[BUILD] New FET/RACK Official Help Thread - Please read first post!

[Echo North]

Hi,

We need to get you calibrated, so let's start by looking at why your qbias in't working right.

With the unit powered on, what is your DC V at Pad 18 as you turn the Qbias?

Mike

 

[Manswikenmo]

Hi,

We need to get you calibrated, so let's start by looking at why your qbias in't working right.

With the unit powered on, what is your DC V at Pad 18 as you turn the Qbias?

Mike

I get 0V with qbias ccw and cw.

Måns

 

[Echo North]

I get 0V with qbias ccw and cw.

Måns

Is your -10VDC power supply point testing ok?

 

[Manswikenmo]

Is your -10VDC power supply point testing ok?

Yes. The powersuply is working properly ad measures correctly.

 

[Echo North]

Yes. The powersuply is working properly ad measures correctly.

What's your DC V on either side of R83 and R60?

Mike

 

[nsemanchik]

Hello, this is my first post on this forum! I recently completed a Rev A kit, it powers on and passes audio. When I began to calibrate it I noticed that there was a very low output and high noise floor. I double checked all of my resistors, caps and transistors and they all are all in the correct positions. The goal of this build was to learn more about electronics so I would really like to be able to resolve this issue on my own before I send it out. Any thoughts or input?

Thank you!

 

[Foots]

Finished my first DIY build on the 1176 Rev A. Powered it on, no smoke. Began the calibration procedure and got 1khz 0 dBu signal to input (verified by voltage and hz on DMM). However, when I went to measure the output, I couldn't even get 1 VAC, even with the output maxed. I am getting audible signal through the compressor and out of my system.

Power supply is good with 30.4 VDC at CR8 and -9.7VDC at CR9.

Checked voltage at base and emitters of transistors and received:

Q3:    -.590
Q5:  -.574
Q6:  -.509
Q7:  -.576
Q8:  -.604
Q9:  -.602
Q10:  -.610
Q12:  -.611
Q13:  -.578

As the expect result is -.7, are these values within tolerance? I am going to check the rest of the voltages provided by MNATS and check all my components for connectivity,  and solder joints. I double checked the polarity and value of all components during assembly, but will check that as well.

Thanks so much for your help!!
k

 

[Dacey]

FET/RACK calibration stage.
a) I can only get 0.677VAC on DMM at input, should be 0.755VAC. With the Input signal disconnected I get 1.5VAC.??
b)Metering the  Gain Reduction on any Ratio setting results in a max vu meter reading. Input and Output dials set to infinity is this normal? 
Please can to provide clues on were the fault(s) might be.
Thanks

 

[Echo North]

Hello, this is my first post on this forum! I recently completed a Rev A kit, it powers on and passes audio. When I began to calibrate it I noticed that there was a very low output and high noise floor. I double checked all of my resistors, caps and transistors and they all are all in the correct positions. The goal of this build was to learn more about electronics so I would really like to be able to resolve this issue on my own before I send it out. Any thoughts or input?

Thank you!

Start with the unit in GR OFF mode. Input a 0dBu 1kHz signal as described in the calibration guide. Using chassis GRN as your reference, what is the AC V:

TP1, TP15, TP17, Output Brown

Mike

 

[Echo North]

Finished my first DIY build on the 1176 Rev A. Powered it on, no smoke. Began the calibration procedure and got 1khz 0 dBu signal to input (verified by voltage and hz on DMM). However, when I went to measure the output, I couldn't even get 1 VAC, even with the output maxed. I am getting audible signal through the compressor and out of my system.

Power supply is good with 30.4 VDC at CR8 and -9.7VDC at CR9.

Checked voltage at base and emitters of transistors and received:

Q3:    -.590
Q5:  -.574
Q6:  -.509
Q7:  -.576
Q8:  -.604
Q9:  -.602
Q10:  -.610
Q12:  -.611
Q13:  -.578

As the expect result is -.7, are these values within tolerance? I am going to check the rest of the voltages provided by MNATS and check all my components for connectivity,  and solder joints. I double checked the polarity and value of all components during assembly, but will check that as well.

Thanks so much for your help!!
k

Same answer as above. Check those test points.

 

[Echo North]

Set-up stage.  I can only get 0.677VAC on DMM at input, should be 0.755VAC, Input signal disconnected 1.5VAC.
Metering the  Gain Reduction on any Ratio setting results in a max uv meter reading. Input and Output dials set to infinity. 
Please can to provide clues on were the fault might be.
Thanks

What is your signal source?  The input of the FET/RACK is loading it, that's why you get the drop.

