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Thread: Line 6 XPS-AB Schematic

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    Line 6 XPS-AB Schematic

    Hi there! Iím looking for a schematic or service manual for a Line 6 XPS-AB. This is the unit that powers the 300, 500, 600 and 700 Variax guitars so you donít have to use batteries and also acts as a foot switch to toggle between a 1/4 inch and XLR output. I have no voltage coming out of the TRS input so my Variax is not powering up. Thank you!

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    Hi. PM me.

    I have the Variax Service manual which I can send you. It's too big to put here! I'm pretty sure that what you need is in there.

    Cheers

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    Wow, thanks gaztech! Can you tell me how to pm you? I am logged in but when I tried clicking on your name it says I don’t have permission.

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    Hi, I guess it could be that your profile is not set up to send or receive messaging. I think it's turned off by default. Go to your profile and edit it, Select General and you can edit your permissions there. I can't send to you if you don't have permission to receive messages from members. It's likely if this is turned off you won't be able to send either.

    Once you set it, go to Notifications on the top of the screen select Inbox - which will take you to messaging and then try to send me a message.

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    Thanks for the quick reply! I will see about editing my profile.

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    I seem to be in a catch 22. I click on my name and click on profile but I get the same message - I don’t have permission. Not sure why I can’t get in to edit my own profile unless I haven’t been approved by the administrator?

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    Okay, went to try and edit my profile again and all of the sudden I now have a “Private Message” icon, so sent you a pm.

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    HI Bill,

    Sent to your email. Hope all is well.

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    Thanks gaztech! I really appreciate your taking the time to read my post and send the pdf. Take care!

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    Line 6 Variax Service Manual
    Attached Files Attached Files

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    When the going gets weird... The weird turn pro!

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    BIG Thanks DrGonz78!

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    Big thanks again to gaztech and DrGonz78 for sending me a file of the Variax Service Manual. Unfortunately I must have a later version of the XPS-AB box that supplies power to the Variax. On the circuit board of the XPS-AB it says “MG1 MGB REV B”. Then underneath that is the same part number as the REV A model (35-00-0138) and beneath that is the date 6/9/03. The REV A version is dated 8/20/02. Any idea where I can get a schematic for this REV B XPS-AB? Looks like the REV B model has 2 relays instead of one and various other changes. Thanks so much!

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    Hi Bill,
    Has the unit ever worked?
    The footswitch unit should be powered by a separate mains adapter. You haven't changed the adapter have you? I seem to remember an incident a long time ago regarding one of these where the customer had changed the adapter and it was the wrong one. The original adapter I think was an AC adapter not a DC one - 9v AC @ 2000mA. I just had a quick look at the schematics I sent you and there's not a lot in the box that would go wrong. I would have thought, any fault, if it's just the box, should be obvious.

    If you look at the MGB schematic, you will see that it does indeed suggest that the adapter is AC - not DC. A DC one won't work because of the arrangement of the diodes in the front end of the power supply section.

    I'm wondering now if it's not actually the box at fault. Are you sure it's not the mains adapter? It's difficult without physically looking at it to make a reasonable diagnosis of this. Can you give me some more info? Maybe we can work through this for you.

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    Thanks so much, gaztech, for the reply! I feel I must preface my reply with the fact I am pretty much a noob when it comes to repairing electronics. I’m a musician of 50 plus years and have been soldering guitar cords for many years and over the last 3 years have watched many electronics YouTubes as well as read parts of the NEETS modules on line, but my knowledge is very limited, so any help I can get is greatly appreciated.

    Yes, the unit was working. I bought it used about 6 weeks ago. I haven’t changed the ac adaptor and it is the one made by Line 6 for this unit. You are correct, the adaptor puts out an ac voltage. I measured the voltage coming out of the adaptor and it is putting out around 11 VAC. Is that enough to rule it out or are there some other tests I can do on the ac adaptor?

    I am wondering if the electronics in the box or the ac adaptor could have failed due to a heating problem. I am ashamed to say I left the box plugged into the ac adaptor and guitar for 5 days never unplugging the power, so the box was on 24 hours a day for 5 days. It stopped working on the 5th when I was playing the guitar. I noticed in the owners manual it said to disconnect the box from the power if you aren’t going to be using it for a while. Is it possible something could have overheated?

