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

jgremlin said:

Ok a few dumb questions.
Is this still with a 1k test tone?
Rotate which pot? R59?
GR is definitely off. How do I confirm tp22 is shorted to ground? Ohms setting?

Click to expand...

Yes, you should see less than 1Ω between pad 22 and the enclosure.

Yes R59. No test tone needed.

Then when you do the recheck, with test tone.

Also make sure the 100Ω trim pot it in R86. The others are 2K.

Ok with the unit off, ohms between TP22 and ground are nill. Appears to be no connection there.

No joy setting R59 though. With unit on, no test tone, I get anywhere between +20 mVDC and -100mVDC through the range of travel on the pot.

jgremlin said:

Ok with the unit off, ohms between TP22 and ground are nill. Appears to be no connection there.

No joy setting R59 though. With unit on, no test tone, I get anywhere between +20 mVDC and -100mVDC through the range of travel on the pot.

Click to expand...

What is your DC V on each side of R35 and R60 (chassis as common)?

R35: about +4mVDC to the rear, +14mVDC to the front
R60: about +13mVDC to the left, +24mVDC to the right

jgremlin said:

R35: about +4mVDC to the rear, +14mVDC to the front
R60: about +13mVDC to the left, +24mVDC to the right

Click to expand...

I'm not sure what you're measuring. Nothing makes sense.

Do the +30VDC an -10VDC power supply voltage check out?

Mike

Oh boy, as a matter of fact they do not check out.
CR8 is jumps around just under +1VDC
CR9 jumps around just under -1VDC

Perhaps we've hit paydirt...

jgremlin said:

Oh boy, as a matter of fact they do not check out.
CR8 is jumps around just under +1VDC
CR9 jumps around just under -1VDC

Perhaps we've hit paydirt...

Click to expand...

1. Did they originally checkout after you built/tested the power supply?
2. Do you have your voltage selector switch set to you local mains voltage?
3. What is your AC V on the orange wires where the terminate to the PCB (careful).
4. You have it ON right? Meaning the GR switch is pushed in unlatching the OFF button?

Mike

Yeah, power supply definitely checked out right on the money when I built it. Voltage selector is set correctly. I'm getting 70 VAC on both orange wire pads on the main PCB.

jgremlin said:

Yeah, power supply definitely checked out right on the money when I built it. Voltage selector is set correctly. I'm getting 70 VAC on both orange wire pads on the main PCB.

Click to expand...

70 VAC on each separately against ground/chassis?
or
70VAC measuring against each other? One probe on one orange and one on the other orange?

Mike

70VAC on each against ground/chassis.

jgremlin said:

70VAC on each against ground/chassis.

Click to expand...

That's not right.

Turn the unit off. 

Set your meter to measure resistance.

1. What's the Ω between that power transformer yellow wire (where it meets the PCB) and chassis?
2. What's the Ω between that power transformer yellow wire and each of the oranges?
3. What's the Ω between the oranges?

No continuity between yellow wire pad and chassis.
10.9 ohm between yellow wire and rear orange.
11.4 ohm between yellow wire and front orange.
22 ohm between the oranges.

jgremlin said:

No continuity between yellow wire pad and chassis.

Click to expand...

That's your problem.

Do you have all 3 metal L brackets installed that attach the PCB to the enclosure?

All three need to be screwed into the PCB and chassis tightly.

Mike

Checked all three. All are tight. Then I rechecked yellow to chassis and I get 0 ohms now.

jgremlin said:

Checked all three. All are tight. Then I rechecked yellow to chassis and I get 0 ohms now.

Click to expand...

How are your supply voltages now? (DC)

What are the voltages of the oranges to chassis? (AC)

Back in business now, 30.4 and -9.7

jgremlin said:

Back in business now, 30.4 and -9.7

Click to expand...

Now what do you get at pad 18 when you turn R59?

Hairball Audio said:

Now what do you get at pad 18 when you turn R59?

Click to expand...

Between 0 and -3.09

jgremlin said:

Between 0 and -3.09

Click to expand...

Cool. Set it to -3.09 and do this again:

Set your unit to:
Input: 12 O’Clock
Output: 12 O’Clock
Attack: GR OFF
Release: Full CW
Ratio: 20:1
Meter: GR
Signal: Sine 1kHz @ 0dBu

With your DMM measure your AC at the following test points using the chassis as you reference (black probe).

-Input XLR +
-TP1
-TP15
-TP17
-Output Transformer BRN
-Output XLR +

-Input XLR +                                            .430 VAC
-TP1                                                              .123
-TP15                                                          2.46
-TP17                                                          .382
-Output Transformer BRN            7.13
-Output XLR +                                      5.44