Fender Stage 112 se trouble

[mikeaaron_1999]

With out the footswitch, I don't hear much of ANY reverb. If it is there, it isn't very good. The foot switch that he gave me with the amp he said he bought with a reverb unit because when he bought the amp, there was no unit, that is, the RCA plugs were just hanging in the cabinet. So, the footswitch says Fender on it, ASSY. P/N 0071359000. The two switches on it say CH SELECT and EFFECTS. When I plug it in, the CH SELECT light iluminates and the amp automatically goes to the drive side, by hitting the CH SELECT switch, it does not switch back to clean, the light just goes out. And by pressing the EFFECTS button, I still hear no reverb, but by varying the reverb dial, I get somewhat of a "panning" effect if that makes sense. Or maybe a little bit of very slow reverb almost as if someone is varying the volume just a touch slowly.

[52 Bill]

If the reverb tank has been replaced, you need to find out if it is the correct one for that amp. Are there any codes stamped on the casing?

IIRC the footswitch for that amp was one of the trapezoidal aluminum extrusion ones with black end caps. You need a 2 conductor cable to plug it in. And as Enzo has mentioned, there is circuitry inside it that cannot be replaced with just an ordinary switch. Is this what you have?

[mikeaaron_1999]

Yes, that is the footswitch I have, and I am using a 2 conductor cable. BUT.....wait for it!!! I could just smack my self. I removed the tank to see if the springs or wires were broken/detached, and guess what I found INSIDE the tank???? Anyone???? Ok, I found a piece of foam stuffed in there preventing the springs from "springing". After removing the foam, it works just fine! Both in the clean and drive channels! So, I went ahead and put it all back together again, cleaned it up, polished the "Fender" logo and I believe it's ready to be given back to my buddy! I'm sure when he sees it and hears it he will be very happy! So again, Thanks to everyone on here, 52 Bill, Enzo! You guys ROCK!

[mikeaaron_1999]

Oh yea, I was so excited I forgot to answer your code question 52 Bill, sorry about that, the model number on the tank is: 8EB2C18 with a date of 2010 04 20. It is an Acutronics unit. Thanks again!

[Noel]

Using 1n4007 to test bias diode

Hi!
First of all, thanks for everyone here. This topic was very usefull for me too.


Enzo, I saw you talking about use 1n4007 in the place of byv26d, for a test.

Why can't we let them on the amp? The datasheet between them are very similar, and I like the way it sounds. I'm just worried about how long it can work with 1n4007. What do you think?

Thanks a lot!

[Enzo]

1N4007 is a common general purpose rectifier diode. The BYV26D is an ultrafast recovery diode.

http://www.vishay.com/docs/88554/byv26dgp.pdf

[Noel]

Hi Enzo,

I know that the original diode is a fast rectifier, but what I am curious about is: If I use a 4007 it can blow some componentes or be prejudicial to the circuit. I did the change for a test, and I thought that it sounds good. Both diodes can handle the voltage and current from this circuit. I was thinking what else can be prejudicial...

Thanks a lot!

[Enzo]

What you don't want is transient current spikes when a diode doesn't turn off fast enough on transitions. You might not hear them, but that doesn't mean they ar not stressing the circuits.

Imagine a two-man lumberjack saw, cutting a tree. They take turns pulling towards themselves. Imagine if the one guy pulls the saw towards him, but doesn;t quite stop pulling when the opposite guy starts his pull. That little moment of delay means the second guy has to overcome not only the friction of the saw blade, but also teh resistance of the other guy still pulling. They each start each pull fighting some of the other man's pull. This will tire them out faster than if the timing was correct between them.

The push pull output circuits in a SS amp take turns conducting current to the load. If the one side needs to turn off so the other side can take its turn, but is still trivkling some current atthe start of each half cycle, it will stress things.

They used regular old vanilla diodes all over this circuit, but those few bias diodes are fast, it is for a reason. That poor little op amp U7 has to yank the bases of the output transistors up and down with the signal. When higher frequency parts of the waveform try to reverse course, you don't want those diodes acting like molasses.

