Guitar Amp w Cement Resistors Loud Pops & Noise

Discussion in 'Technical Repair' started by ColoradoRobert, Apr 29, 2017.

  1. JoeJester

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    Apr 26, 2005
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    Robert,

    Try looking for your parts in Mouser or Digikey. I've have good success with quick deliveries from them. When I lived in the panhandle of OK, Mouser got to me within two days, if not one.

    My regular job is retirement. Unfortunately, my grandkids are here during the day and I am trying to overhaul a website as well as answer your questions. I know it's slow, but you had asked about learning how to troubleshoot.

    I hope you enjoy my latest two postings.
     
  2. ColoradoRobert

    Thread Starter Member

    Jan 22, 2016
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    Hey Joe, I know the feeling we have 3 grandkids (17,15, &11 ALL boys) and I have looked at your most recent posts = Wow! That is a lot to chew on and I am investigating returning the Klein today because it has been less than a month. I do like the Klein probes though and the meter you posted does not go into detail about their probes. I have a feeling they are not CAT III (1000v) and that is the biggest drawback. Thanks again for your help.
     
  3. JoeJester

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    Probes are inexpensive, especially at Amazon.
     
  4. ColoradoRobert

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    Jan 22, 2016
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    So I thought I was done with this Crate amp repair but I discovered today,that channel 3 is dead.
    I was going to sell it and figured I better test everything first, when I discovered it. Hope Mr Chips is
    still around.
     
  5. JoeJester

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    He probably still is. Look at the schematic. See where the channel three input goes. You know everything after where it joins the main floor flow is good. I'll look at the schematic when I get home .. after midnight.

    on edit: inserted the correct work, vice the one my phone decided was correct.
     
    Last edited: Jun 16, 2017
  6. ColoradoRobert

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    Jan 22, 2016
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    Thanks Joe. I still don't have the new meter yet, so right now I am unable to test stuff.
    It might be that Q2 but that's just me guessing.
     
  7. JoeJester

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    Robert,

    Q2 is the peak detector. IC1A is the amplifier, whose output exits on J6 Circle A. On page three, J14, circle A goes to R29.

    I would not suspect Q2 because you reported no audio. This doesn't mean that once you have audio and you crank it up ... if the LED doesn't work, I'd have Q2 as a suspect, assuming the audio got past the diode.

    Input 3 is a line level input. That means a higher level than a passive pickup. It parallels Input 4, so if Input 4 works, you eliminated everything to the right of that connection. That only leaves the path from the input jack to where it joins up again with the Input 3 signal. (R29).

    This is why one does a full functional check. To know all the faults. That would be especially important if your reselling.

    KX160-block.png

    I see there is an effects send, effects return, etc as well as the four inputs. I also noted they have a line out and line in labeled pre-master loop.
     
    Last edited: Jun 16, 2017
  8. ColoradoRobert

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    Jan 22, 2016
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    So I put a new battery in my analog meter and these are what came up off the 50vdc scale.
    -15 at leg 4 on the IC1 and 14v on the 8th leg. 14v on the diode above beside it (to the right).
    -15v on the diode below it (to the left). O zero on both sides of the diode to the right and
    0 zero on both ends of the circled 680k resistor. Now because the boards inside this amp
    are not printed I am not sure if I am testing the right things or not but they do correspond with
    the face of the amp and the location of Channel 3 input (top board). 680k-1.jpg
     
  9. JoeJester

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    Apr 26, 2005
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    Robert,

    do you have an audio generator that you can connect to input 3 and 4?

    I would connect to 4 to ensue it works. if it does, you only have one circuit to look at for channel 3. MrChips labeled one of his photos with the testpoints on an earlier page. The expected conditions for input and output are specified on page 1 of the schematic. There is a table.
     
  10. ColoradoRobert

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    Jan 22, 2016
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    So I did download the same function generator that you showed me on the other post
    and I do have a cord so I can put the signal into jack 3.... but what settings on the generator
    and what setting on the amp? After I get those, then what do I do? BTW, I have not gotten
    the new meter yet it may be enroute but wasn't in the mail.
     
  11. JoeJester

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    1 kHz 100 mV according to the table on page 1 of the schematic. Measure the test points for for the defective channel, but first, see if channel four is working.
     
