[Gian]

Hi, having trouble on Step 7 of the set up guide. I cannot get enough voltage when setting T1, it only goes up to +1.754 and I am trying to get to 2.00 when aiming for no level change.

PCB is Rev 1.4
Here are my voltages:

This starts to go wrong in step 1.6
Step 1.1
V+=+16.06
V-=-16.21
+12=+11.74
-12=-11.71

Step 1.2
TP1 = -0.006
TP2 = -0.003
TP3 = -0.014
TP4 = 0.000
TP11 = 0.005
TP12 = -0.004

Step 1.3
TP12 goes from -0.005 to -2.292 VDC

Step 1.4
TP13 goes from -1.764 to +2.808

Step 1.5 (with input of +3.003VAC)
TP4 goes from 0.080 to 0.199VAC
TP5 goes from +0.335 to -1.785VDC
TP11 goes from 0.005 to -3.669VDC
TP12 goes from -0.005 to +3.665VDC

Step 1.6
Here is where things are not correct
TP1 = 1.954VAC
TP2 = 0.039VAC
TP3 = 1.959VAC
TP4 = 0.199VAC
DC voltage at pin 1 of U6 = 0.213VDC

Step 1.7
TP1 = 1.954VAC
TP2 = 0.487VAC
TP3 = 1.959VAC
TP4 = 0.199
TP11 = -3.669
TP12 = +1.377
TP13 = +1.905

Thanks

Gian

[JPK]

In Voltage Checks step 1.2, please report the DC voltages on  each pin of U6.
Same question in step 1.6 ?

[Gian]

Hi, thanks for your help on this. It is very much appreciated.

for step 1.2 (comp engaged)
DC voltages on U6
Pin 1:  0.000 VDC 
Pin 2:   0.000 VDC
Pin 3:   0.001 VDC
Pin 4:   -16.20 VDC
Pin 5:   0.000 VDC
Pin 6:   -0.001 VDC
Pin 7:   -0.001 VDC
Pin 8:   +16.03 VDC

for step 1.6 (comp disengaged)
DC voltages on U6
Pin 1: 0.000 VDC
Pin 2:  -0.001 VDC
Pin 3:  0.000 VDC
Pin 4:  -16.20 VDC
Pin 5:  0.000 VDC
Pin 6:  -0.001 VDC
Pin 7:  -0.001 VDC
Pin 8:  +16.05

[JPK]

Was that done in step 1.2 or 1.6 ?
I would need the measurements in both cases.

[Gian]

hi, apologies. I have now updated my previous message (above) with step 1.2 and 1.6 voltages

[JPK]

There is something wrong with the measurements:
In a previous message, you reported DC voltage at pin 1 of U6 = 0.213VDC for step 1.6 and now it is 0.000 ?

[Gian]

Hi, yes I reported +0.203VDC at pin 1, 2, 3. But I think I had incorrect front panel settings that were not 1.2 conditions.

Conditions:
Mix 100%, Ratio 10, Attack 0.1, Thresh +15, Makeup 0
For step 1.2 (no input, compressor IN), for step 1.6 (input of 3VAC, compressor OUT)
My values are the same for step 1.2 and 1.6
Pin 1: -0.001
Pin 2: -0.001
Pin 3: 0.000
Pin 4: -16.22
Pin 5: 0.000
Pin 6: -0.001
Pin 7: -0.001
Pin 8: +16.05

[JPK]

ok, wrong lead.

Step 1.6
Here is where things are not correct
TP1 = 1.954VAC
Please double check that the input voltage is correct at 3VAC

TP2 = 0.039VAC
Check the value and solder joints of trimmer T1 and R54.
Make sure all 2180A's are properly inserted into the sockets and that JMP1 is in place.

TP4 = 0.199VAC
Do you confirm this value ?

