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Thread: Blues Deluxe Reissue-No Sound

  1. #36
    Supporting Member Jazz P Bass's Avatar
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    Quote Originally Posted by Perkinsman View Post
    What ac voltage should I input to the amp?
    TP1.
    4mv @ 1KHz

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  2. #37
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    I went thru the TP ac & dc voltages and about 35% of them are 50% off and 65% were very close to listed value. I'm still not sure 150mV is the correct input voltage. Will doubling or halving the input voltage change values significantly?

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    Quote Originally Posted by Jazz P Bass View Post
    TP1.
    4mv @ 1KHz
    Oh jeez, I went thru almost all the the TP ac & dc voltages earlier with 1k 150mv....about 35% of them were 50% off and 65% were very close to listed value. Will that much input voltage difference change values significantly?

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    Quote Originally Posted by Enzo View Post
    But really, you have the HP unit, why not take a moment and complete the instrument? Make up a cord with 1/4" male on one end and a connector to match the HP on the other. In your case a dual banana plug. You know you are going to need it again and again. I always had a couple such cables on my bench rack.

    Got a guitar cord with a bad end? Clip that end off and wire a banana plug there. Two minute job.

    I had a few more that were the same but with zip cord for use as speaker cables. Good for connecting amps and cabs to my speaker/load patch panel on my bench.
    That's on my add to the bench list this weekend, along with an RCA jax to 1/4"!

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  5. #40
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    Manufacturers often specify very low signal levels, like 4mV or 6mV input signal. Such low levels ensure that each following stage is operated within its linear range and stage gains can be exactly determinated and verified from the ratios of output to input voltages.

    With large input signals the gain of a stage typically changes (mostly drops) even without actual clipping. Also DC voltages shift.

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    Last edited by Helmholtz; 01-17-2020 at 04:28 PM.
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  6. #41
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    If the amp clips then the AC voltage measurements would be very difficult for a manufacturer to specify. The easier and more consistent way to do this is to ensure that the test voltages are easily reproducible and this means keeping everything clean.

    Also, different meters can give wildly different RMS readings for a distorted AC waveform.

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  7. #42
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    Quote Originally Posted by Mick Bailey View Post
    If the amp clips then the AC voltage measurements would be very difficult for a manufacturer to specify. The easier and more consistent way to do this is to ensure that the test voltages are easily reproducible and this means keeping everything clean.

    Also, different meters can give wildly different RMS readings for a distorted AC waveform.
    Not exactly sure what you’re saying here...but without an accurate way to measure my input voltage, I think all my TP measurements may not be accurate either.

    I would love to get this amp’s volume to increase today...I have another observation that may or may not help solve this mystery. Neither the “bright” or the “channel select” switches are working. Could this be related to the low volume issue? I’ve cleaned both switches but no improvement. If either switch is broken, would that prevent the volume from increasing?

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  8. #43
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    I’ve been going over power supply voltages. Can someone tell me whether D13 cathode should read .7? It looks like +17 on the schematic. If this diode is bad, would it prevent the volume from this increasing?

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    Quote Originally Posted by Perkinsman View Post
    I’ve been going over power supply voltages. Can someone tell me whether D13 cathode should read .7? It looks like +17 on the schematic. If this diode is bad, would it prevent the volume from this increasing?
    D13 and D14 are 16V zeners. What are DC voltages at TP45/TP46?

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  10. #45
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    Quote Originally Posted by Helmholtz View Post
    D13 and D14 are 16V zeners. What are DC voltages at TP45/TP46?
    I’m calling TP 45 the cathode side of D13 & as mentioned, measured.7vdc....TP 46, the cathode of D14 measured-17.3vdc.

