Great forum. So glad it is here. Thank you in advance.
I was playing the other night and my Fender amp started acting up. Loud humming noise and low output of music as it warmed up.
I can't afford a shop right now. I have been home injured for 19 months, so any help would be most appreciated.
Where do I start? Willing to follow directions explicitly.
The amp is a Fender Chorus.
Again, thanks in advance.
David
Welcome to the place! Well if you and your amp are both broke then this might prove to be a great idea fixing it yourself. Do any of the control knobs on the preamp side of the amp have any effect on this humming sound? Volume knob makes it louder/quieter? EQ controls effect the humming sound in anyway? So this amp has two speaker, correct? Which model of chorus amp is it exactly so we can find the right schematic to post. Look at the speaker, if possible, to see it is being pushed forward in conjunction with the humming symptom. A hum symptom can be DC voltage at the output of the amp and putting vDC on the speaker can ruin the speaker(s). Do you have a multimeter for testing voltages?
I'm in the process of posting a video for the guru's.
To answer some of your questions while loading the video...
Yes 2 12 inch speakers.
Volume makes it louder/quieter.
Ultimate chorus is the model.
Yes I have a Multimeter.
videos.... turn volume up...
https://www.youtube.com/watch?v=dppKTAfFdAo&feature=youtu.be
https://www.youtube.com/watch?v=4EzkYLA9E5E&feature=youtu.be
Does whacking the top of the amp with your fist give any noticeable difference to how the amp is behaving? What I am thinking here is that perhaps there is a loose connection inside or something on those lines. Bad solder joints on the filter caps might produce hum or other symptoms. Lets us know.
Also check this thread here
http://www.ssguitar.com/index.php?topic=617.msg4256#msg4256
Read and follow Post #2 on that thread about checking the send/return signal paths on the amp too. Send a signal to another amp or send a signal of another amp to the return on your chorus amp. If the return jack inputs a nice loud clear signal then that clears the power amp as the culprit. If the Send effect output is problematic then it is something in the preamp section. If they both sound bad then we will go further from there once we find out.
Gotcha...will do in am after Physical therapy. (jacked up back and neck)
1) that narrow image is annoying/uncomfortable
2) what happens to noise if all pots are on 0?
3) if hum/buzz dissappears, please post which pot is the one which kills it.
If you can't hit it with your hand, try a rubber mallet or big phone book or even lift one end of the cab and drop it back down on the floor.
The purpose is to see if there is a loose connection inside.
Sorry about the video...all I have is my iPhone for video.
I will go make another video...turning all knobs to zero and then each one on to see if it affects it.
I will also give it couple whacks....lol.
Brb.
Ok...today...will not play sound at all....but if I waited a few days, it will play for a bit and then do the same thing. Whacking it did not help.
https://www.youtube.com/watch?v=Md7zTkUfOu4
Bash on it a few more times if you get bored lol. Try wiggling the input jack to make sure it is not something cutting in and out on the signal. The fact that it got worse could be caused by an intermittent connection. Honestly, I would open it up and take some power supply test point voltage checks. Also, at that point I would start checking for bad solder joints. Did you try injecting signal into the return effects jack socket? Also, send the preamp send to another amp to figure out if it is a preamp or power amp issue, or both.
As far as the trying the hooking another amp up to it, to be honest...I don't know how to do that...lol.
I'm going to order a pencil style solder gun kit with a solder sucker tomorrow. All I have is a big gun style one.
And get some pot cleaner and a resistor to build a little discharge tool. Been collecting amp and electronics books.
Might as well learn the theory as I go. Make it an educational affair. I'm gonna fix this amp. It's in perfect shape
....other than being broke...lol
Quote from: mauser on December 11, 2014, 12:05:17 AMAs far as the trying the hooking another amp up to it, to be honest...I don't know how to do that...lol.
Well the mono effects send is essentially the preamp out on your amp, everything before the power amp. The mono effect return is basically a way to input signal into the power amp section and bypass the preamp.
So connect a guitar cable from mono effects send and plug the other end of that cable into the input of another amp. This will test the preamp section of your amp, which at this point it might have the fault. We need to just test it to see/hear what it is exactly going on.
On the other amp look for a line out or another send effects jack. On the other amp we are playing guitar through that amp and sending that signal through effects send(or similar line out) to the effects return of the bad amp. If you want just take an mp3 player and input that signal into the effects return to test the power amp section of the chorus amp. Be careful to keep the volume lowered at first so it is not really loud.
This test will tell us if the preamp is at fault or if it is the power amp.
Ok. I ran the effects out from the Ultimate to a good amp effects input. Was the same...garbage.
