Fender Twin Amp Tremolo not working

[gretschman2112]

The tech never fixed it.

[Enzo]

Did he charge you and tell you it was fixed? or did he return it and say he couldn;t fix it? if he charged you, then return with it and show him that it doesn;t function.

Midnite - Hi, welcome to the forum. let me suggest you start a new thread for your amp. it gets real confusing when we have more than one repair going on in the same thread.

[gretschman2112]

I didn't pay anything since it was under warranty. He said it was working but it is clearly not. I didn't really have the time to deal with it and take it back. So I'm still stuck with it not functioning.

[garytronix]

Tremolo cure

Alright! I finally tracked the problem to R146 off of pin 3 of V6. Check the resistance of R146. Most likely it's open. Should be a 150K/ 1/2W. This is somewhat of a common problem.

Good luck all!
Garytronix

[oc disorder]

gretschman2112 you should really take it back and demonstrate that it's not
working.And in this case I'm sure the tech won't mind if you check it before
it leaves the building. That's what warranty service is about and in this day
and age we want all the warranty service we can get particularly with all this
modern consumer junk cluttering up the world !
Having said that I realize that its a heavy amp the kind that pulls your arms out of their sockets so I appreciate sometimes its difficult to return a unit for service.
I agree with garytronix although from fading memory I thought I replaced
R147 an 100k 1/4 watt .. with exactly the same symptoms however its probably wise to measure R144,146 and 147 .

See attached

[gretschman2112]

well I finally got around to cracking it back open. It appear R146 is open. It also appears to only be a 1/4W resistor. I'm gonna replace it and let you guys know.

Sorry for digging up an old post.

[gretschman2112]

Sweet, I switched it out and have success. That resistor was the culprit. The others measure fine.
You guys are better than the factory authorized repairman!

[midnitecruzer]

Nicely done. Been awhile since I looked at it, but that seems like the one. Thought the value was around 150k; R one forty somethin'. Also, be wary of the reverb tank rattling it's connectors loose. I hard soldered mine and cut the connectors off. Mine did that about 3 months later. Instant oscillation after you crank the knob up above (mine at least) 4. Tisk tisk, Fender. Whatever happened to the days of simpler design aka 1960s lol. Oh well. Can't make em like that; too slow to produce now.

[mgouin]

Opening the cabinet

Hello all,
I'm new to the forum and I have the exact same problem. I'm very glad that I found this tread. You might find my question strange, but I'm wondering where to start from to open the cabinet on my Twin Amp. Once I see the PCB, I'll have no problem because I'm very familiar with electronics and soldering. My only issue is how hard is to open the cabinet to access the inside PCB, and if by opening it, it will break/alter the outside black wrapping.
Thanks in advance.

[Enzo]

Look at the rear of the amp. There is space to see inside across the center of the rear. Above and below that opening will be thin wooden panels covered in the black tolex like the rest of the amp. FOur screws removes the top one. Do that. Now you can see the amp chassis more clearly.


Unplug the speaker cord from the jack. Unplug the cables down to the reverb pan in the bottom. Unplug any footswitches. Before doing all that, please note where each thing goes so you can get it right upon reassembly. The AC mains cord should be screwed to the side wall with a cable clamp. Pull the screw to free the clamp and thus free the cord. Now ther should be nothing in wiring to get in your way.

Along the top rear edge of the amp chassis you should find three wood screws. Look up from below to see them. They fit through holes in the mounting flange of the amp chassis and are screwed into the top of the wooden cabinet. remove them.

Now on top of the amp there should be four phillips screws near the corners. There may be a shiny metal strap beteeen two of them near each end. Depends which Twin you have. If no metal straps, then there will be finish washers under each screw head. Depending upon which amp you have there may also be a few more screws through the sides of the cabinet into the ends of the chassis. remove any of these screws. As you do, suport the rear edge of the chassis, because with the screws gone it will want to follow gravity.

MOST time the tilt back legs do not get in the way. Check, but I have only had to remove them like twice in my career. I forget on which model.

Now the amp chassis should slide out the rear. Support it, I usually put one hand under the powr transforme and the other on the cap cover.

SOmetimes the chassis is a tight fit. They glue aluminum foil to the insides of the cab as shielding. The chassis edges can catch on this, and sometimes they catch the tolex. You just have to be careful about that.

[mgouin]

Hi Enzo, thank you very much for your help.

[francy_lab]

Hello everyone,
I ask support to anyone who can give me some suggestions for a rather unusual question.
I fixed my "EVIL TWIN PRO-TUBE" TYPE: PR 449 by the fault "no tremolo" replacing the R146 found open.
Now the tremolo works again, but if I leave the potentiometer intensity open, when I turn off and then turn on the amp, you hear a strong BUMP.
In short, I must remember to lower the intensity of the Tremolo to zero every time I turn off the amp.
How can I remedy this defect?

I thank everyone in advance

[pdf64]

I assume that this is a Pro Tube? http://bmamps.com/Schematics/fender/pro_tube.pdf
The Evil Twin is a different model from the early 1990s, no trem http://bmamps.com/Schematics/fender/the_twin.pdf

How about if you don't use standby?

[Jazz P Bass]

but if I leave the potentiometer intensity open, when I turn off and then turn on the amp, you hear a strong BUMP.

Why are you turning the amp off & then on again?
Is there a pause between the off/ on?
If you are doing it without a pause, that has got to be playing heck with the power supply & logic voltages.
If you really do feel that it is a problem, it may be that you will have to check the bias / balance adjustments, as that is what feeds the Intensity control.

Pro Tube.pdf
Page (2) Lower right corner

[pdf64]

Yes, best to leave it a couple of minutes after switching the power off before switching back on again, to allow the line current inrush suppressor RT1 time to cool down.