Sound Skulptor forums

Build help and troubleshooting => LA502 Optical Compressor => Topic started by: F.R: on April 24, 2022, 04:01:51 PM

Title: LED MEtering
Post by: F.R: on April 24, 2022, 04:01:51 PM

Unconventional question.

When I setup the compressor everything works soundwise, but I can't get the LED meterbridge running, I resoldered everything, triple checked Resistors etc. Rebuild the LED meterbridge. But it won't work.

I case I f***ed up completly, can I run the compressor without having the potentiometers set up? SO I can work with it "blindly" at least?

Title: Re: LED MEtering
Post by: JPK on April 25, 2022, 03:08:34 PM

Yes the compressor can work without the LED meter.
Check you didn't reverse the LED's.
What is the revision number of the PCB ?

Title: Re: LED MEtering
Post by: F.R: on April 25, 2022, 03:13:41 PM

Revision is the Scematic 2.1 PCB rev 1.4

I did in fact setup the LED the wrong way at first. bought some new LEDs cause I heard they're done if setup wrong, and soldered a 2nd set with the added PCB part given, but still didn't work, maybe I killed the IC's?

Title: Re: LED MEtering
Post by: JPK on April 25, 2022, 03:23:35 PM

Reversing the LED's won't destroy them.
What DC voltages do you get on U8 pin 13, against 0V? does it changes when changing P4?
What DC voltages do you get on U9 pin 2, against 0V? does it changes when changing P5?

Title: Re: LED MEtering
Post by: F.R: on May 03, 2022, 04:34:03 PM

Following measurements:

U8 Pin 13 to 0V-TP : 0,444VDC
U9 Pin 2   to 0V-TP : 1,277VDC

no changes on turning p4/p5

Title: Re: LED MEtering
Post by: JPK on May 04, 2022, 05:14:44 PM

Check the solder joints on U7 and R36.
Check U7 = TL431A.
What are the DC voltage on the 2 pins of R36, against 0V?

Title: Re: LED MEtering
Post by: F.R: on May 06, 2022, 11:45:45 AM

Solders are good U7 is the TL431A

Voltages on R36 are 15,9V left 2,49V right

Title: Re: LED MEtering
Post by: JPK on May 06, 2022, 05:01:13 PM

All good!
Can you report the DC voltages on all the pins of U8 and U9?

(https://www.soundskulptor.com/prodimages/debug/ic8pins.png)
For 14 pins, same principle.

Title: Re: LED MEtering
Post by: F.R: on May 08, 2022, 05:04:37 PM

Are the Voltages dependant on any input source or is it just the Box that has to deliver it's +/-16V? From what I "guessed" from the scematics they aren't, but I'm quite a newbie.

Title: Re: LED MEtering
Post by: JPK on May 09, 2022, 10:12:31 AM

U8-pin 5, 7, 9 and U9-pin 7, 9, 11 are all connected together and receive the sidechain generated control voltage. This voltage depends on the input signal and on the PEAK pot position. You can check if these pins do receive this voltage.
The other pins are independent of the input signal.

Title: Re: LED MEtering
Post by: F.R: on June 09, 2022, 02:22:25 PM

Hope this image gets uploaded properly^^
(https://pasteboard.co/kLjaURTfLjQr.jpg)

Title: Re: LED MEtering
Post by: JPK on June 09, 2022, 03:04:31 PM

It didn't!

Title: Re: LED MEtering
Post by: F.R: on June 10, 2022, 10:40:00 PM

la502 measurement (https://pasteboard.co/kLjaURTfLjQr.jpg)

Title: Re: LED MEtering
Post by: JPK on June 11, 2022, 09:43:37 AM

It looks like D12 cathode is not connected to V-.
Check that you have -15V on CN1 pin9 (pin1 = white dot).

Also U9 pin4 and pin5 should have the same value.
Check the connection between U9 pin5 and trimmer P5 center pin.

Title: Re: LED MEtering
Post by: F.R: on June 11, 2022, 02:33:49 PM

resoldered. cn1 pin 9: -16.02V

U9 Pin 4 1.38V
U9 Pin 5  2.49V

Title: Re: LED MEtering
Post by: JPK on June 13, 2022, 09:59:54 AM

Check the connection between U9 pin5 and trimmer P5 center pin.
Try replacing U9.