4PM troubleshooting

I have finished building a Yellow Magic successfully, but my 4PM is having an issue.
When I plug in in, it powers up normally. All controls work as expected. The display and LEDs are all working, including the two LEDs on the 4PM board.
I am using a 9V 650mA power supply, which works fine with my Yellow Magic Shruthi.
The Filter menu is set to 4PM and saved.
I can hear a slight low frequency thump on every key press via MIDI, and upon release of the first button for the test note - but no real “sound”.
I have removed all IC’s on the board except the LT1054 and tested all sockets for +5V and -5V with 100% success.
All IC’s are installed correctly.
I noted my TL072 and TL074’s are actually TL072CN and TL074CN - not TL072P and TL074P - not sure if this is an issue.
Not sure how to perform the test “A quick check if something goes wrong: Probe the signal at those points – their voltage is the signal 1, 2, 3, and 4-pole filtered.” on the resistors around the Coolaudio V2164 IC.

Also - when I go into the menu for CV settings (next to where you select the filter board type), if I turn the encoder, the synth interface goes nuts, and I hear the patch currently selected making a bunch of strange noises - definitely sounds like the current patch being filtered by what I expect the 4PM board to sound like… which leads me to believe the 4PM board is working fine.

I have connected the control board from my Yellow Magic to the 4PM and had all of the same results…

I think the 8-pin and 6-pin headers with the stacking headers are properly connected - tonight I am going to test continuity from top board to bottom board on each of these connections.

Anyone have any other ideas or things I should check?

Regarding the Yellow Magic - DAMN this is an awesome synth. The addition of the 2290 delay is WICKED. Just wish we had the ability to put some modulation in there.

> not TL072P and TL074P

Fine. There are dozen of variants with different performance, temperature sensitivity, manufacturer… does not matter here.

> Probe the signal at those points

There are many different ways of doing this, but it boils down to this: the point to probe must be connect to the tip of an audio jack plugged into your sound-card, while the ground must be connected to the sleeve of the audio jack. You can achieve this by destroying / splitting / cutting / soldering audio cables and/or multimeter probes.

> when I go into the menu for CV settings (next to where you select the filter board type), if I turn the encoder, the synth interface goes nuts

This is absolutely normal - by doing so you enable the external programmer, and from your message it looks like you have no external programmer connected to the synth. So it’s picking up random values.

Make sure the filter board type is to 4PM and that the setting is saved. Do not mess with the CV setting.

Regarding the yellow magic, you can actually modulate delay time and level by routing stuff to CV1 and CV2 in the modulation matrix. But feedback amount and flavor cannot be modulated.

Thanks Olivier - I will probe those points and check my header’s continuity on the 4PM when I get home tonight… as well as modulating the 2290 on the YM - just to keep my spirits up.

Yes the 4PM filter board setting is selected and saved to memory.
Just curious though - why would the synth make fully 4PM filtered sounds of the current patch when I adjust the CV Programmer setting, but not under normal playing conditions…?

Cheers.

> why would the synth make fully 4PM filtered sounds of the current patch when I adjust the CV Programmer setting, but not under normal playing conditions……?

This might be a hint of a problem with the 1x6 pin connector and/or the 74hc595 on the filter board.

ok… will check that I have a spare 74hc595 too… Thanks!

Turns out I had a combination of problems…
Not sure if this had anything to do with it, or it was just a bad IC, but in the IC9 I had a CD4051BE. I replaced it with a 74HC4051 and then the left side (1- and 2- pole sides of the V2164 started working.
I am thinking it was just a bad CD4051BE, I can’t seem to find any technical differences between them.
Then I probed out where the loss of signal was occurring for the 3- and 4th poles, and found the TL072 in IC6 was not working - I replaced it with a spare Texas Instruments one I had, and everything started to work perfectly.
I had a spare probe for my oscilloscope, bought a BNC-RCA adapter, and that made it easy to listen to any point on the circuitboard. Sometimes, what you see on the scope, just doesn’t mean as much as to hear it. Olivier, I am sure you would agree - I’d advise anyone having problems to go download Eagle, download the schematics from GIThub and trace the audio path through the circuit board. It makes it very easy to track down the failing point.
Last night was a disturbing shruthi duel between a dubbed-out Yellow Magic and a squawking 4-Pole Mission.