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

[Echo North]

Nope, I got no low end frequencies, looks like an hpf filter on.

Same test still applies.

 

[Echo North]

Mike - any ideas?

Looks like an older build.

Have you confirmed continuity in your cassis and to the IEC ground.

 

[RobertBraz]

I believe I have isolated my issue to the input section. I am only reading 0.07VAC at TP1. I have triple-checked my solder joints on the input transformer, input pot, and Q1. Where should I look next?

It is probably worth noting that I'm not getting any voltage at any of the other test points in that section of the troubleshoot guide (TP15, TP17, output transformer BRN).

 

[Echo North]

It is probably worth noting that I'm not getting any voltage at any of the other test points in that section of the troubleshoot guide (TP15, TP17, output transformer BRN).

0.07 VAC is ok.

Check your transistor DC voltages in the preamp section. There is a doc in the troubleshooting guide.

 

[RobertBraz]

0.07 VAC is ok.

Check your transistor DC voltages in the preamp section. There is a doc in the troubleshooting guide.

Q2, Q3, and Q14 all measure the correct amount of DC voltage across the B, C, and E pins. Q1 does not have any values displayed in the troubleshooting schematic but measures G: -2.41DC, S: 0.00DC, D: 0.00DC.

 

[Echo North]

Q2, Q3, and Q14 all measure the correct amount of DC voltage across the B, C, and E pins. Q1 does not have any values displayed in the troubleshooting schematic but measures G: -2.41DC, S: 0.00DC, D: 0.00DC.

-What is your AC V at the base of each of those transistors (Q2/Q3/Q14) under the testing (1K/0db/GR off/controls midway)?
-What is your AC V at the Drain of Q1 under the testing (1K/0db/GR off/controls midway)?

 

[kingofspain2]

Mike - any ideas?

swapped everything except the input attenuation transformer and power transformer. Noise did not migrate, new 60hz noise can now be heard when output in turned down, 120hz is still present with output turned up.

 

[RobertBraz]

-What is your AC V at the base of each of those transistors (Q2/Q3/Q14) under the testing (1K/0db/GR off/controls midway)?
-What is your AC V at the Drain of Q1 under the testing (1K/0db/GR off/controls midway)?

Q2: 0.022 VAC
Q3: 0.000 VAC
Q14: 0.000 VAC

Q1: 0.067 VAC

 

[frenkonio]

New Rev. A built today. Issues:

- Vu meter doesn't go on the right when in GR mode (completely not moving in GR) but works in output mode
- Output knob is scratching a lot and has some crazy spikes in volume when moving (reflected also on the vu meter when in output mode)
- There's hum in the signal

I'm having very low voltages at TP1, TP15 and TP17. Are they consequential?  From the troubleshooting guide I get this explanations for low voltages on TP1: Tpad, Input transformer, Q1.
The Tpad seems to work, I can barely hear the 1kHz input from the signal generator and it changes when going from ccw to cw. How can I understand if the issue is on the input trafo or Q1? I don't see any voltages to check for Q1 on the troubleshooting guide.
Hope someone could help me. Thanks.

 

[Echo North]

Q2: 0.022 VAC
Q3: 0.000 VAC
Q14: 0.000 VAC

Q1: 0.067 VAC

What is your DC V at the Gate of Q1?

 

[RobertBraz]

What is your DC V at the Gate of Q1?

-2.41 DC V

 

[Echo North]

-2.41 DC V

Safely remove Q1...put it in a static free bag or somewhere safe and see if that get's you signal to Q15.

Mike

 

[RobertBraz]

Safely remove Q1...put it in a static free bag or somewhere safe and see if that get's you signal to Q15.

Mike

Assuming you mean TP15, still 0.00 VAC there with nothing in Q1.

 

[Echo North]

Assuming you mean TP15, still 0.00 VAC there with nothing in Q1.

ya sorry.

Keep Q1 out for now.

Which Rev PCB do you have again?


Mike

 

[RobertBraz]

ya sorry.

Keep Q1 out for now.

Which Rev PCB do you have again?


Mike

Rev D. Bought it a few months ago so it is the newest version.

 

[Echo North]

Rev D. Bought it a few months ago so it is the newest version.

Tripple check all of these values and confirm continuity from pad to pad.  Something is up in here.  Make sure that trimmer is the correct value too. Make sure C2 (and anything else) isn't shorted across it's pads.

 

[RobertBraz]

Tripple check all of these values and confirm continuity from pad to pad.  Something is up in here.  Make sure that trimmer is the correct value too. Make sure C2 (and anything else) isn't shorted across it's pads.

Seeing a couple of weird things. R4 is reading as 12.4 ohms instead of 270 ohms. Color code checks out so could it just be bad? And I have no continuity from R5 to R8 with C1 metering at 0.4 ohms.

 

[Echo North]

Seeing a couple of weird things. R4 is reading as 12.4 ohms instead of 270 ohms. Color code checks out so could it just be bad? And I have no continuity from R5 to R8 with C1 metering at 0.4 ohms.

You can't measure resistors in circuit without doing the parallel math.  Trust the codes or lift a leg and measure.

Reflow joints in that section. You sad all of your transistor DC voltages checkout?  Do you have AC at the Drain of where Q1 would be with test signal?

Mike

 

[RobertBraz]

You can't measure resistors in circuit without doing the parallel math.  Trust the codes or lift a leg and measure.

Reflow joints in that section. You sad all of your transistor DC voltages checkout?  Do you have AC at the Drain of where Q1 would be with test signal?

Mike

Yes, transistor DC voltages check out. AC at drain of Q1 is 0.058V with Q1 removed.

 

[Echo North]

Yes, transistor DC voltages check out. AC at drain of Q1 is 0.058V with Q1 removed.

Weird...I'll need to poke around a working unit tomorrow and get back to you.

Mike