Mesa Boogie Nomad 45 - Reverb INOP

[thelastleroy]

Is anyone familiar with this amp? I hadn't used the reverb on it for a long time, and when I tried to fire it up, there's nothing on any of the channels. I tried replacing the RCA cables that connect the spring tank to the board but no love. I took the chassis out of the box and had a peek inside and nothing appears damaged, loose or burned. Someone please help me troubleshoot this thing!

[52 Bill]

Is anyone familiar with this amp? I hadn't used the reverb on it for a long time, and when I tried to fire it up, there's nothing on any of the channels. I tried replacing the RCA cables that connect the spring tank to the board but no love. I took the chassis out of the box and had a peek inside and nothing appears damaged, loose or burned. Someone please help me troubleshoot this thing!

First thing to check is the tank. Look for broken wires that connect the transducers to the RCA jacks.

Then test the transducers with an ohmmeter for continuity. The input side should read only a few ohms, the output side should read around 200 ohms.

[Don Moose]

I tried replacing the RCA cables that connect the spring tank to the board but no love.

This question sounds stupid, but were these Known Good cables? ... or just assumed good?

Hope this helps!

[thelastleroy]

...were these Known Good cables? ... or just assumed good?

Yeah the cables i bought new to check with a known good set. I'm gonna try to check the resistance on the input and output sides tonight (I'm assuming i'm just checking the resistance from the center of the RCA jack to ground???) as well as checking for broken wires in the tank. Gotta find that multimeter.....

[tim]

center of the RCA jack to the outside ring of the RCA jack. not every reverb RCA jack is grounded to the tank chassis...it depends on the type of tank if it is or not.

[thelastleroy]

Ok, I checked the resistance of the jacks....
The input shows 27ohms and the output shows inf. I'm assuming I need to trace the signal path throughout the tank and find where it stops.... but there doesn't seem like a lot of places for this thing to screw up... any ideas??

[thelastleroy]

Ok, it appears the output transducer is pooched. I've resolved to buying a new tank. does anyone know if you can substitute an Accutronics 9BB2A1B (full size 6 spring medium decay) tank for the 9BB3A1B long decay tank without any further modification?? I would like a longer decay, but would settle for stock if its going to be a pain in my ass. anybody done this before??

[Enzo]

Yes, the only difference is the long springs themselves. Electrically they are the same.

[thelastleroy]

Great. thanks for all your help guys. I'll let you know how it all works out!

[thelastleroy]

Output transducer coil

Well, I checked with my local music shop, and a new tank is gonna cost me $80. Today i took the tank apart, and got the output transducer coil out to check it. I'm getting INF resistance on the coil and now i'm wondering if its possible to rewind it??? where on earth can I get wire that thin?

[tim]

You can buy the tank from www.tubesandmore.com for about $25.

[52 Bill]

The easiest solution is to just replace the tank. But if this is a learning experience, then go for it. The worst you can do is damage the tank beyond repair, and then you're at the same place anyway, needing a new tank.

Most of the breaks in the coils are at the ends where the wire solders to the connector pins or terminals. If you use a sharp knife or razor blade you can carefully scrape off the insulation from the end of the wire and see if you can get a resistance reading from there. If you do, then you'll need to remake the connection to the terminal with a short jumper wire. Be careful, as the plastic coil forms melt very easily and can be damaged from too much heat.

If you can't get a reading from the ends of the coil wires, the problem is further in the coil. The only solution is either replacement or rewinding the coil.

If you choose to rewind your coil, you will have to drill out the rivet that holds the laminated transducer core in place. After the core has been loosened from the tank tray, the coil will slide off of the laminations.

Carefully unwind the wire from the coil onto a spool of some sort, maybe a cardboard tube or a short dowel rod. There isn't a lot of wire on there, so it isn't that too hard to do. If you find a break in the wire solder the two ends together and coat with some clear nail polish, then rewind the wire back on the form and reassemble the transducer. You will need a small brass nut and bolt to re-mount the transducer in place.

[thelastleroy]

Success!

Thanks for your advice everyone...

I removed the output coil from the transducer core and unwound it, counting the number of turns as i went. I got about 1700 turns.

Next, I compared the wire size to the wire from an old poor quality single coil pickup winding wire (a pickup I didn't mind loosing, as I replaced it years ago) and luckily, it's the same stuff!

I made a primitive winding device out of a BBQ skewer, shaving down the round profile on two sides to slide inside the coil bobbin (where the laminated core would go). This way I could twist the skewer with my right hand while guiding the wire onto the bobbin with my left. The pickup was on the floor and I worked from my dining room chair.

Carefully unwinding the pickup as I went kept the wire organized, and after breaking the delicate wire a few times and re-starting I found a technique that worked. I unwound enough wire off the pickup to put 100 windings at at time on the bobbin, which kept the loose wire managable and counting easier.

after 1700 turns, I put a few turns of the wire around each terminal and (carefully) soldered the wires. i re-assembled the tank and installed it.

IT WORKS!!!



Thank you again for all your help guys, I probably would have just paid the $80 at the guitar shop for a new tank had I not found this board. I will come back forever!!!! :-)