[Gian]

Hi

Confirmed 3.003VAC on edge connector terminals 8 and 10
R54 correct at 4k7 ohms
Confirmed T1 correct at 1K
Reseated all THAT2180A
Reseated JMP1
Reflowed solder on R54, U6, and T1.

New test results
TP1= 1.504VAC
TP2= 1.719VAC
TP3= 1.506VAC
TP4= 0.059VAC

What should I check to get TP2 more correct?

[JPK]

Check all your solder joints and reflow any that seem suspect.
Then retake all measurements.

[Gian]

Reflowed solder on whole board.
TP1=1.509VAC
TP2=1.719VAC
TP3=1.509VAC
TP4=56.4mVAC

[Gian]

U2, U3, U4, U5 Pin 5= -2.9VDC, Pin 7= +16.06VDC

then I did step 1.7
TP1= 1.506 VAC
TP2= 0.451 VAC
TP3= 1.511 VAC
TP4= 0.182 VAC
TP11= -3.487 VDC
TP12= +1.198 VDC
TP13= +1.724 VDC

I am happy to trace voltages around components. If you can guide me.

[JPK]

Looks better!
Only TP2 is too high in step 1.6.
Can you try to replace the 4 VCA's by the ones from the other channel, in case there is one which is not correct?

[Gian]

Yes. Better but…
I swapped them and got the same result. TP2 still too high. TP2=1.719VAC

[JPK]

Puzzling!
Do you confirm pin1 of U6 is 0VDC in step 1.6 conditions?
If true, the issue must be around U2...U4.
Check the value and solder joints of R43 to R53, sockets of U2 to U4.
Try swapping U6 with another OPA2134.

[Gian]

Pin 1 of U6 = 0VDC in step 1.6 conditions (comp out and comp in)
Values R43-53 all check correct, and solder points good
Swapped U6 with U21 and here is where some things don't seem right.
TP1=1.5VAC
TP2=8.2VAC
TP3=1.5VAC
TP4=57.8mVAC

But I checked TP2 for DC volts and it had -13 VDC

U6 (first value is comp out, second value is comp in)
Pin 1=0, 0 VDC
Pin 2=0, 0 VDC
Pin 3=0, 0 VDC
Pin 4=-16.21, -16.19 VDC
Pin 5=0, 0 VDC
Pin 6=0.431, 0.119 VDC
Pin 7=-8.21, -13.12 VDC
Pin 8=+16.04, +16.02 VDC

During my tests, when I went back to TP2=-13VDC, 0.240VAC

[JPK]

U21 must be in the circuit to get correct results.
Swap U6 with an IC from the other PCB.

[Gian]

U21 was in the circuit.
I swapped U21 and U6 around. All chips were in circuit.

[JPK]

Swap both U6 and U21 with 2 new OPA2134's.

[Gian]

Swapped U6 and U21 from the other board
So, I didn't blow up any chips, I disconnected power each time I took a new reading
Both U6 and U7 get very hot!

Step 1.6 compressor out
TP1=1.5VAC, 0VDC
TP2=0.245VAC but this value decreases as you hold probes
also checked DC volts on TP2=-12VDC
TP3=1.5VAC, 0VDC
TP4=57.8mVAC, 0VDC

U6 (gets hot and I disconnect power every 5 seconds, taking readings in each 5 seconds)
Pin1=0VDC, 0 VAC
Pin2=0VDC, 0 VAC
Pin3=0VDC, 0 VAC
Pin4=-16VDC, 0 VAC
Pin5=0VDC, 0 VAC
Pin6=0.437VDC, 0.370 VAC
Pin7=-8.18VDC, 8 VAC
Pin8=+16VDC, 0 VAC

C23-TP2 = -8VDC, 8VAC
C23-R55=-5VDC but drops quickly, 8.2VAC

U7 values(Gets very hot)
Pin1=0.228VDC, 0VAC
Pin2=3.68VDC, 0VAC
Pin3=0VDC, 0VAC
Pin4=3VDC but drops quickly, 8VAC
Pin5=-16VDC, 0VAC
Pin6=+16VDC, 0VAC
Pin7=3.675VDC, 0VAC
Pin8=-0.427VDC, 0VAC

