fender frontman212r

[blaise mac neil]

got power #1 check speakers and they are fine with second amp

QUESTION: I recently got a Fender Frontman 212R, and I sometimes get
a horrible crackling noise. It happens across all channels,
and all volume and drive levels .can i get some help with this or how to troulble shoot this problem

[Enzo]

Hi, welcome to the place.

We have recently had several in depth discussions about this amp's circuits. I suggest you do a search for both Frontman 212R and FM212R, and read through the analysis.

First place I'd check is any power amp in jacks or FX return jacks.

[blaise mac neil]

they are all clear all working good i think it in the board

[Enzo]

The idea with the jacks is to use a spare cord and plug from send to return on the FX loop or from preamp out to power amp in for those jacks. This is an external bypass of a sort for teh contacts in those jacks. The jacks themselves may work fine, but they also must carry the signal past themselves when not in use, and those innner contacts can get dirty.

A separate test would be to plug the guitar into each power amp IN jack to test each power amp individually. Plugging in there bypasses the preamp.

[blaise mac neil]

thanks everyone for the help

[blaise mac neil]

(starting over) the first gig i played with the amp might got 20 tune off and the amp began to fade out in the middle of some tunes. i fig it was guitar cord change it with a new cord same thing fadding out as time went on the amp got worst might been 10 tunes and it started fading .now here what happen now when i play lightly on the strings it not to bad but when i play power cords the amp has a horrible crackling noise over top of the sound. like 2 dollar amp so then check the speaker with second amp they worked fine check all bypass and did not impove anything still the same a horrible crackling noise i think its got something to do with the fender board .like im new around this so any help is great cheers blaise

[Jazz P Bass]

So the amp works then it does not.
Amps that I have seen that come in for repair exibiting crazy symptoms cry out for a resolder of the ampifier.
Front to back. Top to bottom.
One hour resoldering or 2-6 hours chasing a demon.
Not a hard decision.
Plus you get peace of mind knowing the connections are perfect.
(Especially when you get finished with the reflow & the amp still acts up)
Combo amps are especially bad because everything in the amp is vibrating.

[Enzo]

Well, one thing that could cause what you describe is an op amp stage drifting up to some DC offset voltage. It could be anywhere along the signal path.

[andyjazz]

I am working on a Frontman 212r right now. I did what Enzo suggested and read through the other posts about this amp - got the schematic etc...What this amp does is just a horrible distorted output. If you plug a guitar in it's like the output is constipated. Anyway I tested all "Test Points" for the various IC's and found everything to test within what the schem says. I'm almost ready to just go ahead and order some new output transistors, they seem most suspect as far as I can tell. I'm a little stymied at this point. Anyway, guy a Fender says that model doesn't even get serviced "in the field." They just ship it back to the factory and replace the board. Wonder what that's all about?

[Enzo]

He is talking about the warranty coverage. The amp is inexpensive, and warranty labor is not. Fender finds it economical to exchange the whole amp rather than pay me $50 to fix it. SO when an amp comes to them, instead of wasting time, they just swap a new board in it for a few bucks and sell the amp as B-stock.

It has nothing to do with whether the amp can be repaired or not, it is about that AT FENDER they don't bother fixing them. They will get defective FM212R amps coming in at their facility, but they won't be getting for example Fender Twin Reverbs shipped in. SO since no one there ever really works on them, no one will have any clever insights into the circuit.


Before you start throwing parts at it at random, have you actually isolated the problem to the output stage? In other words does the signal coming out the FX send sound OK? Does plugging a signal into the FX return or PA in sound bad?

[andyjazz]

Enzo,

Thanks for the reply. Reminds me of what my brother -in-law says about the handheld radios at the radio shop. If a cop had a broken radio - at one time they used to find the bad chip or component and replace it. Then they went to just replacing the entire board. Now they just chuck the thing on a shelf or in the trash and order a new radio. It's the way of our "Great and Glorious Market Capitalism"

Seeing as this is a lower end model of Fender I was thinking maybe there is a chronic defect in the manufacture of this model. What you're describing I'm sure is more the case. Anything can be fixed - it's just a matter of who and how much. I have a friend who was looking into becoming a factory service guy for Fender guitars - till he found out how much they would pay him for a refret. It was better for him to ship a twisted neck or one with damaged frets back to Fender and have them bolt on a new one. I'm sure they churn out about 1000 a day.

The 212R I have here has a preamp out and power amp in - I'm guessing this is what you mean by FX send and return? I think I see where you're getting at - I'll check these again to make sure the problem isn't somewhere in the preamp section.

