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PostPosted: Sat Sep 03, 2016 4:34 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2505
Location: North Carolina
A few weeks ago I had some friends over. I decided to play drums and let my friends use my amps. The Roadster was a power house by all means and so was the RA100 head. However sometime during the session the RA100 started fading in and out. I did not stop to diagnose it at that time, instead I wheeled in the RA100 Combo to take its place. I have played thought he RA100 head a few times after that and nothing seemed to occur so I thought it may have been cable or guitar related (my friend usually plays with his Stratocaster with the volume set so low as it did not come to mind there would be an issue with the amp). I also thought the tubes may be on the way out (thinking power tubes). Power tubes appear to be fine. What did occur today was the Hi/Lo channel faded, it can be heard but sounds thin. The Clean channel is unaffected and still loud and strong. Not using the power soak but did turn it on to check. Master volume for Lo and Hi do not seem to do very much at all. Tone controls are working.

Just for diagnostic purposes, I let the amp cool down and decided to replace all of the tubes. I had kept the one's that were in the amp marked so I can return them. Problem is still there. Disconnected the footswitch, turned off the reverb. changed power settings. Clean channel is strong and stable but Hi/Lo channel is attenuated. At least that rules out V3, V4, V5, V6, V7 and the power tubes. I thing this time I will have to pull the chassis and inspect components. It could be as easy as cleaning the metal dust off the circuit board. That would be my major complaint on any amp that uses the aluminum shields that twists into place, especially when the tubes point upward. I am sure I will find the issue. Just wondering if anybody else has encountered a similar issue with the Hi/Lo channel.

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Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sat Sep 03, 2016 5:54 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2505
Location: North Carolina
It is not the aluminum flakes I have seen around the preamp tube sockets. There was some but did not seem to cause any shorts. I did pull all of the tubes and cleaned the flakes. This time I removed the chassis from the shell and wanted to determine if there is a preamp tube issue or not. I had tried several tubes in V1, V2 and even replaced V3 with my spare tubes. I have a box full of preamp tubes so I have many to choose from, even swapped tubes from CH1 and that never seemed to have issues. I checked the tone controls on the Hi/lo channel, turns out that the bass and mid are not functional but the treble is. At least that is a starting point. While the chassis is out I can check the pots. Too bad I do not have a schematic for this amp as it would be helpful.

_________________
Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sat Sep 03, 2016 10:15 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2505
Location: North Carolina
Oh well, got my RA fix with the RA 100 combo. I will have to give Mesa a call on Tuesday about the head having issue. More than likely I will have to ship it in for repair. Not sure what is wrong, if I had a schematic I could probably fix it or determine where the fault occurred. . I checked the impedances on the pots and everything checks out but without a schematic it would be guess work unless I pulled the main board out. I really do not want to go to that trouble.

If the head is dead, more reason to get the JP-2C. I would like to get the RA100 head fixed as I wish to keep it. I may as well have Mesa replace the power tube board too as the sockets are in bad shape. Why would all 4 sockets have the inner hole chipped out? It sounded great if you install the power tubes in properly. I can manage as I marked the place where the key would have been. Also some of the ceramic sockets are loose and rattle. I should have bought the new one when I had a chance vs the Ebay route.

_________________
Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sun Sep 04, 2016 12:21 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2505
Location: North Carolina
I doubt it is the tone stack if my assumptions are correct. I believe the tone stack components are shared between the clean channel and the Hi/Lo channel but the connections are managed through some small relays. I could be way off with the assumption. I could confirm this if I dared to remove the main preamp board and follow the traces from the tone controls of the Hi/Lo channel. I did pull the chassis of both RA100's so I could compare the two. It does appear there was some repair work done on the amp I am having issues with. Perhaps there was reason why the amp was up for sale in the first place.

I will see what I can do for repair. There seems to be a location that is 2 hours away but not sure if they are still certified as the list on Mesa's website is not always up to date. I was planning on using compressed air to clean off all debris on the circuit board but found that my air compressor was missing the regulator. It is possible it came loose as I found some of the parts on the floor near the compressor, but some parts are missing and not in the location they should be unless the frogs that have invaded my home have a taste for compressor parts. They are rather big in size and so are the spiders on occasion. I better stop while things are still okay as far as I know or something else will be not as it should be. I blame it on the Gremlins or perhaps the amplifier gnome that lives under my house who wants me to get the JP-2C instead. I did see the gnome on a few occasions. Here is a quick picture I took of him looking at my RA100 Combo when I got it.

Image

_________________
Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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PostPosted: Sun Sep 04, 2016 3:27 pm 
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Dual Recto

Joined: Fri Feb 22, 2013 7:31 am
Posts: 2505
Location: North Carolina
This is becoming a Whiskey Tango Foxtrot day for me but there is hope....

After repairing my air compressor with new pressure regulator, I was able to apply compressed air into the holes where the preamp tubes sit. Also applied compressed air to the top side of the PCB as I have seen solder balls and metal fragments, loose solder debris. Since I had the Combo chassis out I cleaned that one up too but does not have the same issue as the tubes are facing downward. Reassembled the combo and whaled out a few tones before I brought in the RA100 head chassis. Figured just to leave it on the cab and install all the tubes and power it up just for kicks. It appears to be working again. Not sure if this is temporary or what but all seems well so I may not have to ship it to Mesa Repair Service. Perhaps I wound up with a spider in the amp as that has happened before with my Mark IV after I took it out of storage. I never thought spiders were electrically conductive. Needless to say for the moment that it is working again, compressed air did the trick or did it? :P

_________________
Current amps:
TC-50, JP-2C, MK V, Roadster, RA100
Old friends I sometimes miss:
Mk III (blue stripe), Mark IVb-WB


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