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  • Roland VS-840 sliding pot replacement

    Hello all,
    I am going to replace the sliding potentiometers in a Roland VS-840 digital multitrack recorder. I have the Roland VS-840 Service manual which specifies 50K/B taper pots. I believe the pots are 45mm and I have found a candidate from Bourns. It is a p/n PTA4553-2015-CPB-503 and costs $1.13 each in a quantity of 10.
    The PTA series is a low profile lever and I am not quite sure if I need this one or a PA (taller tab). The pots are mounted on a circuit board and soldered at 10 spots. I have a bit of experience in removing and replacing pots on a circuit board from having to replace all the pots in a Peavey Classic 50 head. This digital recorder has track 1-4 as single tracks and 5-6/7-8 ganged together. Does this mean I need a 4 single pots and 3 ganged pots (added one for the master output too)? I will post a picture or two for your viewing pleasure. Give me any cautionary advice you deem necessary. It's going to require a ___load of desoldering and soldering and some improved organization skills to keep track of all the fasteners removed from the main board and components. Click image for larger version

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ID:	876674Bourns PTA.pdfVS 840 Service Notes.pdf

  • #2
    Parts soldered to a circuit board have a "footprint". Some 45mm pots may have the legs on the ends of teh part, others have the legs on the side of the pot near the end. You REALLY want to get a new part that fits the footprint.

    You have the old parts, get out a ruler and measure the dimensions of the slider post. Also pay attention to the shape of the slider shaft, because that is what your knobs are expecting.

    As to whether you need mono and dual pots, you have the parts there, look at them to determine this. They are either all 50kB or they are 50kBx2.
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      All my pots appear to be the same style...I am referring to the exploded parts list...can a single gang volume pot be used on a stereo (2 track) channel? I have not yet disassembled the 840 so I guess I should do so and remove one of the pots and examine it before I get ahead of myself with ordering new ones. I am attaching a picture of a supposed replacement pot sold by a 3rd party. The leg positioning mirrors the solder pads on the circuit board. If I waited to order I could also be more certain about the style of lever and the length needed.
      Attached Files

      Comment


      • #4
        Lok at the two photos. Clearly they do not have the same leg positions as each other, so at least one of those does not match your board. The one on the left - with the long shaft - has two terminals on each end. They are bent so they stick down a little inboard from the end, but the end is where they are. The extra two "terminals" closer to the center are just support points for the frame. The one on the right is even shown from the bottom. There are NO terminals on the end, there are FOUR terminals NEAR each end, but they are on the sides. And the two extra legs near the center are frame supports.

        SO these are two different products. If the seller is showing these pictures as of the same part, they are not.

        Your left one has the end legs positioned inboard a little. There are also end-legged ones where the pins are RIGHT at the end.

        Are mono and stereo the same part? In an analog circuit, no, you can't control two volumes with one resistor. But your mixer is digital, so the pots may just be controlling a control voltage. In that case a stereo channel COULD have a mono control. But I have no idea the inner arrangement of your unit. The mixer part could be analog or digital. You need to find out. And really, just look at the parts.


        SOme stereo sliders with the 8 legs might look the same as mono. On mono not all legs may be in use. If you have the parts blowup, look on the parts list. I see seven sliders. Does your parts drawing call all seven as the same item on the list? And what is the complete listing description of that part?
        Education is what you're left with after you have forgotten what you have learned.

        Comment


        • #5
          So the picture on the left with the tall lever is not the correct one. I attempted to edit my post and get rid of that picture but could not. The correct picture is the one on the right with 4 tabs at each end and 2 tabs in the middle slightly offset. I enlarged the picture of the circuit board as much as I could and located the attaching points for the pots. I think the exploded parts drawing is on page 3 or 4 of the service manual. At any rate, I believe I have at least the proper configuration for the pot. The other specs I got from the parts list where it specifies 50K for the pots. For some reason the service manual for the 840 does not specify the 45mm figure but the Syntaur website does. I happen to have a VS880 as well as the 840. The 880 service manual specifies a 60 mm throw. When I compared the two, side-by-side, I can see the 840 is shorter than the 880 pot. As I mentioned before, I probably should wait until I remove one for examination before I order something with an incorrect lever length or style. When it comes to the mono vs stereo debate, I seem to recall some discussion about the volume pots controlling a control voltage. It will all become clearer when I have the pots exposed. In the parts section it only mentions one part number as a fader. That would imply that all the pots are identical. Once again, having one in hand will solve these and other mysteries. The original part number is said to be a "EWA POAC 10B54 50KB". When I search that part number I hear only crickets....

