[BUILD] CAPI LC53A~500 Series~Love Child EQ Kit~Official Support Thread

[Mr. Steve]

Hey Jeff!

My first Love Child is already working and sounds nice, but now I have a problem with the second one.

When I tested only the Main PCB, the +16/-16V voltages on the sockets were ok.
Then I assembled the rest and wanted to do a signal test.
Before that i checked for solder bridges.

I turned on my Lunchbox and the +16V led was blinking, telling me there is a problem.
I checked all the components on the CB PCB, but everything seems to be in the right place.
Then I removed the op amps and checked the voltages on the sockets.
Now the voltages on the Main PCB sockets are at -16V but +0V.
I checked the CR1 and CR2 diodes with my DMM and they seem to be ok.

Do you have any ideas, what could have caused the problem and what i can check?
Without schematics I don't know what else to do, other than look if I maybe swapped some parts.

I would really appreciate any help or input!
The first built went really smooth, so it's kind of a bummer

Oh and the Lunchbox is ok, other modules are working just fine!

 

[jsteiger]

.....Now the voltages on the Main PCB sockets are at -16V but +0V.
I checked the CR1 and CR2 diodes with my DMM and they seem to be ok.....

It sounds like something is shorted to the +16V rail somewhere on the EQ build. Was this last test done with the steel cover in place? My first guess would be that a component leg is shorting out to the frame or cover? It could be opamp or follower related as well. With the module not connected to the rack, measure DCR from a +16V socket to ground to see if the resistance is near a direct short. I would one by one pull the opamps and followers and keep checking. Since it was OK when you first checked, its most likely something you did after that step. Maybe a bad opamp build on the main PCB?

 

[eqp1a]

Just finished my first LC53A build. Everything seems to be working, except the signal is about 20dB quieter on the output than the input (also, inserting the EQ causes another approximately 2.5dB drop in signal). I followed Jeff's instructions of tracing the signal through the circuit, and found everything to be OK until the 4th reading, the output pin of A4. I then swapped the two DTO5s and the same problem persisted. Thoughts? Anything else I should be checking? I believe I've scoured this entire thread, but apologies if I've missed something and a similar problem has already been addressed.

Cheers

Ian

 

[Mr. Steve]

.....Now the voltages on the Main PCB sockets are at -16V but +0V.
I checked the CR1 and CR2 diodes with my DMM and they seem to be ok.....

It sounds like something is shorted to the +16V rail somewhere on the EQ build. Was this last test done with the steel cover in place?

Well, I'll be double dog damned!

Long story short, C13's +/- was bridged resulting in 0V at all +16V sockets.

When it didn't work, I also figured, that there must be a short somewhere.
C13 looked suspicious, so I removed some of the solder, but apparently not enough….
When you also said it must be a short I rechecked everything with a mangnifying glass and removed all of the solder from C13 and redid the joints.

It's crazy how a little solder bridge can be responsible for the failing of the whole +16V circuit… 


To answer your other question and describe my steps,
I just tested the Main PCB with the CB PCB, without the steel cover.
So I knew it must be one of the op amps, followers or the CB PCB itself.
First step was to remove all of the op amps and followers.
The voltage was still at +0V, so I knew it must be something with the CB PCB!

I unplugged the unit and like you said, checked the DCR on all +16V sockets.
All of them showed 0 resistance, so I got my magnifying glass and checked all of the joints.

Now I found the tiniest of bridges on C13 and redid the joints.

Then I put all of the op amps and followers in and turned the unit on.
The +16V rack led wasn't blinking so it was time to do another signal test.
The waveform recorded in my DAW was a nice 1K sinus as it should be!

Thank you very much for your input Jeff!
You motivated me to check the joints again for bridges!

everything to be OK until the 4th reading, the output pin of A4. I then swapped the two DTO5s and the same problem persisted. Thoughts?  Anything else I should be checking?

Hey Ian!

Did you check the voltages on A4?
C to -V and +V.
That's the first thing I would check!
If you already did that, better wait for Jeffs input

 

[eqp1a]

everything to be OK until the 4th reading, the output pin of A4. I then swapped the two DTO5s and the same problem persisted. Thoughts?  Anything else I should be checking?

Hey Ian!

Did you check the voltages on A4?
C to -V and +V.
That's the first thing I would check!
If you already did that, better wait for Jeffs input

Hey Steve! Yes, I'm reading +15.45VDC and -15.33VDC respectively.

 

[Mr. Steve]

I'm reading +15.45VDC and -15.33VDC respectively.

That's good, but also bad, because there must be a problem somewhere else
I would first check for solder bridges and then  if every component is in the right place.

