[Stam]

 I have built the main PCB and the front PCB on the CP5176. I connected them and did the setup test. I connected to my 500 box with XT500. Pushed the red button-the green led lighted up. I connected the multimeter black probe to OV and the red probe to the V+. Perhaps I did something wrong and made some connection with something because it came smoke from the area where the red probe sat. Unfortunately (it was late at night) I moved the red prob to the V- test pin and did get another smoke from the big transformer area. I saw that the R57 was burned. I replaced R56 and R57. Started the process again. The green led light up, but it turned off after a while. I measured direct on the replaced resistor R56 volt and it was +16.03v in, and +0.04 v out. On the R57 was -16.12 in and -0.54 v out. They were broken again. I replaced them again and also replaced the two TL074CN Quad Op-Amp. Started up the compressor again. Now I did get the right measurement on V+, V- and on TP7. Everything seems okey so far.
I build the SK25 and put it in place and send the 1khz sinewave to the compressor. Turned the in and out potentiometer up. No signal passed through the compressor. I measured the L1 with DC and did get 0,057 V, and the SK25 became warm after some minutes. Can’t find any misplaced components on the SK25 or obviously bad joints, but something is wrong I suppose. I also did the measurement on the resistors A to G without the SK25 described in the forum: https://www.soundskulptor.com/forum/index.php?topic=402.0  
Every value was right except D: that should be - 0.2 V, and I did get - 0.133 V.
I have also checked this: https://www.soundskulptor.com/forum/index.php?topic=9.0
Can’t find any problem so far. How Should I proceed?

[JPK]

Every value was right except D: that should be - 0.2 V, and I did get - 0.133 V.
This is probably OK.

You must try to follow the signal as mentioned here.
It will tell you where the signal chain is broken.

[Stam]

Hi!

Nr 3 on the checklist:

I have put a 1VAC sine 1 Khz signal to the input of the compressor and I don´t get any VAC reading on TP1, Tp2 and L1.

Nr 4:

I am not a skilled electrician and did not understand input sine 100hz at 100mVAC? Can’t even get that low signal from the software generator so did send a 100Hz at 1VAC instead. Maybe you can teach me there …

Ac level on TP3:
My multimeter read 0.04 VAC on every ratio.

DC level on PT4:
All value where correct on all ratio.

DC level on JMP1 pin 1:
Did not get any reading on any ratio

DC level on TP6:
Did get -2,7 VDC so it seems okey.

DC level on TP5 with jumpers JMP1 on 2-3 and 4-5:
 Was correct, I did get exactly 0.32 VDC

[JPK]

I have put a 1VAC sine 1 Khz signal to the input of the compressor and I don´t get any VAC reading on TP1
Check the solder joints on transformer T1, connectors CN3a and CN3b, potentiometer P1.

With a signal at the input, check that you get an AC volts reading on pot P1 top pin, against 0V, then on TP1 with P1 set at max.

[Stam]

Hi again!

I found a bad solder joint on the transformer T1 and resolder it. The connectors CN3a and CN3b are fine and solder joints on P1 also. Now there are signal coming through the compressor. But the signal is weak and lack all bass. When I send a 1khz sine 1VAC to the compressor I get only 0.11 VAC in the pot P1 top pin. With the P1 set max I can also read 0.11 VAC on TP1. I also did the checking Nr.4 again. This time there was I very weak signal AC coming through on TP3 and also a very weak DC level on JMP1. All other test was okey like it were before. I tested the compressor with the GR installed with the jumper on pin 1 and 2 an it seems as it kind of works. But the signal is lacking all bass.

[JPK]

With the P1 set max I can also read 0.11 VAC on TP1
Does this voltage vary, from 0 to max) with the P1 rotation?

Check the input transformer coils resistance:
Between edge connector fingers 8 & 10 (counting down, including absent fingers): 2k
Between side pins of P1: 1k6

But the signal is lacking all bass
Are you sure you are connecting the output with a balanced cable? This lack of bass happens when only one phase is connected.

[Stam]

Hi!

Does this voltage vary, from 0 to max) with the P1 rotation?
 Yes. But still just 0.11 VAC at maximum P1 on TP1. On L1 I get from 0 VAC on P1 at minimum and 10.8 VAC when P1 at maximum. (1Khz 1VAC)
 
The resistance between side pins of P1 read 1.69 K when front PCB is attached to main PCB.
 
I´m really confused when it comes to check the input transformer coils resistance …
I suppose that you mean the fingers on CN3a? Shall the front PCB be attached? And without any power I suppose? When I see the main PCB so I can read text “SOUNDSKULPTOR” on It. I got one upper row of 10 solder joints and one row under with 10 solder joints on CN3a. If the upper row is 1-10, and the lower row is 11-20. Between which numbers shall I test the resistance?  
 
I have balanced cable in and out. Checked with another 500 series module on the XT500 extender and it sounds fine.
 

[JPK]

I suppose that you mean the fingers on CN3a?
No. I mean the card edge connector at the back of the card with golden fingers (connecting to the lunchbox).

And without any power I suppose?
Correct

[Stam]

Ok, I see ...


Between edge connector fingers 8 & 10 I get 2.16 Kohm

[JPK]

The values are correct.
Check that the input transformer is inserted the right way around, with the markings facing upwards.
Check that the relay is inserted the right way around, with the white line down.
Check that the resistance between TP1 and ground goes from 0 to 1k6 when turning P1.

[Stam]

If I have the compressor vertical as it should sit in the 500 rack the input transformer got it´s marking upwards.
The relay got the line downwards.
The resistance goes from 0 to 1.785K on TP1 when turning the P1 pot from min to max.

 

[JPK]

I am running short of ideas. 
Do you want to send it to us for a check? Contact me at jpk@soundskulptor.com