HELP!! Express 5:25 Contour is not working

[blaren]

Hey all,
I was here almost a year ago when I had a Stiletto Ace that I LOVED. Got lots of help here. Added an adjustable bias and then wound-up selling it :-(
Oh well.

Now three days ago in another trade deal I found myself owning a Mesa Express 5:25.
Like the Stiletto, it was trade bait that I would have to sell.
Like the Stiletto I made the mistake of trying it out first. It isn't going ANYWHERE soon unless it doesn't ring my bell at a gig. And that is the true test.
I'm an old 100W Marshall guy who has been playing 18 or 36W amps since late '06.
Just recently fell back into the 100W CRUNCH when I finally got myself an old DSL100 (in another trade...been GASsing for a DSL for a long time). I can't believe I was thinking the EL84 amps could replace 100W of vintage-ish EL34 Marshall goodness.

Well this 5:25 is turning me back yet again to the EL84s. MAN this is a GREAT little amp. It's the 1-12 version.
I haven't even bothered loading it up with some awesome old glass yet.
I'll be bringing it to an outdoor gig on Saturday and then to an outdoor jam on Sunday. We'll see how it holds-up in the real world.

ANYWAY...my point/question is...the Contour knob on this amp does nothing. Whether I have the Contour switches to ON or Footswitch and try turning it on via the footswitch (the footswitch LED comes on and changes colors as it should and the contour LEDs on the amp light up)...it doesn't do anything no matter where I crank the knob or where the master and gains and channel tonestacks are set-up. Whether I play in 5W or 25W mode...nothing.
Whether I unplug the 3-button fswtch or not...nothing from the Contour knob.

I can crank the contour and engage and disengage it via the switch OR pedal and no change.

Any suggestions?
Maybe I'll check the tubechart. I don't imagine one of the 12AX7s or one half of one of the AX7s powers the contour does it? Maybe I have a bad preamp tube?
I'll check the tubechart now.

 

[bgh]

I don't think any of the preamp tubes are used to specifically drive the contour controls. I don't have a schematic, all I did was look at the tube assignment picture in the manual.

Do I understand you correctly that both contour knobs do not work? If that is the case, would the only thing in common be the foot-switch? It would be very odd for both contour knobs to fail at once. Could it be a ground issue in the foot-switch jack that is making the circuit think that the contour has been disengaged?

 

[b00g13mk2B]

The Mesa EQ is transistor driven normally. Found a non-plus schematic, V3 may to the one at the point. But the tube does not do the switching, that you hear signal means the tube is probably not bad.

Assume this is not the plus version, no sliders. Other things to try include not having the foot switch hooked up while you exercise the toggle switch. Use a 1/4" plug contour selector on the back panel. Think shorting tip to ring selects contour, see if that makes it come on.

Try a guitar cord between effects send and return. That is in the contour circuit.

Otherwise, could be some problem with optoisolators, relays, the 12V used for switching and EQ transistors or some connection.

 

[blaren]

Thank you very much for the replies fellas.
Yes...no it is not the PLUS model. Hey wait...I don't think the + has a contour circuit? No matter..

I keep forgetting to try that 1/4" contour jack on the back. Thanks for the reminder.
And another yes..we have no banan...oopsies...YES...no it doesn't work with or without the (normal) pedal with the microswitches set to on, pedal, or off.

Such a FANTASTIC little amp. I wanna keep it. I probably wouldn't even USE the contour but maybe. I'd love to at least experience it.

Thanks again and if anyone else has anything to add/suggest...KEEP EM COMIN please.

 

[blaren]

Well I haven't yet tried the loop but I will maybe tonight.
I did try a 1/4" cable into both channels' contour 1/4" footswitch jacks on the rear (instead of the stock pedal's goofy jack) and shorted it and nothing.

Still haven't tried messing with V3, V4, or V5 yet. Fingers are crossed.

I have been hoping all this time that I'm just doing something really stupid. Don't know what but I don't think that's it. I've tested a couple of times to make sure that it isn't just a more subtle effect than I'm expecting and am just not hearing it but there is NO difference.

Worse comes to worst and I ever feel the need for a scooped graph in it I'll toss one into the loop.

I listened to a couple of youtube clips of some non-Plus 5:25s with the Contour in and out and there is a BIG difference...and a GOOD one. I'd like to get it working.

I sent Mesa's CS an email on Friday asking for help but...crickets. :-(

 

[b00g13mk2B]

Mesa customer support is closed on Friday. No telling what is going on this week during the Holiday Season. The Express (non-plus) manual is online if you don't already have one.

Not sure, but if the toggle switch is "off" (middle position), the foot switch and the 1/4" jacks in the back will have no effect. If you are so inclined and know to discharge the caps, you can take the chassis out and dig in. Maybe as simple as a wire not connected to the switch or PCBA, or a bad switch(s). Do the contour LEDs work at all? It is typical that the switch would either ground an input to a transistor or relay, or connect the input to a pull up resistor (to +5V or some voltage that is "on"). Without a schematic, can't tell if the default for a missing switch wire would be no contour function or always on.

 

[b00g13mk2B]

Mesa customer support is closed on Friday. No telling what is going on this week during the Holiday Season. The Express (non-plus) manual is online if you don't already have one.

Not sure, but if the toggle switch is "off" (middle position), the foot switch and the 1/4" jacks in the back will have no effect. If you are so inclined and know to discharge the caps, you can take the chassis out and dig in. Maybe as simple as a wire not connected to the switch or PCBA, or a bad switch(s). Do the contour LEDs work at all? It is typical that the switch would either ground an input to a transistor or relay, or connect the input to a pull up resistor (to +5V or some voltage that is "on"). Without a schematic, can't tell if the default for a missing switch wire would be no contour function or always on.