    When I opened up the box then plugged in the ac adaptor, U6 (the quad comparator model LM339 located on the right side of the board between the TRS IN and ac adaptor input) and the area around it felt very hot.

    The next thing I did in order to confirm what part was getting hot, (and might not have been the smartest thing to do) was put some flux in that area and proceeded to watch pin 3 (VCC in) on the LM339 burn up, then the light emitting diode D16 stopped glowing. I have since replaced the LM339. I also replaced U2 (C082C op amp) and D8 which are located above and to the left of the ac input) as they looked like they had some heat damage too after I put flux around the LM339 area.

    In the process of removing the op amp by using some Chip Quick low temperature melt solder I must have gotten some solder on 2 resistors (R 28 & 33) that are very close to the op amp, because to my surprise there were both missing after I removed the op amp. So I am waiting to get the 2 resistors in the mail before I try plugging in the box to ac. They are supposed to arrive Saturday, so hopefully by Sunday at the latest I will have soldered them in and report back.

    In the mean time any help or advice is greatly appreciated. I just posted a couple of pics in my albums of the circuit board in case that may help. Thanks!

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    Last edited by Billguitarvin; 04-16-2020 at 06:20 PM.

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    HI Bill,
    You really must be careful with soldering on something like this! It's very easy to break the copper tracks...

    Ok, so when you have the resistors soldered back in, you are only concerned with the voltage across 3 capacitors. These measurements will tell you what is going on:
    Across C12, should be -5V (with negative probe on the -ve of the capacitor)
    Across C11, should be +5V (with negative probe on the -ve of the capacitor)
    Across C2, should be +7V

    It's probably worth taking a measurement across C9 too - that should read about 9V.

    All of the above are DC readings of course!

    Report back on your findings. If any of these are missing then it's a relatively simple job to fix (probably). If these are all up and working then the problem is more serious and I doubt you will be able to fix it yourself.

    Let me know how you get on.

    Cheers.

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    Thanks so much gaztech! Iíll check the voltages on the caps you talked about once I get the resistors soldered in. Hopefully by Sunday.

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    Here are the voltages now that I have replaced the resistors.


    C 12 +4.99 volts with black probe on negative side of cap, red probe on positive side of cap (I triple checked this - not sure what I did wrong or why it is a positive voltage).


    C 11 +4.99 volts with black probe on negative side of cap, red probe on positive side of cap


    C 2 0 volts (On my board this was a surface mount)


    C9 +13.09 volts with black probe on negative side of cap, red probe on positive side of cap


    I have an ac adaptor for my Line 6 pod xt that is the same adaptor that is used for the XPS-AB, so I tried using the pod adaptor and nothing changed.


    Red power light LED is now intermittent. Thanks for taking the time to look at this!

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    Hi Bill,

    Hmm... something isn't right here... either your measurement technique is off or we have a serious issue. Let's take these readings one by one:

    C 11 +4.99 volts with black probe on negative side of cap, red probe on positive side of cap

    This one looks ok.

    C 12 +4.99 volts with black probe on negative side of cap, red probe on positive side of cap (I triple checked this - not sure what I did wrong or why it is a positive voltage).

    That one is ok too. If you look at the drawing, the "+ve" side of the capacitor is what is actually connected to the 0V line so the way you are measuring it will yield a positive voltage. What you should be doing with that one is putting your black probe on the "positive" lead of the cap to take the measurement - which will then show you -5V on the negative lead.

    C9 +13.09 volts with black probe on negative side of cap, red probe on positive side of cap

    This voltage looks ok.

    C2 0 volts (On my board this was a surface mount)

    Now, here's a problem. You should get a reading of about +7V on this point. I need to know if you are taking these measurements with the guitar connected or not. This makes a difference. Also, does the guitar work if you use it on batteries? If it doesn't then the issue could be with the guitar and not this unit!

    The odd thing here is that the unit was working then it mysteriously stopped. You didn't really do anything to it when it was on. You'll need to take some readings around the FET (Q9) as this is effectively the turn on/off for the 7V supply. Since you're not an electronics guy, it's very tricky knowing what to tell you to do next. I could say "test Q9 and Q7" but I'm not sure if you'd know how to do that!

    Q6 could also be a contender here as if this is short circuit, it will take the 7V line down. My money is on the TL082 (U2) or Q9 (MTP2955V). These parts supply the switch line for transistor Q7 - which looks like it turns the unit on. If the unit had been left on for a long time then the majority of the current would have been travelling through Q9 - so it may have given up. Q7 could be the cause too but I doubt it as there isn't much current actually flowing through it when the unit is on.

