Author Topic: Boss GEB-7 ICs Help!  (Read 185 times)

LipePereira

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Boss GEB-7 ICs Help!
« on: December 25, 2017, 08:42:23 PM »
Some time ago (a few years actually) my GEB7 got fried when someone hooked it up to the wrong power supply. Long story short, I sent it to a "electronics repair" shop and they said it was fixed, but whenever I tried hooking it up only a loud buzz would come out. I, today, like 5 years later, decided to give opening it a try, since I had nothing better to do. After some cleaning and re-soldering the messy work of the shop guys made back then it seems to be mostly working. However, when I move the 2 lower frequency's pots (50 and 120 hz) upwards (from 0 to +15 Db) a loud fart noise comes out (like when you unplug your cable without turning it off first).

I'll set up some wave form analyser on my computer tomorrow to check if the other pots are actually giving me enough results or if I'm just hearing stuff that is not there.

Now to the actual question: The built in ICs are the JRC 14558D and there should be 3 of them. However IC1 (the one they replaced back then) is now an CHN 4558C KF8726. I know from some schematics I found online that IC1 is the one hooked to the lower freq pots (and I can also see it on the circuit board). Is this circuit apropriate? From datasheets I found online they seem to bee way too different to work as replacements, but I need the opinion of someone with more experience first.

I've read online that  you can actually replace all 3 ICs for better ones, does anybody know where to find good resources for that?

Any help would be apreciated.

For now, my next steps on this project will be:

- Remove the pots to check them for resistance and see if they work properly, also take not of their specs if replacements are needed.
- Set up a wave form analyser and see if I can visualize the boost on the other frequencies.
- Order some JRC 14558D from https://br.mouser.com/ProductDetail/513-NJM14558D (JRC seems to be NJM now), even if not necessary since it's only like 2 bucks each.

In the end if it all fails, I'll end up building some random custom pedal inside the case so I don't lose ALL the money I spent on it :p
« Last Edit: December 26, 2017, 06:47:10 AM by LipePereira »