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

SunkenCity said:

Yeah that would be great thank you.

I built another meter switch assembly with the parts you sent and it worked fine. I looked over the old one pretty thoroughly couldn't find a problem with it and assumed in was a short inside of the off button.

on the unit that came with a good switch:

I've been over every component in the line amp section to make sure it's the correct valve, color code, orientation. 

I checked continuity from component to component marking off the schem as I went along which eliminates a bad solder joint as the problem.

output transformer is wired correctly.

with the resistor legs lifted it removes those sections for the power, right?

does that mean that other sections wouldn't be effecting the line amp or power supply?

that leaves Q6, the output transformer, and the caps to check right?

Click to expand...

Send us an email about Q6.

What about output transformers?

SunkenCity said:

What about output transformers?

Click to expand...

I can't remember a bad output transformer in 10 years.  Maybe 1 or 2.  Not impossible, but not the kind of thing we ship out without hard evidence and they are hard to test because they are part of the feedback and power network. You'd be better off spending $7 to ship the PCB's to us and if it's a transformer issue you'd be getting a free repair.

If you unsolder BRN, GRY, WHT/BLK, and WHT/RED from the PCB, I can give you the DC resistance for each winding, then you would check for shorts between windings.  That would confirm basic functionality.  Let me know.

Failed Q6 would be a fairly common issue. One of the most common. That transistor does all the heavy lifting.

Mike

After I desolder them where should the test leads be connected for the dc resistance measurement for each winding?

to the chassis?

from winding to winding the only reading I get are:

white/black to white/red= 1.3m

brown to grey = 4.590k

SunkenCity said:

After I desolder them where should the test leads be connected for the dc resistance measurement for each winding?

to the chassis?

from winding to winding the only reading I get are:

white/black to white/red= 1.3m

brown to grey = 4.590k

Click to expand...

No it’s more complicated than that.  I need to take some measurements and explain some stuff.  I’m out of town today visiting family.  I’ll post the info/measurements when I get back tomorrow.  Hopefully you’ll get those Q6’s tomorrow too.

Mike

Alllllllright. Here we go.

First thing, I was thinking in bed about this last night (I obsess over these issues) and your issue is you're getting too much voltage drop across R80 (75Ω/3W). I assumed is was because too much current is being drawn through it (still likely). However, there are two other explanations

1. R80 is the wrong value (ohms law!). So start by testing that. It's not in parallel with anything so you can test it on the PCB. Should be 75Ω +/- the tolerance which is 1 or 5%, I don't recall.

2. Another possibility would be an issue with your CR8 zener diode.  They are VERY sensitive devices. Having two crap out would be weird, but not insanely weird. Make sure it's properly grounded. With the power OFF, measure the base of it where the part number is printed, against your chassis.  You should get <1Ω.  If that's good, maybe they are crapped out, we'll cross that bridge later. You must have all 3 rear l-brackets secure and in place for the power system to function.


Output transformer:

Look at this drawing:
http://library.hairballaudio.com/datasheets/5002.pdf

Ignore the 600Ω stuff. That is IMPEDANCE, you're going to measure DC Resistance.

A transformer is a series of windings around a magnetic core.  I winding is just a long piece of wire. It's DC resistance is directly related to how long that wire is.  Brown/Black is one winding, WHTRED/WHTBLK is another winding and so on.  When you measure the windings, for example BRN/BLK put one prob on Brown and one prob on Black measuring Ω. Here are the DC resistances you should see for each winding. DISCLAIMER: I've told you which leads to lift to avoid the PCB giving you bad readings, I might be wrong....I'm just looking at the schematic, if you get an odd reading desolder all leads and test again.

Black/Brown: 47Ω
WHTRED/WHTBLK: 1.3Ω
Blue/Red: 46.3 (Yellow/Orange need to be connected on the PCB or tied together off PCB)
Grey/Violet: 249.2Ω

Obviously yours may be a little different but should be within 5%. What you don't want to see is an OL reading for a winding. That would indicate a winding wire is broken.

Now measure to see if a winding is shorted to another. So like measure Black vs Grey should give you an OL reading, they should not be touching and so on.

Educated guess would be weird Q6, weird CR8, or build mistake.  HIGHLY doubt it's the output tx, but anything is possible.

Good luck, that's about all I have for you unless some new info comes to light.

Mike

R80 is reading 74.5 ohms

I started testing CR8 and got a really funky reading  on the anode's tip of thread to chassis Fluctuating all around. I took it apart and there was a weird bit of corrosion under the washer. Like dissimilar metals corroding. put the meter across the washer and got a lot of resistance for a washer.

cleaned the pcb surface with some alcohol and put it black together minus the flat washer but left the lock washer on.  It measured 1 ohm

plugged it in and got 30vdc at the cathode, soldered back in the transformer leads(with it unplugged) and it went back down to 20vdc.

Idk know if the that means anything like the transformer is dragging it down or its just reconnecting the circuit but I figured I try and see.

The diode did smoke a bit when I finished the power supply on both units but I figured it was normal because the voltages were right.

the dc resistance readings were all spec more or less

there is continuity between the windings.

It looks like Grey/violet is shorted to black/brown and blue/red.

the resistance settles around 18 but  grey/violet to red/blue is 35.19

SunkenCity said:

I started testing CR8 and got a really funky reading  on the anode's tip of thread to chassis Fluctuating all around. I took it apart and there was a weird bit of corrosion under the washer. Like dissimilar metals corroding. put the meter across the washer and got a lot of resistance for a washer.