My whole +16V circuit wasn't working because of a tiny solder bridge…
Also I had a problem on a 1176 built with one resistor too much and the whole compressor wasn't working.

Little things can cause big problems!

But I'm sure Jeff can tell you where to look exactly!

 

[NoahShain]

Just finished my first LC53 build.
:-\
Not passing signal at all...just a buzz. Like a nice loud 60 cycle hum.
Any tips where to start diagnosis? My instinct says the little op amps or followers...they're tough!

Thanks all

 

[Mr. Steve]

Any tips where to start diagnosis?

Hey!

I would remove all the opamps and followers and check the resistance on the turned off module.
Every +V and -V to C on the DOA sockets.
Jeffs FC526 manual says, that the resistance should be greater than 500Ohm.
Also you can turn on the module and check the DCV on the sockets.
Again +V and -V to C … should be about +-16V.
If it's smaller than 500Ohm/not +-16V you have a short somewhere, which is what we are looking for!

Get a magnifying glass and check every solder joint for little bridges.
All of the 3 PCBs and especially the opamps and followers, cause they sure are tricky!
Also check again, if the metal cover is not touching any of the joints!

If both of these steps are ok, you know it's one of the opamps and followers.
Put them in one by one and check the DCV again.

That's the easiest way to find something suspicious!
Also check the polarity of all the diodes and caps.

The next and very useful step would be, to check, if every component is in the right place!
That can be a lot of work, with all the resistors, but I'm sure, that your module will work, if there are no bridges/shorts and every component is in the right place!

You could post a picture of your module, maybe that helps to help you!

Good luck!

 

[okdaniel]

Any word on when these will be available for order again on the site?

 

[jsteiger]

Any word on when these will be available for order again on the site?

The new PCB's are fully tested and ready. I need to make some small adjustments to the BOM's and get a round of parts sorted. I had a small surgery 1.5 weeks ago and have spent my recovery time laying out an exciting new module. I am almost fully done with that so getting these LC kits ready will be my next main goal. I know that doesn't exactly answer your question but it should be fairly soon now! 

 

[NoahShain]

Thank you for the detailed reply!
All of the resistance and DCV measurements are correct. WELL over the suggested resistance and 15.8 (or so) vdc everywhere. I removed all 4 of the little opamps and followers, got 16vdc everywhere and replaced them 1 by 1.  Same measurements. I can see no solder bridges anywhere and all caps are placed in the correct spots and with proper polarity.
Any tips as to what to check next?
Output transformer is wired correctly.
Maybe I check for other test points?
This isn't my first build but I am an electronics newbie.
Any additional help will be GREATLY appreciated.

Thanks!!!

Any tips where to start diagnosis?

Hey!

I would remove all the opamps and followers and check the resistance on the turned off module.
Every +V and -V to C on the DOA sockets.
Jeffs FC526 manual says, that the resistance should be greater than 500Ohm.
Also you can turn on the module and check the DCV on the sockets.
Again +V and -V to C … should be about +-16V.
If it's smaller than 500Ohm/not +-16V you have a short somewhere, which is what we are looking for!

Get a magnifying glass and check every solder joint for little bridges.
All of the 3 PCBs and especially the opamps and followers, cause they sure are tricky!
Also check again, if the metal cover is not touching any of the joints!

If both of these steps are ok, you know it's one of the opamps and followers.
Put them in one by one and check the DCV again.

That's the easiest way to find something suspicious!
Also check the polarity of all the diodes and caps.

The next and very useful step would be, to check, if every component is in the right place!
That can be a lot of work, with all the resistors, but I'm sure, that your module will work, if there are no bridges/shorts and every component is in the right place!

You could post a picture of your module, maybe that helps to help you!

Good luck!

 

[jsteiger]

@Noah, there are some test points listed in this post http://groupdiy.com/index.php?topic=48426.msg618790#msg618790

A few threads after that Doug (emrr) and I discuss the results.

The only way to figure out what your trouble is, is to isolate where things go south. Did you have a close look for trimmed off pads?

 

[NoahShain]

@Noah, there are some test points listed in this post http://groupdiy.com/index.php?topic=48426.msg618790#msg618790

A few threads after that Doug (emrr) and I discuss the results.

The only way to figure out what your trouble is, is to isolate where things go south. Did you have a close look for trimmed off pads?

