Magnetron Delay... Simple issue I THINK??

[tony311]

Hello everyone.

I have been battling with this issue for some time now. I believe it must be a simple issue, but I'm just not smart enough to work it out!

I have built the Delay above. In Australia so got the board from the US and parts here.
When I finished it, I tested it with a breakout box.... Worked fine, sounded great. Wired up the plugs and switch and tested again, all still good. Put it in the case and Bypass worked but when switched on it would kill the sound or just buzz.

So I pulled it out and took jacks and switch off. Hand wired with jumper leads and worked great. So I soldered different plugs on and soldered the switch back on. No bypass ok, but when I switch it on, no sound. At one point, when it was on, and I shorted the input lead to the plug sheild, it started working. But now its back to not working when on. Its intermittent. I have soldered and re-soldered the connections and even the components. I tried a new PT2399 with no difference. I have been battling with this for a few days and I am just about to give up but it is bugging me. I can read schematics as far as seeing what's what and what they are connected to, but I don't know how to determine what MAY or may not be causing the issue and how....

Any advice or guidance would be greatly appreciated.

[niektb]

Did you by chance flip your switch by 90 degrees?

[tony311]

Did you by chance flip your switch by 90 degrees?

Thats a really good question... But I metered the connections on the switch and I'm certain it is round the right way... Won't hurt to have another look.. Thanks.

Come to think of it, no I that would mean that the pins are vertical rather than horizontal. I would have picked that up.

[duck_arse]

if the build works out of the box, but not when it's in the box, we should really see a picture of the build as it lies in the box - visual clues and all. and, really, you should have done voltage measures when it wasn't working .... and and and ,,,,

but, put simply, you are showing a metal bodied DC jack, which will short (+) to the case. either isolate that jack from the metal case, or use a plastic DC socket.

[tony311]

if the build works out of the box, but not when it's in the box, we should really see a picture of the build as it lies in the box - visual clues and all. and, really, you should have done voltage measures when it wasn't working .... and and and ,,,,

but, put simply, you are showing a metal bodied DC jack, which will short (+) to the case. either isolate that jack from the metal case, or use a plastic DC socket.

No, its not working either way. In the box or out of it. It has never worked whilst in the box, but I it will sometimes work out of the box...

[duck_arse]

alright, bad on me for not paying attention. your in/out jacks - you have wired the tip/signal on both to the ground pads at top of board, and both sleeves are being switched on the footswitch. swap the wires at the jacks and yo should be some way closer to the desired outcome.

this is one of the errors you catch if you do resistance measures on jack and supply connections before first power on.

[tony311]

alright, bad on me for not paying attention. your in/out jacks - you have wired the tip/signal on both to the ground pads at top of board, and both sleeves are being switched on the footswitch. swap the wires at the jacks and yo should be some way closer to the desired outcome.

this is one of the errors you catch if you do resistance measures on jack and supply connections before first power on.

Sorry, I am a little confused. What makes you say the signal wire is wired to the wrong part of the jack? The in wire is going to the in tip shield comes from switch and the out wire goes to the out tip and shield from switch. This is the way I have done all the pedals and my understanding of what the documentation states.. Am I wrong??  If so, why do the other pedals I've built and wired this way work?

[ElectricDruid]

No, Duck's right - you've definitely wired the ring connection to the switch (long black wires in both cases) and the tip wires are wired direct to the PCB (blue and white wires). You can see it here:


The wiring diagram on page 5 of the build document shows this, but it's not very clear because they've used different jacks:

https://www.pedalpcb.com/docs/Magnetron-PedalPCB.pdf

The significant thing here is that black wires (grounds) go to the board, whereas orange wires (signal) go to the switch.

[tony311]

No, Duck's right - you've definitely wired the ring connection to the switch (long black wires in both cases) and the tip wires are wired direct to the PCB (blue and white wires). You can see it here:


The wiring diagram on page 5 of the build document shows this, but it's not very clear because they've used different jacks:

https://www.pedalpcb.com/docs/Magnetron-PedalPCB.pdf

The significant thing here is that black wires (grounds) go to the board, whereas orange wires (signal) go to the switch.

Ok... Thats really interesting. A lot of the other pedals I have done were wired the way I have it and work  Anyway thank you... I will give that a try today... SHould make all the difference... I'll post back.

[tony311]

Well, I went into swapping the cables with such optermism, But no go. It bypasses perfectly, but as soon as you switch, no sound comes out but the LED power states its on and the Activity light works and changes when I turn the depth and speed just as its supposed to, just no output.

I have gone through and checked all voltages and reference points. Replaced a couple of resistors I felt may be an issue, tested the diodes changed the op amp, The only thing I havent swapped is the OPA2134 because I don't have another... I also just believe it is somthing simpler than that but I have no idea what...  About to give up I think.!

[Locrian99]

Have you checked the voltages on your ic's since you've soldered and resoldered.   That might give a big hint as to what the problem is, also do you have an audio probe?   Voltages and audio probe could at least narrow it down to where the problem is happening.   And using the audio probe to trace the signal my last build I couldn't get to work was literally able to audio probe right to where the problem was (bad soldering job). 

[tony311]

Have you checked the voltages on your ic's since you've soldered and resoldered.   That might give a big hint as to what the problem is, also do you have an audio probe?   Voltages and audio probe could at least narrow it down to where the problem is happening.   And using the audio probe to trace the signal my last build I couldn't get to work was literally able to audio probe right to where the problem was (bad soldering job).

I went through the voltages on the ics again today and all good.. yes I do have a probe. I will hunt around the board with that tomorrow. Thanks

[ElectricDruid]

About to give up I think.!

