SOLVED Magnetron screw up

[Jeff C]

Continuing from my tremolo thread here………
I recently built the Magnetron. I was delighted when it cranked right up on the first try (I am a rank amateur who makes lots of mistakes - as one can see from my comically epic Cobalt Drive thread and slightly less comical EA Tremolo thread…..). Then after I mounted it in the enclosure - nada. It was quite a struggle getting it into the enclosure so perhaps I damaged something in the process. So I hate like damn to have to start this one as I actually had it working!! The bypass works fine. But one of the LED’s just stays lit, whether the pedal is switched on or not. It does dim when I turn the level pot and flutters with the speed pot. The other LED never lights up - perhaps I burnt it out……. When I put my audio probe on the level pot, I get nothing. On speed and depth pots, I can hear the clicking of what the delay should be. And with feedback I can hear it distorting as it turns up, but no audio sound. I tried following the audio path. I get a clear signal from the in pad, so I don’t think it’s the switch. I also get audio to r1, r2 and r3, and c1 and pin 2 on IC1. No audio on the outgoing pin 1 (according to the schematic). I get audio on one pin on the gain trimmer pot. I tried three different op amp 2134’s at the IC1 slot with no luck (using a socket). Same with IC2 and IC3. (I was hoping my problem was that I had damaged one or more of them when I was wrestling the board into the enclosure - a very tight fit!) I went ahead and reflowed EVERY solder and inspected under good light with a magnifier glass - although my skills are questionable. I then did continuity tests on all points and reflowed solder where it did not ring out consistently. All ground connections have continuity.
But I still get nothing. On the schematic I’m not sure where the point is that connects the LFO to the depth pot and C8 cap, and from the LFO to R103. Nor do I know where the +5v point is that connects to IC3 and 4. On the power side, I get continuity everywhere but tomorrow (it’s late!) I’m going to reflow a few points that are a little hard to get to ring out (but eventually do).
Any suggestions in the meantime are most welcome!

 

[Jeff C]

Well, got the 100 out. Looks like the pads are still there but no continuity to either C or R 101. Looks like a jumper may be necessary……Any advice on that? Solder in the new 100 and test? If still no continuity, then do a jumper between R100 and R101, then test to both 101’s? I tested resistance on the new 100 and it comes up 47k.

 

[Jeff C]

Put the new one in. No continuity put a jumper on. Continuity to both 100 and 101. Voltage is weird, though. 9v on both sides of 100. 9v on the R101 side connected to 100. 0 volts on the other side. 9v on C101+ side. 9v on IC1.1-3. No audio out…..

 

[Sturdag Lagernathy]

Do not check continuity with the circuit energized!!!!!

 

[EGRENIER]

Put the new one in. No continuity put a jumper on. Continuity to both 100 and 101. Voltage is weird, though. 9v on both sides of 100. 9v on the R101 side connected to 100. 0 volts on the other side. 9v on C101+ side. 9v on IC1.1-3. No audio out…..

Well it’s not perfect but it’s progress…

And yes, as @Sturdag Lagernathy said, no power in the circuit when testing for continuity. If you think about it, your DMM is applying current to the probe for your continuity test. If there is a path, it will send current from your red probe, pick it up from the black probe and make your DMM beep. If you test continuity with power on, you may be picking up current from the board to make your DMM beep. Hence a false positive result.

 

[EGRENIER]

So, how did you select which side of R100 to jump ?

Normally, when R100 was removed, you should have read 9V on one pad and 0v on the other. The jumper needed to be put between the 0v pad and the + side of R101.

You should get continuity between one side of R101 and the - of C101 and continuity between the other side of R101 and the + of C101. When you find this, you know where the the + side of R101 is. So your jumper should be between the 0v pad of R100 and the + side of R101.

Right now, you may be jumping over R100 which would explain why you read 9V at R101 and at C101.

Also it’s important that you have a good ground on the - side of R101. So a continuity check of the - side of R101 to ground and the - side of C101 to ground would confirm that.

One more thing, in all your troubleshooting session, I tend to remember that you have needed jumpers quite a bit. If this was caused by pulling pad off while removing parts, it’s one thing, but of it was caused by the board being damage, it’s a different story. This brings me to wonder how you store your boards and what‘s your setup to work on the board.

I’m bringing this up, because if the board failure are caused by your setup, every time you fix something, you may be breaking something else.

Ideally, you should use either a PCB holder like this:

Or some sort of third hand helper like this:


If you don’t and simply put your board on a flat surface, make sure that surface is clean and soft…just a thought…

 

[Jeff C]

So, I jumped from the left side as shown in the pic (but on the solder side of course). seems correct but let me know if I erred. And yes, I SHOULD have gear like that but what I’ve been using is in the second pic (you can see my jumper there) and it doesn’t work very well and I often have to take it off the stand…….

 

[EGRENIER]

So, I jumped from the left side as shown in the pic (but on the solder side of course). seems correct but let me know if I erred. And yes, I SHOULD have gear like that but what I’ve been using is in the second pic (you can see my jumper there) and it doesn’t work very well and I often have to take it off the stand…….
View attachment 30203View attachment 30204

If those alligator clips don't have rubber cover, that could be the source of many of your problems. Last thing you want is metal touching/scratching the board.