    Bill, you need to have a look at the above but it might be time to give it to someone that knows electronics so that they can take a look and take some meaningful measurements. Using a shotgun approach and just replacing parts might yield a result but it's very easy to damage other stuff in the process.

    You replaced the LM339. You put it in the correct way round - right?

    There is also some switching going on around the guitar jack. It looks like there should be a plug in the socket to turn the unit on. You could try taking the measurements again with JUST an unconnected stereo jack cable attached- (nothing connected on the other end. (That's a cable with a three pole jack on both ends plugged into the guitar input socket). This may give you different results. The power LED coming on/off is intriguing me...

    The tests you would have to perform to narrow this down further now get to component level and some knowledge is required to work out what each component does and then figuring out why they are not doing it!

    Have a prod around with your meter but be careful. Any further info might be useful but we might have gone as far as we can without starting to remove components and checking them.

    Let me know how you get on.

    Cheers.

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    Thanks so much for the quick reply! Thanks too for educating me what “-ve” and “+ve” means. For some reason I thought electrolytics always had the negative going to ground, so right there is a valuable lesson for me. I can see on the schematic how the “+” is indeed going to ground or 0 volts.

    All the readings I took with the guitar not plugged in and no TRS cord plugged into the guitar input on the box. Fortunately the guitar does work with batteries. I will try taking some readings with a stereo guitar cord plugged into just the box and not the guitar.

    As far as testing Q9, l looked up the model number and then was able to find some info about testing P Type Mosfets by taking it out of the circuit and using a multimeter. Is this the kind of testing you were referring to, or were you thinking about testing components around Q9 or some other way of testing? If you are ok with telling me what to test, I am totally into researching what I have to do to test a part, or if you have suggestions on studying a type of circuit used somewhere in the XPS-AB box, I am fine with that too. Since I have some time on my hands, I’d love to learn more about repairing this box and understand more about what the various circuits are doing. I totally understand though if you aren’t into guiding a noob through repairing this unit.

    I replaced U2 as it looked like it had some heat damage. When I replaced U2 and U6 I replaced them so the etched line on the replacements were on the same side as the notch in the silk screen on the pcb. This was the way they were placed before I replaced them.

    I just took out Q9 the P Mosfet and you were right. If I did the test properly, with the mosfet in the on position, the multimeter showed “OL” between drain and source. Also only 56 ohms of resistance between gate and source.

    Please feel free if you have any other suggestions and I will be happy to carry them out. All the best and take care!

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    Bill,

    Did you check Q6? You could try removing it to see if the 7V comes back...

    You should also have around 2.5V across two of the pins of Q8. This voltage is used as a reference elsewhere. If its not present that coukd be a problem.

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    Thanks gaztech!!!! Got my Q9 replacement yesterday so hope to put that in the next couple of days. I’ll check the voltage on Q8 and remove Q6 to see if I get the 7V back. I really appreciate the help!

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    Greeting gaztech! I installed the new Q9 then took some measurements. I did these all with the negative probe on ground. Here is what I got

    Q1 - 4, -4.9V
    Q1 - 8, 1.6V (Should be 5V)

    Q8 2.49V

    R16 9.5 (Should be 7V)

    I made some other measurements around the board where the schematic showed some voltages:
    U1 - 4, -4.9V
    U1 - 8, -.6V (Should be 5V)

    D9, -9.9V

    L2 10.8VAC (Should be 9VAC)

    D6 -4.9V

    After the above measurements I took a stereo guitar chord, inserted into TRS IN and got these measurements with the negative probe on the sleeve and the positive probe on either the ring or tip. Did I do this backwards, as I got a negative voltage reading? I thought on a TRS cord the ground or common is usually the sleeve so that’s why I put the negative lead on the sleeve.
    Sleeve to Ring -.02V
    Sleeve to Tip -8.3V
    Ring to Tip - 8.3V

    So the good news is after replacing Q9, I am now showing a voltage on the TRS cord, but unfortunately did not power up my guitar. I also noticed it stating on the schematic “min 7.02V max 7.06V” by where the +7V arrow is between C2 and R16. Is this staying what the voltage of the +7V should be, or is referring to something else? Thanks again for all your help!