Ran the effects out from good amp to effects in on Ultimate....bingo...played perfect.
So from what I have gathered...it's in the preamp of the Ultimate...possibly reaffirming it's the filter caps.
Am I correct? And thanks for explaining that to me.
Not so sure that test reaffirms anything to do with the filter caps. Really it splits the amp in half, pre-amp or power-amp. So we know there is something going wrong in the preamp section and you have narrowed down where to look for the fault. I think it is time to test some voltages to make sure we have good power going to the preamp section. Ask as many questions as you need answered and the crew here will help.
So it's time to pull the chassis?
What do I need to avoid touching? everything on the board? just touch outer chassis? use just one hand to pull out?
I don't like getting zapped.
Disconnect speakers and reverb tank. There is possibly one screw on each side of the amp (not always) and four or more screws on top of the cab that need to be removed to get the chassis out. Removing the handle is probably optional as the bolts usually don't stick out that much, still sometimes good measure to remove handle too. Turning the amp on it's side and gently pulling out the chassis is how I recommend to get it out smoothly. There are times that the tolex is loose and it can make the chassis get jammed up trying to pull it out or putting it back in. Just go slow and patiently as to not bend or force it.
Touch just the chassis and avoid the circuit board for now. The one hand in your pocket thing is a reference to your left hand. The idea is that getting zapped through left hand is closest to your heart. Look it up online for more references. When we are working and testing voltages(live amp) we say to keep one hand in your pocket. Just be careful and do not proceed if you do not feel confident in your abilities. Take it slow and ask questions.
Do not just simply remove any circuit boards just yet. We want to check voltages on certain test points. We will be measuring with the red probe to test points on the circuit board and the black probe to ground/chassis. What I do is to connect a wire with alligator clips from chassis ground to the end of the black probe. That will free up one hand. With my right hand I then probe to specific points on the circuit board to test voltages, keeping my left hand away from the live circuit. Obviously nobody likes to get zapped and this is a dangerous hobby or job. So no question is a dumb one here, except the one you don't ask. There is more I want to type or advise but I will leave it there for now. Got to go make some food for a holiday party tomorrow, good luck!
In case it wasn't clear, UNPLUG AMP FIRST , then you proceed with disassembly.
The idea is to have the chassis outside the wooden cabinet, with guts visible, and stable on a table, use some books or pieces of wood as necessary to hold it .
We want the knobs pointing towards you and the open side of the chassis up, so you see all insides at a glance.
Have it in a place under good light and take a full picture so we agree on what is right/left/front/back .
You can have a little trouble getting it out because a few wires will go from the chassis towards the cabinet, you might have to unplug some to have free movement: 2 shielded cables with (usually) red/black RCA plugs going to the Reverb springs tank, 2 cables (sometimes black/white or green/white or black/red) going to the speaker(s) , sometimes the power (120/240V) cable is clamped inside to protect it from yanking.
If you wish post a picture of the amp inside from the back, showing the underside of the chassis and speaker(s) for clues.
1) yes, "the guy is happier with the camera angle now" :lmao:
Which is good for you, at least labels are now readable.
2) hum/buzz goes substantially down at 1:29 ..... what did you do there? 8)
3) at 1:43 there appears a motorboating sound when you rise mids.
Add to the suspects list.
At 2.03 buzz increases although now I suspect you just put camera closer to speakers.
Around 3:30 buzz becomes not only louder but deeper, when you turn chorus on.
So far it sound like you lost grounding, in a bad way, but not sure where.
You also lost all guitar signal.
I expected , say, 70% guitar, 30% buzz, which is unusable but the amp is somehow working but it's 99.5% buzz and 0.5% guitar.
4) does the amp have an effects return or power amp in?
Plug the guitar straight there, or even better through a distortion pedal (if you have one) to use it as some kind of crude preamp.
If so, set pedal volume to 10, distortion to 0 or 1 (we don't really want it now ;) ) and tone to flat or trebly.
Guitar straight into that jack will be too weak, although if clean humless that's already an important sign.
Ok!! on the double !!! :grr
:lmao:
posting schematic
Thanks guys. I'm going to pull the chassis tomorrow. I had PT today and had to go pick up some medical records today...so I didn't have time today.
I'm going to go get the pot cleaner and a resistor to build the discharge tool tomorrow at radio shack. What resistor do I need to get to protect caps from discharging to quick? The amp is 65w x2.
I'll label any connections I take apart...like speaker wires etc...
Silly question, do latex gloves keep you from getting zapped?
NO
Way too thin and easy to puncture.
