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Laney TT50H No Outout

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  • Helmholtz
    replied
    Originally posted by g1 View Post

    I think we have seen on several occasions where the practical results do not match up perfectly with the theory. A shorted turn or winding will not necessarily kill the output 100%. In this case the output was very weak and distorted, but the 16 ohm output was louder. That's why I said the 16 ohm output 'sort of' worked. I should have said it gave more output.
    It will depend on the effective shorting resistance which is composed of the winding DCR + external wiring DCR.
    Assuming a shorting DCR of say 0.2R at the 4 Ohm winding, the 16 Ohm output will appear loaded by 0.8R parallel to the speaker.
    Consequently output power could be up to 5% of nominal.
    But as the tubes will see a very low Raa, which allows for only little voltage swing, output power should be much less than 5%.
    Nevertheless a few hundred mWs of output power seem possible.

    Leave a comment:


  • g1
    replied
    Originally posted by Helmholtz View Post

    The 16 Ohm output shouldn't work either, as shorting one (part of a) transformer winding essentially shorts all other windings including the primary.
    I think we have seen on several occasions where the practical results do not match up perfectly with the theory. A shorted turn or winding will not necessarily kill the output 100%. In this case the output was very weak and distorted, but the 16 ohm output was louder. That's why I said the 16 ohm output 'sort of' worked. I should have said it gave more output.
    Sometimes we have reports of weak output from OT's (or PT's) that fail the neon bulb test due to shorted turns. They still have some output.
    Definitely something that could use some actual data under test conditions, if anyone were to feel inclined.

    Leave a comment:


  • Helmholtz
    replied
    Originally posted by g1 View Post
    The 16 ohm jacks would still sort of function because the 4 or 8 ohm tap would serve as ground for it, and it's tip did not get grounded with the others..
    The 16 Ohm output shouldn't work either, as shorting one (part of a) transformer winding essentially shorts all other windings including the primary.

    Leave a comment:


  • ca7922303
    replied
    Originally posted by g1 View Post
    The sleeve (neg.) terminals of the speaker jacks are all connected together going to circuit ground which also connects to chassis ground. Then there is that black wire which also goes directly to chassis from the sleeve terminals of the spkr. jacks. I guess the connection is duplicated to prevent burning of the narrow trace on the board that goes from those jacks to ground.
    The black chassis wire got moved from the sleeve terminal to the tip terminal of the 4 & 8 ohm jacks. That shorts them out so they can barely work. The tip and sleeve of those jacks are now both going to ground, so the only reason you can hear anything is the tiny resistance of the traces themselves.
    The 16 ohm jacks would still sort of function because the 4 or 8 ohm tap would serve as ground for it, and it's tip did not get grounded with the others..
    With barely any output, you would have had to really crank the level. That much signal along with the oscillation is probably what caused the arc over at the preamp tube socket.

    Click image for larger version

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    Thanks again for everything, your the best!

    Leave a comment:


  • Jazz P Bass
    replied
    G1 gets the "all saints award" for mulling through this fiasco of a repair.,

    Leave a comment:


  • g1
    replied
    Originally posted by ca7922303 View Post
    Can you summarize what you recall about the how and why it got completed? Thanks again.
    The sleeve (neg.) terminals of the speaker jacks are all connected together going to circuit ground which also connects to chassis ground. Then there is that black wire which also goes directly to chassis from the sleeve terminals of the spkr. jacks. I guess the connection is duplicated to prevent burning of the narrow trace on the board that goes from those jacks to ground.
    The black chassis wire got moved from the sleeve terminal to the tip terminal of the 4 & 8 ohm jacks. That shorts them out so they can barely work. The tip and sleeve of those jacks are now both going to ground, so the only reason you can hear anything is the tiny resistance of the traces themselves.
    The 16 ohm jacks would still sort of function because the 4 or 8 ohm tap would serve as ground for it, and it's tip did not get grounded with the others..
    With barely any output, you would have had to really crank the level. That much signal along with the oscillation is probably what caused the arc over at the preamp tube socket.

