Standby Does Not Turn On

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by atonofclay66, Jun 30, 2008.

  1. atonofclay66

    atonofclay66 Member

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    I was having a problem with where non of the tubes were lighting up except for the rectifier and the standby switch wasn't turning on. Fixed the tube problem by replacing one of the fuses on the circuit board BUT the standby switch will still not light up and there is no sound. Any ideas?

    Thanks
     
  2. jbird

    jbird Member

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    Bad Power Tube?
     
  3. JimmyR

    JimmyR Member

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  4. atonofclay66

    atonofclay66 Member

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    I pulled the tubes out of my working ac30 and put them in the broken one so they should still be good. I've also checked the switch itself and its fine.
     
  5. atonofclay66

    atonofclay66 Member

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    Ac30cc1
     
  6. VikingAmps

    VikingAmps Member

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    If none of the tubes are lighting up except the recto you probably have something wrong with the 6.3v supply feeding those tubes. Theres probably an internal fuse for it. The recto uses a separate filament supply so it's not affected.
     
  7. tlpruitt

    tlpruitt Member

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    I believe I have read here on TGP about filament fuses blowing on the AC30CC. Do a search and see what you find.

    -Tim
     
  8. atonofclay66

    atonofclay66 Member

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    Yeah, that's what I was saying earlier. At first the power tubes weren't coming on but the recto was. I found the fuse for the power tubes and replaced it and that fixed that problem. But I'm still having an issue with the standby switch. I've checked the switch and it shows to be good but when I turn it on, nothing happens. No little green light and worst of all, no sound.
     
  9. tlpruitt

    tlpruitt Member

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    There are at least 3 fuses in that amp. There are 2 fuses for the filament circuit marked FS2 and FS3. They are 6.3A fuses. Look for them and replace them if they are blown.

    Some have mentioned it is okay to up them to 10A fuses.

    -Tim
     
  10. atonofclay66

    atonofclay66 Member

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    Did that last night. Pulled each one out last night and tested them. Only found one to that was blown. Replaced it and it fixed the power tube problem but not the standby.
     
  11. tlpruitt

    tlpruitt Member

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    Was the one that was blown a 6.3A fuse? Did you check and see if it blew again or one of the other fuses blew after you replaced the blown one and fired it up again?

    I still think it has to be a fuse or a tube problem or a combination of those 2 components. A bad tube can cause a fuse to blow repeatedly.

    I am looking at the schematic and there are 4 fuses in the AC30CC. FS1 is a 500mA fuse, FS2 and FS3 are 6.3A fuses on the filament supply, and FS4 is the main fuse.
     
  12. phsyconoodler

    phsyconoodler Member

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    There is definitely a blown fuse.I have worked on a few of those AC30's and they blow those filament fuses on a regular basis.You should ideally replace all the fuses.You are missing one in your search.
     
  13. atonofclay66

    atonofclay66 Member

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    I have checked all four but tlpruitt bring up a good point that it could have blown another one after I replaced the bad one. The one I replaced is obviously still working since the power tubes are still getting power but it could be a different one now. I'll pull it back apart in a little while and check them all again.
     
  14. tlpruitt

    tlpruitt Member

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    Correction, FS3 is a 5A fuse for the rectifier.

    Check those fuses and try, if possible and without electocuting yourself, to fire it up while the PCB is exposed so you can watch the fuses.

    -Tim
     
  15. atonofclay66

    atonofclay66 Member

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    Bought 4 all new fuses today and replaced them all. Nothing changed. All the tubes will still light but but the standby light won't come on and there is no sound. All the tubes are from my working ac30 so the problem shouldn't be with them. Any more ideas? I'm all out?
     
  16. Lyle Caldwell

    Lyle Caldwell Member

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    Check R188 on the bottom board when viewing the back of the amp (not the board that has the fuses and filter caps). Its the first resistor from the right by the far edge, just to the left of two turret posts. This is a fusable resistor that is designed to blow if you have a big spike in the power (more on that in a moment). It's supposed to be 2.2ohms - measure across it. If it has opened up then you will have no DC to the opamps in the effects/reverb section and an incorrect bias for the trem circuit (hence no sound), plus no green Standby light.

    As to the power surge, never use the Standby switch on any TB/TBX or CC AC30. It's a dumb dumb dumb addition that only causes a huge inrush current with big instantaneous power spikes. Just turn the amp on/off - the GZ34 will give a nice slow start all on its own, with no possibility of cathode stripping or voltage spikes.
     
  17. atonofclay66

    atonofclay66 Member

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    I'm get 2.6ohms from R188. What kind of reading should I be getting from R203?
     
  18. Lyle Caldwell

    Lyle Caldwell Member

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    R203 is a 3.9K, though it may be tough to measure in the circuit.

    Is your power LED coming on, just not the standby LED? If so, then there's something wrong in your HT_2_A path. What AC voltage do you read across TT26 and TT27?
     
  19. atonofclay66

    atonofclay66 Member

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    Yeah, it's just the standby led not the power led. I'm getting 5.3 across TT26 and TT27.
     
  20. Lyle Caldwell

    Lyle Caldwell Member

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    That's good. Now measure DC between TT21 and ground, then between TT20 and ground.
     

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