In your case just turn amp off, noise will discharge it :(
Just to make certain, measure main cap voltages; ON is + or -40V ; they will rapidly discharge below 3 or 4 V in a minute or two.
If not, we'll suggest some resistors to be permanently soldered to them.
Cap voltage there won't zap you, but wall voltage will, so be aware of whatever's connected to mains, including power switch and fuse (which is clipped to the main board) :duh :loco
Cool. I'll pull chassis...with it unplugged. Carefully not touching board or anything. Get it setup as described above...then get some pictures up. I'll test the caps for voltage with the multimeter...ground probe alligator clipped to chassis...red probe on + of caps.
The caps are c84 and c85 on the schematic, correct?
Be nice to the tolex when removing the chassis, they can be a pain, be patient.
If someone previously has over-tightened the side screws the chassis wings will be bent and it may damage the tolex.
Quote from: mauser on December 12, 2014, 08:04:33 PM...I'll test the caps for voltage with the multimeter...ground probe alligator clipped to chassis...red probe on + of caps.
The caps are c84 and c85 on the schematic, correct?
Those are the correct caps except we have a split rail power supply. This means there is a positive and a negative +/-40vDC. C84 you will measure the (+) positive side of that cap to test for +40vDC. On C85 you are to test for voltage on (-) negative terminal of that cap, to read -40vDC. Same thinking will apply to testing the vDC on C88 and C89, those are +/-16vDC. Those lower +/-16v voltages are what powers up the circuit for the preamp portion of the amp.
Cool...thanks guys!! I read somewhere if you use a bar type clamp...you can reverse it to push outwards a little and it makes taking the chassis out easier by spreading the enclosure a little bit. I wont tear the case up. I'm pretty gentle with stuff. And having worked with vinyl flooring and doing upholstery work with carpet...I bet I could recover the whole thing if it needed it...lol. But it is nearly brand new looking on the outside. The guy I got it from took great care of it, and it has never left my guitar room.
I will leave you guys with some guitar porn for all of the helpful help...lol
My stuff and guitar room...also is the bedroom of Elsa...one of my 3 German Shepherds.
Epiphone Les Paul Plus Top Pro. Love this guitar. Has the coil tapping. Someday I will have a real Gibson like her.
I call her Maybellene.
(http://i935.photobucket.com/albums/ad197/highluxx/photo29_zps4c74d35f.jpg)
(http://i935.photobucket.com/albums/ad197/highluxx/photo5_zps08196910.jpg)
Epiphone SG400 1966 Reissue. First guitar I bought. I'm a huge Sabbath fan. I usually keep this one drop tuned
for my Sabbathy noodling. Name is "El Rojo Diablo"
(http://i935.photobucket.com/albums/ad197/highluxx/sg5_zps9883884a.jpg)
(http://i935.photobucket.com/albums/ad197/highluxx/photo23_zpsbba59ed5.jpg)
Fender Stratocaster 50th Anniversary. My baby.
(http://i935.photobucket.com/albums/ad197/highluxx/photo21_zpsecb5c95a.jpg)
Salt and Pepper. An affinity and a bullet. Both actually sound halfway decent. I set them up nice. Will do some pickups someday soon. These are ones I can leave on a stand and not worry about casing all the time. Beaters...but not too bad for beaters.
(http://i935.photobucket.com/albums/ad197/highluxx/photo12_zpsf4bc2f0a.jpg)
Elsa...official guitar guard. She sleeps on the bed in the guitar room.
(http://i935.photobucket.com/albums/ad197/highluxx/photo24_zps7b03dd2c.jpg)
See ya guys tomorrow for the chassis pull. Really appreciate all the help. Hope you liked the pics.
Nice! I feel sorry for any poor bastard that tries to break in and steal your guitars! :lmao:
Same here. :lmao:
Ok. Despite being mortally wounded today, I was able to hobble to radio shack.
I procured:
40 watt soldering iron with pencil tip.
Solder sucking bulb.
96/4 tin/silver solder .032 gauge
some pre made alligator clip leads. well insulated.
Some DeOxit D5
1k 1 watt resistor for discharge tool
some shrink wrap..may have some in garage...but motorcycle in the way of that tool box. I cant move it right now.
I'm going to tin the iron and cut one of those alligator clip leads in half and solder the resistor inline...cover the whole deal with shrink wrap. Then I should be able to drain the caps if I find voltage.
Any flaws or ideas while I make up my discharge tool?
Then I'll pull the chassis. With pics. Might as well document everything, maybe a picture will help someone putting one of these back together or something.
Elsa checking stuff out.