    I will try taking out Q6 tomorrow and see what that does. Thanks again for all your help!

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    Hi Bill,

    I'm glad to see you're sticking with it! Ok, so we now have some volts. What you should NOT have done at this point was to plug in your guitar! If the supplies are not 100% correct, don't do this. You can damage the guitar. Hopefully you haven't already...

    I think there are some measurement errors in there - probably due to probes being the wrong way round when you took them...

    The thing that bothers me now is your statement : U1 - Pin 8, 0.6V. This is wrong. It really should be +5V. If it isn't then everything will be wrong. You need to check the voltage regulator U4 (or the anode of diode D7). Pin 1 of the regulator should be +5V. This supply feeds several of the chips in this unit and it is required.

    If it's not 5V then you "could" have a bad regulator (LM78L05). If not the regulator then U1 or U3 could be bad and are dragging the supply down. It's likely that there will be some decoupling capacitors on these lines too which could also be at fault (these may not be shown on the schematic).

    However, you replaced U3 already I think. I would start there. You might have shorted a couple of pins together when you soldered it in. Check the soldereing with a magnifying glass.

    If Q9 really was the major culprit of thie unit going off (looks like it might have been) then I doubt this would have affected the other parts so we need to assume that somethng else happened here. Replacing the only part that is tied to the 5V rail seems likely... Check this lot and let us know what you find. Good luck.

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    Thanks gaztech! I am glad you have stuck it out with me. I don’t totally trust my readings as I have to fool around with the probes to get any readings. I don’t know if some thinner probes would help. I’m using the stock probes that came with the meter which are a bit big. I’ll see if some thinner probes help and remeasure as well as check out the parts you suggested. Many thanks and I’ll let you know what I find out.

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    Thanks for the warning about waiting to plug in my guitar. I was lucky nothing got messed up. So I took some voltage readings from U4, U1, U3 and anything else in the schematic that showed 5 volts coming out of it. I got some thinner probes which seem to be helping getting the readings.


    U4 pin 1 1.6V (should be 5V)


    U1 pin 8 1.6V (should be 5V)


    U3 Pin 3 3V (should be 5V)


    R26 3V (should be 5V)


    R27 -10.3V (should be 5V)


    C11 1.6V (should be 5V)

    I checked most of the caps on the top of the board and here is what I found. I didnít see any caps that werenít on the schematic. Not sure if I need to take these out of the circuit to get an accurate reading, or if I was doing something wrong, but here goes.

    C1 4.4 microfareds (should be 4.7) 1M ohms


    C2 OL (should be 2.2), .3ohms


    C3 19 nanofareds (should be 10 nanofareds), 43 M ohms


    C4 2.3 microfareds (should be .1microfared) 1M ohms


    C5 50 nanofareds (should be 10 nanofareds) 3.6 M ohms


    C15 2 nanofareds (should be 10 microfareds) 1 M ohms

    I replaced U6 and U2, but havenít replaced U3. Iíve looked closely with a magnifying glass and donít see any solder bridges on U2, U3 or U6. Thanks again for all the help!


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    Hi Bill,

    I think that you're going to have to start removing components to find this...

    There should be +5v on the regulator. Therefore, I would start by removing U1 and U3. Do that to see if either of these chips are dragging the supply down. Take them out, then measure the output of the regulator. If it comes back to +5v then it's likely a chip is at fault.

    Be careful not to damage any tracks when removing these parts! It's very easy to mess things up with too much heat...

    BTW, you can't measure caps accurately with them in circuit - you have to remove them. Resistance measurements for caps are meaningless.

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    Hi gaztech and thanks for the quick reply! I’ll try removing U1 and U3 and see what happens. Thanks too for the info about capacitors. One question I have is if a capacitor shows very little resistance (like .3 ohms on C2) could that be a possible sign that the capacitor may have a short? Or if the ohms read OL In circuit it could mean there possibly is an open circuit in the capacitor? If not in circuit, would this apply to out of circuit, or am I not correct?