    Click image for larger version

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    Leave a comment:


  • nosaj
    replied
    Originally posted by ca7922303 View Post
    Your a genius! No ocillation at any point, output is normal on all channels. Really appreciate it. Apologize for wrong wires soldered, etc., etc. Can you summarize what you recall about the how and why it got completed? Thanks again.
    I know you can't be asking him to give you what to put on the service ticket are you?
    nosaj

    Leave a comment:


  • ca7922303
    replied
    Originally posted by g1 View Post

    That means the red and brown wires to the 4 and 8 ohm lugs are in the right place, so you won't have to flip the board again.
    Of the green and blue wires going to the lugs marked 'grids', judging by the oldest pictures, the green one should be on the grid lug closest to the lug marked 'GND'.
    If it's not that way, swap the green and blue around.

    Test it out but be careful because it will probably be 100 times louder than it was before.
    If presence works backwards, swap the green and blue at the 'grid' lugs around.
    Your a genius! No ocillation at any point, output is normal on all channels. Really appreciate it. Apologize for wrong wires soldered, etc., etc. Can you summarize what you recall about the how and why it got completed? Thanks again.

    Leave a comment:


  • g1
    replied
    Originally posted by ca7922303 View Post

    Moved black wire to yellow arrow R(0.6 ohms)
    4(0.4 ohms)
    That means the red and brown wires to the 4 and 8 ohm lugs are in the right place, so you won't have to flip the board again.
    Of the green and blue wires going to the lugs marked 'grids', judging by the oldest pictures, the green one should be on the grid lug closest to the lug marked 'GND'.
    If it's not that way, swap the green and blue around.

    Test it out but be careful because it will probably be 100 times louder than it was before.
    If presence works backwards, swap the green and blue at the 'grid' lugs around.

    Leave a comment:


  • ca7922303
    replied
    Originally posted by g1 View Post

    Ok. Someone moved the black wire going to chassis. From the very first pics on pg.3 from a year ago, it was already in the wrong place. Whether it was like that when you got it, or you moved it there, it was the fatal mistake.

    Move the black wire to the yellow arrow point in the picture below.
    With nothing connected to output jacks, put your black probe to that black wire and measure resistance to point marked R. Then measure from black wire to point marked 4. The difference will only be a fraction of an ohm, maybe .1 or .2 difference. Repeat several times until you are sure one is consistently higher than the other, post result.

    Click image for larger version

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    Moved black wire to yellow arrow R(0.6 ohms)
    4(0.4 ohms)

    Leave a comment:


  • g1
    replied
    Originally posted by ca7922303 View Post

    16 ohm jack black wire to board.
    Ok. Someone moved the black wire going to chassis. From the very first pics on pg.3 from a year ago, it was already in the wrong place. Whether it was like that when you got it, or you moved it there, it was the fatal mistake.

    Move the black wire to the yellow arrow point in the picture below.
    With nothing connected to output jacks, put your black probe to that black wire and measure resistance to point marked R. Then measure from black wire to point marked 4. The difference will only be a fraction of an ohm, maybe .1 or .2 difference. Repeat several times until you are sure one is consistently higher than the other, post result.

    Click image for larger version

Name:	gnd.jpg
Views:	24
Size:	54.0 KB
ID:	957629

    Leave a comment:


  • ca7922303
    replied
    Originally posted by g1 View Post

    Ok, we are almost there now. Take a pic of where the 16 ohm jack black wire meets the board.
    16 ohm jack black wire to board.

    Leave a comment:


  • g1
    replied
    Originally posted by ca7922303 View Post

    Chassis ground and back to board(photo)
    Ok, we are almost there now. Take a pic of where the 16 ohm jack black wire meets the board.

    Leave a comment:


  • ca7922303
    replied
    Originally posted by ca7922303 View Post

    R34(12.9v/-0.2mv)
    R44(12.9v/41v)
    Anything to test on xpand/boost switch? It was replaced with PIC. Maybe remove it and retest?

    Leave a comment:


  • ca7922303
    replied
    Originally posted by g1 View Post
    Measure DC volts at both sides of R34, and both sides of R44.
    R34(12.9v/-0.2mv)
    R44(12.9v/41v)

    Leave a comment:

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