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  • #16
    Originally posted by Jazz P Bass View Post
    How did you measure that 15Vdc?

    That circuit is a little different than the B2R.

    This one employs +15Vdc on the coil at all times.
    When it is engaged, Q120 will provide -15Vdc to the coil.
    Thus the -11.5 Vdc of TP12.

    You really should check that TP11 does NOT have gross amounts of volts dc on it.
    I have an 8 ohm load on it, which I'm not sure if that matters. I'm getting 15.3 vdc on one side of the relay and -11.2 from the other side. Tp11 fluctuates between 0 and -.001 vdc. I measured all terminals on q120, because I don't quite understand which one I need to be looking at, and I'm getting -12.63vdc on the middle terminal and -11.98 on the outer terminals. I hope this helps.

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    • #17
      Surprising that you cannot hear it click as the circuit appears to be working.

      It may very well be that the contacts are not closing.

      I would put a new relay in.

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      • #18
        Originally posted by Jazz P Bass View Post
        Surprising that you cannot hear it click as the circuit appears to be working.

        It may very well be that the contacts are not closing.

        I would put a new relay in.
        I have one on the way now. I'll let you know how it goes. I appreciate all of the help

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        • #19
          Well I put the new relay in, and while that is working and I'm now getting signal to the speaker, the amp sounds very quiet and distorted. I'm not really sure where to go from here.

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          • #20
            You start as if the amp just now came in. Forget the problem you just fixed. Isolate the problem. use the power amp in jacks to decide if the low level is due to the power amp or preamp circuits.

            You spent time and energy finding the bad relay and replacing it, but we cannot assume all the things we did to cure the relay will impact this issue. It may or may not be related, so we clear our minds of baggage and just approach the problem by itself, not in the context of the relay problem.
            Education is what you're left with after you have forgotten what you have learned.

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            • #21
              Originally posted by Enzo View Post
              You start as if the amp just now came in. Forget the problem you just fixed. Isolate the problem. use the power amp in jacks to decide if the low level is due to the power amp or preamp circuits.

              You spent time and energy finding the bad relay and replacing it, but we cannot assume all the things we did to cure the relay will impact this issue. It may or may not be related, so we clear our minds of baggage and just approach the problem by itself, not in the context of the relay problem.
              Yes, very true. I did isolate it to the power amp. I'll dig into it more tomorrow and come back with the results.

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              • #22
                , the amp sounds very quiet and distorted. I'm not really sure where to go from here.
                Ok, thatīs what your ear tells you.
                Now letīs check what instruments tell:
                Crate/Ampeg schematics are the best in the Industry, period, because they are chock full of Test Points, showing voltage and (incredibly) waveform at each one.

                Look at schematic Page 1 and 2, TP tables show you that by feeding 0.68V RMS @ 1kHz at power amp direct input jack, you will reach 40VAC at the speaker out into a 4 or 8 ohm load.

                Just for testing, work without load, simply to avoid overheating it (if you use a resistor) or becoming deaf (if you use the speakers).
                If you can get clean 40V there, then we will try the same with a load.
                Ok, do you?

                Start building a load capable of dissipating 400 or 500W RMS without catching fire, not an easy task.

                Search for water heater resistors which are close to speaker impedances, drop one or two inside a water bucket (not kidding) and wire them to a plug or speakon to load the amp head.

                For example, a 120V 2000W water heater resistor, price between 10 and 20 bucks, is nominally 7.2 ohms and can be considered 8 ohms for all practical ends.
                Juan Manuel Fahey

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                • #23
                  Ok, so I had more time to work on this thing today. I made a test probe that runs to a little battery powered amp and started testing. as soon as I get to zener diode d110 at tp9, I start getting really distorted signal, and everything after either sounds quiet and or distorted. I took some readings at tp9 and this is what I got: -11.2 vdc on the negative side of d110 and on the positive side it started at -10vdc and gradually kept going down. On r135 I was reading 67.1vdc on one side and -9.71vdc on the other. Any thoughts?

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                  • #24
                    This was all with no load

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                    • #25
                      I should also state that both aforementioned components test fine out of the circuit with my dmm

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                      • #26
                        Please:
                        1) when talking about a diode, use "anode" and "cathode" rather than "the positive side" which can be understood in different ways.
                        And D110, a 1N914, is not a zener diode but a regular one, although somewhat smaller and lower powered.

                        2) a test probe wonīt help you much here, we are not searching "where" signal stops, but "what" is happening, so use a scope if possible or at least a multimeter.

                        The test point table shows whatīs to be expected at TP9 , under different conditions.

                        You quote some 10/11V negative, but I guess itīs with signal, not what the TP table asks for.
                        They ask for a DC voltage at idle (no signal) *or* 40VAC when fully driven, so please search for that.

                        In fact, Iīd start with DC readings which I presume bad.
                        Also measure and post what you have on TP10 - TP11 - and to have the full meal, also TP12.

                        For now: no signal and DC only.

                        EDIT: Voltages on power transistor boiard TP9 - TP10 actually come from the main/driver board, and we might hava a cable/connector problem here, so follow the wiring (on schematic and physically inside the amp) and measure same on the other end, we *might* have a connection problem here.

                        I mean [B_lo] and [B_hi] and also J45 and J46 on page 1 , so I expect 4 DC voltages, besides TP9 -TP10 ones.

                        I guess we are getting close to the core of the problem.
                        Last edited by J M Fahey; 10-16-2017, 08:51 PM.
                        Juan Manuel Fahey

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                        • #27
                          ah, yes I was measuring with signal. Ok, I'll check what you mentioned and get back to you.

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                          • #28
                            Awesome, I'll check that. In the meantime, here are my readings:
                            TP9- d110 is getting -14.5vdc on the cathode, which drops steadily abd -13vdc on the anode which reacts the same way. R135 has -11.35vdc on one side that steadily drops and 67.6vdc on the other side.
                            TP10- D113 has -5.93 on the cathode and -5.15 on the anode, both measurements steadily drop. R136 has -10.83vdc that drops on one side and a steady -67.4 on the other.
                            TP11- .005vdc
                            TP12- just about -12vdc on outside terminals and -12.68 on the center terminal.

                            I noticed that the readings changed after the fan kicked on. Is it necessary to note those as well?

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                            • #29
                              Also, I'm working on a b5r, but using the b4r schem via LOUDs advice. I thought that power amp "b" wasn't in this amp I have because it's not an amp with 2 power sections

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                              • #30
                                When giving voltages at test points, please give only that voltage. Describe other voltages elsewhere.
                                For example, TP9 is exactly the anode of D110. Not the cathode. TP12 is the emitter of Q120, not inner or outer terminal.
                                You should be able to mention any test point and we will know the exact point.
                                When you get DC voltages that seem to change, or drop steadily, check that you are connected to the proper ground for the board you are working on, or use the ground at the main filter caps.
                                Originally posted by Enzo
                                I have a sign in my shop that says, "Never think up reasons not to check something."


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