Mesa Bass Prodigy Four 88 problem crackling sound

[Godixon]

Hello,

I've got problem with this awesome amp. I hear some crackling noises. Please see the video. https://youtu.be/LL6wPFKGEPM
The full schematics is avaiable here https://www.dropbox.com/s/skiiez86tp...me%7D.pdf?dl=0 Thanks to doctor.



What I have done it is listed below. The preamp is ok, clean sound is coming from preamp output. So I preasume, the problem is within the power amp and driver.

1. Checked all tubes, put the new ones, still the same.
2. Checked all joints under tubes sockets. It is clean and new solders.
3. All the voltages from power supplies are ok. Before I've checked it, I have found R106 10k was overheated ( instead 10k was only 170ohm ), changed but problem is still here.
See attached picture.
4. Checked bias current, it is approx.30ma. I can adjust using the trim pot, but the green led is not running.
5. All voltages within power amp and driver section are ok.

Any ideas what should I check more?
Thanks
Tom

[juanteleca]

Hello Godixon, I have the same problem in a prodigy, I have located the noise coming after the master to the inverter and the power stage, I suspect some ceramic capacitor, did you manage to solve it?

Your experience would be very helpful
Thank you!

I've got problem with this awesome amp. I hear some crackling noises. Please see the video. https://youtu.be/LL6wPFKGEPM
The full schematics is avaiable here https://www.dropbox.com/s/skiiez86tp...me%7D.pdf?dl=0 Thanks to doctor.



What I have done it is listed below. The preamp is ok, clean sound is coming from preamp output. So I preasume, the problem is within the power amp and driver.

1. Checked all tubes, put the new ones, still the same.
2. Checked all joints under tubes sockets. It is clean and new solders.
3. All the voltages from power supplies are ok. Before I've checked it, I have found R106 10k was overheated ( instead 10k was only 170ohm ), changed but problem is still here.
See attached picture.[ATTACH=CONFIG]51486[/ATTACH]
4. Checked bias current, it is approx.30ma. I can adjust using the trim pot, but the green led is not running.
5. All voltages within power amp and driver section are ok.

Any ideas what should I check more?
Thanks
Tom

[J M Fahey]

Does your amp use the same schematic?

[juanteleca]

Does your amp use the same schematic?

yes, of course .... I only know a scheme for the bass prodigy

[bielmunar]

Hello, good evening, warm regards to all forum members from Mallorca, Spain.

Mr. Godixon, can you please tell me if you were able to solve the Mesa Prodigy problem, if so can you tell me how?

I have the same problem and I don't know where to start.

Thank you.

[FaultyMesa]

Hello, I just joined so I can share my experience. I have exactly the same problem that you describe. The noise comes from the V2 tube, the inverter.
Some days after I checked it, the amp started working normally, but a week later, the noise returned, so it reinforces my idea that it has to be a loose component, or something caused by heat.
I have tracked the noise with an oscilloscope, and I found the following:
- The noise comes from the output of the V2 tube (plate). The signal in the input is clean.
- If I replace the tube with a good one, the noise remains, so it's not the tube.
- I checked the signal at the cathode and heater, it's clean.
- If I remove the tube from the socket, there's no noise at the output (plate) of the tube

My best guess is that the noise is caused by a faulty tube socket, or the resistor that supplies voltage to the plate.
Unfortunately, this amp is a PITA to work into, because I think that resistor is located under some capacitors, because I haven't found it yet.
I already ordered replacement components for it, I hope I can fix it.

[dstrat]

Hi, That sound in the video is usually a leaky cap.
but you guys would do better here if you started new post as this one is old.

[Arbutt]

prodigy_160322.pdf i don't know if this can help but its the mesa boogie service manual, i looked at the link, but the file was deleted

[FaultyMesa]

I fixed the amp. In my case, I suspect it was either the V2 tube socket, or the plate resistor. The plate resistor is below some orange drop capacitors, so, to play it safe, I changed those capacitors and all the resistors below them, and the IRF82 transistors related to V2. It may seem extreme to replace them all, but working in this amp is very difficult, and I didn't want to do it again.