Don't let someone do this to your amp...

[J M Fahey]

When I was a kid I was quite terrified at the movie "The Blob"
The Blob (1958) - Theatrical Trailer - YouTube
I guess kid amplifiers are terrified at .... " The solder Blob"

I couldn´t eat strawberry jelly for ages ... I guess they´ll run when they see a smoking sodering gun

[Enzo]

R94 is tacked on the copper side of the PCB because whoever did the layout forgot to include it on the board,

That's not how the board is laid out and they didn't realize it until after the boards were made.

Oh, stop that. Fender is not a couple guys in a basement drinking beer. Yes, they make mistakes. They also decide engineering changes should be made. That is why boards come in revision versions.

Rather than someone "forgetting" to include a part, how about they realized later that certain instabilities can result in some conditions, so they ADD a part. The change is made to existing boards during production and once the edited board is available it is now part of the trace art.

Wiring layouts can change for a variety of reasons. They may decide to run the power cord directly to a power switch in one version, then later decide they'd rather run to the board first and from there to the switch. SO they change the boards to accomplish that. Your later revision schematic should match the later revision boards, but I am not surprised the later schematic does not match the earlier board.

And sure enough, on the revision A drawings, R94 is neither there on the schematic nor there on the layout. They decided it was a needed change and implemented itas a modification until the later boards came out. They didn't "forget."

STandby switches can be wired in in a variety of positions, and they decided between revision levels that they would rather have it before the rectifier instead of after. If I had to guess why, it made the standby switch less likely to arc over when turned off. SO they changed the boards. And a simple wiring change to the boards currently in production allowed the change not to have to wait for new boards. It was not a matter of "didn;t reailze." It isn't an error either, it is just a change.

The changes are purposeful. Tech Note 94-5 describes a problem: Under either low mains voltage conditions or when playing very loud, the reduced voltage in the circuit COULD make U4b unstable, and it would send out pulses to mute JFET Q1. That would cause intermittant interruptions in the sound. The addition of 2.2M R94 is the solution. They considered this important, so they implemented the change immediately and issued the bulletin. We are to make the change as a warranty repair EVEN IF THE AMP IS NO LONGER UNDER WARRANTY.

You mention poor scans. The Fender web site has a lot of schematics under support. The newer style rev G schematic is there, as well as the even newer reissue on that model. Scans look good and clean to me.
http://support.fender.com/schematics..._schematic.pdf

I suggest you CONTACT, preferably CALL, Fender and ask for the revision A drawing for the Blues DeVille. It should match your board, though the changes will not be on it.

[drewl]

heh, that one was pretty bad alright.
I've come across plenty or real bad "repair jobs" like this one, I always let the customer know what someone did to their poor amp!


If you ever need that type of ribbon cable, look around for an old computer, they have some inside that should do the trick.
Just make sure the wire in the ribbon cable is a proper gauge.
We have tons of it at work already loose.

[hasserl]

But the mods added some "hand wiring", surely it must have been better. And now that you've removed that hand wiring the tone must suck.