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YAMAHA RBX 774 FAULTY ELECTRONICS FIX

LYNCHMAN

LYNCHMAN

Nov 15, 2017
462
562
Richmond VA
#1
Does anyone know just what the fix is? i am pretty good with electronics and have gutted and totally re-done several basses...but i am having some difficulty finding just what the fix is....can anyone point me in the right direction, as i'd like to do this myself rather than get someone else to do it for me....

thanx in advance for any help ...
 
#5
LYNCHMAN said:
i'm sorry....i've been reading that there are faulty electronics (design flaw) in all rbx 774's shipped from yamaha, most talk about the fact that they have fixed it or had it fixed but no one tells what the fix actually is....i have no doubt i can do the mod but i need to find out what the mod is.
Click to expand...

If you cannot say what the problem is, then you have no problem at all.
 
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#6
well i thought i did say what the problem is...a design flaw seemingly very well known, and also a mod to fix it that is talked about in all the forums i have frequented so far...however no one has detailed the mod so that someone like me could fix the design flaw myself....thats the problem....
the solution would be to find the mod in detail so i know what to do....

thanx killed by death for the service manual...
 
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#7
line6man said:
If you cannot say what the problem is, then you have no problem at all.
Click to expand...
It's a mystery wrapped in an enigma...

A google search only turns up a thread on a UK-based bass forum, and it's cryptic. The OP states he "got the bass fixed" but is very vague about what exactly was "fixed"... As near as I can tell, a modular connector was miswired so that the switchable 'boost' didn't work properly. Another poster claimed that all these basses had their pickups wired out-of-phase, which frankly would be pretty obvious to anyone who's played bass more than a month or two.

So the issue, if there IS one, would be either the boost switch has no effect, OR the sound is very thin and trebly with both pickups on. The service manual is very detailed, and includes a schematic of the preamp, so you have all the info needed to hunt this down. Good luck.
 
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#8
LYNCHMAN said:
well i thought i did say what the problem is...a design flaw seemingly very well known, and also a mod to fix it that is talked about in all the forums i have frequented so far...however no one has detailed the mod so that someone like me could fix the design flaw myself....thats the problem....
the solution would be to find the mod in detail so i know what to do....

thanx killed by death for the service manual...
Click to expand...

I know it looks like some folks are being picky or smarmy about the problem, but what they are asking is, what are the symptoms of the reported problem? Noise? Something not working?

It looks like you found some details discussing the problems and how to fix them, so that’s good.
 
#9
the problem as i have a read about it in several different articles and forums is that the 774's were shipped with a design flaw where the boost switch for the active electronics was either wired improperly or the switch was bad...the symptom was that the boost switch when turned on didn't really do much of anything but after the fix the boost was tremendous...but no one details just what the fix is...thats what i'm looking for...do i rewire something or do i replace a part?
 
#10
Make sure the wires from the boost switch are going to the right spots on the circuit board:

upload_2017-11-16_14-58-37.png

I assume GR & OR = green & orange respectively.

upload_2017-11-16_14-59-56.png


If those are indeed connected properly, make sure that the Boost Switch is indeed shorting/closing that connection when you turn it on. You can check this with a Ohm meter.
 
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