  12. John Furystrom

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    Jun 19, 2017
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    so happy to find topic with tons of useful info about guitars electronics stuff, thx everyone.
     
  13. ColoradoRobert

    Thread Starter Member

    Jan 22, 2016
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    The frequency is easy to set on the generator but how do you set the 100mv on it OR am I not understanding things right? The new mv meter has not arrived yet but I want to be ready. My old analog meter does not go that low.
     
  14. JoeJester

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    100 mV is what you adjust the volume control to read when you are measuring the tip and sleeve with the meter in the AC position and the range close to 1V or something above 100mV with the mV range.
     
  15. ColoradoRobert

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    Jan 22, 2016
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    So you plug the cord into the 1/8th jack and leave the 1/4 inch plug unplugged from the amp.
    Then you take a reading out there on the tip and set the the volume like that. Is there a
    separate volume control coming off the generator app or just the volume control off our new
    tablet device?
     
  16. JoeJester

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    Set the generator to mid level. Then ask that soundcard volume to 100 mV
     
  17. ColoradoRobert

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    Jan 22, 2016
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    Looking over this again and to answer your question Joe = Yes, channel 4 does work and I did get the meter last night so I can start checking stuff but I need a little more information on everything. First, I have the generator set to 1khz and adjusted the volume coming out of the tablet to as close to 100mv as I could get (104.4acmv). This is as close as I can get it. I do not know if you can set it or ask it to set at exactly 100. Please explain if you know how. Next I plug into channel 3 is the amp plugged in and on to do this test? I checked 'without' the power on and at tp8 in acmv I get .08 both ends. With the power on 00.48acmv both ends. BTW should the channel 3 gain and the master volume be turned up a little or does it matter.

    As I said earlier this board does not have the numbers printed on it so I hope the cap I am reading is the right one. I took a couple pictures for you to see which one I checked. If I am on the right one and have everything going into the amp right this reading is no where close to 540mv which the schematic says it should have at this point. DSC02425.JPG DSC02426.JPG DSC02427.JPG
     
    Last edited: Jun 22, 2017 at 12:55 PM
  18. JoeJester

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    Once you plug the generator into Jack 3, you can measure the test points associated with that jack. Your reading is 104.4 mV. That's 4.4 percent higher.

    I just reviewed the table again, and those values are p-p (peak to peak). Reset the volume, adjusting both controls if necessary, to try and read 35.35 mV rms. With the generator set to 50%, adjust the audio volume to get as close as you can, then change the generator's value up or down to bring it in closer. For instance, if you adjust the volume and it reads 40 mV, all you have to do is reduce the generator to 44.1 percent.

    Now, for what to expect.

    TP5 is 0.9 times the input voltage.
    TP6 is 88 times the input voltage.
    TP7 is 80 times the input voltage.

    I'd say that would be +/- 10% of the calculated values. TP6 and TP7 may require you to max out the gain adjustment. I would keep the master volume to a minimum but you can plug some headsets into the Effects Out or Line Out.

    Can you post a picture of the specifications page for your meter?
     
    Last edited: Jun 22, 2017 at 1:19 PM
  19. ColoradoRobert

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    Jan 22, 2016
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    So the amp is turned on when I do these tests and your saying these tests are done in ACmv?
    How can that be when the tp expected volts at 7 is 8 volts? Another example TP5: this concerns me
    because if I hit the wrong diode or end the schematic says there is 15 volts there. Testing on mv scale
    1/1000th of 1 volt I would think is no good for the meter.

    I don't want to damage this new meter by trying to test for voltages that are higher than the range it is set on.
    Can you show me from my picture where is tp5, tp6 and tp7 are?
     
  20. JoeJester

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    Input: 35.35 mV

    TP5 is PIN 3 of IC1 : (32 mV)
    TP6 is PIN 1 of IC1 : (3.11 V)
    TP7 is the junction of C21 (1 uF) and R29 (680k) : (2.828 V)

    Once you move to a reading greater than mV, I expect you to change ranges on your meter. You need to KNOW what your going to read and adjust your meter range accordingly. If you take a reading you DON'T KNOW, start at the highest range and work down.

    These are AC voltage measurements.
     
    Last edited: Jun 22, 2017 at 5:21 PM
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