Definitely don't give up yet! We've only just started!

A problem where you're getting nothing at all is often much simpler than one where something's happening but it's not quite right. So don't despair. It'll be some stupid thing, and then it'll all magically start working and you'll feel like a dork (Ask me how I know ) That's how it goes.

If you've got the correct voltages on the ICs (can we see them?) then that's a really good start. If the chips are happy, but there's still no signal, we might be looking for a short somewhere. I definitely second Locrian's suggestion of an audio probe - that's the next step, for sure. We can give you a series of points to check on the board/schematic if that would help.

Tom

[tony311]

I don't know what I'm doing!!!!

I have gone through with the probe. I have traced the signal to the IC2 LM358. When I put the probe on any of the pins on this chip all i get is a sort of humming tapping sound. However I have found that later in the signal, well after IC2, there is signal but it is not being effected by the effects in any way. It is just as if in bypass. I have attached an image as to where the sound is just noise not rather than the signal I am feeding into it....
I have changed a couple of resistors that were feeding IC2 going by the circut, because they too had the same sound as the chip. I know the chip is good, because I went out today and purchased another one and put it in. I was suspecting a track shorted or broken but been over it twice and cant seem to see that....So it is somthing before that but everything else seems ok with the probe. Hence I dont know what I'm doing.....

As for the Voltages..
PT2399- Pin1=4.9V, Pin2=2.49V, Pin5=4.9V, Pin6-9=4.5V, Pin10=0.5V, Pin11-16=2.5ish Volts..... Opa2134.... Pin1=4.76V, Pin2&3=4.7V, Pin4=0V, Pin5-7=4.7, Pin8=9.5V......
LM378....Pin1-3=5.7V, Pin4=0, Pin5-7=5.8, Pin8=9.5V.

[anotherjim]

PT2399 Pin5=4.9V. This says the internal clock is not running so you won't get any delay which could also explain pin10 voltage being so low.
The chip could be fried.
The chip could be locked up by static charge in its internals. Sometimes this can be fixed by switching off and shorting out all of the chip pins together with conductive foil for 10 seconds or so. Any rogue charge can bleed away.
If the clock is running, pin5 should be around 2.5v-ish.

[Locrian99]

I would try as Jim said a new chip if you have it or the foil trick.   That being said mt albeit limited experience with this something seemingly unconnected can make all of the voltages funny.   Different pedal but some idea I just built a deep blue delay clone (sea urchin on pedal pcb) I did a vero layout though.   And I left out a resistor off pin 16 and I had weird voltages all over.   So I would check all resistors/connections around the pt2399 (bad solder connection would be the same as the resistor just not being there).   That being said here are the voltages for a working pt2399 delay, I did have some variance from these in mine but i believe it should be in this ballpark.   



Mine works fine with pin 5 voltage in the 3.3 range, and I have 400-500 mv on 7/8.   But 9-16 all are right at 2.48.   Just as an fyi pin 14 should have the audio of the delay (so if you probe it, you hit the note and the delayed signal will come out there).   And 15 or 16 has both signals.   I appreciated that info when doing mine. 

[ElectricDruid]

I've sketched the signal path on the schematic so you can see what's going on:



The dry signal is the blue path to the output. The red path is the delayed signal, which joins the dry signal at the output mixer (IC1.2) I've ignored the feedback path for now.

Some good points to check for audio are marked in green. They are:

The output of the input op-amp.
The output of the pre-delay filter
The output of the post-delay filter
The output of the final mixer

What others have said about voltages is crucial though - until you get good solid voltages around the PT2399, the thing isn't happy and it's not going to work. So work on that first - otherwise you'll probably have audio at the first two test points I mentioned, and no delay at the post-delay filter or mixer.

Hope this helps, good luck!

[tony311]

PT2399 Pin5=4.9V. This says the internal clock is not running so you won't get any delay which could also explain pin10 voltage being so low.
The chip could be fried.
The chip could be locked up by static charge in its internals. Sometimes this can be fixed by switching off and shorting out all of the chip pins together with conductive foil for 10 seconds or so. Any rogue charge can bleed away.
If the clock is running, pin5 should be around 2.5v-ish.

I actually tried another chip the other day as I do have a spare. Made no difference... I will give it another go.

[tony311]

PT2399 Pin5=4.9V. This says the internal clock is not running so you won't get any delay which could also explain pin10 voltage being so low.
The chip could be fried.
The chip could be locked up by static charge in its internals. Sometimes this can be fixed by switching off and shorting out all of the chip pins together with conductive foil for 10 seconds or so. Any rogue charge can bleed away.
If the clock is running, pin5 should be around 2.5v-ish.

I actually tried another chip the other day as I do have a spare. Made no difference... I will give it another go.

Thank you. It looks like the path I was following. Good to know I was sort of on the right track... I will swap the PT2399 today and follow the path again. Still concerned with the silly noise on the op amp though... Thanks..

[tony311]

FINALLY!!! Yes finally working. Not that I can take any credit for it. Thanks to all of you on this forum for 1.) your expertise and knowledge and 2.)Giving me the morel support to keep going. I would have thrown it in the bin days ago otherwise..

You were correct with the PT2399. I put the new one in this morning and at first it was the same. So I pulled it out, used the aluminium foil, made a coffee and put it back in. I tidied up some of the soldering and wiring and it worked... I couldn't believe it after trying and trying and nothing working. I finally got to put it in the case with knobs and all.

Don't know how to thank you enough..... I wish I could support members with info, but I have made a donation to the forum as I think it is invaluable...