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I'm at the Control Voltage adjustment. With 2.45 VAC measured through the CP554, once I depress the Bypass button I can only get the VAC up to .35 before the CV trimmer is maxed (the first time I ran at the setup it maxed at .41 VAC.) I'm thinking the U6 IC might be suspect, so my question is does it matter if I go with an TI version of the OPA2134PA or should I try and run down a BB?
And, is there somewhere else in the circuit I should start?
Thanks!

[JPK]

It doesn't make a difference between TI and BB.
In the same configuration, what DV voltage do you get on the CV test pin (3V) and on the anode of D14 (1.05V) ?
If you don't get similar voltages, you must check the value, direction and solder joints of R83, R85, R86, R87, D12...D15, U6, trimmer TR5.
In order to check U6, you can try with U5 in the U6 socket (in this test configuration U5 is not used).

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Thanks for the reply!
The DV at the 3V test pin is 3.00V and the anode of D14 is .94V.
I checked all the resistors, diodes, TR5 and the socket for U6 and all the joints are good (re-flowed a few just for good measure) and the orientation and values are all correct as well.
I tried swapping U6 and U5. The reading at the CV test pin is now .28VAC; so not that I suppose. The reading at the CV pin does drift down while the CP554 is powered- after another 30 minutes or so, the reading is .25VAC.
Any other thoughts?
Thanks!
Jake.

[JPK]

The DV at the 3V test pin is 3.00V and the anode of D14 is .94V.
How many VDC on the CV test pin (near the CV trimmer)?

The reading at the CV test pin is now .28VAC
The voltage measurements on the CV test pin are DC only.

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Man,
I was fixating on my misread of the question and then gave a wrong answer anyway.
Sorry about that.

The DV at the CV test pin (not the 3V test pin) is also 3.00V.


The reading at the CV test pin is now .28VAC
This whole piece in my last reply was actually in reference to the readings AC from the XLR output not the CV test pin- just tripped myself up there

Thanks for your patience.

[JPK]

Can you check that the trimmer TR5 is OK by measuring the resistor value between the 2 side pins? it should go from 0 to 4.5k depending on the screw rotation.

In the same configuration as "Control voltage adjust",
what is the minimum DC voltage (TR5 fully CCW) you get on U1 pin1?

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Can you check that the trimmer TR5 is OK by measuring the resistor value between the 2 side pins? it should go from 0 to 4.5k depending on the screw rotation.
I measure .6 ohms to 4.9k on the trimmer TR5 (Right PCB out of unit.)

In the same configuration as "Control voltage adjust",
what is the minimum DC voltage (TR5 fully CCW) you get on U1 pin1?
With a tricky probe extension and all PCBs installed, pin 1 of U1 reads .94V (same as anode of D14.)

[JPK]

OK, the attenuator control voltage seems to work.
Do you get the same output AC level as when bypassed when you remove the jumper JMP1 (it cancels the attenuation)?
Were you able to set the 0dB gain and check the max gain in step 7 of the setup guide?
There may be an issue around the diode bridge in U1. Check that it is well inserted, and the socket well soldered.

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Do you get the same output AC level as when bypassed when you remove the jumper JMP1 (it cancels the attenuation)?
In the Control Voltage Adjust section for setup step 9, with the bypass button up I set the input VAC to 2.45 then press in the bypass button and the VAC drops to .11VAC (it is even lower than before now.) If I remove the jumper on JMP1, the VAC goes to .22VAC with bypass button still in and back to 2.45VAC with the bypass button out.

Were you able to set the 0dB gain and check the max gain in step 7 of the setup guide?
Yes, everything before the Control Voltage Adjust section of step 9 went fine (though the Max Voltage was a hair over 13V.)

Looking at the U1 socket, the joints are all good and the IC is fully inserted.
If I'm going to need another THAT300, would this be the one?
https://www.mouser.com/ProductDetail/THAT/300P14-U?qs=9Udfh7QmL4vaHxAiVJNK9A%3D%3D

Thanks!

[JPK]

If I remove the jumper on JMP1, the VAC goes to .22VAC with bypass button still in
And, in this situation, does the control voltage on the CV pin (and on D14 anode) go to 0VDC?

If I'm going to need another THAT300, would this be the one?
Yes this is it.

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If I remove the jumper on JMP1, the VAC goes to .22VAC with bypass button still in

And, in this situation, does the control voltage on the CV pin (and on D14 anode) go to 0VDC?

Yes, the CV pin and the D14 anode both read 0V with the JMP1 removed.

[JPK]

The next step would be to try a new THAT300.

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I figured. I ordered one already, so it should be here in a few days.
Thanks!!

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So- got the replacement THAT300, but after restarting the calibration process I cant get past step 5. The difference between fully clockwise to cc on TR2 is about 6mV between TP2 & 3. I looked at the schematic and traced things a bit, but I am not sure what I'm supposed to find probing resistors voltage-wise. I will say that after having the thing powered for over an hour, Q7 never even got slightly warm.
I just don't really know what I could have disturbed while gently removing and re-installing the boards a few times- I made it all the way to step 9c before I replaced the THAT300.
Now it's kinda broken out the gate.
I imagine it's just pull it apart and make sure again (I've done that 3 times today) that nothing is miss-soldered/in the wrong place/obviously busted/etc.
Just figured I'd ask if you have any ideas about what I might have done/gotten even less luckier with.
Thanks-
Jake.

[JPK]

I imagine it's just pull it apart and make sure again (I've done that 3 times today) that nothing is miss-soldered/in the wrong place/obviously busted/etc.
Correct!

Also check that the connections to the output transformer are good.

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Going through everything again (and again), I noticed that C25 is distended. I'll see about getting a replacement tomorrow, but as the polarity is correct is there anything in line with that cap that could cause this that I should check? Or is it likely that it's just a bad part?
Thanks!

[JPK]

C25 destruction could be the consequence of a short circuit in the output stage.
After replacing, unplug the output transformer and check immediately that the voltage on TP3 is negative, around -10VDC.
If not, D20 might be dead also.

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Replaced C25, powered the unit without the output transformer and the reading at TP3 starts at +4VDC, goes up a bit then starts to drop slowish. I assumed that since you said it should immediately be around -10V I shouldn't wait to see where it lands (hoping not to blow anything else up), so I ordered a replacement for D20.

[JPK]

You can check the forward voltage drop on D20 with your DMM in the diode mode. It will tell you if the diode is damaged. If it is, then replacing it will probably cause the destruction of the new diode if you do not eliminate the short circuit.

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Got the D20 replacement for good measure replaced U3, everything is copacetic, calibrated and working now. Not sure what shorted, but it's not in the circuit anymore.
The only problem now is that SW2 ate it. Do you have a part number for the switch and button that I could find on Mouser?
Thanks for everything!
Jake.

[JPK]

Congratulations !  

SW2 = PVA2EEH11.7NV2
Available at Mouser.