          Comment


          • #6
            I disassembled the VS-840 and bagged each component's attaching screws and taped the bag to each part. It came apart fairly easily and I located the malfunctioning slider pot. When I worked on the Peavey Classic 50 board, I clipped off the legs for each pot to be replaced and it simplified desoldering the legs because I didn't have to tray and wrestle the entire board to free all 10 attachment points. Is there a reason why you would not recommend doing that same process with the Roland VS-840? It is a lot easier to heat and remove a leg remnant and solder suck the attachment hole than to try to remove the pot intact. The underside of the pot is keyed and can only be attached to the board in one possible orientation. The pots I settled on are Bourns PTA4543-2015CPB503 . Mouser has none in stock but 708 at the factory. I will order 15 or so as I own 3 ea. VS-840's. At that quantity the price is $1.13 each. I will let you know when/if the repair attempt is completed and the issues I encounter. There are a lot of connections and details to attend to in the reassembly process and I am working hard to be patient and thorough in my approach. Click image for larger version

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            Comment


            • #7
              Originally posted by dkevin View Post
              The pots I settled on are Bourns PTA4543-2015CPB503 .
              Why these? One of the more critical aspects is that the pins line up with the holes in the board. From what I can see from the datasheet compared to your pictures, the pins will not work. Am I looking at the wrong datasheet?

              (your picture from post #3, the second one with the slider on it's side, looks like the pin configuration that your pictures show)
              Attached Files
              "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

              Comment


              • #8
                It is true, the #3 post and the picture to the right hand side is the one that is recommended by Syntaur as a replacement pot. I was under the impression that the Bourns pot I listed in post #6 was of the same configuration and size. Could you share with me your thoughts about it not being a potential replacement for the original pot? The originals have 4 pins at each end and two pins located along the sides slightly offset from each other. When viewed from the top of the pot the left side attachment pin is slightly higher than the right side attachment pin. When viewed from the underside of the board, the side pin orientation would be reversed.

                I think I understand why the pin arrangements do not seem compatible. My picture of the circuit board in post #6 does not contain an entire track's worth of attachment pins. I cropped and enlarged the original pictures to get a selective view of one track slider's attachment points. But when I upload the cropped, enlarged photo it shifts the picture's center and omits part of the attachment points. I will work on getting a picture of one track slider's attachment points on the circuit board without attempting to crop it so you can see what I am trying to replace.
                Last edited by dkevin; 05-25-2020, 05:49 AM.

                Comment


                • #9
                  But look at the data sheet g1 posted for your PTA series part. The pins are two directly on one end and one directly on the far end. The ones you need have four pins on the sides near the ends, not any pins right ON the end.

                  The two in the center offset a little are just tabs from the frame and are there only for support.

                  Your photo clearly shows the four pins near one end of the pot. The other end is offscreen but looks similar. And the two center support post are seen soldered to the large ground trace, on which the numbers 1,2,3 are written. That picture is perfect to show how the data sheet picture of the PTA series differs.
                  Education is what you're left with after you have forgotten what you have learned.

                  Comment


                  • #10
                    Thank you for pointing out my error...I am (more than) a bit befuddled by all the details involved in sourcing the correct replacement parts. I will go back to the drawing board and give it another try. Thank you again Enzo and g1 for your timely intervention! For those who want to assist in locating the correct parts, I quote from post #5..The original part number is said to be a "EWA POAC 10B54 50KB"...(this information from the Roland VS-840 Service manual parts list)

                    Comment


                    • #11
                      I don't know who made the originals. Alps, Noble, Alpha were common brands.

                      Look again at the data sheet g1 posted. Do you realize almost all pots and certainly sliders are custom made for the OEM? Roland orders what they need, they don't find them on the shelf at a big supplier. On the data sheet right by the top upper right, HOW TO ORDER. These companies put out catalogs that all work similarly. You pick the features you want and generate a part number, which they then make for you. Each digit in the part number indicates the type of shaft, the size of shaft, the travel etc.


                      Did you try contacting ROland directly to ask if they can supply this part OR if they can suggest places to order from?

                      https://rolandus.zendesk.com/hc/en-u...acement-Parts-
                      Education is what you're left with after you have forgotten what you have learned.

                      Comment


                      • #12
                        I found this thread in a Roland VS-840 user forum about replacing volume pots: "I traced the circuit and the pots are simply voltage dividing across the 5 volt supply and the resistance is NOT critical. I have found a 10K taper "B" pot works fine. The extra 3 ma drawn by replacing all 7 sliders with 10K instead of 50K is minute and inconsequential.

                        The part number, available at DigiKey is PP1045SB and costs around $2.27 each in quanity 10."

                        When I traced the part number I came to this part number-EWA-P12C15B14...I will attach the data sheet...of course, this part is obsolete....

                        Comment


                        • #13
                          PP1045SB at Digikey comes up with the EWA number but for me lists it as non-stocked.

                          But at least it identifies EWA as a Panasonic number series.
                          Education is what you're left with after you have forgotten what you have learned.

                          Comment


                          • #14
                            Well this is a good start. So far you need a 45mm panasonic EWA series and 10k, 20k or 50k should all work.
                            EWAP1 indicates 45mm single type so that is the prefix you need.
                            Attached Files
                            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                            Comment


                            • #15
                              The EWA series is getting hard to find, even on ebay. Are they discontinued? I need a pair of 60mm for a Yorkville mixer. I'll be checking with Yorkville.

                              Comment

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