Announcement

Collapse
No announcement yet.

70s Ampeg V4B Blows Fuses

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • This one measures 0.5v/311v.

    Comment


    • R52(587v/9mv), R53(620v/5mv).

      Comment


      • I'm guessing the resistor that measures 311v/0.5v is the one that popped causing vdc to go to mvdc?

        Comment


        • Originally posted by ca7922303 View Post
          This resistor measures 620v/311v.
          What you are showing are 100k / 2W resistors (most likely R56, R57)
          The voltages you measured (620v / 311v) are OK because the resistors are connected in series.
          Compare the detail that you show with the schematic, and it will be immediately clear what is about.
          For R52, R53 (4.7k / 2W) use schematic and find them.
          Who does not know and knows that he does not know - teach him Confucius)
          Who knows and does not know that he knows - wake him Confucius)

          Comment


          • Only other resistors off the board are these two. They both measure 4.7k resistance and 570v so I'm wondering how they be an issue?

            Comment


            • Originally posted by ca7922303 View Post
              Only other resistors off the board are these two. They both measure 4.7k resistance and 570v so I'm wondering how they be an issue?
              Somewhere you wrong in measuring or interpreting schematic.
              Who does not know and knows that he does not know - teach him Confucius)
              Who knows and does not know that he knows - wake him Confucius)

              Comment


              • Not sure what you mean?

                Comment


                • Originally posted by vintagekiki View Post
                  Yes R52 & R53 is 4.7k 2 watt resistors.
                  When measuring the voltage, in which position is SW4
                  Standby switch is in on position.

                  Comment


                  • Originally posted by vintagekiki View Post
                    Somewhere you wrong in measuring or interpreting schematic.
                    Not sure what you mean? Can you explain further?

                    Comment


                    • Originally posted by ca7922303 View Post
                      Not sure what you mean? Can you explain further?
                      OK. Let's go step by step.
                      Checking how the power amp works.
                      Follow the schematic.
                      Connect speaker to J6 SPKR
                      StandBy (SW4) in position ON
                      Measure and upload the voltage measurement results at points 1, 2, 3, 4
                      Remove V201 (6K11) to turn off the preamp.
                      Plug the guitar into jack J4 or J5.
                      If the output stage is correct you should get a clean guitar sound of the order of 10-15W
                      Descriptions of how the V4B responds.
                      Click image for larger version

Name:	V4Bpwr.jpg
Views:	86
Size:	2.42 MB
ID:	929994
                      Who does not know and knows that he does not know - teach him Confucius)
                      Who knows and does not know that he knows - wake him Confucius)

                      Comment


                      • Do you have the resistors like in the bottom right of this pic?

                        Click image for larger version

Name:	v4b res.jpg
Views:	63
Size:	60.5 KB
ID:	930001
                        "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


                        • He only has good will and time to lose.
                          Who does not know and knows that he does not know - teach him Confucius)
                          Who knows and does not know that he knows - wake him Confucius)

                          Comment


                          • Originally posted by g1 View Post
                            Do you have the resistors like in the bottom right of this pic?

                            Click image for larger version

Name:	v4b res.jpg
Views:	63
Size:	60.5 KB
ID:	930001
                            Yes, I will post a photo, but they both meadmea 4.7k redisresis and 570v
                            Don't see how they could get causing the issue and they seem to be connected to impedance switch. Can you explain how they are connected to R52,53 on board? Thanks for your help.

                            Comment


                            • Originally posted by ca7922303 View Post
                              ... ...
                              Compare the layout of the V4B in front of you with the schematics
                              Look where all the wires are going from R52, R53
                              Who does not know and knows that he does not know - teach him Confucius)
                              Who knows and does not know that he knows - wake him Confucius)

                              Comment


                              • Originally posted by g1 View Post
                                Do you have the resistors like in the bottom right of this pic?

                                Click image for larger version

Name:	v4b res.jpg
Views:	63
Size:	60.5 KB
ID:	930001
                                Here's the photo

                                Comment

                                Working...
                                X