check of both speeds after this should make sure that the method was correct. How are you going to check you have the speed absolutely correct, I know there are many here who are absolutely fanatical about such things? Do you have access to something simple like a test record or an accurate set of pitch pipes or even a tuning fork? I think you can probably do better than just rely on settings from a mains strobe type card.

    Me, although I have played piano and guitar for the whole of my (longish) life, I do not have perfect pitch. As long as it is holding speed rock solid as it plays, do I care if it is a fraction of a semitone out in absolute terrms? Would I ever know?

    (Now let's dig in and watch the fallout! ;-)
     

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