BossAreaForum

Let's use this thread to collect some helpful information for all the people who want to calibrate their vintage effects (non-BOSS). For some units there are no service manuals or schematics around. And some don't have labelled components on the boards, making it quite difficult to find out what is what.

The two units I begin with have already been posted in other parts of the forum, but I'd like to gather everything in this topic.

KORG FK-1 V-C-F

There is no service manual around, in the internet only this same lo-fi photograph of the schematics can be found, that I uploaded a copy of here:
KORG V-C-F schematics

The big 10kΩ trimpot adjusts the main voltage for the circuit and should be set to 15.0 V.
The two 1kΩ trimpots seem to adjust the intensity of the "Expand" function of the lowpass and highpass filter.
The 100kΩ trimpot that is sitting right next to the one 1kΩ trimpot sets the high-pass filter frequency, the other 100kΩ trimpot is for the low-pass filter.

Pearl AD-33 Analog Delay

AVR1: Feedback Channel I
AVR2: Feedback Channel II
AVR3: BBD Bias (not 100% sure)
AVR4: Clock Cancel (not 100% sure)
AVR5: Clock Frequency
AVR6: Filter

Aria AD-10 Analog Delay

The trimpot labelled "1" in this picture adjusts the longest, "2" the shortest possible delay time.
The other two trimpots are supposedly for bias and feedback (I didn't touch them).

Pepe wrote: ↑

Sat May 10, 2025 12:39 pm

Pearl AD-33 Analog Delay

AVR1: Feedback Channel I
AVR2: Feedback Channel II
AVR3: BBD Bias (not 100% sure)
AVR4: Clock Cancel (not 100% sure)
AVR5: Clock Frequency
AVR6: Filter

Thank you!

Ibanez UE 303 B Multi-Effects

A bassist from Belgium sent me this Ibanez UE 303 B after I recapped his KORG PME-40X pedal board. He asked me if I could do some maintenance here as well. His main problem was that the Auto Filter needed very hot signals to get working somehow. It was really awful when I received it, also the chorus effect sounded underwhelming.

I did a full recap, swapping all the old electrolytic capacitors for high quality Panasonic FC (and NHG) and Nichicon MUSE capacitors and I also replaced the old tantalum caps, of course. It was a very tough job, because the old solder wasn't flowing well and I had much trouble getting clean solder holes, although I used quality desoldering braid that does normally not let me down. Two solder eyelets came off, luckily they had no function on that side of the circuit board apart helping to keep the capacitor in place. I had to replace 72 capacitors! And none of them were easy to desolder. And the holes had to be super clean, because they barely provided enough space for the legs of the new capacitors. I was so glad when I was finally finished. I think I never want to touch another Ibanez UE pedal after these horrific days, not to mention to do another full recap!

But the result was phenomenal! All of a sudden the chorus did instantly sound so good with a bass guitar. The Auto Filter was still very weak, But after some time fiddling with the trimpots it came alive in a great way. I was able to shift the range of the envelope in UP mode into the higher frequencies in a manner that the overall sound was maintained, but completely expanded. Now it is really fun(ky) to use this auto wah in all modes. I am satisfied and I am certain that the Belgian will love it.





SR1: Auto Filter DOWN mode envelope filter frequency
SR2: Auto Filter UP mode envelope filter frequency
SR3: Auto Filter basic filter frequency
SR4: Chorus/Flanger Offset (Manual - there is no dedicated Manual knob on control panel)
SR5: Chorus/Flanger Bias
SR6: Flanger Feedback
SR7: Flanger Clock
SR8: Chorus Clock
[The trimpots SR1, 2 and 3 do interact with each other - it needs some time to find the sweet spot.]

Circuit board before the recap (click on the images for photos in higher resolution):





Sadly there is no service manual or schematic around, so here is a full list of the electrolytic and tantalum capacitors of the Ibanez UE 303 B:

Nice! Great work. Great result.

This is probably also how you do it, but just in case this helps... For tight/difficult component swaps I usually cut the component from its legs then heat and pull one leg at a time. Add some new solder to the old solder just before pulling the leg. Clean the hole with braid.

I also use one of these, but they are pretty expensive:
https://www.amazon.ca/Hakko-FR-301-Deso ... 07BKSLLG9/

In most cases Stannol No Clean desoldering braid is simply magic, so normally I don't need to do that. But for the next fiddly project I'm going to try the method with cutting the legs off. The trick with new solder didn't help too much. It might be because nowadays I only use lead-free Stannol HS10 Fair solder, but the holes were too tight for anything.

Pepe wrote: ↑

Mon Dec 01, 2025 6:57 am

In most cases Stannol No Clean desoldering braid is simply magic, so normally I don't need to do that. But for the next fiddly project I'm going to try the method with cutting the legs off. The trick with new solder didn't help too much. It might be because nowadays I only use lead-free Stannol HS10 Fair solder, but the holes were too tight for anything.

Ah. Yes. Solder containing lead isn't available in Europe. Makes repairing old equipment a little more problematic.