Hahahahahaha!!!! I did not trim any pads off THIS TIME!!! I was EXTREMELY careful about it while trimming component leads.
Just to double check, is my DCV reading of 15.8 v acceptable or should I be getting precisely 16vdc?
Also, as I check resistance from C to V- and V+ (On all opamps and followers) I get well over 500ohms on V- but V+ sends my Klein digital meter to O.L. Which I understand to mean OverLoad. It's shows an M in the display to indicate it's into Megaohms but beyond the meters range. Is this acceptable?
And, since I'm such a newb, I have to ask...to do the readings of the test points you referenced me to, do I need to send a signal in to the module?
Sorry to ask 101 type questions here among you experienced, educated folks. Is there an easy reference for basic test procedure?
Or maybe I do it with the unit just powered up?

Also worth mentioning that I am doing all this testing with just the main and CB pcbs in place. I completed the build and installed the complete unit and got the hum so I took it back apart and started testing (like the build guide said to do :-[).
Also, the metal cover is NOT installed.

Again...apologies for all the face palming that I must be causing and THANKS A MILLION for the help!!!

BTW Jeff, all 4 of the 553s are up and running and they SLAY on guitars. I love them! I didn't have any experience with them before and I can't believe how great they are.

 

[Mr. Steve]

hey,

check this post out http://groupdiy.com/index.php?topic=48426.msg619418#msg619418
he's sending a 1kHz sine signal at +4dBu (1,228V).
compare your values and you know where the problem is!

and 15.8V is totally fine!
for the resistance, as long as you are above 500ohm, it's ok!
i think i got some overloads myself

 

[NoahShain]

hey,

check this post out http://groupdiy.com/index.php?topic=48426.msg619418#msg619418
he's sending a 1kHz sine signal at +4dBu (1,228V).
compare your values and you know where the problem is!

and 15.8V is totally fine!
for the resistance, as long as you are above 500ohm, it's ok!
i think i got some overloads myself

Thanks for the help boys. I'm set up to do this testing.
500hz sine  @ 1.233v AC
Going in to the powered up module. All DO5 and followers installed. 2 known working opamps in A1 and A2...
Here's where I show my inexperience... I don't know where to clip my black test probe?
Ground?

 

[jsteiger]

Thanks for the help boys. I'm set up to do this testing.
500hz sine  @ 1.233v AC
Going in to the powered up module. All DO5 and followers installed. 2 known working opamps in A1 and A2...
Here's where I show my inexperience... I don't know where to clip my black test probe?
Ground?

This is one of the things I have added on the soon to be released latest version.

For your test, with the EP inductor board unplugged, the easiest spot to clip onto ground is pin #3 of J1 on the CB PCB. See the attached jpg

 

[NoahShain]

Thanks for the help boys. I'm set up to do this testing.
500hz sine  @ 1.233v AC
Going in to the powered up module. All DO5 and followers installed. 2 known working opamps in A1 and A2...
Here's where I show my inexperience... I don't know where to clip my black test probe?
Ground?

This is one of the things I have added on the soon to be released latest version.

For your test, with the EP inductor board unplugged, the easiest spot to clip onto ground is pin #3 of J1 on the CB PCB. See the attached jpg

Thanks Jeff and Mr Steve

I did some testing.
Results are:
1st reading: negative side of C2 on the Main PCB.  - 0.617VAC
2nd reading: output pin of A1, DF on CB PCB  - 0.615VAC
3rd reading: output pin of A2, DF on CB PCB  - 0.610VAC
4th reading: output pin of A4, DTO5 on CB PCB  - .417VAC
5th reading: output pin of A3, DTO5 on CB PCB  - wacky wildly fluctuating OL dmm reading
6th reading: neg side of C12 on the Main PCB - 0VAC

Then I swapped A4 and A3 and got the wacky reading 1 step earlier and 0s after that.

I pulled the DTO5s and made sure there are no solder bridges and all leads trimmed tight.
Indeed.
I have another kit.
I can build another set of DTO5s.
Is that a good next step?

Gracious thanks.

 

[jsteiger]

Yes it sounds like you have a bad or faulty DTO5.

 

[NoahShain]

Yes it sounds like you have a bad or faulty DTO5.

That's what it was.
I had 2 transistors in the wrong spots. Swapped them and we're good!!!
CMRR done!
1 problem, which I think, based on posts earlier in the thread, will be a Cap in the CB board...

12k shelf is boosting a LOT. +2 on the knob produces a 5db increase in level.

I'll read back through tonight later but if this is an easy fix I'll be building my 2nd tomorrow.

Thanks again for all the help Jeff!!

 

[NoahShain]

Yes it sounds like you have a bad or faulty DTO5.

Morning!
So I can't find anything in the thread about a volume jump happening with the 12k shelf.

Is there a schematic that might help me check the caps in that path? Not that I'd be able to read it!!!

Any tips here Jeff?

Thanks again