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

[Echo North]

Thanks.  I spent the day reading every single one of the 973 (now 974) posts on this thread while taking meticulous notes on everything you and mnats said...while continuing to study the schematic which I don't really know how to read but am trying to learn. It gave me some more ideas for troubleshooting strategies but as usual am thinking about everything in the world that could ever go wrong now or in 20 years and way too out of touch with the moment. If I keep chasing this and if there is a faulty pot, I have deduced that the Bourns B25 is exceedingly hard to source. I couldn't find any in the store but would you have another for sale if need be? Otherwise, would something like the 5 Mohm Alpha pot (with that round base behind the shaft) have enough room to clear the Ratio board behind the front panel, like, if I had to wire one up from the pads? I don't want to waste your time with hypothetical questions but since now I'm wondering about the pot it made me wonder. Any perspective would be valued. Yes. Exactly like that.Thanks for the kindness. I beat up on myself often and that makes me feel much betterFirst thing I did notice visually is that R4 looks noticeably damaged. It's been chipped away somehow. Maybe from the Hekko getting too close to it while removing the hard-wired Q1 from the sockets and replacing the matched pair. In any event, it's reading way low. Like 12-ohms. I realize that's in circuit so I can see what it reads after taking one lead out but it seems to be a bit of a no-brainer & the first thing I'll try. I may just replace R5 along with it. I ran the transistor voltage tests & most of them looked  unsuspicious but....

At Q4, I got 1.91 VDC at the gate (you'd listed 2.21 VDC).  Then 4.72 VDC for Source (not 4.32). Then 12.22 VDC for Drain (13.38 was the number in your guide). On Q2 the Gate matched up but I was a little off on Source. I get 4.995 VDC (not 4.79). For the Drain I get 6.68 VDC (instead of 6.94). As I recall Q2 & Q4 are matched, correct? I looked in the store but could not find J309s. If it comes to replacing those let me know if you have a set available. I realize R4 is the obvious place to start and maybe it wouldn't hurt to replace R5 too. I should've left the soldered socket debacle alone like you said and probably screwed it up in the pursuit of perfection.

Right now I've put life on hold so much over the holidays that my visit up here's been extended to Wednesday to tie loose ends together like packing and laundry before I go but if there's a way to send out a couple resistors Monday let me know. They'd probably arrive by Tuesday. I'm almost crazy enough to drive north tomorrow (Sunday) to track one down if I can find one anywhere in Seattle/Bellevue/Tacoma. I don't presume anything is simple but am interested to see what happens.

We can send you a new pot.

 

[seanweaverguitar]

Thanks for the time/answers Mike. At this point I'm sleeping on it and I may be stubborn enough to keep trying but the reality is I'm flying home tomorrow and have taken the boards out of the chassis and am prepping the parts to make it easy for my folks to box it up and send it to you since...that's probably what's going to make more sense. I really gave it a lot the past 3 or 4 days looking for anything and reading every word.....but (1) I'm out of time up here and (2) probably don't have the experience or basic electronics education to jump into the DIY pool successfully at this level after one Lola build (which went great...provided phantom power works when I get home to my condensers).

I can tell that the Amplification stages are all low but don't know what else to do at this point without blindly taking things out and replacing them and common sense tells me that's not the way to go about this or to even learn what went wrong for the next time. It does seem that the joints I reflowed changed something. A few voltages went up but not enough. Still way low. But the needle drift as the Release knob is rotated CCW seems to have improved at last and I have no idea why (I really scrubbed that board harder tonight but had already cleaned everything like 10 times). Among the attempts I measured the voltage drop across the Base & Emitter for each bipolar transistor like MANTs says to do in his article....all of them are dropping more like .6 and none are dropping .7VDC . But it's the amplification stage test points that are low by like 2-3 volts AC no matter what I've stared at, read, looked at in a different light, or tried.

(every resistor was checked, rechecked and then gone through for hours during troubleshooting....just looking for a dumb mistake but they all matched up)

Now the meter pegs/pins to the right when changing to a lower ratio (say 20 to 12 or 12 to 8, etc.). I'm assuming it shouldn't do that.

That said, I can only get 540-ohms when measuring my T-pad input but screwed up by not measuring before installation. Is there any accuracy measuring that one  in circuit or would I have to remove it to tell anything? 

I'll keep you posted and assuming I don't have a breakthru,  send a Repair Request via email in the next few days. First sleep & going home.

 

[Echo North]

The meter should shoot in one direction as you move down the ratios and in the other direction as you move up the ratio. It should pin right in ABI mode. That is all normal.

Tpad is a nominal 600Ω so the reading your getting is normal.

