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

[Echo North]

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?

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.

 

[jgremlin]

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.

 

[Echo North]

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.

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

 

[jgremlin]

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

 

[Echo North]

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

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

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

Mike

 

[jgremlin]

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...

 

[Echo North]

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...

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

 

[jgremlin]

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.

 

[Echo North]

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.

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

 

[jgremlin]

70VAC on each against ground/chassis.

 

[Echo North]

70VAC on each against ground/chassis.

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?

 

[jgremlin]

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.

 

[Echo North]

No continuity between yellow wire pad and chassis.

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

 

[jgremlin]

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

 

[Echo North]

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

How are your supply voltages now? (DC)

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

 

[jgremlin]

Back in business now, 30.4 and -9.7

 

[Echo North]

Back in business now, 30.4 and -9.7

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

 

[jgremlin]

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

Between 0 and -3.09

 

[Echo North]

Between 0 and -3.09

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 +

 

[jgremlin]

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