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  11. #46
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    Quote Originally Posted by Perkinsman View Post
    I’m calling TP 45 the cathode side of D13 & as mentioned, measured.7vdc....TP 46, the cathode of D14 measured-17.3vdc. I see that TP 45 should be +17. Would this cause low volume? Is this part of the grid bias circuit?
    Looks as if D13 is shorted (but could be other reasons as well). What is the voltage at TP42? If you lift one leg of D13 you can test it with an Ohmmeter.

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  12. #47
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    Quote Originally Posted by Helmholtz View Post
    Looks as if D13 is shorted (but could be other reasons as well). What is the voltage at TP42? If you lift one leg of D13 you can test it with an Ohmmeter.
    TP42 is 47.8vdc. Pin 8 on U1 is also .7. I pulled D13 leg & in diode mode measured .63, reversed leads & got OL. In Ohm mode, measurements were 385k & OL.

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  13. #48
    Lifetime Member Enzo's Avatar
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    I think it cute the TP calls it 17v, but the schematic calls it 16v. I generally refer to these as 15v rails anyway. Point is your +15/16/17v is missing. Until that is restored, nothing that uses it will work right either. That includes the channel switching, the FX loop, the reverb, and any other op amp stuff.

    So if D13 isn't shorted, then is 470 ohm R78 open? Is D13 parallel cap C40 shorted? C40 is hard to get at, but measure resistance across D13 while it is in circuit. Does it measure low?

    A shorted op amp COULD do this, but I tend to expect a shorted op amp to lean on both rails rather than one.

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    Quote Originally Posted by Enzo View Post
    I think it cute the TP calls it 17v, but the schematic calls it 16v. I generally refer to these as 15v rails anyway. Point is your +15/16/17v is missing. Until that is restored, nothing that uses it will work right either. That includes the channel switching, the FX loop, the reverb, and any other op amp stuff.

    So if D13 isn't shorted, then is 470 ohm R78 open? Is D13 parallel cap C40 shorted? C40 is hard to get at, but measure resistance across D13 while it is in circuit. Does it measure low?

    A shorted op amp COULD do this, but I tend to expect a shorted op amp to lean on both rails rather than one.
    R78 measures good. D13 in circuit measures approx .6M ohms, is that expected? Cant get to c40 unless I pull the board but I will if needed.

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    Lifetime Member Enzo's Avatar
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    C40 is in parallel with D13. By measuring across D13, you are also measuring across C40. Look at the schematic.

    Any chance D13 is in backwards? The cathode - the lined end - is the end NOT grounded.

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    Quote Originally Posted by Enzo View Post
    C40 is in parallel with D13. By measuring across D13, you are also measuring across C40. Look at the schematic.

    Any chance D13 is in backwards? The cathode - the lined end - is the end NOT grounded.
    D13 appears to installed correctly. The cathode leg is attached to the + side of c40....but so is d14. Is this correct?

    Ok, so if d13 is parallel to c40 & it’s measuring high ohm resistance than that would also mean that c40 has a high resistance, which implies that it’s good? I also measured 974uf across d13 on UF mode. So what else can cause .7vdc at pins 8 of U1, U2, U3?

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  17. #52
    Lifetime Member Enzo's Avatar
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    Sure, use a fingertip. ANy of them getting hot?

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    Lifetime Member Enzo's Avatar
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    but so is d14. Is this correct?
    I don't know what this means. The cathode of D14 is also connected to the + end of C40? The cathode end of D14 should be grounded, which is the NEGATIVE end of C40. And of course the positive end of C41. The anode of D14 connects to the negative end of C41.

    You need to find where your +17 went. You have the +48 at TP2, right? That is ultimately the source of +17. Your R78 measures OK. So either the +42 is not getting to R78 , or the downstream end of R78 is shunted to ground. SO is R78 getting HOT? If it is cold, then voltage isn't getting to it. it it is real hot, then something is loading it down.

    I am not sure WHERE you measured TP42. I mean it applies to the end of D11, C39, R78. We expect all those to be wired together. But they might not be, so is there the 42v right on one end of R78?