(http://i935.photobucket.com/albums/ad197/highluxx/photo211_zpse7238740.jpg)
Mauser and Zeus have to have a look as well.
(http://i935.photobucket.com/albums/ad197/highluxx/photo55_zps7812e951.jpg)
Nice guitars! :)
I have the Epiphone Tony Iommi Signature guitar in what ;) else... Black...
I got the last one in Canada after they went out of production. Not that that is any big deal... You can still find them on Ebay etc...
I love the Iommi Guitars! I have a set of Iommi signature pickups from one a guy took apart and painted the whole guitar with a Sabbath theme...why he would take the black chrome pickups in it out...I do not know...he put some purple ones in it now. I got those pickups for $50 on ebay make an offer!! Real Gibson 4 wire Iommi's. I'm gonna put them in my SG with coil tapping pots and have a screamer.
I have the discharge tool made. It measures 970 Ohms resistance. Also temporarily soldered one of those alligator clip leads to the black lead on my Multimeter. Now I can ground it on chassis and probe one handed...right handed...lol.
Going to pull the chassis after dinner.
Am I missing anything? I'm not plugging it in and doing any testing live till I get schooled by you guys on what to do. Just checking caps for voltage and discharging and inspection all unplugged.
Chassis out. Pics coming.
(http://i935.photobucket.com/albums/ad197/highluxx/photo120_zpsd35dcb75.jpg)
(http://i935.photobucket.com/albums/ad197/highluxx/photo212_zps535a12e4.jpg)
(http://i935.photobucket.com/albums/ad197/highluxx/photo38_zps43728a7e.jpg)
(http://i935.photobucket.com/albums/ad197/highluxx/photo48_zps5b067337.jpg)
(http://i935.photobucket.com/albums/ad197/highluxx/photo56_zps4e13b391.jpg)
So the next obvious move is to take the board off the chassis to inspect the back of it. Looks like I have to take all the knobs off and the heat sink deal screws from under the chassis. And slip board back and flip it over.
So guess what? I FREAKING FIXED IT!!!!! WHOOOO HOOOOO 8| <3) :dbtu: :tu: :duh xP 8| :loco <3)
You have to add more than all those emoticons as to what fixed it!! lol. Of course very glad to hear that it works now :dbtu:. But seriously we're all on the edge of our seats wondering what was wrong.
Pics uploading and video.
I was pretty excited. So it was a solder joint on the filter cap. Only one on board that looked funny. Like fractured around the perimeter. Could barely see it. There was no voltage higher than .2 v So I went ahead and re-soldered all the 4 joints on the 2 filter caps. I cleaned the pots while I was at it and the input jacks. Put it back together...said a prayer. Bam. Flipped the switch and was rewarded by the amp gods.
I got sooo lucky...cause I don't know a damn thing about electronics...lol.
Bad joint
(http://i935.photobucket.com/albums/ad197/highluxx/photo121_zpsfd329f01.jpg)
Fixed
(http://i935.photobucket.com/albums/ad197/highluxx/photo213_zpsa5103d58.jpg)
I must thank you all VERY much!!
Videos
https://www.youtube.com/watch?v=QQaBn3JVp3I&feature=youtu.be
https://www.youtube.com/watch?v=wvOdHOgAQ10&feature=youtu.be
:dbtu: <3)
Now you are enjoying your amp, congratulations :dbtu:
Compare your results with those of the guy wo did not want to look inside his Yamaha amp .... and to boot blamed us for not adivinating his problem :loco
Guess who's happy playing guitar tonight ? 8|
Nice Job!! :dbtu: Those loose/cracked solder joints on the filter caps can cause all sorts of strange symptoms in the amp. Shhhhhhhh.... Juan that Yamaha was a surprise "Secret" gift...
I have a compulsion to fix broken things. Drives me nuts till I do. You guys gave me the confidence to do it. This amp has a beautiful clear channel now. The chorus is awesome. Never sounder better. The pots turn like butter. That DeOxit stuff is a miracle worker. The pots where moderately hard to turn....now I could roll them all walking by with a pinky finger.
Next project...
Replacing two input jacks on another Fender Amp. An old Red Knob Twin Solid state.
If that's a red knob "the twin", it's a tube amp.
If it's a solid state twin, then it's from the late sixties and I was not aware that they had red knobs, but could have been replaced.
If it's "the twin", you will need the special 9pin Fender jacks. Don't even think about trying to modify to use anything else, too much switching going on in those jacks.
Still working. Played it several times today. So quiet now. The pots are just ridiculously easy to turn. Can't say enough about that DeOxit D5. Stuff is magic. I'm looking for other pots to clean now! On guitars and stuff.
:dbtu: