[Build] CAPI LC25-LC40, 500 Series Rotary Graphic EQ's, Official Support Thread

[jsteiger]

No noise at TP1
Noise at TP2,TP3, TP4...

Per my email, its most likely the DTO5.

 

[mrdarwin]

Per my email, its most likely the DTO5.

Sorry but on the 1st page of the thread, you write "TP1 after DTO5". There is no noise at TP1.
Anyway, I traced the signal after each ICs and found the faulty: LME49720 A6.
Unsoldered, put an IC support and new LME and everything looks ok now.

IMHO perhaps you should add ic support in the kits.

Thanks for help.

 

[franktree]

Hi all. First CAPI build -- an LC25. I tried to be incredibly careful, but sad to say that the unit powers up, and passes audio when in bypass, but when active, no audio passes through. The peak light is also on at all times, from the instant I turn on the 500 rack. I'm really unsure of how to go about troubleshooting this, so any thoughts for how to try to diagnose the problem would be much appreciated. Thank you!

UPDATE: In case anyone else has a similar issue, my problem was the DOA (everything is so small and tight!!). I rebuilt a new DOA and now it seems like the LC25 is working. It looks like I stupidly put in a couple of the transistors backward in the other DOA, so I'm going to see if I can fix that without ruining everything else. Fingers crossed!

 

[RandyBeast]

Hello,

I just finished a LC25 Build and tested it out, When bypass is flipped off, the unit is muted, and when its on, I get sound, but its very quite, I have to crank to Preamp to get signal. any Ideas?

Thanks

 

[CFrentzen]

Hey there,

I built a few capi modules last year and everything worked very well - been using my VP28 and LC25 for recording and mixing. Now I've finished two LC40 which are a great addition to my rack.

One of 'em has a little issue: if I turn two or more low frequency knobs and add some frequencies, there is a sudden point where a loud and pulsating sound (sounds almost like a distorted machine gun to me) comes out. Doesn't make a difference if I run audio through it or not - sounds like it is self-oscillating. If I just use 40Hz on its own that's fine. Same with 80 Hz. But if I combine two or more low frequencies I either get a low sub frequency or a very broad pulsating sound with high and low frequencies. And its character changes when turning a few knobs. It's so loud the peak LED flashes. I compared all resistors, diodes, DOAs on the main pcb and the switch pcb. Because I have another LC40 which works just fine I thought I might see where I made a mistake. But I can't find it. Any idea, where this comes from? I swapped opamps, but that doesn't solve the problem.
Might be a wrong resistor in the low freq eq circuit? Could this happen on the switch pcb or more likely in the gyrator section on the main pcb?
Thanks for your help!
Christian

 

[jsteiger]

Hey there,

I built a few capi modules last year and everything worked very well - been using my VP28 and LC25 for recording and mixing. Now I've finished two LC40 which are a great addition to my rack.

One of 'em has a little issue: if I turn two or more low frequency knobs and add some frequencies, there is a sudden point where a loud and pulsating sound (sounds almost like a distorted machine gun to me) comes out. Doesn't make a difference if I run audio through it or not - sounds like it is self-oscillating. If I just use 40Hz on its own that's fine. Same with 80 Hz. But if I combine two or more low frequencies I either get a low sub frequency or a very broad pulsating sound with high and low frequencies. And its character changes when turning a few knobs. It's so loud the peak LED flashes. I compared all resistors, diodes, DOAs on the main pcb and the switch pcb. Because I have another LC40 which works just fine I thought I might see where I made a mistake. But I can't find it. Any idea, where this comes from? I swapped opamps, but that doesn't solve the problem.
Might be a wrong resistor in the low freq eq circuit? Could this happen on the switch pcb or more likely in the gyrator section on the main pcb?
Thanks for your help!
Christian

Most likely on the gyrator R section. I would also make sure the R's around the LME49720 are correct as well as checking the DTO5 PCB's.

 

[RandyBeast]

Hello,

I was able to get further with my LC25. I finished the LC40 and it works perfectly. however, the LC25 works in active mode, but if I bypass the unit, it mutes everything. would this be an issue with the relay?? any help would be appreciated.

DC Link = NO

 

[ChristianFrentzen]

Most likely on the gyrator R section. I would also make sure the R's around the LME49720 are correct as well as checking the DTO5 PCB's.

Hey Jeff,
thanks for your reply. I spent two days checking all resistors. they look identical to my other LC40. Same goes for the resistors around the LME. The DTO5 looks fine, too. I checked all transistors, resistors and capacitors. It's all good. I'm confused. What could I look for?

As I mentioned, the unit works - all EQ bands work fine if I use them separately. Just when it comes to lower frequencies I can't boost several of them too much. Here's an example:
1.
40Hz +12db and then 80Hz +2dB immediately results in that weird pulsating / self oscillation, a lot of overtones (very loud, PK LED is flickering)
2.
40Hz +12db and 160Hz +4dB (takes one second and then it comes) -> same loud noise
3.
80Hz +12db and 160 Hz +12dB = no noise BUT if I turn up 40 Hz then it comes again. Same goes for 320Hz (80 Hz +12db and 160Hz +12db plus 320 2dB}
4.
40Hz +12dB and 320 + 6dB same noise
5.
If I boost 80Hz and 320Hz full on (+12dB) and then either push 160Hz or 640 Hz I get a less overtone-like sound. It's a super low sub bass (around 30hz... makes my windows and doors shake).

I have absolutely no clue what I can do now.

 

[RandyBeast]

Ok, I fixed the bypass, I was stupid and put the relay in backwards. However, my 50hz frequency does nothing, no boost or gain, everything else is perfect. Here is a pic of my gyrators, did I mess up some resistors values?

 

[jsteiger]

Since you have a good working unit, swap the switch PCB assemblies and see if the issue stays with the main or follows the switch PCB.

 

[RandyBeast]

Since you have a good working unit, swap the switch PCB assemblies and see if the issue stays with the main or follows the switch PCB.

I have already tried that didn't fix the issue. so it’s definitely with the main board. Sorry, should have mentioned that.
Thanks

 

[ChristianFrentzen]

Another night looking for a fix. I took the DTO5 out oo both LC40s and looked for anything wrong. Since they looked perfectly the same I put them back in. Of course that's a bit risky - unsolder components etc.
Measured and compared all resistors on the main pcb. Perfect, everything is at its right place. Again swapped the switch pcb - that didn't change things. Ok. I still get those loud pulsating kind of self oscillating sounds.

Then I did a tragic mistake. I thought "maybe it's the LME". Took them out of both LC40s and put them in the respective other unit. I'd say I'm fairly good at soldering and I've already buildt many DIY modules. But these small things are fragile. One of my LMEs now has a broken leg - the complete leg broke off so there's no way to attach it. On the other unit the main PCB looks a bit damaged - there is solder somehow underneath the green surface and I can't get rid of it. Don't know how it got there, it seems to be trapped underneath the surface and it's fairly close to a pad. I guess it's safe to say - even if things will still work - I ruined both units now. Maybe I can still rescue one, but even that feels like it's not really a proper module.

Probably the most frustrating day I've had in a long time. I thought I was so close to fixing it. Damn that really hurts after days of work and troubleshooting. After two VP28s, 2x LC25 and 2x FC526 that was really not what I expected, I thought that would be an easy thing to do.

Hey Jeff, when's the next batch of LC40s available? Can I get spare parts or do I have to order a full kit? I guess I'd rather have a fresh start than solderings things out. I could maybe use the input and output transformers, and I can keep the switch pcb. but that's about it. Arrrrrg.

 

[RandyBeast]

Since you have a good working unit, swap the switch PCB assemblies and see if the issue stays with the main or follows the switch PCB.

Well Jeff,

I went through and checked all solder joints and everything seems fine on the mainboard. I am still unable to get the 50Hz knob to gain or attenuate the frequency. I am stump at this point. could the opamp be bad?

 

[RandyBeast]

Since you have a good working unit, swap the switch PCB assemblies and see if the issue stays with the main or follows the switch PCB.

Hello Jeff,

So I did some math and think I figured out which Gyrator runs the 50hz frequency.

L = GR9 * GR10 * GC7
7.375H = 1.91K * 143K * .027 uf

f = 1/ 2pi * sqrt L * GC8
58 hz = 1/ 2pi * sqrt 7.375 * 1uf

let me know if these are the right components for the 50hz Gyrator. I so far, have not been able to figure out why this one frequency is getting no response from the potentiometer.

thanks

 

[CFrentzen]

So I managed to get one unit running (YES!).

The other one is still a work in progress. I sent a sine wave (400Hz, 0 dBu) through the unit and checked the testpoints.

I get signal at TP1 (around 260 mV), but at TP2 there is nothing. I am not sure where the signal stops... Any suggestions?

 

[greenhorn]

Hi.
After 10+ pres, 2 BT50s, 2 CAPI 500 racks (plus PSU) and a 32 ch. SumBus it finally happened. I just built 2 LC40s, and only 1 works. The other one does not appear to even get power (no lights).

I've tested several slots in the rack, and tested it with op amps I know to be working. No luck.

I've visually compared the two, and everything looks to be identical. Nothing seems to be blown either.


I am unfortunately absolutely sh!t at troubleshooting a stuffed PCB, so any pointers as to where - and how - to begin, would be greatly appreciated.


Regards,
Kai

 

[djones]

HI Jeff!
I have 3 LC25's. One works completely. All main PCB's work, as I tested the working rotary board with each PCB and everything is good.

On one Rotary PCB the 50hz rotary is none responsive. On the second Rotary PCB its the 6.4k band. The 6.4 seems to randomly come in or completely short out if I wiggle it around or continue turn it. The 50hz is just completely non responsive.

I had some issues with two of the grayhills where they wouldn't turn and I had to force it. Unfortunately I don't remember which rotary's those were, but I'm suspecting that it might be these two and I'm curious if the grayhill itself is damaged if that's the case.

I've touched up all the grayhill leads and the jumpers with no change to response. Any ideas? I've ordered a couple replacement Grayhills that will be in tomorrow just to swap out and check but I'm looking for any other ideas you might have in troubleshooting.

 

[jsteiger]

HI Jeff!
I have 3 LC25's. One works completely. All main PCB's work, as I tested the working rotary board with each PCB and everything is good.

On one Rotary PCB the 50hz rotary is none responsive. On the second Rotary PCB its the 6.4k band. The 6.4 seems to randomly come in or completely short out if I wiggle it around or continue turn it. The 50hz is just completely non responsive.

I had some issues with two of the grayhills where they wouldn't turn and I had to force it. Unfortunately I don't remember which rotary's those were, but I'm suspecting that it might be these two and I'm curious if the grayhill itself is damaged if that's the case.

I've touched up all the grayhill leads and the jumpers with no change to response. Any ideas? I've ordered a couple replacement Grayhills that will be in tomorrow just to swap out and check but I'm looking for any other ideas you might have in troubleshooting.

You can beep out the switch(es) in question to see if there is continuity between the wiper and location of the pin that is selected.

 

[djones]

You can beep out the switch(es) in question to see if there is continuity between the wiper and location of the pin that is selected.

Ended being faulty Grayhills. Replaced the two problem rotary pots and all three units work perfectly.

 

[coldwar]

Just got an LC25 together and it is always on bypass. when switched into "act" im getting no noise from the relays. The Switch is getting 4v dc