mesa problems

[T-bone]

hi all,,

im wondering if anyone can give me some advise on a mesa boogie nomad 55 head that is stuck on chaneel 2 and has only buzz as output,,
ive never owned this brand amp before,,, are there any generic common problems with this model i sould know about , before i start mucking around?

ive changed the tubes cables, speakers, the basic stuff, can anyone think what this particular prob might be,,, ive heard relays are a constant problem with these amps,, but would that create the buzz only as output?


mmmmmmmm the board is a pain in the proverbial to accsesss from solder side...

any thought at all anyone??????

thanks in advance

[Jazz P Bass]

Mesa Nomad 55

These amps are a reat PITA to work on.
To get the board out all the controls have to be removed.
It ends up like you are working on an octopus.
Anyway, the channel 2 stuck on, is acting like that with the just the footswitch ?
You need to determine if it is a ftsw problem or an internal amp problem.
Mesa uses a lot of jfet transistors as switches internally on the amp.
Sometimes they fail.
The ftsw uses ICs to do the switching, along with the actual push button switches.

[T-bone]

thanks in advance

hi mate thanks for your reply,

this amp head seems to be stuck in 2nd ch, foot switch dosnt do a thing,, back controls dont work at all either,, ive injected a sig to eff rtn, and its the same deal low output

ive done as much as i can think of for the simple stuff, pulled knobs while playing etc,, noiw its time to take some voltage mesurements,,, this prob seems like a relay or jfet fault as you say,,,

maybe someone with the same amp could verify if these are home mods or factory spec mods???

any thoughts??
thanks in advance

[Jazz P Bass]

Mesa Nomad 55

Sounds like you lost your +15 Vdc supply.
Here is the schematic.

[T-bone]

thank you reply

thank you muchly jbbass



thanks for the reply mate really appreciate your time with this project

i buy amps all the time, mainly broken ones,, and train myself to repair them. had a lot of shitty amps,, but its the experiance i love..
some i give away to local schools or kids with special needs,,,, some i keep and sell to students for cost... some i keep myself!!
thanks for leanding me your experiance with this!!

seems like the same scematic ive got here,,,
do you mean ive lost my 15+ in swiching cuircit, or output b+?


thanks again

[Jazz P Bass]

Mesa 55 low voltage supply

Page 3, lower right corner.
Low Voltage Supply.
Check for +15Vdc & -15Vdc.

[T-bone]

thanks with reply

need to thank you again

cheked for volt in power cuircit,, all fine

took tube sokets off bak section,,
plate lead to ot had come off!!!!!!
resolderd,, fired up,, no prob,, this one will go in my collection sounds great

be buggard!! cheers for the quick reply \

very warm regards