SOLVED Magnetron screw up

Jeff C

Active member
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!
 
Ah, I see. So it doesn’t even get the 9v unless it’s grounded. I was always checking the voltage with the switch on. Once I switched it off, 0 volts at the LED pin. But then you knew that already……..😆
 
So, still can’t get that LED1 to light up. There is continuity from the LED pad to R102 and from there to the SW pad. That pad is connected to the V+ pad on the switch daughterboard, not the ground. And the V+ pad on the daughterboard is connected to the V+ pad of the daughterboard incoming power ground/V+ pair. And that pad is connected to nothing. You can see all those daughterboard pads on the pic at the top of the thread. But I am not running power into the daughterboard, I’m running it through the PCB at the top of the board. Could this be why my LED1 is not grounding and if so, any solutions? As the V+ pad on the daughterboard basically goes nowhere, could I just jump it to the ground pad right next to it? Or, more weirdly, a jumper from R102 to the ground pin on the depth pot? Clearly showing my total lack of electricity understanding……😜 hmm, I guess jumping to the pot would take the switch out of the equation and leave the LED on all the time. Never mind. But what about the other idea? Or putting a jumper between V+ and ground where the power pads on the daughterboard are?
 
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2 things come to mind here:

-I think you are using a different 3pdt daughterboard than the PPCB one. That's throwing me off a bit and causing your issues for the LED not working. The PCB has 4 pads: IN, OUT, GND, and SW. In and out are self-explanatory. GND is a solid connection to ground. SW is the connection from the - side of the LED. When you wire the footswitch and engage the circuit it finalizes this connection to ground and allows the current to flow through the LED and turns it on.

-In order to light the LED there needs to be power (say, 9v) going to a resistor (4.7k standard in PPCB circuits) then to the LED itself and then to ground. The main board/circuit has taken care of the first three (power, resistor, LED). We now have to make the connection to ground via the stomp switch. It looks like you are using the daughterboard for the circuit itself (bypass/engaged), plus the jacks.

The PCB itself allows you to ground the in/out jacks directly. That's what these pads are for here:
1659975520339.png

What I would do if I were you, I would replace the 3pdt stomp switch with no daughterboard, ground the in/out jacks via the connection pads listed above, and wire up the stomp switch per the build doc
1659975776876.png
 
1659977263196.png

I don't think so. This daughterboard looks like it does many of the things a PPCB board does: Power, grounding of the jacks, and LED section. Installing the resistor and LED, and wiring the power up directly to the board in addition to the main PCB would allow this to work. It would be easier all around and to avoid more troubleshooting to go with what I suggested in my previous post.
 
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I don't think so. This daughterboard looks like it does many of the things a PPCB board does: Power, grounding of the jacks, and LED section. Installing the resistor and LED, and wiring the power up directly to the board in addition to the main PCB would allow this to work. It would be easier all around and to avoid more troubleshooting to go with what I suggested in my previous post.
Well if the pedal is working, why not just put a resistor on the daughterboard and connecting the LED to it also ?

You're likely right in your assumption that it could be caused by the PCB to daughterboard relationship, but it seems a waste to dump the switch and daughterboard...
 
Well if the pedal is working, why not just put a resistor on the daughterboard and connecting the LED to it also ?

You're likely right in your assumption that it could be caused by the PCB to daughterboard relationship, but it seems a waste to dump the switch and daughterboard...
I’d have to drill another hole in the enclosure much closer to the switch……but that’s an option!
 
So, I soldered power to the daughterboard and put a tested 4.7k resistor in the correct place in the daughterboard. Then I ran two wires from the LED pads on the daughterboard to the (new) LED and it burned it right out. I tested voltage on the daughterboard and it’s getting 9+v, as are both sides of the resistor And the + LED pad. Not sure what’s happening……other than bad.
 
So, I soldered power to the daughterboard and put a tested 4.7k resistor in the correct place in the daughterboard. Then I ran two wires from the LED pads on the daughterboard to the (new) LED and it burned it right out. I tested voltage on the daughterboard and it’s getting 9+v, as are both sides of the resistor And the + LED pad. Not sure what’s happening……other than bad.
Why did you add power to the daughter board ? Don't you already have that from the main board ?

Disconnect that power and test the led pad... you'll probably be right where you should... test it first don't burn more leds...
 
Why did you add power to the daughter board ? Don't you already have that from the main board ?

Disconnect that power and test the led pad... you'll probably be right where you should... test it first don't burn more leds...
Too funny! I connected power to the daughterboard based on Buddy’s guidance, which has always been spot on……
so, if I disconnect the power to the daughterboard, what should the voltage be at the resistor and LED pads on the daughterboard?
 
Why did you add power to the daughter board ? Don't you already have that from the main board ?

Disconnect that power and test the led pad... you'll probably be right where you should... test it first don't burn more leds...
Disconnected the power to the daughterboard and now get no voltage readings from the LED pad. Not sure where power would be coming into the daughterboard from……..
 
Disconnected the power to the daughterboard and now get no voltage readings from the LED pad. Not sure where power would be coming into the daughterboard from……..
Hmmm, I was expecting the daughter board to be supplied by the main board. If I get this right, right now you are supplying power directly to the main board and it’s working, so ….

Where did you get the daughter board, do we have specs or instructions with it.
 
Ok not much information there, but let’s see if we can hack this…

Check if you have voltage in the V+ (Red) on the daughter board. Then you should read the same voltage on V+ (green). If this works, then jump V+ (green) to the resistance, blue jumper. Check the voltage at the LED. You will still read 9V, but this time the current load will be split with the resistance.

If you don’t read voltage on V+, then check the ground, you may have reverse the connections which, I think, would still work as it open and close the circuit through the switch.

No guaranty here… like I said trying to hack a board I can’t see the wiring. Word of advice for .25c more get your daughter board from pedalpcb. Anyway, that’s what I would try.

AF1FE5F1-7B18-460F-A677-FE69D1A9457D.jpeg
 
Will do! I know I don't get voltage to either V+ pad. I'll check tomorrow to see if I have ground and V+ reversed but I don't think so. I get continuity between V+ on the daughterboard and SW on the PCB and between grounds on both.
 
Will do! I know I don't get voltage to either V+ pad. I'll check tomorrow to see if I have ground and V+ reversed but I don't think so. I get continuity between V+ on the daughterboard and SW on the PCB and between grounds on both.
Don’t go to fast if you don’t get voltage on V+…

Tell what’s connecting to what on between DB and MB…

Of course the easy route is to wire you switch without a DB… but what’s the fun in that ?
 
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