I can't tell if this jump (ends) is correct. Maybe you could check if you have continuity from the protection diode to R101 or + of C101, if you do that means you have jump "over" R100 instead of from it.

 

[Jeff C]

I try to connect the clips to unused space on the board, but I guess I should just not use that stand. By protection diode, I guess you mean D100? If so, I do indeed have continuity between D100 and R101 and C101+. So, I don’t screw it up again, do I just switch the jumper to the other end of R100 and leave R101 as is? Oh boy, more tricky soldering!

 

[EGRENIER]

I try to connect the clips to unused space on the board, but I guess I should just not use that stand. By protection diode, I guess you mean D100? If so, I do indeed have continuity between D100 and R101 and C101+. So, I don’t screw it up again, do I just switch the jumper to the other end of R100 and leave R101 as is? Oh boy, more tricky soldering!

Yes, connectivity between D100 to R101 and C101+... because you do, it sounds like you jump over R100.

Just change the jumper end from one side of R100 to the other side of R100. After doing it, you should no longer have connectivity between D100 and C101+. But connectivity should remain between you jumper end of R100 to C101+.

Apply power and test for voltage. You should see 9V on the non jumped side of R100 and 4.5V on the jump side of R100 and R101 and C101+.

Take your time, keep it clean...

 

[Jeff C]

 

[Jeff C]

Success! Woohoo! Pedal works with full effects! Thank you guys so much!! My first troubleshooting experience with the Cobalt Drive took a record 423 posts to solve; then the EA tremolo 79 posts; and now I’m down to 50! Who said you can’t teach an old dog new tricks?
Two little codas: LED one still doesn’t light up, even though it gets 9v as the schematic shows (at least as I read it….). Perhaps I burned it out at some early stage (it’s never lit up through this whole process); and also something very strange happened when I first put the jumper in incorrectly. My in pad on the switch daughterboard that connects to the PCB no longer connected to the in pad that connects to the in jack and instead had continuity to the ground?!?! Really bummed me out because I just couldn’t figure out why. But when I pit the jumper in correctly, suddenly it resumed connection to the proper in pad. Weird to me, but if you guys know why , I’d love to hear it.

Now if I can just put this thing back in the enclosure without screwing it’s up again!

 

[EGRENIER]

Success! Woohoo! Pedal works with full effects! Thank you guys so much!! My first troubleshooting experience with the Cobalt Drive took a record 423 posts to solve; then the EA tremolo 79 posts; and now I’m down to 50! Who said you can’t teach an old dog new tricks?
Two little codas: LED one still doesn’t light up, even though it gets 9v as the schematic shows (at least as I read it….). Perhaps I burned it out at some early stage (it’s never lit up through this whole process); and also something very strange happened when I first put the jumper in incorrectly. My in pad on the switch daughterboard that connects to the PCB no longer connected to the in pad that connects to the in jack and instead had continuity to the ground?!?! Really bummed me out because I just couldn’t figure out why. But when I pit the jumper in correctly, suddenly it resumed connection to the proper in pad. Weird to me, but if you guys know why , I’d love to hear it.

Now if I can just put this thing back in the enclosure without screwing it’s up again!

Great news... about your LED, you can try replacing it, but I suspect you might have just reverse the polarity. Take the existing one out and using a 9V battery just test it. That will let you find out with leg is positive, mark it with a bit of tape and re-install it paying attention to the A and the K on the board.

 

[Jeff C]

Great news... about your LED, you can try replacing it, but I suspect you might have just reverse the polarity. Take the existing one out and using a 9V battery just test it. That will let you find out with leg is positive, mark it with a bit of tape and re-install it paying attention to the A and the K on the board.

Took it out. Doesn’t light up either way on the battery (or my transistor tester). Had another LED, tested it on the 9v battery - brief spark and now it doesn’t light up either way.

 

[EGRENIER]

Took it out. Doesn’t light up either way on the battery (or my transistor tester). Had another LED, tested it on the 9v battery - brief spark and now it doesn’t light up either way.

That's my bad, I should have mention the use of the 4k7 in the LED circuit... Sorry about that...

 

[BuddytheReow]

When testing it on a battery you need a CLR (current limiting resistor). Otherwise you'll blow out the LED. Connect the LED to the CLR (it doesn't matter which end of the LED it's hooked up to) and then hook it up to a battery. PPCB "standard" is 4.7k ohms.

 

[Jeff C]

Yeah, that’s what I thought. Scratch one LED. Curious thing (for me, at least) is that on the Magnetron schematic, it shows power coming in direct to LED 1. And when I test the voltage at the LED 1 pad, it reads 9v……….

 

[Jeff C]

That's my bad, I should have mention the use of the 4k7 in the LED circuit... Sorry about that...

No problem - I should have known better, but see my reply above…….

 

[Jeff C]

Also, there is continuity between R102 (4.7k) and the SW pad and also to the K pad for LED 1, but how does that do the LED any good by coming after the 9v hits the LED?

 

[BuddytheReow]

In terms of the LED, it doesn't matter if the CLR (4.7k) comes after 9v or before ground. Intuition tells you it should only be right after 9v and before the LED itself. When I lit up an LED on a breadboard I tried the CLR both before and after the LED and worked just fine. Either way, the current is getting slowed down.

 

[Jeff C]

On the schematic it goes to the switch before going to ground, so if the switch is off, there is no route to ground……sorry to belabor this, just curious……….