Then I pulled out U6, U7 kept getting very hot
With U6 pulled out...
U6 values
TP1=0Vdc, 1.5Vac
TP2=1.26Vdc, 0.1Vac
TP3=0Vdc, 1.5Vac
TP4=0Vdc, 58mVac
TP11=0Vdc, 0Vac
TP12=0Vdc, 0Vac
TP13=2.8V(dc I think)

U6 (not inserted, but U7 inserted)
Pin1=0.63Vdc, 0Vac
Pin2=0.63Vdc, 54mVac
Pin3=0, 0
Pin4=-16Vdc, 0Vac
Pin5=0, 0
Pin6=1.25Vdc, 0.1Vac
Pin7=1.25Vdc, 0.1Vac
Pin8=+16VDc, 0Vac

Both U6 and U7 pulled out
U7 values
Pin1=0Vdc, 0.65Vac but keeps dropping
Pin2=0Vdc, 0.65Vac but keeps dropping
Pin3=0, 0
Pin4=-0.955Vdc, 0.1Vac
Pin5=-16Vdc, 0Vac
Pin6=+16Vdc, 0Vac
Pin7=0Vdc, 0.7Vac
Pin8=0VDc, 0.7Vac

[JPK]

Both U6 and U7 get very hot!
No need to look further, they are dead. No IC should get warm in this design.

Misplacing a THAT1646 in a OP2134 spot kills it immediately.

[Gian]

Hi, I did not misplace those components.
I was meticulous in my placement and orientation.

I will swap them for the ones on the other board and see what results I get.

[Gian]

with no input signal

with control panel (front) board pulled and with U7 pulled out and U6 pulled out
TP2=1.192VDC

Wth U7 pulled and U6 inserted
TP2=-16DVC

I have built over 16 different 500 series mic preamps and at least 8 500 series EQs and Compressors. I am very careful with placement and soldering.

What can I trace to see where this is coming from?
What are my options here?

Where can the -16VDC be coming from? I have checked all solder and washed both sides of the board.
I don't know what else to do.

[JPK]

It is now necessary to sort out the bad chips. This is what I would do:
- Check that the diode bridges BR1 and BR2 are in the correct direction.
- Remove all the IC's from the PCB (U1 to U9, U21, U22).

- Insert the first THAT1246 in U1, power, wait until you are sure it doesn't get hot. Check that the DC voltage on TP1 is close to zero  (less than 10mV).
- Do the same with the second THAT1246.

- Insert the first THAT1646 in U7, power, wait until you are sure it doesn't get hot. Check that the DC voltage on pin1 and pin8 is close to zero  (less than 20mV).
- Do the same with the second THAT1646.

- Insert the first OPÄ2134 in U6, power, wait until you are sure it doesn't get hot. Check that the DC voltage on pin1 and pin7 is close to zero (less than 5mV).
- Do the same with all the other OPA2134's.

[Gian]

Very much appreciate your help JPK.

Both Bridge diodes were in the correct orientation.
Removed all chips.

Added only one chip on the board, the THAT1246 (U1) inserted:
TP1=0VDC, TP2=0VDC, but TP2=0.9VAC

Then left THAT1246 in U1, and added THAT1646 in U7 (cool one):
TP1=0VDC, TP2=-0.232VDC (TP2=0VAC)

Inserted second THAT1646 and this one got super hot, but I pulled it after a few seconds (have put it aside).

Put good THAT1646 in U7, left THAT1246 in U1,
U7, Pin 1=0VDC, Pin 8=0VDC

Then, added each OPA2134 one at a time in U6. Same values for each OPA2134
TP1=0VDC, TP2=0VDC, Pin 1=0VDC, Pin 7=0VDC

What's the next steps?