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Fender Stage 160 DSP weird issues

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  • Fender Stage 160 DSP weird issues

    Sorry for posting on here, if this doesn't belong here or you feel like it should be moved/removed please do so and I apologize in advance. I'm only posting here because, and I suck at fixing solid state gear!

    So I picked up a vintage solid state Fender Stage 160 DSP guitar amp and I'm running into a small issue. The amp powers on and plays just fine, but only sometimes. I usually have to tip the amp forward and power it off and back on, but sometimes it's at random, then right after hitting the power button it comes alive and amplifies the guitar signal like it should. Whenever I turn it on and it doesn't amplify guitar signal the red power light always stays on, however.

    I took the amp completely apart twice already trying to locate something out of place, a loose solder joint, connection, but to no avail. Checked the caps for leakage, but the board looks almost brand new. I cleaned all the contacts with DeoxIT and yet the issue persists. One interesting thing is, whenever the amp is on and not amplifying input signal from the main input, I can plug in the guitar in the back into an input labeled "PWR AMP IN" and it will amplify the signal at average volume, however none of the tone or volume controls work. That led me to believe that there must have been something wrong with that board so I took it apart, checked all the connections for shorts and everything reads out just fine. Without the inputs board plugged in the amp stays silent and two small red lights light up on the main board.

    So I'm not quite sure where else to look, could it be the preamp section? What else can cause such strange issue? I tried wiggling different components see if it makes a difference but it had no effect whatsoever. Only tilting it forward and powering it off and back on seems to bring the amplifier to life, and that works about 70% of the time. I haven't checked the tone controls, as I don't think they could cause such issue, but that's my next move.

    Do you guys have any other suggestions as what to check next?

    Schematic:
    https://drive.google.com/open?id=1Hc...S1aq-_YW6-s6nH

  • #2
    You could have a bad switching jack. Try running a short cable from preamp out to power amp in and see if the amp works.
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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    • #3
      Good suggestion thank you. I've connected a cable from preamp out to power amp in as you suggested and plugged in the guitar yet there is still no sound. Had to tilt the amp backwards for the issue to appear as when I tilt it forward it seems to work just fine.. so odd!

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      • #4
        OK, so the power amp works, but something before that isn't right. When it is NOT working, ball up your fist and whack the top hard. Does that cause a reaction? Turn down the reverb in case. That will reveal loose connections that just poking around and looking will not.
        Education is what you're left with after you have forgotten what you have learned.

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        • #5
          Originally posted by Enzo View Post
          OK, so the power amp works, but something before that isn't right. When it is NOT working, ball up your fist and whack the top hard. Does that cause a reaction? Turn down the reverb in case. That will reveal loose connections that just poking around and looking will not.
          Been there done that. Once the amplifier powers on in it's not working state, there is nothing I can do. I tried hitting it as hard as I could. Also, I opened it up, powered, and poked around the main board slightly touching electronic components on the board. There was absolutely no change. Unless it starts right up, it doesn't start at all

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          • #6
            OK, then move on. Start wwith preamp voltages. Got good +15/-15 on teh ICs? APPly a steady strong signal at the input, follow with a scope down the channel looking for signal at pins 1 and 7 or U1,2,3,4. We want to see how far the signal goes before stopping.

            We also know the power amp works, so we can input at the FX return. Then we can move back towards the input stage by stage inputting signal, looking to see how far back we get before it no longer works.

            The entire idea is to isolate the problem.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              I will have to check the ICs. So far I have only worked on tube radios and tube gear so this might be a challenge for me. I will try and trace the signal to see where the path ends with my old scope.

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