Ibanez DB800 active, no treble control?

[Rattanee]

Hey folks!

Happy new year!

Is there anyone out here who knows about the old Ibanez active setups? I bought a DB800 Destroyer (1985 Fujigen). It's got it's share of scratches, but after a cleanup it looks good, and mechanically it's working all the way. When I plugged it in though, monster sound by the way(humbucker at the neck is insane), I got clean tone, volume works, blend control works, bass control works, treble control... no audible change...

Basically no matter which direction I turn from the center notch, there is no change in tone. I thought it might be because my tweeter is missing from my practice cab, but I know both speakers in it are wired direct to the input so there should be no high-cut on them. I then tried it on my Peavey Studio Pro 112 guitar amp, just in case, and the problem's definitely with the bass' electronics.

So I opened up the electronics compartment, and checked the obvious, the pot itself measures fine, however it's active EQ, and that's where I get lost, I'm not sure how to go about checking components because I have no idea how this is wired/about the theory of operation behind active EQ.
To add insult to injury, the pot knobs are not secured by screw, but are push-on knobs, and after 30 years, they really don't want to let go of the pot shafts (If I pry I'm afraid of breaking the pots, which are all noiseless so I would prefer to keep the originals). This makes troubleshooting particularily troublesome as I cannot remove the circuit boards...
The two tone control boards are daisy-chained with yellow, orange, and black wires. Does someone know which is which wire?
Since the bass control works, and they are daisy chained (checked the wires, they all conduct), it seems logical that the problem should be on the treble tone control board... However I've no idea what the circuit on that board is supposed to look like or a theory of operation... the components I can actually see are a ceramic cap, an inductor of sorts (ferrite cored), a resistor, and possibly something else I cannot see without the board removed...

Umm... halp!?

 

[Rattanee]

So it cost me a new crack in the paintjob to get the damn knobs off. Not exactly happy about that, but at least now they all come off more or less easily so I can send'em off to get freshly powdercoated along with the bridge.

Anyways, I found the problem after replacing everything one by one, and that not actualyl fixing the problem. Turns out one leg of the inductor was not soldered correctly in the factory. I somehow doubt this control ever worked correctly! After pulling off all old solder, reinstalling all the original components (hey let's have it all original!), it works great. This bass is the boobies! :3

 

[Killed_by_Death]

The trick to getting stuck knobs off split-shaft pots is to wrap a shoestring around the shaft under the knob & then you have two strings to pull on to get it off evenly, w/o bending the pot shaft.

Another way is to put cardboard around the knob a something to leverage with on either side, say for instance two pencils.
Then you take two thin-blade standard screwders to pry the knob up simultaneously.
This is only in an extreme case where the shoestring trick didn't work.

 

[Rattanee]

The trick to getting stuck knobs off split-shaft pots is to wrap a shoestring around the shaft under the knob & then you have two strings to pull on to get it off evenly, w/o bending the pot shaft.

Another way is to put cardboard around the knob a something to leverage with on either side, say for instance two pencils.
Then you take two thin-blade standard screwders to pry the knob up simultaneously.
This is only in an extreme case where the shoestring trick didn't work.

I did not try the shoestring, that's a good idea, but it would not have worked in this case. This guy was on -hard-. With all the strength I could muster (and I'm no twig) I could pull it up about 2mm by hand, then it stopped solid. I actually ended up using the plastic electronics cover as support for my screwdriver as it is harder then cardboard and distributes the pressure more evenly, but even so, it needed so much force that the clearcoat underneath developed a 5mm or so crack. It's not like the paintjob is flawless on this guitar so technically this is no big deal, it just annoys me that I did that. I don't like to do damage to any instrument even if it's not pristine. On the upside, all the pots survived, none are scratchy!