Help. My amp is broke! Oh noes!

[mauser]

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.

[DrGonz78]

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.

[mauser]

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.

[DrGonz78]

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! 

[J M Fahey]

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.

[J M Fahey]

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? 

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:

[g1]

posting schematic

[mauser]

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?

[J M Fahey]

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

[mauser]

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?

[g1]

 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.

[DrGonz78]

...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.

[mauser]

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.




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"




Fender Stratocaster 50th Anniversary.  My baby. 



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.



Elsa...official guitar guard.  She sleeps on the bed in the guitar room. 



See ya guys tomorrow for the chassis pull.  Really appreciate all the help.  Hope you liked the pics. 

[DrGonz78]

Nice! I feel sorry for any poor bastard that tries to break in and steal your guitars!  :lmao:

[J M Fahey]

Same here.  :lmao: