4-Pole Filter Board problems (solved)

Hey Folks, first post, first experience with shruthi and electronics - so i’ll apologize for my lack of basic knowledge.
I soldered the filter and control board, ready to make some tunes BUT i saw it coming - it doesnt work.
First I have to get the filter board working.
It’s weird - sometimes the LEDs will work, sometimes they dont, sometimes just one ist lit. When moving the board a little or connecting the Control board they go out
Maybe its a cold solder joint? How to test wich one? How to test anything?
I checked the voltages with a 9V DC 500mA +tip power supply. Voltages:

SW: 9.08
7805: O: 4.97V I: 8.31V -: 0V
7905: O: -4.96V I: -7.71V +:0v
all in reference to one of the “green” IC points, the voltage check on the ICs is also alright, it always says -4.97 and +4.97

The Values on the 7805 and 7905 I’s seem to be a little strange, or is the difference normal?

BTW, i got one 16.5k remaining, is it my mistake or is the BOM wrong, saying you need 2 of them - i only found one on both boards.

Please help me, I like the soldering - but i want to make MUSIC! :wink:

There is only one 16.5k on the filter board.

That’s close to 5V it may be okay. Not all meters are super accurate.

I would check all of the connector pins, make sure they are well soldered. Look from the side, they should look like volcanos not round blobs. If they are fine then is the stackable connector making good contact between the control and filter board?

You got one of these for your first electronics project?? Eek…
The voltage at the regulators look fine to me though. I imagine you have a bad joint or 2… Visually check them. Either they look clean and tidy, or they don’t. Reheat anything that looks suspect.

Voltage readings are OK.

> It’s weird - sometimes the LEDs will work, sometimes they dont

Which LEDs are you referring to?

Did you install jumpers on both sides of the audio connectors?

Hey, thanks a lot for your fast responses,

>Which LEDs are you referring to?
I mean the two eye LEDs of the Filter Board, I was assuming that they have to light when powering the unit on.

>Did you install jumpers on both sides of the audio connectors?
Yep, i soldered in a little piece of thin cable on each side

And the connector, well, no, after soldering in the wrong part on the control board (the female one) i had to desolder it, it was a pain in the ass - so i had to remove the plastic cap and solder out every connector one by one and stick them in again - Im going to buy a new one once the filter board is running properly.

Are there other spots where I can measure the functionality of the filter board?
And how easy is it to destroy the parts by heating them up too long? I tried to avoid long heating but i have no reference.

Tomorrow I’ll upload a photo of the board and the solder points.

Yeaah I know it’s maybe not the best kit to start - but on the other hand - i was 1 click away from ordering a x0xb0x kit :wink:

I had a similar problem with the male header; I soldered it on the wrong side of the board. It’s easy to get the sandwich shape mixed up when there are parts on both sides of the digital board.

Eventually you get used to it… But I sympathize with trying to desolder and remove those male headers. I had extras so I just destroyed the part to get it out. The solder really gets into the joint from trom top to bottom and they are terrible to remove.

Use your meter to check the consistency of the signals on each corresponding pin on either side of the header sandwich. Do they fluctuate if you move the boards around slightly? That might help to isolate a bad solder joint or perhaps a fried out pad…

The experts will jump in and help you, I’m sure.


The LEDs behavior is undefined unless the control board is connected. Unless you have test equipment (signal generators, or maybe a modular synth), you cannot test whether the filter board works unless the control board is finished.

Is the control board working? Do the LEDs on the control board light up? And the LCD? Does the unit receives MIDI?

okay, after resoldering all the joints on the filter board, at least the filter board seem to work properly now.
The “eye” LEDs will flash up every time i plug the power in. But in the moment i connect the digital board the LEDs go out.

I tested the 5v on the J4 - it has the same 4.96 volts as usual on it - when i test it on the filter board only.
With the digi board plugged in, there is NO 4.96 on the input expansion 5v of the digi board (which is connected directly to the before tested J4)
. is there a short on the digi board or why do the LEDs go out?
No LEDs on the Digiboard are working, LCD isnt working.

I want to resolder the joints on the digiboard too, but im ashamed - i soldered the LCD already - is there a way to get it out again easily?

2 points to check - the Resistor Network goes with the point on it directing to the LED8 ?
I resoldered the 68ohm resistor because of a mistake (yeah i know) - is it possible that it was destroyed by heat and due to that the circuit doesnt work anymore?

ok one thing is very confusing… when the digiboard is not connected, i get the 5V on the 7805.
Once the digiboard is plugged in there are only about 200 mV on it?
All the other voltages on 7805 and 7905 stay the same as before.

As I said: The behavior of the LEDs is undefined unless the control board is fully connected (the LEDs are driven by a shift register, its state is undefined at boot, unless it receives data from the control board). The “eye” LEDs light in some circumstances, depending on what you play, LFOs, arpeggiator speed etc ; and this blinking pattern is sent by the control board. Don’t make any conclusion based on the state of the LEDs.

Please state clearly:

  • Is the control board working? Do the LEDs light up? Is the display working? Can you navigate through menus?
  • Is the control board receiving MIDI data? Do you see anything flashing on the screen when you play notes or move mod/bend wheels on your controller?

Ah, if the voltage on the 7805 output drops to 5V when you plug the control board, then there’s a short somewhere on this board.

Take the two boards apart, unplug them. If you use your multimeter in continuity testing mode, does it beep when you touch the +5V and GND pins of the control board?

if the 5v rail stay at 5v (or 4.96 in your case) with digital board connected it doen`t theem like a short between 5v rail and ground
maybe some bad solder joint at the digital board.

i think, after you manage to power up the digital board, you should make sure it works properly, before trying anything else with the filterboard.
make sure, it recieves midi (it indicates that in display)
make sure, the cutoff and reso pins change their value when turning the pots on the filter page (voltage messured between those pins and ground)

as pichenettes mentioned, the filterboard leds need the digital board to function, so you shoudn`t worry about them right now.

ok i get it with the LEDs - it was just strange that after resoldering all the LEDs light up nearly every time the power is plugged in

and yes… there’s a connection between the 5v and GND on the out and in expansion of the control board.
from what i know this should be a good thing? :wink:

after looking under the LCD (as far as this is possible) theres only a ceramic (C5) having a connection to one of the metallic spacers of the LCD,
this should be fine?

another thing is on the output expansion i see a little bit of copper has got free (from the ring surrounding the 5V in direction to the GND - on the LCD side of the board).
It’s hard to see but it doesnt look like theres a connection. does this matter?

i think i didnt state it clearly, the voltage on the 7805 Out (the outer left connector when the 7805 is on the left) drops from 5V (filter only)
to nearly 0V (it says 0.2 V) when i plug in the control board.
Just the other values dont change (7805: In 8V 7905 stays the same as before)

If the voltage drops then that is due to something dragging it down. Most likely a short circuit.

You need to check the GND and 5V pins on the connector of the control board. Do this with the control board not connected to anything. Stick the meter in continuity mode and put the leads on the GND and 5V pins. You shouldn’t get a very low resistance reading like 0 or a few ohms.

ok, like i said - in continuity mode i get a connection between 5V and GND.
At the Input expansion I get a very high resistance (its raising till it says overload). So this means all the resistance of the circuit adds up and its correct?

But at the Out Expansion, where the bad copper is seen i get a resistance of 0 ohms. Does this mean my supspicion was right that i damaged the board so that theres a direct connection between the GND and 5V because of the free copper?

Im sorry for my lack of knowledge, but i need to get this solved :frowning:

Any solutions for the problem (if this is causing the short)?

Maybe I’m missing something here, but don’t we have to address the broken pad the “free copper” before we go any further? It’s the 5V pad that’s broken right?

Yes, 5V pad on the out expansion. It doesnt seem like theres a solder connection, but since a small amount of solder is enough it seems possible that the GND and 5V is bridged.
Is the zero resistance a hint for this?

Here are some pictures - it looks messy because of the flux:

Huh. I don’t see the problem with the pad. Maybe it’s the pics.

OMG them white PCBs are sexy!