Starting a Ceriatone Plexi All Access build!

  • Thread starter Thread starter ledvedder
  • Start date Start date
Well, first power on didn't go so well. I'm hoping you guys can give me some ideas what could be wrong. First, I turned on power in standby with no tubes. With my meter set to AC volts, I checked all heater voltages and they were correct. 5v on rectifier socket, 6.3v on v1-v5 sockets. Then I powered off and installed the rectifier tube. Powered on and came out of standby. With my meter set to DC volts and the black probe to chassis ground, I started checking the power tubes pins. Pin 3 on each read about 460v. Then, I accidentally touched pin 2 on V5. It sparked, so I shut the amp off. I checked both fuses. Mains is OK, but the HT fuse was blown. I'm assuming the spark when I probed pin 2 caused it. I'll have to order some 500mA fuses. Any thoughts about anything else that could have caused this? Also, can I only use a 500mA fuse for HT?
 
I replaced the fuse and it powered up successfully. So far, all voltage readings seem correct, except that I was getting a positive reading on pin 5 of the power tube sockets. Turns out I had one of the diodes backwards. I fixed it and was getting correct negative voltage. It was late last night, so I didn't do much more.
 
Time for troubleshooting to begin. I've tested all voltages and they are within spec. Bias is reading 35. I'm getting sound to my cabinet when probing the PI. But I'm getting no sound from my guitar.
 
ledvedder said:
Time for troubleshooting to begin. I've tested all voltages and they are within spec. Bias is reading 35. I'm getting sound to my cabinet when probing the PI. But I'm getting no sound from my guitar.
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Do you hear anything when probing around the V2 area and corresponding area of the board? That area is notoriously 'hot' in terms of its ability to pick up nearby capacitance (just from your body) and other noise...it's really sensitive. If you don't hear anything when probing that area then that could help you locate the problem. This is just before the PI so if you're hearing PI noise that would narrow it down.
 
SpiderWars said:
Do you hear anything when probing around the V2 area and corresponding area of the board? That area is notoriously 'hot' in terms of its ability to pick up nearby capacitance (just from your body) and other noise...it's really sensitive. If you don't hear anything when probing that area then that could help you locate the problem. This is just before the PI so if you're hearing PI noise that would narrow it down.
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I ended up figuring it out. It was one of the shielded coax runs going to the effects board grounding out.
 
I was doing some more troubleshooting with my build today. If I disconnect the shield of run Q from ground at the effects loop switch, I get signal. As soon as I connect the shield to ground, it cuts out. Why could this be?
Screenshot_20220418-173407_Gallery.jpg
 
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