Not sure about your low gain stages., I wonder if it's just a measurement error, or your test signal is low?  You might be fine.

Has one of the leg on your release pot broken off?

Mike

 

[seanweaverguitar]

The meter should shoot in one direction as you move down the ratios and in the other direction as you move up the ratio. It should pin right in ABI mode. That is all normal.

Cool. Thanks for the clarification & time.

Not sure about your low gain stages., I wonder if it's just a measurement error, or your test signal is low?  You might be fine.

I wondered this myself. I didn't have alligator clips on the probes but had a firm contact with the probes. I was using the TL75 leads that came with the Fluke What was concerning was the consistency.  Like every time (5 or 6 test sessions). Every time I measured an exact .775 VAC input signal at 1khz....and every time the measurements everywhere beyond TP1 were fairly low.

Has one of the leg on your release pot broken off? Mike

I don't think so but was always a little unclear on what to look for here to be honest. I see the metal band securely attached behind the blue back of the pot, and the pot leads are all soldered in. It's flush to the board so I think they're securely on but what/where should I exactly be looking for to identify these legs and to look for if one of them is broken off?

Thanks again Mike

 

[Echo North]

Cool. Thanks for the clarification & time.

I wondered this myself. I didn't have alligator clips on the probes but had a firm contact with the probes. I was using the TL75 leads that came with the Fluke What was concerning was the consistency.  Like every time (5 or 6 test sessions). Every time I measured an exact .775 VAC input signal at 1khz....and every time the measurements everywhere beyond TP1 were fairly low.

I don't think so but was always a little unclear on what to look for here to be honest. I see the metal band securely attached behind the blue back of the pot, and the pot leads are all soldered in. It's flush to the board so I think they're securely on but what/where should I exactly be looking for to identify these legs?

Thanks again Mike

On the levels you could also have your FET over biased. Try re-biasing it.

Just look on the PCB and see where each leg connects to next and see if there is continuity. Also make sure they are not shorted (unless they are on the schematic).

Mike

 

[seanweaverguitar]

On the levels you could also have your FET over biased. Try re-biasing it.

Just look on the PCB and see where each leg connects to next and see if there is continuity. Also make sure they are not shorted (unless they are on the schematic).

Mike

Thanks again Mike. I thought I checked that but to confirm (I'm now back home 2,000  miles away from the boards & left the build in Olympia) I had my Dad check continuity between the traces again last night & it passed the test evidently...

On the levels, I tried re-biasing about 3 or 4 times over the last week I had up there, and then just before I left I rotated the Q-bias to the side that is most negative (as per the guide) and checked voltages for an "UB" voltages. They were still low all thru the amplification stages...except for TP 1 which was never too alarming (I think biased I was getting 108 mV AC and by the last day there I was getting 110mV...it never went all the way to 113 mV but consistently TP1 was never very far off at all. It was everything else after that all the way from TP15 through Output XLR + -  no matter how many times I tried re-biasing or not biasing at all....

If you have any other suggestions on what else might be worth checking let me know (currently I spent a week checking every component value & orientation, tracing the entire main board schematic with the Fluke for continuity which passed everywhere, shining bright light & magnification looking for bad solder joints and touching up a few. Maybe there's still a bad solder joint in there that passes continuity but is dragging down the voltage? I watched all the Dave Jones videos and practiced...and the Lola build went fine so I'm not sure)

The only things I did not check before installation were the input, output, attack & release pots (but checked after installation in troubleshooting and couldn't find anything bothersome there), small blue ceramic caps since they were too small to measure (but checked, rechecked, installed and then checked the labels again with magnification), and transistors since I didn't know how to measure those and don't (yet) have a meter to check hFE on BJTs. Also, that pad on CR9 I had the question about was checked for continuity. I was always getting between -9.7 to -9.75 VDC there ever since the Power Supply build. Just about 30VDC perfectly (maybe something like 30.20) on CR8.

Thanks again for the time and you've been the greatest. I may learn more at this point by having it sent up to you and getting a report back about what went wrong so I'll send an email once I know for sure. It's probably counter-productive to have it shipped to me now....just to keep wrestling for another several weeks or months by myself....and wouldn't want to ask too much of you for free on here anyhow...when I keep trying and the solution keeps eluding me. I value the time, generosity to help troubleshoot here on the boards, and ultimately expertise to rescue it once it (most likely) winds up back in your shop....you'll send a report of what went wrong, right? Mostly that's all I want. The learning. I love gear and the music is #1 but above and beyond having a great sounding Rev A (which will be cool), it's the learning I'm borderline-desperate for. So that's what I have left to decide. What's going to teach me the most...trying to keep troubleshooting it myself or delegating it to you at this point. That'll be the deciding factor and I'm chewing on it over this weekend).

