Newer Fender amp disassembly...

[Bob M.]

I had the pleasure of removing the chassis from a Fender Hot Rod Deluxe III - a newer Fender amp. While trying to get the chassis out of the cab, I ran into some problems distressing the aluminum foil shielding on the sides of the amp cab that is there to shield the chassis. Some areas of this foil got crinkled, some got torn a little.

I'm wondering if you repair guys out there have any pearls of wisdom to share about removing the chassis while doing little or no harm to this shielding material. Part of my problem was that the parts of the black Tolex on the amp sides were insufficiently glued, came loose and got hung up also in the chassis removal. And, yes, I did removed all the side screws from the cabinet. I did calm down the sharp side edges on the chassis a little before returning it to the wood. It was the first time this chassis had been removed from the cabinet.

Thanks in adv,

Bob M.

[52 Bill]

Start by removing all of the tubes.

It helps to burnish the foil down to the cabinet with a small flat stick to keep it out of the way. I then remove the two top screws that hold the chassis in place. Next turn the amp upside down so that the weight of the chassis is resting on the cabinet top that way you are not fighting to hold the chassis up as well as away from the speaker magnet. Then remove the side screws.

If the chassis is still sticking, check the points where the insert nuts are and see if they have been bent outward by the force from tightening the side screws. You may have to bend the chassis back in to help clear the sides.

Finally, if you still need additional clearance, get one of those squeeze type clamps that can be reversed to push things apart and push the sides of the cabinet outward.

This happens with a lot of amps and the aluminum chassis' are the worst to deal with, as they will almost always bend at the screw points. Those Ampeg bass amps seem to be the worst of these, as the insert nuts will pop out as you try to remove or replace the chassis.

Once the chassis is out, I always burnish or glue down the foil or felt or tolex so that reinstalling the chassis goes easier.

Hope this helps.

[g1]

If the chassis is still sticking, check the points where the insert nuts are and see if they have been bent outward by the force from tightening the side screws. You may have to bend the chassis back in to help clear the sides.

This often happens when people get over-zealous about keeping their chassis hardware tight. Even where the amp has never been opened.
The Fender chassis with the aluminum 'wings' at the sides are even worse.

[Enzo]

And knowing that the tabs with threaded inserts can bend out into the wood... Resist the urge to back out the screws a little and push in on them to bend the tabs back in. The nut or threaded insert can pop out of the chassis.

Don't ask me how I know this...

[xtian]

All the Hot Rods I've seen already have the aluminum tape shredded. I thought this was a factory option?

[52 Bill]

All the Hot Rods I've seen already have the aluminum tape shredded. I thought this was a factory option?

No, Fender made this a standard feature back in the eighties with all of those red knob amps.

[The Dude]

Agree with the above and add: I rarely have to take the entire amp chassis out of these. You can remove the preamp board with the chassis installed in the cabinet if you need to. Can I ask what the reason is that you had to remove the entire chassis?

[Bob M.]

I was removing the entire chassis so I could have access to the solder side of the main circuit board, to, of course, improve the sound of the amp. Yes, sometimes, I will work on an amp chassis 'in the wood' depending on what operations I'm doing.

I guess I though the shredding was supposed to happen between the input jack and the speaker but not to the shielding material. I guess Fender is now adopting a scorched-earth policy toward all types of shredding with their amps.

I have to say, from experience, I know what I'm going to encounter in a newer Fender amp and I'm ever-so-careful with disassembly and I take my time but I'm not always 100% successful. I can't imagine what it's like in these (volume) amp repair shops where speed is everything and usually the head-tech is training a group of newbies and getting the trainees to take the amps apart.

Bill M. is right. The right tool is something (that I don't have) that temporarily pushes the sides of the amp a little farther apart in order to be able to remove the chassis cleanly. I like some of the build features I see in new Fenders nowadays but I have to say they are doing a piss-poor job of gluing down the tolex. This last case I had, the un-glued tolex got hung up and made the chassis removal a much bigger deal. I still think the blackface/silverface tray chassis gets the all-time award for removeability, servicibility, modification and ease of work (component replacement) once inside and ease of replacement into the cab. Thanks for all of your comments,

Bob M.

[J M Fahey]

I was removing the entire chassis so I could have access to the solder side of the main circuit board, to, of course, improve the sound of the amp.

Sadly, only useful improvements come from fully gutting it and building some classic, your choice, using just chassis, iron and harware.

Clipping a cap here, adding a resistor there, what 99% of "forum/internet suggested" mods consist of, often long lists of things to do with no explanation why, the telltale sign is no schematic involved, are a waste of time, they don“t change the nature of the beast and often sound worse than original.

[52 Bill]

Pulling the chassis will not allow access to the solder side of the pc board. About the only time the chassis has to come out is to replace a transformer or the speaker.

[Mick Bailey]

As above, I rarely find the need to remove the chassis but if it is necessary I use shims cut from those cheap £shop (probably $ store in the US) kitchen cutting mats and slide them down each side. Also useful for taking a head from its sleeve where there's foil on the base that tears up with the cage nuts.

By far the worst amp I've ever come across for damage to the covering is the Fishman Loudbox mini. A worse amp I have yet to encounter when pulling the chassis and the most fragile covering in the history of amps. I don't know if the chipboard swells after leaving the factory but often the biggest challenge is to fight the grip of the sides of the cabinet to dismantle it. Zero clearance and as tight as a tyre-fitters handshake.

[nevetslab]

Ah, what I have to look forward to...the Fishman LoudBox mini amp. One of our Audio Dept staff just dropped on off with me that he had inherited someplace.

On the Hot Rod Series or Blues Series Fender Amps, the only time I have to remove the chassis is to get at the speaker baffle mtg hardware or remove one of the failed upper speakers, as well as being able to tighten ALL of the speaker mtg screws.

Otherwise, I"m always removing all the panel hardware, all the primary and secondary wiring (while labeling the push-on connectors), cutting cable ties on the wire bundles coming from the output transformer, so you can get the main PCB dropped down low enough to pull the main PCB out beyond the chassis lip that hangs up on all the pot shafts. Once you've gotten that free, it's there dangling down giving you psuedo access to everything. Watch those solder pads. Fender uses the worst quality PCB material (make that their Asian PCB vendor), where the solder tabs lift off the PCB with the greatest of ease regardless of how good your soldering technique is!

Once I have the PCB out, I'm looking with my bright headlight & loupes for all the solder fractures lurking about. Beginning with the input jacks! Close inspection of all the soldering will invariably reveal tiny annular rings around component leads, particularly those of the pots and their support tabs. Also on the bias pot, the large filter caps, 5W bathtub resistors, other parts that have heat coming off them. While this board is out, it gives you much better access to the tube PCB's, where I often find more solder fractures. I probably spend 90% of my time repairing solder fractures to restore order than anything else.

[The Dude]

Ah, what I have to look forward to...the Fishman LoudBox mini amp. One of our Audio Dept staff just dropped on off with me that he had inherited someplace......

Enjoy! I agree with Mick. Those things are a PITA to get into without damaging something. The covering is as flimsy as cheap contact paper.