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    Quote Originally Posted by Enzo View Post
    I don't know what this means. The cathode of D14 is also connected to the + end of C40? The cathode end of D14 should be grounded, which is the NEGATIVE end of C40. And of course the positive end of C41. The anode of D14 connects to the negative end of C41.

    You need to find where your +17 went. You have the +48 at TP2, right? That is ultimately the source of +17. Your R78 measures OK. So either the +42 is not getting to R78 , or the downstream end of R78 is shunted to ground. SO is R78 getting HOT? If it is cold, then voltage isn't getting to it. it it is real hot, then something is loading it down.

    I am not sure WHERE you measured TP42. I mean it applies to the end of D11, C39, R78. We expect all those to be wired together. But they might not be, so is there the 42v right on one end of R78?
    Ok, so I turned the amp on this afternoon to start working on it again & it worked!....for 5 mins, then I heard a distinct click & the sound died again. While it was running I grabbed the dmm & measured D13 & pins 8 on the IC’s. Sure enough, all +17vdc so I know they’re fine. They’re back down to .7 again. I see that there are 2 relays, K1 & K2. Would one of these be suspect & how can I test them?

    Another observation is that R79 is hot while R78 is not. Is that unusual?

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    Last edited by Perkinsman; 01-19-2020 at 01:38 AM.

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    Lifetime Member Enzo's Avatar
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    R78,79 both do identical jobs and should be identical hot. They normally get pretty warm. If no current if flowing through them they stay cold - room temperature. If the 17v end of one is shorted to ground, it gets REAL hot. Could possibly unsolder itself.

    Relays? Unlikely. Does the red channel LED come on still or does it stay dark when in failure mode?

    Cold R78 means current not getting through it. Check voltage right on the wires of R78. SHOULD have 48v on one end and 17v on the other. If you get zero volts on the 48v end that means the 48v ain't getting there. If you measure 48v on both ends that means the end that should be 17v is not connected to the circuit.

    The fact that resistor is cold tells me the circuit is not loading this down. The problem is in the supply.

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    Regarding the red LED, yes it worked during the 5 minutes the amp worked. I tested each of the functions during that time & everything else worked as well, Reverb, Bright Switch, etc. Now that the amp isn't working I measured 54Vdc at both ends of R78, which is cold R79 will burn if touched and measured 48 & 17. So are you thinking that the cold resistor has a bad solder joint?

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    Yes, it is quite common in this series of Fender. Resolder both those 5W resistors and both those zeners. Check to make sure the pads are not broken from the traces.

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    I've read alot of threads about these resistors & it was the first thing I checked. I've been under the impression that if they measured in spec & the board wasn't burnt & tapping on them didn't help, they were ok. I'll jump on this first thing tomorrow. Man, it will be great if all it needs is a few solder joints resoldered.

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    Quote Originally Posted by Perkinsman View Post
    I've read alot of threads about these resistors & it was the first thing I checked. I've been under the impression that if they measured in spec & the board wasn't burnt & tapping on them didn't help, they were ok. I'll jump on this first thing tomorrow. Man, it will be great if all it needs is a few solder joints resoldered.
    Success! Thats all it was...just a lousy solder joint on R78! Voltage back up to 48 & 17! Everything works! Much thanks to you guys again! I love this hobby & site!

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    Supporting Member Randall's Avatar
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    For the record, that is one of the first things to automatically check for on this series of amps. That, and the solder connections on the tube sockets. Both are very common failures.

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    It's weird, because it WAS working fine.....

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    Also, earlier amps had 330R resistors which were later replaced with 470R to give the zeners an easier time. I usually replace the resistors if they're 330R and form the leads of a pair of new zeners to give them a 3/8" standoff from the board. As an upgrade I offer a pair of 15W metal clad resistors mounted on a heatsink connected back to the PCB with flying leads, though sometimes this is necessary anyhow if the board is well toasted.

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