Click to expand...

Never seen that before.  Were you scrubbing off flux and some got in there.  You're not soldering that to the PCB are you?

SunkenCity said:

cleaned the pcb surface with some alcohol and put it black together minus the flat washer but left the lock washer on.  It measured 1 ohm

Click to expand...

Well that's good.

SunkenCity said:

plugged it in and got 30vdc at the cathode, soldered back in the transformer leads(with it unplugged) and it went back down to 20vdc.

Idk know if the that means anything like the transformer is dragging it down or its just reconnecting the circuit but I figured I try and see.

Click to expand...

Q6 is connected through to the rail supply through the transformer, so still could be Q6. Have you tried the new Q6's?

SunkenCity said:

The diode did smoke a bit when I finished the power supply on both units but I figured it was normal because the voltages were right.
and see.

Click to expand...

Smoked or smelled like smoke? This should not be soldered in place or tightened to the PCB to an extreme.

SunkenCity said:

the dc resistance readings were all spec more or less

there is continuity between the windings.

It looks like Grey/violet is shorted to black/brown and blue/red.

the resistance settles around 18 but  grey/violet to red/blue is 35.19

Click to expand...

Did you complete remove all wires from the PCB and try again? There should not be continuity there unless they are connected to the PCB.

Mike

Ya you've got some weird shorting in your output if those readings are correct.  I've never seen anything like that in several thousands of these, and keep in mind they are custom made for us and every unit is tested before they ship them.

Makes me worry that there is an issue somewhere else pulling too much current through the output transformer and damaging it.

If a new Q6 doesn't fix your issue, you'll need to send in at least one of the units. I can't afford to send out output transformers if they'll just get fried again.  There is just too much weirdness. If it's an issue with the output I'll waive the repair fee regardless of the root issue (which we may never know).

Mike

It was corrosion the surface layer came off but stained the pad on the pcb.

No I didn't solder the anode to the pcb.

tracking says the Q6's will be here tomorrow.

Smoked for a couple seconds out the top on both units.

I unsoldered em all and tested it again, no shorts.

That looks like flux to me but either way that diode doesn't look great.

Good luck. I'm going to be offline for the long weekend.  Shoot me an email if you want to arrange for me to look at it. We need to get these cursed units working. 

Mike

What kind of solder are you using?

Hard to tell, but it looks like there is a lot of flux all over.  Look at the stud diode anode. That brown stuff must be flux that oozed down from your joint.

Might not be your issue, but flux, especially that much is very corrosive. I've had repairs in with that heavy flux, I'm always curious what type of solder it is.

There's a shit ton of dust on it cause it's been sitting on my bench too long.

that stuff bubbled out of the diode.

I'm using  the kester you recommend the same stuff I use at work.

I cleaned the pcb with 99 percent and esd paper wipes when I finished soldering.

SunkenCity said:

There's a sh*t ton of dust on it cause it's been sitting on my bench too long.

that stuff bubbled out of the diode.

I'm using  the kester you recommend the same stuff I use at work.

I cleaned the pcb with 99 percent and esd paper wipes when I finished soldering.

Click to expand...

Well stuff shouldn’t be bubbling out of the diode.  You’ve got like 2-3 things happening I’ve never seen before.  Just send one in, I’ll fix it for free.  It’ll be cheaper for me than sending random parts out and fixing it blindly.

Shoot me an email. Let’s solve this mystery.

Mike

Hairball Audio said:

I meant you +30V rail. Is that ok?

Seems like either Q8/Q9 or one of the two might be shorted.  I would start by replacing those.  Send us an email.

Mike

Click to expand...

Ah, okay. Yeah, that +30V rail gets a reading around +12.45V DC.

Just sent you an email regarding the parts!

saqeef said:

Ah, okay. Yeah, that +30V rail gets a reading around +12.45V DC.

Just sent you an email regarding the parts!

Click to expand...

Ya those transistors should not be hot. The F has a class A/B output and it stays pretty cool.  Very different than the A/D output.

Mike

Hey everyone, I just finished building my Rev D and went to calibrate it today, but ran into an issue. I'm read 0.775 VAC across the input just fine, but am not seeing anything at the output. My VU meter doesn't show anything happening either, even with the input and output controls cranked. I've looked over all the solder joints and they all look good. I am new to building things like this, but have been soldering for years so I trust my skills there. Where is a good place to start looking?

Thanks,
Rob

RobertBraz said:

Hey everyone, I just finished building my Rev D and went to calibrate it today, but ran into an issue. I'm read 0.775 VAC across the input just fine, but am not seeing anything at the output. My VU meter doesn't show anything happening either, even with the input and output controls cranked. I've looked over all the solder joints and they all look good. I am new to building things like this, but have been soldering for years so I trust my skills there. Where is a good place to start looking?

Thanks,
Rob

Click to expand...

Start here:
https://www.hairballaudio.com/blog/resources/post/fetrack-troubleshooting-guide

Mike

Hi.  I took my perfectly good RevD build and did the orange drop mod and now I have a ground hum in the unit and was wondering where the likely trouble spots might be...?  Thanks in advance for your input.

kingofspain2 said:

Hi.  I took my perfectly good RevD build and did the orange drop mod and now I have a ground hum in the unit and was wondering where the likely trouble spots might be...?  Thanks in advance for your input.

Click to expand...

Those are not part of the ground system. So I doubt it's the caps.  I would make sure a connector or L-braket PCB mount hasn't become loose.

Mike