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ROLAND BOLT 30- 60 cycle hum...

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  • #16
    The TP's are at C (7.5Vdc) & D (15Vdc).

    As there is not a board layout available, you will have to find where the points are.


    • #17
      Use a scope or an AC volt meter to check for ripple on the preamp power supplies.


      • #18
        I'll try to answer..
        And one more question, the two blue 16uf filter caps were originally 22uf, but I upped the large single filter cap from 47uf to 80uf. Any problem there?
        Well they are the ht filter caps (high voltage) shouldn't be a problem well they only feed the tube output stage which you say is working fine .. there is normally no reason to change the value but a lot of people do !

        There is a layout diagram in the "Service Notes (with schematics) >Bolt 30/60 (zip file)" in the link G-one provided.

        The components and test points JPBass mentioned are in the middle of the pre-amp board.
        Click image for larger version

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        Please tell us what you measure between those and ground.

        You will notice this area also has a series pass regulator but this time on board AP 142 D9 is a 15volt zener.. !!

        Also C26 47uF 25v,C27 100uF 16v, & C28 another 47uF 25v perform the smoothing/filtering function here.

        I presume the switching function works ? as it uses a cmos ic TC 4016 which contains 4 switches .
        If there was ac ripple in the supply to this it would infest most of the preamp.
        One footswitch controls 4 "electronic" switches at various points in the schematic which reconfigures the pre-amp for overdrive!
        Click image for larger version

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        Also, is there a common sub for the 2sc1624 ? I have some L7812CV voltage regulators here..
        No... the 2SC1624 is a NPN transistor it might look like a regulator but it's not although it's kinda acting like one !!!

        You haven't told us what you measured ..measure first then replace if you have that 47 volts or near enough (it's not Nasa here)
        there is no need to investigate further.

        Also, would a 1N5368 zener be suitable for D9?
        No! Check the part list it's a RD 47E - from the NEC data sheet it's a 500mw diode. Although the diode you saw is 47 volts it's a 5 watt
        one , the currents here are miniscule .. the 5 watter wouldn't even know there was any current flowing and thus wouldn't work.
        i.e. wouldn't turn on !
        The data sheet is here for interests sake
        RD4.7E datasheet - 500 MW DHD Zener Diode Do-35

        And to satisfy a nagging thought I have could you make up a shorting jack wire the tip to sleeve (ground the tip)
        and insert it in the reverb switch jack. To make absolutely sure the reverb circuit isn't humming !

        Good luck on your mission !!


        • #19
          Thanks OC.
          I missed the board layout.


          • #20
            Ok, I went ahead and replaced all the electrolytics in the preamp [among them were C26 47uF 25v,C27 100uF 16v, & C28 47uF 25v] and I thought it was quieter.......until I put it in the cab and sat next to it. Still got that annoying loud buzz that seems to shift audibly between 2 tones at 2 second intervals. The amp has a Celestion century neo in it with 102DB efficiency. But unfortunately this efficiency really aids that hum too.....
            So tomarrow I'll post my readings at 15v / 7.5v
            Last edited by czech-one-2; 09-15-2014, 09:14 PM.


            • #21
              Thanks OC for taking the time to post the layout with the component circled, thats going to make taking a reading possible for me.


              • #22
                Originally posted by oc disorder View Post
                You haven't told us what you measured ..measure first then replace if you have that 47 volts or near enough (it's not Nasa here)
                there is no need to investigate further.

                Guess I'm a little slow at heeding advice. At least I know its not the electrolytics...
                Last edited by czech-one-2; 09-16-2014, 10:34 AM.


                • #23
                  Please check the 48 volt supply too and let us know . If you can find R 59 on the pre board ..Roland have it connected to terminal 4 which goes back to terminal 15 on the power supply board. The resistor is 120 ohms (Brown Red Brown) and should have 48volts on one end and 45v on the other with your negative meter probe on ground.

                  Attaching a picture showing a regulators internals compared with a transistor.
                  As I remember regulators in a 3 pin package were not so readily available back then so people rolled their own as their fathers before them etc etc..

                  Here's a 1 meg jpg which may be of use particularly if you can read in reverse !

                  It may help to print it out so you can jot notes on it. This should help you find the points and figure out where everything is ..
                  you could probably take a better shot of the back of your board and print that too although it may take adjustment of contrast etc.
                  With unfamiliar amps I find photography helps to find components on densely packed pcbs.
                  Attached Files
                  Last edited by oc disorder; 09-16-2014, 01:50 AM.


                  • #24
                    Oc, I should have checked your last post before removing all those nuts again You guys are incredibaly helpfull.

                    Ok, here's the reading:
                    TP 15V = 13.4v / 29.2v AC
                    TP 7.5v = 6.7v / 14.3v AC
                    48volt supply/R59 = 47.3V and 44V

                    Just want to confirm that this is the correct AC setting on my meter-

                    And while I'm trying to learn and have no shame, what does TP stand for?
                    Last edited by czech-one-2; 09-16-2014, 10:43 AM.


                    • #25
                      Yes thats the right setting for AC - you would probably find it would read the same on the 600 volt setting but maybe without the decimal place.
                      Hmm that ac seems very high even though you have replaced all the electrolytics !
                      There's a possibility the chassis ground point is a bit far away and giving us oddball readings.
                      Could you do it again but this time use a ground point on the pre-amp board.
                      Where C30 and C29 negatives go to ground there is a terminal 5 not far from terminal 4.
                      Try re-measuring with black (-'ve) probe on terminal 5 while you're there might as well give us the low down
                      on terminal 4 ...'sposed to be 47 volts probably be around 45.
                      Those DC readings are near enough .. for interests sake with your meter on AC measure the 6.3 volt tapping on your transformer.
                      It should read 6.3 volts unless your wall power is lower than 220volts.
                      Be careful .. it may be easier to measure on the tube/valve sockets


                      • #26
                        The amp has been warming up for 30 min or so and using ground pad #5 on the preamp board here are my new readings
                        R58 44.6 / 40.6 DC , 12.5 / 12.5V ac
                        R59 45v /48v DC , 12.5 / 12.5 AC
                        Last edited by czech-one-2; 09-16-2014, 11:18 AM.


                        • #27
                          OK, little confusing,
                          Now I'm Getting
                          R58 98v / 89v AC and R59 98v / 105v AC


                          • #28
                            Well its ridiculous... actually I'm curious if the 13 and 6 volt readings were the same measuring this way with terminal 5
                            new test.. measure from that ground point with power off to the ground point you used before resistance reading on 200 ohms scale.


                            • #29
                              Actually is there any history ? did it suddenly start humming at a gig or did you turn it on one day and hummmmmmmmmmm ?


                              • #30
                                Originally posted by czech-one-2 View Post
                                OK, little confusing,
                                Now I'm Getting
                                R58 98v / 89v AC and R59 98v / 105v AC

                                ok oc, I just took the reading from the chassis ground point, same results as above