SB4000 Support Thread

[Bowie]

I soldered a wire directly from the center pin on the Gain pot to R123 to get the 0-12v there and got around -.32mv at the other end of R123.  The -.32mv arrives at pin 6 of U13 but does not change at all when the Gain pot is adjusted.
So, to re-phrase, after the jumper I get 0-12v on one end of R123 and an unchanging -.32mv at pin 6.

Already told you the opamps inverting input pin6 is a current node (not a voltage node). 

I checked pin 7 and it sweeps from -19.4mv to -.40mv.

Looking back on your pics from previous page, just exchange the (looks like 1K) R119 with its supposed to be 100K resistor value and pin7 will increase by factor 100 for an about -1.935VDC readout with makeup gain turned full CW.
This will fix the unit not compressing as well.
Good luck

Thanks, I'll get on that.  One issue I found which caused intermittent issues was that the ribbon cable contained 3 shorts.  This wasn't caught before because I was tapping the bare/exposed cable ends for testing.  But, when I stuck some jumpers in the boot I found issues at 3 of the terminals.  Even testing at the "teeth" of an opened connector showed a short so I believe the contacts in the boot are faulty/malformed.  I tried re-building it 4 times and it didn't help so I've got two new ones on the way and will report back.  Thanks again for all the help!

UPDATE; the resistor change didn't show anything at first because of the faulty cable but after re-building it again, I got reverse action (Gain worked , but in opposite direction).  Then, re-built again and I attained correct Gain knob function and, for the first time, no overall volume loss when the compressor is engaged!  As great as that is, the compression is not working now.  It was never audible but now, is not even visible in the meter.  After the 3rd cable re-build yesterday, the Threshold stopped responding, only resulting in  some distortion when fully CCW.  I'm hoping that's just the cable and not the result of something else getting fried while troubleshooting. 

 

[ruckus328]

Bowie, what are you using to terminate your ribbon cable?  It should be one shot and done.  Do not try and re-use it once it's been terminated.  If it wasn't terminated correctly and your'e getting shorts then you've likely twisted/bent the pins, etc.  You're playing with fire this way as if things are shorted/not going where they're supposed to you could fry something and cause a whole new set of problems.  Throw it away, start with fresh connectors and fresh cable.  Just put it in a vice clamp to terminate it, have done countless cables this way.  Or, buy a tool:

Part #HWS9377, only  $17.

http://www.king-cart.com/phoenixent/product=TOOLS+FOR+INTERCONNECTS+%2526+WIRE/exact_match=exact

After it is terminated, buzz out every single pin.  Then, plug the cable into the connectors, and buzz out every single pin on the connectors (to weed out any bad/missing solder joints).

 

[Bowie]

Thanks for the help.  It was indeed the terminals in one of the ribbon cable connectors.  I got a replacement and it solved the issue.  Compressor functions wonderfully and the new owner picked it up today.  Thanks Ruckus and a special thanks to Harpo for the extensive help!!

Oddly, the VR9 and VR10 pots (T1 and T2) don't change anything when panned.  T1 and T2 are already pretty much on-point so adjustment isn't needed but turning the pots had no effect so I just centered them.  All the other calibration went smoothly.

 

[Harpo]

Oddly, the VR9 and VR10 pots (T1 and T2) don't change anything when panned.  T1 and T2 are already pretty much on-point so adjustment isn't needed but turning the pots had no effect so I just centered them.  All the other calibration went smoothly.

You probably ment VR5 and VR6 (not VR9 and VR10). You need to be in Stereo/Oxford mode in order to steer signal to the right side sidechain filters. Trimmers can vary the filtered signal level by about factor 2.5 or -4.9..+3dB to adjust unity gain at 1kHz.

 

[Mike Mike]

Hey you all, Ive got a problem with the power section of this build. I cant seem to get a reading on the power rails. The transformer is wired in parallel. Blue & violet to the Live tab, plus Gray & Brown to the Neutral tab. Now the output of the transformer is where I am confused. I can't seem to find the schematics for this build. I'm not sure if the out put is supposed to be in serial or parallel and how the PCB has it laid out at J16. I have tried just about every configuration there is with these four output wires yet still no significant voltage is coming through. I'm so close yet so far away. Any help would be greatly appreciated. I'm dieing to hear this bad boy in action!