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    Quote Originally Posted by Billguitarvin View Post
    Hi gaztech and thanks for the quick reply! I’ll try removing U1 and U3 and see what happens. Thanks too for the info about capacitors. One question I have is if a capacitor shows very little resistance (like .3 ohms on C2) could that be a possible sign that the capacitor may have a short? Or if the ohms read OL In circuit it could mean there possibly is an open circuit in the capacitor? If not in circuit, would this apply to out of circuit, or am I not correct?
    The readings that you got on C2 caught my eye too. However, I am more confused by the readings than anything. So one way I read it is that C2 measures 0.3ohms and the other way I read it is that it measures OL. There seems to be a contradiction in that it can only be one or the other if it is in circuit. So to clarify, are we talking about two different measurements? One in circuit and the other out of circuit.

    Edit: Also, I can read this as that when checking with capacitance setting it reads OL and it reads 0.3ohms with resistance setting. Perhaps the problem reading it in circuit is due to the Q6 Jfet in parallel to C2.

    ..."C1 4.4 microfareds (should be 4.7) 1M ohms


    C2 OL (should be 2.2), .3ohms


    C3 19 nanofareds (should be 10 nanofareds), 43 M ohms" ,,,

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    Quote Originally Posted by DrGonz78 View Post
    The readings that you got on C2 caught my eye too. However, I am more confused by the readings than anything. So one way I read it is that C2 measures 0.3ohms and the other way I read it is that it measures OL. There seems to be a contradiction in that it can only be one or the other if it is in circuit. So to clarify, are we talking about two different measurements? One in circuit and the other out of circuit.

    Edit: Also, I can read this as that when checking with capacitance setting it reads OL and it reads 0.3ohms with resistance setting. Perhaps the problem reading it in circuit is due to the Q6 Jfet in parallel to C2.

    ..."C1 4.4 microfareds (should be 4.7) 1M ohms


    C2 OL (should be 2.2), .3ohms


    C3 19 nanofareds (should be 10 nanofareds), 43 M ohms" ,,,
    Thanks again for the quick reply! Yes, both of these readings were taken in the circuit, and yes, per your edit, with the capacitance mode on the multimeter I got OL, while with the resistance mode on the multimeter I got .3 ohms. Sorry for the confusion on that. One other weird thing is I can not find Q6 anywhere on the top or bottom of the circuit board. It’s probably staring me right in the face, but I’ve gone over both sides of the circuit board with a magnifying glass as well as enlarging pictures I took before I started mucking around with the electronics but can’t find it. I see it on the schematic, but not on the circuit board.

    If I may, one other question is why are some parts on the board in what I would call a “grayed out” font? For example C1 and C2. Another thing is “Do Not Stuff” written for C1. I googled it and it said it was for something to use for testing at the factory but was to be taken off the board after completing final inspection. If that is true, C1 is still on my circuit board. Not that that has anything to do with getting this unit working, but just curious about that. Thanks again!

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    Hi Bill.
    Iím baffled by the readings too. You can of course show a shorted capacitor using a resistance test. A reading of 0.3 ohms usually shows that it is short circuit but it does depend on the components in parallel with it. Can you post some photos of the board so that we can see what you have. It may help.

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    BTW, components that are shown ďgreyed outĒ on the schematics usually are not on the actual board but... you may find these parts on some versions of the board. Sometimes these parts are optional and installed on final test. ďNot stuffedĒ just means that the part is not installed on the board. It may have been an afterthought which was removed later. All of these are nothing to be concerned about.

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    Oh, and if youíre concerned about C2, remove it and test it. It shouldnít be 0.3 ohms!

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    Hi gaztech and thanks for answering my questions! I posted a couple of shots of the circuit board in “Albums” under my profile. Is that something you can access? If not I can see about posting some pictures of the board. I don’t totally trust the readings I am getting, as I sometimes have to move the probes slightly before I get any reading. That as well as not knowing a lot of times which probe should be where. Could be a lot of user error going on on my part. Thanks for continuing to help me out with this!

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    Blimey! I blew out L2 on the circuit board checking some voltages. I’ve tried with Digikey parts supplier, but according to the info on the parts list, the only thing they can find for a “TL431” is a 3 pin through the hole inductor. The schematic shows L2 being a coil and underneath says “600R@100M”. The parts list for L1-4 says:
    IC REG ADJ PREC SHUNT <36V
    TO-226AA(LP) TH TL431”

    I gave all this info to digikey but they say if it’s adjustable, it would have to have 3 pins. Any idea what this might be? L2 is the first thing the AC coming from the AC adaptor sees when the 9VAC comes into the unit. Thanks!

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    I’m thinking L2 is a ferrite bead rated at 600 ohms?

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