[Noel]

Thanks a lot Enzo.

I've tried 4007 in my amp, and it seems good for 5 minutes, then it turns the amp of.

If I wait some time and turn on the amp again, it works! But just for a little while.

I'm going to put fast diodes back. I was wondering what made the amp turn off (I think that problem the non fast diodes made the transistor work too hard, and made them get hot, so TS1 turned off the amp).

Anyway, thanks a lot again!

Cheers!

[musicamex]

hope enzo and 52 bill are still monitoring this thread. i am a tube guy and manage to build and maintain a variety of tube amps, but because of lack of formal training and a mental block against circuits with 10 times more components than my tube amps have i pretty much suck at diagnosis and repair of solid state circuits. none the less they make their way to me ("i know a guy who builds amps so he can fix this in a NY minute---NOT"). anyway a fellow musician and friend who had his car broken into and all of his gig gear ripped off brought me a dead stage 112 se to get back on stage--we have a 6 month season here to store up acorns---how could i say no. it was one of those "it's only a blown fuse" stories so i made no promises and pulled it down. i noticed a few things wrong before i even pulled it apart. the tab with the speaker tabs on it had come loose from the speaker frame and the wires attached to the cone, though still attached were resting against the speaker frame. i re riveted the tab after being sure the wires were actually still intact at the attachment to the cone.

once the chassis was out i smelled trouble before i even saw it r75 and 76 had gotten so hot the board was burned black right through to the trace side and the copper traces had lifted almost an inch from the solder pads. the 4a fuse had indeed blown, but not nearly fast enough it seems. one leg of L1 which i assume was a choke had a loose solder connection and the 2 3300mf 63v caps (c52 53) had been replaced by correct value caps jumpered to board and wire tied to the the xformer wire bundle. this is the 3rd world and that repair is a 9 on a 10 scale compared to some stuff i have seen that actually worked.

i called my amigo and asked exactly what had happened before the "fuse blew". he said he dropped the amp down a flight of stairs and then plugged it in to see if he hurt it!! it worked just long enough to fry the resistors and then blew the fuse. i looked a little closer and found 2 other small poly caps (like generic orange drops) that had one leg shaken loose from the board. i tested and re soldered them but the schematic numbers are in my notes at the shop.

i jumpered the r75 and r76 in place (should have checked c49 but it was close to dinner time), replaced the fuse and it promptly blew. i removed the red wires from the xformer and hooked the chassis to my limiter light. just a dim glow. reconnected the red wires---bright glow. it was now dinner time and i thought i would do a little reading and try to find some logical help from someone who didn't stop going to school in the tube era. when i saw ENZO and this thread i knew i should say HELP PLEASE. i know i should check for c49 being shorted. i have a pretty good supply of parts, but almost nothing in the way of transistors. i had to bring most everything from the states, and am hoping for a simple solution but suspect there was a cascade failure involving the output transistors.

btw, i see some of the same names all over the internet endlessly and seemingly tirelessly helping people like myself and mikeaaron solve these problems. i really don't know how some people like enzo can be so prolific and have answers to help on multiple sites. always in a courteous manner that doesn't make us feel like giving up because the questions that we ask are so basic. ENZO, 52 BILL you and others like you are good teachers of more than electronics. i try to pay forward all of your kind help. thanks in advance. in the mean time i have 49% left in my laptop battery before bed so i will keep reading for another hour or so.

[Enzo]

Well, do yourself a favor and start a new thread for your amp instead of starting at post #40 of an old thread.


Tube, solid state, troubleshooting is troubleshooting regardless the technology.

If a tube amp blows fuses, what is your order of approach? Mine is to look for failed output devices, then rectifiers, then filter caps and wiring. SOlid state is the same. BLows fuses, then check output devices for shorts, then rectifiers, then filter caps.

You have six output transistors, are any shorted? I see 8 rectifiers in the power supply, are any shorted?