Here is a link that includes the schematic and where someone had issues with things under the hood being bent out of connection.

http://music-electronics-forum.com/t22508/

The contour foot switch and rear 1/4" jack work the same way, switching to ground. This is on page 8 of the schematic. If the front panel toggle switch is in the "off" position, the function is OFF, no way to switch. So quite possible there is simply a wire not connected somewhere. There are a lot of relays and optoisolators in this circuit, but if everything else seems to work (channels switch, LEDs other than contour light as they should), should be simple.

 

[blaren]

Hey THANKS for the help and suggestions boogie.
The first link to the schem wont work for me but don't worry...I'm pretty useless with one anyway.
I do know how to safely discharge caps and root around inside an amp and chopstck it and look for clearly visible issues.
I opened it up last night actually. Hadnt been back here for quite a while but I brought it to a jam on the weekend. A country jam with some new faces and I don't think I've ever received as many compliments that were crazy good.
I'm no rookie or jam-warrior. I've been bar gigging for 38years since I was 12.
All these country guys just wouldn't stop. I jammed with a bassist who I had never played with and the house band bassist was starting and adjusting the time of the drum machine for us on the fly :-O
That's IT. Me and a bassist. Playing my PRS Studio (Stock except for a Duncan CC in the bridge).
OMG!! Your overdriven tone is AMAZING!!!
OMG!!! That amp is RIDICULOUS!
A bass player said..that thing sounds KILLER! Does it have a tube preamp? I'm like...uhhh yeah. It's got tube everything (well...you know)...ahh no WONDER!! He says. But, it could be the guitar though too. That thing is BEAUTIFUL!!

Hey THANKS man! I agree. This is my favorite amp EVER and I got it in a TRADE. I didn't even know I wanted it.

Alright so anyway...sorry...last night I was playing then I was...hey I haven't even ever opened this thing UP yet :-O !!!
What am I THINKING? What if it's just a plug or a fuse(?) or a wire hanging there or an arc and a busted trace somewhere???

FIRST thing was....Are you KIDDING me right now? :-O If the chassis weighs ten pounds it weighs a million. And it does NOT weigh a million.
I didn't weigh it but...6lbs? Probably felt lighter than it is but still...2 puny little transformers.
If this had been in a headcase and not a combo with the name Behringer on the front I wouldn't have even tried it and if I had I would have went...yeah it sounds amazing but it's just tricking me and..it'll blow-up after 6 hours of playing the lightweight POS. You call that IRON?? PUHLEASE!!
How is this thing my FAVORITE amp EVER???

Everything inside looked fine...except, the plug that plugs onto the little board that contains the switches and LEDs isn't plugged all the way down. It can't come all the way off because of the chassis face but there's like 1/8" of the pins showing that the plug could/should(?) go further onto. I tried pushing it on further but I didn't want to put too much force on it. I couldn't get it to budge. The LEDs work fine and they get power from the same ribbon cable that that plug is part of.
I didn't take the wee sub board off (I think I only would have had to remove the nuts and washers from the switches to pull the sub board free and be able to properly push that plug onto the pins/board?) and try to really push that plug on because since I couldn't get it to move at ALL..it's probably proper. And, the LEDs work.

I just turned the amp on (it's back together...I'm an idiot) and I'm gonna go play it now and see if just PUSHING on that plug may have had an effect. If not, I'll pull it all apart again tomorrow and see if I can get the plug on further.

I'll let you know what happens...in 100 words or less.

 

[Topher]

Sorry for bringing this old thread up...but I have the exact same problem. I wonder if blaren got this fixed?

 

[user 21540]

Sorry for bringing this old thread up...but I have the exact same problem. I wonder if blaren got this fixed?

Did the problem just start happening? Have you owned the amp for some time and this is a change of behavoiur? When you flip the contour switch on both channels are you getting the confirmation visually from the amp that it is selected? Is the problem still the same when you assign it to the footswitch with the chassis switches? I believe what happens with that part of the circuit is it brings a pre-set solid state graphic EQ circuit into the signal path. Rather than sliders, the resistors are fixed values set for the classic Mesa GEQ scooped V sound and it allows you to blend that in with the contour knobs. If it is switching in correctly visually and there is no sonic difference on either channel when turning the contour knobs you can assume there is some problem with that section of the amp or the switching part of the amp. It would mean it is not bringing that EQ circuit into the signal path if there is no difference in sound when contour is selected.

 

[Topher]

Yeah, lights are on but nobody is home. Contour lights activate on both channels when using the switches on the front, the mesa DIN footswitch and the 1/4" plugs. No difference in sound. Nothing changes when you turn the contour knob.
It's always done this since I got the amp a few years ago in a trade. It's a great little combo even without the contour, but I'd like to try and get it working if possible.

 

[user 21540]

Yeah, lights are on but nobody is home. Contour lights activate on both channels when using the switches on the front, the mesa DIN footswitch and the 1/4" plugs. No difference in sound. Nothing changes when you turn the contour knob.
It's always done this since I got the amp a few years ago in a trade. It's a great little combo even without the contour, but I'd like to try and get it working if possible.

I would take it to a tech for sure. That contour feature offers a huge change in sound so you are missing out on a lot of tonal flexibility.

The most approriate posts here though are by b00g13mk2B at #6 and #7

You can also see how the contour circuit comes into play from the schematic.

 

[DrKev]

The two JFETS, J175C1 and J175C2 are the possible culprits here. When they are faulty, the contour circuit won't work right. They are also easy to change without totally dismantling the amp. Easy and fast job for a tech. I just changed mine and now I hear what the contour is supposed to do!