(far far off even years from now I want to learn enough to become capable of doing more advanced or unsupported projects like an 1108 build, but obviously I have a few (more like many) foundations to continue learning before then. I'm starting to read electronics texts and books though, trying to learn more about how this stuff works. A dear friend gave me a copy of Howard Tremane's AudioCyclopedia but a lot of that's still way over my head so I'm starting back at the basics. Ohm's Law. Series & Parallel circuits, playing with batteries and resistors....I want to learn enough to order yet another one (or few) and not have to bug you so much on here. Thanks again for everything)

 

[bjohnsonaudio]

Hey guys! I just purchased the FET Rev A and am on the power supply portion of the build. I put everything together as per the instructions and when I went to test it, I am receiving little to know power on the DC current test.

My resistance test with the IEC meter was totally normal and when I go to check the DC Voltage for both zener diodes I am getting readings like .03 and -.05 ... I was wondering what could be the cause for this issue? I checked the fuse (400mA 120v) and it works great. I really don't think I am getting any power when turning on. I plugged it in with the IEC cable and didn't even get a smell of smoke or feel any heat.

What could be the issue?

Thanks for your help!

 

[Echo North]

Thanks again Mike. I thought I checked that but to confirm (I'm now back home 2,000  miles away from the boards & left the build in Olympia) I had my Dad check continuity between the traces again last night & it passed the test evidently...

On the levels, I tried re-biasing about 3 or 4 times over the last week I had up there, and then just before I left I rotated the Q-bias to the side that is most negative (as per the guide) and checked voltages for an "UB" voltages. They were still low all thru the amplification stages...except for TP 1 which was never too alarming (I think biased I was getting 108 mV AC and by the last day there I was getting 110mV...it never went all the way to 113 mV but consistently TP1 was never very far off at all. It was everything else after that all the way from TP15 through Output XLR + -  no matter how many times I tried re-biasing or not biasing at all....

If you have any other suggestions on what else might be worth checking let me know (currently I spent a week checking every component value & orientation, tracing the entire main board schematic with the Fluke for continuity which passed everywhere, shining bright light & magnification looking for bad solder joints and touching up a few. Maybe there's still a bad solder joint in there that passes continuity but is dragging down the voltage? I watched all the Dave Jones videos and practiced...and the Lola build went fine so I'm not sure)

The only things I did not check before installation were the input, output, attack & release pots (but checked after installation in troubleshooting and couldn't find anything bothersome there), small blue ceramic caps since they were too small to measure (but checked, rechecked, installed and then checked the labels again with magnification), and transistors since I didn't know how to measure those and don't (yet) have a meter to check hFE on BJTs. Also, that pad on CR9 I had the question about was checked for continuity. I was always getting between -9.7 to -9.75 VDC there ever since the Power Supply build. Just about 30VDC perfectly (maybe something like 30.20) on CR8.

Thanks again for the time and you've been the greatest. I may learn more at this point by having it sent up to you and getting a report back about what went wrong so I'll send an email once I know for sure. It's probably counter-productive to have it shipped to me now....just to keep wrestling for another several weeks or months by myself....and wouldn't want to ask too much of you for free on here anyhow...when I keep trying and the solution keeps eluding me. I value the time, generosity to help troubleshoot here on the boards, and ultimately expertise to rescue it once it (most likely) winds up back in your shop....you'll send a report of what went wrong, right? Mostly that's all I want. The learning. I love gear and the music is #1 but above and beyond having a great sounding Rev A (which will be cool), it's the learning I'm borderline-desperate for. So that's what I have left to decide. What's going to teach me the most...trying to keep troubleshooting it myself or delegating it to you at this point. That'll be the deciding factor and I'm chewing on it over this weekend).

(far far off even years from now I want to learn enough to become capable of doing more advanced or unsupported projects like an 1108 build, but obviously I have a few (more like many) foundations to continue learning before then. I'm starting to read electronics texts and books though, trying to learn more about how this stuff works. A dear friend gave me a copy of Howard Tremane's AudioCyclopedia but a lot of that's still way over my head so I'm starting back at the basics. Ohm's Law. Series & Parallel circuits, playing with batteries and resistors....I want to learn enough to order yet another one (or few) and not have to bug you so much on here. Thanks again for everything)

Yes if we repair it we'll give you a report on what we found/fixed.

Mike

 

[Echo North]

Hey guys! I just purchased the FET Rev A and am on the power supply portion of the build. I put everything together as per the instructions and when I went to test it, I am receiving little to know power on the DC current test.

