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

Hairball Audio said:

You've got some disconnect between your TP15 and TP22.  Have a look at the schematic:

http://mnats.net/files/fetrack/fet_rack_d_doc_v1.11.pdf

This is the D but this part is the same for the A other than a few resistor values. Or you can go to MNATS.NET and download the A if that's what you're working on.

http://mnats.net/files/fetrack/fet_rack_d_doc_v1.11.pdf

Find TP15...it's right before the output pot along the top in the middle. Look how the AC travels down through the relay then to the ratio PCB, exists the ratio PCB at the bottom depending on what switch is enabled then through the attack switch to PAD 22.

See if you can trace that AC to pad 22...it's dying somewhere along that short linear path.

Probably a bad joint or lifted pad somewhere.

Mike

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landispearce said:

Mike, So i was able to find the issue, it was in the ratio board. I was able to complete the calibration without  problem. Thank you for your help!

Also, seems to be quite distorted when i test with actual audio. I understand that blue stripes are indeed distorted more so but it seems like there is something wrong. First blue stripe I've built so I could just be wrong.

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galloni21 said:

Hi,

I'm building the revA new kit and just finished the power supply. When I go to check voltage measurements I am getting the same readings as when the unit is not connected to power

1) I'm measuring -0.275V where I should be measuring -10V at the capacitor.

2) I'm measuring 0.181V where I should be measuring 30V at CR8

I tried using different power cords and different multimeters but get the same readings. I am switched to 115V and double and triple checked I followed all instructions.

The only confusing thing is I was sent two IEC connectors in the build. I used the one that already as the nut/bolt grounding assembly on it, and followed instructions.

Please help!

Thank you

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Hairball Audio said:

Weird that you got an IEC without ground on it. That was definitely a mistake.

1. Check your fuse. Make sure it's in there, not blown, and seated correctly.
2. Confirm you are measuring DC V
3. Confirm the unit is on, which means you have GR, +4, or +8 pushed in and not the "OFF" button.

Mike

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galloni21 said:

Hey Mike, it wasn't that I received an IEC without ground, but I received TWO IECs (both with ground green wire), but one already had the nut/bolt/screw assembly on it, so I used that one.

I'm using a DMM that I believe automatically reads in DC or AC V. It's radio shacks DMM.

I had the unit set to GR so it was on.

Also, I'm measuring 0.3 ohms resistance at IEC ground.

Just tried switching out the fuse since the pack came with two (the one I had in didn't look blown), and still not getting good readings.

Any other ideas?

Thank you!

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galloni21 said:

P.S. the DMM was correctly set to DC voltage measurement.

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Hairball Audio said:

You need to consider how the voltage moves through the circuit and figure out where it's stopping.

AC enters at the IEC and travel to and back from the OFF switch where it enters the voltage select switch and exists to the power transformer primary. Then the AC leaves the transformer secondary to the PCB where it's rectified to DC. Let's work our way back.

With the unit ON. Check for AC V between chassis ground and each orange wire coming off the secondary into the PCB.

Please keep in mind for your unit to be properly grounded, you need to have all 3 L brackets screwed in place from the PCB to chassis.

When measuring these voltages use caution.

Mike

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galloni21 said:

I'm only getting 0.9 V at both of the orange wires measured at the secondary transformer where they leave to go to the PCB.

The PCB is screwed in. I also tried switching out the IEC with the second IEC you sent.

Could it be a bad transformer?

Thanks

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Hairball Audio said:

It's always possible it's the transformer. However, that is the last part I would suspect. They are tested before they ship and we haven't had a bad new version yet. Odds are you have a bad solder joint somewhere or bad measurement set up. It's funny how people always assume it a transformer issue (power and audio) and it pretty much never is. They are very simple parts that don't really break.

We can figure out the issue, we just need to walk through it and you need to be careful because at some point I make ask you to test areas that carry mains AC voltage.

FOR THIS PART UNPLUG THE UNIT FROM THE WALL

Again remove the power cord completely, no power. We're just checking continuity.

1. Make sure the unit is switched to GR mode on the meter switch. We just need the switch in the position but NO POWER.
2. Disconnect the 7 pin transformer connector from the voltage selector switch.
3. Pull back the N (white) IEC upper connector so you can probe N tab but keep the connector connected to the tab. What is the DC resistance (Ω) between that N IEC tab and the far left pin on the 7 pin connector (the one closest to the main PCB).
0 ohms

3. Pull back the L (Black) IEC lower connector so you can probe L tab but keep the connector connected to the tab. What is the DC resistance (Ω) between that L IEC tab and the far right pin on the 7 pin connector (closest to the enclosure side).
0 ohms

4. Plug the 7 pin connector back in (still no power to the unit). There are 6 soldered tabs on the voltage selector switch sticking out. Measure the DC resistance (Ω) between the two on the far left.  By the words "High" and "Do".

I don't get a measurement... I tried several times and the 7 pin connector and other two connectors on the IEC are connected


5. Measure the DC resistance (Ω) between the yellow secondary wire and each orange.

11.2 ohms (top orange on pcb and yellow middle)
11.6 ohms (bottom orange on pcb and yellow middle)

Report all that back. Again, at no point should you have your unit plugged into the wall.  You need to have it in GR metering however.

Mike

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Hairball Audio said:

Step 4 is your problem.

Try this, remove the power transformer from the build. See if you can get your DMM probes to the metal contacts in the 7 pin header. This is easier to do from the side where the wire goes into the header. See if you can get a DMM Ω reading between white and black and then red and blue.

Mike

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galloni21 said:

I can't get my DMM probe into the metal contacts, the opening is much too small for my probe.

Are there other measurements I can do to check where the failure point is?

If it's easier to walk thru other troubleshooting by phone I'm available at 6087129753

Thanks again Mike.

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Hairball Audio said:

Actually just remove your voltage selector PCB from the enclosure and your power transformer.

Then plug just the power transformer primary into the 7 pin connector. With the 7 pin connector attached to voltage select PCB, you can now measure the Ω between blk/wht and blu/red by using the 7 pin connector solder pads that correspond with those wires.

Mesure those Ω with the switch in 115 and 230.

Mike

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galloni21 said:

with the switch in 115V...

blk/wht resistance: not getting a reading
blu/red resistance: not getting a reading

with the switch in 230V...

blk/wht resistance: 97.6 ohms
blu/red resistance: 116.2 ohms

is the voltage selector switch bad in 115V (my region)?

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csavetman said:

Hey Mike,

Just wanted to check something with you.
The build guide says on V 1.11 PCB of Rev D FET rack, that input transformer should be soldered slightly off the PCB because of the soldering pads on the top.

There's no need to do that on the newest version 1.12 PCB, right?

Carlos

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csavetman said:

Hey Mike,

One more thing. On the Rev D PCB, there's a spot for a diode, CR10 next to the stereo link relay. I don't see CR10 on the BOM however. Does that get left empty?

Carlos

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Hairball Audio said:

Possible, but I'd first suspect a solder issue.

Your transformer seems fine. The 115V switching is problematic. I would start by reflowing the solder joints on the voltage switch PCB including those on the 7 pin connector. If you can see the traces on the PCB follow them to the next pad and check for continuity.

Make sure the switch is full in place in the 115V position and test again after examining all joints for continuity.

If it's still bad after that, we'll send you a new switch/PCB.

Mike

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