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70s Ampeg V4B Blows Fuses

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  • V5,6,7,8-pin#8(0.00mv)

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    • R201,202,203,204,206,207,18,19,20,28 still measuring resistance per schematic. No components appear burnt.

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      • Originally posted by ca7922303 View Post
        V5,6,7,8-pin#8(0.00mv)
        normally pin8 is the PT cathode that goes to gnd
        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)

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        • Originally posted by ca7922303 View Post
          No components appear burnt.
          In order for measuring instruments to serve their purpose, they should occasionally be made happy for their birthday with a modest gift.
          The new batteries in the measuring instruments are a miracle.
          They broaden the horizons.
          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)

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          • Any thoughts on why I'm getting millivolts instead of volts after a loud pop near V5?

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            • Be more specific in describing the symptoms.
              You are very stingy on words.
              For V5 you asked a question, got an answer, what is the problem now.

              About V5
              #123
              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)

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              • One of the supply voltage dropping resistors may have opened up or have a bad solder connection.
                These would be the voltages on either side of resistors R51,52,53, & 55.
                "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

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                • vintagekiki
                  vintagekiki commented
                  Editing a comment
                  I guess he learned something from these 127 posts.
                  At least now knows that dmm requires the correct battery.
                  I regret the master who will take over the repair this "70s Ampeg V4B"

              • R51(2.2k), R52(OL), R53(OL), R55(0.46K) resistance. R51(570v/570v),R52(-4mv/570v), R53(585v/5mv), R54(585v/585v). When I replace R52 & R53 are they 2 watt resistors?

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                • 2nd measurements were DCV

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                  • Originally posted by ca7922303 View Post
                    R51(2.2k), R52(OL), R53(OL), R55(0.46K) resistance. R51(570v/570v),R52(-4mv/570v), R53(585v/5mv), R54(585v/585v). When I replace R52 & R53 are they 2 watt resistors?
                    Yes R52 & R53 is 4.7k 2 watt resistors.
                    When measuring the voltage, in which position is SW4
                    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)

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                    • Actually now that i've flipped it over to component side, R52,R53 were never on this board

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                      • Also, not sure what is SW4?

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                        • About R52, R53, SW4
                          Look at the schematics

                          For R52, R53, g1 wrote in previous posts ... I think these are sometimes mounted elsewhere, off the board ...
                          Browse the topic from the beginning.
                          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)

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                          • SW4 is the standby switch. It needs to be in 'play' position for all the testing. R52 and R53 are possibly mounted on the big capacitor cans. I'm not sure if you have your meter on the trace side of the board? You may have to dig in more with your meter to get the reading. Please re-check.
                            "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

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                            • This resistor measures 620v/311v.

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