[km6xz]

This is my first post and I do not have a schematic in front of me but the problem should not be hard to find since the symptoms are so dramatic. The description of "horrible" sound does not give enough information to pin point a cause much less a symptom. Does the amp create this sound in response to mechanical stress or vibration? Is the noise only present with signal? Is there a low frequency fundamental component in the waveform such as 60 or 120 HZ plus its harmonics? Does it stop when putting a dummy plug in the return jack? What amplitude is the sound, full rail to rail or just a loud signal below clipping? The answer to these questions should isolate most likely causes.
Whatever you do, DO NOT put parts in until you have a full understanding of their contribution to the fault. For example putting power transistors in as a shotgunning technique just puts you further from figuring out the cause and fault. Shops that shotgun should be exposed as the frauds they are, the customer surely should not have to pay for parts that were just thrown in due to tech incompetence in diagnostics. Having a skilled knowledgeable tech work on a unit is usually cheaper than someone who isn't.
Don't re-solder the whole board either, that is a form of shotgunning that can introduce ambiguity in masking symptoms. Trace the problem, return the amp to full spec, then if you want to re-solder everything, have at it.
Good luck

[andyjazz]

km6xz,

The "horrible" sound is only present with signal. Plug the guitar in, play a chord, sounds like a badly distorted synth sound from 1969. Just for fun i played some single note melodies. Lovely little Xmas tunes. Sounds like a drunken goose squawking through a kazoo while trying to hold in a fart. Awesome!

Thanks for caring enough to respond. I don't necessarily "shotgun" fix amps. I am still learning to navigate my way through schematics and checking all the "test points." I do have an electronics degree but the VoTech I went to.......Well, I asked one of my teachers one day about how tube amp works. He looked at me like I was asking him how to shoe a horse!

Tube amp? They still use those? What the hell do you want to work on one for? Just buy something digital! - yeah that was his reply!

When I asked him how does a guitar amp actually work he talked over my head for 3 minutes and walked away.
I'm in my 40's. I don't have alot of time for pretentious bullshit. And I may not be a Rhode scholar but I'm a reasonably intelligent person. I post questions here because I'm still learning. There are a lot of us here in the same boat. And I am truly grateful when people with knowledge and experience bother to help us out! thanks again for your time.

[km6xz]

Hi Andy
The second description of the problem getting worse with high levels is a good clue. First off, before doing anything complex, when it is doing this heavy distortion thing, try sliding in a 1/4 in phone plug into the effects return/power amp in jack. Don't put it in all the way, just far enough to feel the tip make contact with the spring loaded tip contact. While playing( a steady tone from a signal generator is best so you have something sustained to work with) giggle the plug by applying a little pressure on axis of the plug. That will slightly disturb the normalizing contacts in the jack. If they are oxidized you should be able to influence the sound of the distortion.
If that does make the problem increase or decrease , apply a little DeOxit D-5 to the jack innards and be done with it.
If it does not help using the plug, try plugging headphones into the jack next to it, "Preamp Out" and see if the sound is clean there. If it is, the problem is in the output section. If the distortion is there, the problem is in the preamp section. Just knowing which cuts in half the area needed to be concerned with so that is a first step towards pin-pointing the cause. To verify that the power amp is working you can plug your guitar into the Power Amp In jack and you should be hear the clean tone if the problem is in the preamp section.
There are a few possible ways the signal is becoming distorted regardless of specific cause. One is mechanical vibration when playing loud with the speaker in the same cabinet can modulate a broken solder joint or broken lead. Another is actual current related problems such as the current amps that the output transistors are.
Before introducing confusion by suggesting too many possibilities, try the first couple section isolation tests I began with and report back. We can get more specific after knowing what part of the amp to concentrate on. Do you have a scope and audio frequency signal generator available. Having a description of what a sine wave looks like on the scope would really help define the type of distortion you are hearing. A current limited clipping on one rail at higher power would be easy to spot visually but hard to describe the sound of for example.

[andyjazz]

km6yz,

Sorry this has taken a little time. I've been busy with some other projects. I did some testing as you suggested and have narrowed it down. The output from the "Preamp out" is clean and normal so the issue is definitely with the power amp or output section. To answer your question yes I do have a scope and a freq. generator. I've had this amp apart once before and went through the "test points" indicated on the schematic. I guess I was reasonably happy with being able to decipher what was indicated on the road map and found readings on the DVM which were consistant with what the map was saying I should find. Next I guess is to actually hook up the scope and do some real detective work. I hear a lot of talk around hear about the "rail." WTF is a rail anyway? I think I have an idea what you're talking about but I've never heard anything like this discussed in electronic school. A low pass filter? yes. A wheatstone bridge? yes. The Armstrong Super Heterodyne reciever? Yup.

A Rail? Huh?

I'll be messing around with my scope and check in later.