The tabs of the power trransistors should be insulated from the heat sink, make sure none are shorted to it and grounded. Those tabs are wired directly to the high voltage rails, so that is a good spot to check if the supplies are shorted to ground.


Work WITHOUT a speaker load until the amp is stable and not producing DC at the speaker leads.

The fuse is there to prevent your house from burning down, it can;t protect the transistors. They can burn out faster than a fuse can open.

If R75,76 burnt up, the amp was oscillating hard. They are important to the amp stability.

[ogeecheeman]

great thread guys. enzo is the man. re-the stage se 112. I have inherited 2 of these things. both had the usual laundry list that comes with a 25 year old S,S, amp.jacks,pots,switches,caps. after getting the nagging stuff out of the way, both amps work equally well.plenty of output on both channels,reverb working,speaker sounds good...just one issue. in clean mode - both amps-I have this aggravating low level hum like line noise. when I switch to overdrive it goes away, completely.on both.with a load on one and a plug into the input I have 60mv AC in clean mode and 42mv AC in overdrive at the speaker output. pulling out the plug leaves zero at the speaker output.with no load the AC is 102mv and 58mv respectively. DC voltage is 0 throughout.I do see pulsating AC on the +15 op amp supply. the level of noise does decrease if I unplug the reverb tank and short out the input rca plug. there it is folks. any suggestions of course are much appreciated.this is for an old friend in the Allman family who is healing from a badly broken arm and needs something light weight to gig with.since I have nothing in it I thought I'd just get it going and let her have it. thanks again.

[g1]

I would think the chance of both amps having the exact same minor fault are fairly slim. The numbers you posted are not that different for the 2 channels.
Is it that noticeable that it could not just be normal for this model?

[ogeecheeman]

yea you know the odds that both have the same issue are great but...after posting yesterday I go through again.hit all of the solder joints.just for good measure replaced the 47uf and 1000uf caps in power supply to + ans- DCV supply. no change. upon further exam and much signal tracing I find this. with speaker plugged up and no signal except an open jack to turn on the input I get the hum on clean channel only. if I plug a cable into the preamp out jack the noise moves to the overdrive channel and the clean channel is usable again. now I'm thinking either a bum JFET switch or a bad op maybe TR 13 and U2?

[J M Fahey]

just one issue. in clean mode - both amps-I have this aggravating low level hum like line noise. when I switch to overdrive it goes away, completely.on both.with a load on one and a plug into the input I have 60mv AC in clean mode and 42mv AC in overdrive at the speaker output. pulling out the plug leaves zero at the speaker output.with no load the AC is 102mv and 58mv respectively. DC voltage is 0 throughout.I do see pulsating AC on the +15 op amp supply. the level of noise does decrease if I unplug the reverb tank and short out the input rca plug.

g1
I would think the chance of both amps having the exact same minor fault are fairly slim. The numbers you posted are not that different for the 2 channels.
Is it that noticeable that it could not just be normal for this model?

^^^^^^^^^^^^^^^^^^^^^ this.

1) looks normal, doubly so because an important component is reverb tank hum, the curse of most of them because of the magnetic pickup.
What happens if you turn reverb down or footswitch it to 0?

2) also the input jack mute mutes it: again normal behaviour.

Amp looks normal to me, even if slightly noisier than others; anyway I am quite certain that in a rehearsal room or live in a Club or something that slight hum/buzz will disappear completely.

Of course, in a quiet home, may seem annoying.

If everything else looks normal and works properly , go do the good deed

That said, it's definitely lighter than a Twin or similar, but not *that* light, it has a *heavy* magnet speaker, a good sized transformer (it's SS but rated 160W RMS and I believe them), wood is wood no matter what you fit inside ..... I mean if we are considering a healing broken arm, strongly suggest somebody else lifts it.

My idea of a light yet still good sounding amp is, say, a Peavey Envoy 110 or similar.
Yes, 35/40W , perfect for rehearsals and can be miked up live.