My resistance test with the IEC meter was totally normal and when I go to check the DC Voltage for both zener diodes I am getting readings like .03 and -.05 ... I was wondering what could be the cause for this issue? I checked the fuse (400mA 120v) and it works great. I really don't think I am getting any power when turning on. I plugged it in with the IEC cable and didn't even get a smell of smoke or feel any heat.

What could be the issue?

Thanks for your help!

Are you sure the unit is on? Meaning your GR button is pushed in?

Do you see an AC V  between either orange wires and yellow on the supply secondary?

Mike

 

[bjohnsonaudio]

Are you sure the unit is on? Meaning your GR button is pushed in?

Do you see an AC V  between either orange wires and yellow on the supply secondary?

Mike

The GR button is pushed in. I am a little unclear about the AC V between the wires. I have my Power Transformer connected to the main PCB board via the connects that has the black-orange-yellow-orange-white wiring. Only the orange, yellow, and orange wires are connected while the other are free.

I'll attach a picture of my overhead view of the board so you can take a look. I did another read on the Volts and the one that should read +30 reads .39 and the -10v reads -.5

Thanks1

 

[Echo North]

Those two orange and one yellow wire connect to the right angle connector that makes the connections to the main PCB.  What is the AC voltage at those connections between one of the oranges and yellow, and the other orange and yellow. You can use the pads on the PCB that correspond to the connections to test the AC.

 

[Echo North]

Also make sure all of your L brackets are in place. They are part of the grounding system.

 

[bjohnsonaudio]

Those two orange and one yellow wire connect to the right angle connector that makes the connections to the main PCB.  What is the AC voltage at those connections between one of the oranges and yellow, and the other orange and yellow. You can use the pads on the PCB that correspond to the connections to test the AC.

Assuming that I checked correctly (put lead to pad) it was reading around 2.3 V. Also all three of my L. Brackets are on my main PCB and secure.

Thanks again for your help!

 

[Echo North]

Assuming that I checked correctly (put lead to pad) it was reading around 2.3 V. Also all three of my L. Brackets are on my main PCB and secure.

Thanks again for your help!

Can you remove your power transformer and get your leads into the contacts?  When it's not connected to anything.

What is the Ω reading between the oranges?

 

[bjohnsonaudio]

Can you remove your power transformer and get your leads into the contacts?  When it's not connected to anything.

What is the Ω reading between the oranges?

I think I am doing what you asked me to do correctly. I removed the connector that is on the power transformer off of the main PCB. I then put my leads on the pad on the PCB and the contact that the connector from power transformer would connect into. And I got a reading of .2

If you meant the read on the connector that has the orange wires on it...I can't really get my leads into the opening holes, but from behind I was able to get my leads to touch the metal connecting parts and the resistance read 22.4 when orange to orange.

I hope that makes sense. I am a relative beginner to this large of build so I am trying to follow you as best as possible.

Thanks!

 

[Echo North]

If you meant the read on the connector that has the orange wires on it...I can't really get my leads into the opening holes, but from behind I was able to get my leads to touch the metal connecting parts and the resistance read 22.4 when orange to orange.

Yes this one. 

No doing that same thing, what is your Ω reading between:

1. white and black
2. blue and red
3. Each orange and yellow

 

[bjohnsonaudio]

Yes this one. 

No doing that same thing, what is your Ω reading between:

1. white and black
2. blue and red
3. Each orange and yellow

If you meant white and black from the connector that goes to the voltage select PCB it reads 98. If you meant the one that are on the ends of the wire that connects to the Main PCB I get OL.

Read and blue is 115.6

11.5 between both orange and yellow.

I think I did that correct. Let me know if that seems off or not.

 

[Echo North]

If you meant white and black from the connector that goes to the voltage select PCB it reads 98. If you meant the one that are on the ends of the wire that connects to the Main PCB I get OL.

Read and blue is 115.6

11.5 between both orange and yellow.

I think I did that correct. Let me know if that seems off or not.

That's all normal.

Are you sure the fuse is seated correctly?

Let me look back through this thread. I walked someone through this once.

Mike

 

[Echo North]

https://groupdiy.com/index.php?topic=63600.msg827201#msg827201

Read that, see if you're seeing your mains voltage.  Be careful.

Mike

 

[bjohnsonaudio]

https://groupdiy.com/index.php?topic=63600.msg827201#msg827201

Read that, see if you're seeing your mains voltage.  Be careful.

Mike

Just to make sure. I checked my Fuse and it is a 400mA 250V. Would this make a difference when my Voltage is set to the 115?