If it's not calibrated, ignore the meter. With this unit, the calibration is no fine tune adjustment, it's the difference between it working, and not working at all.

Mike

 

[lackstudios]

Hi there, I hope I'm posting in the right place

I'm pumped to be in the DIY world, its been awesome...until now :-/ haha

I'm just finishing the power supply on the 1176 rev A and after the first test, I'm getting these  results: CR8= 2.13v  CR9= -0.54v
I turned the power off and got the same results at CR8 & CR9
I'm getting .1 ohms on the IEC ground tab.

I also probed the hot wires following the 120v signal all the way to the transformer, then after the transformer i'm getting nothing...not even sure if thats a proper way to troubleshoot a PCB just an oldschool way of thinking...any help getting me back in the studio doing what I love?

 

[Echo North]

Hi there, I hope I'm posting in the right place

I'm pumped to be in the DIY world, its been awesome...until now :-/ haha

I'm just finishing the power supply on the 1176 rev A and after the first test, I'm getting these  results: CR8= 2.13v  CR9= -0.54v
I turned the power off and got the same results at CR8 & CR9
I'm getting .1 ohms on the IEC ground tab.

I also probed the hot wires following the 120v signal all the way to the transformer, then after the transformer i'm getting nothing...not even sure if thats a proper way to troubleshoot a PCB just an oldschool way of thinking...any help getting me back in the studio doing what I love?

Unplug the power transformer at both ends.  No need for power.  If you can get your probes into the contacts, measure the DC resistance (Ω) between WHT-BLK and RED-BRN on the primary, then ORG-ORG on the secondary.

Mike

 

[Foots]

Same answer as above. Check those test points.

Mike, not sure what you mean by GR OFF mode. I have the unit on with the GR button released (also  +8 and +4). Voltages are:

TP1 -      .1 VDC
TP15      .2 VDC
TP17      0.0 VDC (and starts to pick up radio signals)
Out Brown    27.7 VDC

Voltages are the same with GR button in.
Thanks Mike!!

 

[Echo North]

Mike, not sure what you mean by GR OFF mode. I have the unit on with the GR button released (also  +8 and +4). Voltages are:

TP1 -      .1 VDC
TP15      .2 VDC
TP17      0.0 VDC (and starts to pick up radio signals)
Out Brown    27.7 VDC

Voltages are the same with GR button in.
Thanks Mike!!

Attack switched off = GR off.

Measure AC not DC volts.

 

[Diamondj421]

Hey Mike!
It's funny. As I purchased my second Rev D I pictured you being like "Not this guy again!" Haha. So I'm into the ever so treacherous calibration mode and I can't get R71 to zero. I checked all resistors last night and everything seems to be in its proper place. Am about to begin checking all capacitors but wanted to seek your wizardry for guidance. Also, where can I find the expected values for each test point. Thanks!

 

[Echo North]

Hey Mike!
It's funny. As I purchased my second Rev D I pictured you being like "Not this guy again!" Haha. So I'm into the ever so treacherous calibration mode and I can't get R71 to zero. I checked all resistors last night and everything seems to be in its proper place. Am about to begin checking all capacitors but wanted to seek your wizardry for guidance. Also, where can I find the expected values for each test point. Thanks!

That's the 0 VDC adjustment?  Did you have matched 2N3707/2N37078 transistors in Q11/13?

Mike

 

[lackstudios]

Unplug the power transformer at both ends.  No need for power.  If you can get your probes into the contacts, measure the DC resistance (Ω) between WHT-BLK and RED-BRN on the primary, then ORG-ORG on the secondary.

Mike

Ok, so I'm getting OLΩ between WHT-BLK and OLΩ between RED-(BLUE) I didn't see a brown
then I got 22.5Ω between ORG-ORG

 

[Echo North]

Ok, so I'm getting OLΩ between WHT-BLK and OLΩ between RED-(BLUE) I didn't see a brown

That ain't right.  Should be roughly 100Ω for each.

Sure you're getting to the contacts?  You may have to send that power transformer in.  Email us.

Mike

 

[Diamondj421]

That's the 0 VDC adjustment?  Did you have matched 2N3707/2N37078 transistors in Q11/13?

Mike

I'm using the Mouser BOM so I believe Q2-Q4 and Q14 were 2N3391A, Q5, Q7-Q10 and Q12-Q13 are 2N3708, Q6 is 2N3053 and Q11 is 2N5457.