 

[Bowie]

Hey you all, Ive got a problem with the power section of this build. I cant seem to get a reading on the power rails. The transformer is wired in parallel. Blue & violet to the Live tab, plus Gray & Brown to the Neutral tab. Now the output of the transformer is where I am confused. I can't seem to find the schematics for this build. I'm not sure if the out put is supposed to be in serial or parallel and how the PCB has it laid out at J16. I have tried just about every configuration there is with these four output wires yet still no significant voltage is coming through. I'm so close yet so far away. Any help would be greatly appreciated. I'm dieing to hear this bad boy in action!

Are you using the PT in the BOM?  Post a pic of your work here if you can.
I'll try to attach the schematic below (not sure if it will work).

 

[Mike Mike]

Yes I'm using the PT from the BOM. The one with  dual primaries and dual secondaries. I'm away from my desk right now, I will post a picture some time tomorrow. Thanks for the schematic!!!

 

[Harpo]

Yes I'm using the PT from the BOM. The one with  dual primaries and dual secondaries. I'm away from my desk right now, I will post a picture some time tomorrow. Thanks for the schematic!!!

So you are using the Triad VPT36-1390 (1st.column of toroidal transformers colour scheme) ?
If so, connector J16 pins 1=black, 2=red, 3=orange, 4=yellow
Connecting your transformer primary windings in series or in parallel for 115VAC or 230VAC mains depends on your kept a secret local mains voltage (please update your profile with your location data).

 

[Mike Mike]

Thanks fellas that's exactly what I needed. I am in the US trying to set up my transformer for 115V. I'm on my way home I will post pictures later today. Just to clarify the order in which you would have me place the wires in J 16 is in a series configuration, correct?

 

[Mike Mike]

Ok so here is the primary blue & violet leads tied to the top leg of the on off switch and a black jumper wire from the middle leg of the switch to the Live leg of the IEC.

 

[Mike Mike]

Here is the brown and gray primaries tied to the neutral lug and the black jumper from the middle lug of the on/off switch tied to the Live lug of the IEC.

 

[Mike Mike]

And here are the secondary wires going to J16.

 

[Mike Mike]

I'm doing something terribly wrong. I still have no readings on TP13/TP14/TP15 for the power rail testing.  Does everything appear to be right to you all?

 

[Mike Mike]

Ok I think I figured out the problem. I unhooked all the wires from the PT and tested continuity between the front and rear of each winding. The secondary windings tested with excellent continuity but both primary windings have intermittent continuity. I think this is my problem. What do you all think?

 

[Mike Mike]

So I wired up the new transformer after realizing the fuse in the IEC was in the wrong place. Now I'm getting +/- .700VDC with the power switch off and +/- 28.5VDC at TP13/14/16. This is obviously not right. Do you all have any idea on where I should start troubleshooting?

Thanks!
 

 

[sr1200]

Please be careful when hooking up your mains, it can kill you.

You need to see what the drawing is for your transformer and follow the colors listed on that to your PS board.  If you're using the same transformer thats in the BOM, your secondaries dont look like they're hooked up correctly, and if you're getting voltage with the unit OFF, your primaries aren't wired correctly either.

 

[Mike Mike]

Hey Anthony, yep I'm using the same transformer as the one in the BOM. It's funny because the when I measure at J14 and J15 the voltages are correct. Should I move on and hook up the Main PCB and test TP13/14/15 again for proper rails? 

 

[Bowie]

Hey Anthony, yep I'm using the same transformer as the one in the BOM. It's funny because the when I measure at J14 and J15 the voltages are correct. Should I move on and hook up the Main PCB and test TP13/14/15 again for proper rails?

Don't hook up the main board until your power board is absolutely correct.  I can't tell much from the pic (it's a bit small) but if everything looks correct to you and you've verified all the components to be correct, regulators aren't misplaced, check the bottom of the board for any solder blob shorts, etc.

 

[Mike Mike]

Thanks Bowie, I thought I should be testing voltages at TP13, TP14 and TP15 because They say +/- Rail next to them on the PCB. I think I'm good to go if J14 and J15 are outputting the correct voltage, right?

 

[Mike Mike]

Hey everyone sorry for asking so many question. I'm still learning the basics if you cant tell. I ran into a couple for issues during the calibration proses. First off when testing TP8 and TP10 in SSL mode I was getting 0vac at TP10. But, when I disengaged the Internal Sidechain switch the volts jumped up to .520mvac. The LED light up when the switch is engaged. Did I wire the CM and N/O backwards? Plus my threshold potentiometer is not working. I'm not sure where to start troubleshooting. Any help in the right direction would be greatly appreciated.

Thanks!