I'm a total newbie with a soldering iron, and I'm trying to build Merlin's Glassblower booster from THCustom. I managed to make some magic smoke on my first attempt at powering it up, so trying to figure out now what I've done wrong!
1) I've done some continuity tests with a multimeter, and getting a beep for everything that should be connected to ground from the circuit diagram. But I'm also getting a beep between ground and BI or board input. Is that correct, or does it indicate that I've shorted something out? I'm also getting a beep from three of the 3PDT legs (if it were a smartphone keypad, they'd be numbers #1, #5 and #8)
2) Also, on the 3PDT board, it looked like a white LED was supplied with the kit, so I used a resistor leg to short across the RLED pads. But I notice now that I have one 2.2k resistor left over from the kit - should I have used that in the RLED spot?
3) I've also put the multimeter across each capacitor on the board, and each one is giving me some kind of readout, so does that mean the capacitors are o.k., or is it still possible I've fried some of them? And is it likely I've fried some other components, the transistors or the IC, for instance? Is there a way I can check those with the multimeter?
For reference:
- for wiring the jacks, battery & power socket, I was following this: http://www.diy-musikding.de/content/001-Basics/battwire.pdf
- for populating the board, i followed these instructions: https://diy.thcustom.com/?wpdmdl=3881
Apologies for my newbie-ness, and I'll probably end up ordering a replacement kit from THCustom, but I'm also keen to learn from my stupid mistakes rather than repeat them. Thank you for any help you can offer!
QuoteApologies for my newbie-ness
Not at all!
Quote2) Also, on the 3PDT board, it looked like a white LED was supplied with the kit, so I used a resistor leg to short across the RLED pads. But I notice now that I have one 2.2k resistor left over from the kit - should I have used that in the RLED spot?
Yeah, the LED needs a resistor. Did it ever light up?
Your ground wire might need some soldering.
R5 & R7 on the picture seem like they're in contact. According to the schematic they should not.
Same for R4 & R2.
I would check your board and make sure that there are no contact between component that should not be there according to the schematic.
thank you NorthCoast & djaaz, really appreciate the help on this.
@NorthCoast: yes, the LED flashed once the first time i pushed the 3PDT switch. i'll replace that resistor leg with the 2.2k ohm resistor now and see if i get anything, but i fear i've blown some components.
@djaaz: thanks for looking over the pictures so closely, that's great help and i'll see if there is contact there, and see if i can manage to desolder any offenders...
Quote@NorthCoast: yes, the LED flashed once the first time i pushed the 3PDT switch. i'll replace that resistor leg with the 2.2k ohm resistor now and see if i get anything, but i fear i've blown some components.
Ah, ok, if it flashed quickly, and then went off while there was still power to the circuit, then that flash was the LED getting too much current due to the lack of a current limiting resistor, which is what RLED is. The LED is blown and will need to be replaced.
QuoteBut I'm also getting a beep between ground and BI or board input. Is that correct
Yeah, if it is in bypass, the input is grounded. It shouldn't be grounded when the pedal is engaged, though.
Madbean has a great explanation about footswitch wiring here:
https://www.madbeanpedals.com/tutorials/downloads/MBP_FootswitchWiring.pdf
Thanks, NorthCoast, that's exactly what I need to know. I've just replaced the LED, put in that 2.2k resistor, and SUCCESS! The LED is lighting up and staying lit. Thank you so much for the help with this.
Oh, that's super about the 3PDT grounding - I am indeed only getting that continuity when the switch is engaged - thank you again!
I'll take a closer look at the potential contact issues flagged by djazz now before I count my chickens...
I had a closer look and it doesn't look like there's any stray contacts from my dodgy soldering, as far as I can tell.
I tried passing audio through the circuit. Bypass works fine ;). However I'm getting nothing once the switch is engaged. I presume this is because I blew something in the circuit (there was smoke from *something* the first time I powered up the circuit!). If I remember correctly, the smoke looked to be coming from somewhere around C2/C5, but I can't be sure. Is there any way I can track down what I've blown, or do I need to remove individual components from the board to check them?
Can you take another picture of your board from the top? So that we can see all components just like in the doc?
sure thing:
I don't see an obvious thing. So i'll say congrats, troubleshooting will make you progress.
Take a look at the tech help sections, there should be some post about the troubleshooting steps.
Then you should repost this in the Thcustom section.
I would say in the meanwhile, check your wiring. Check the obvious thing that should not be connected to each other (no continuity between 9v & ground for instance). Make a visual inspection of the different components.
And then you can also check the components that do not need to be removed (transistors)
https://www.youtube.com/watch?v=hBZ9kvkgu8E
Good hunting.
Super, djaaz, much appreciated, and I'll disappear down the rabbit hole for a while and see what I can find...
Thanks, djazz, it looks like I've blown one of the transistors, which leads me to another newbie question: do the numbers/letters AFTER BC327 mean anything on the transistor? The one I've blown is marked "BC327-25 T6 E" on the casing, but I can't find a local replacement with those exact markings. Is, for instance, a BC327-40 BU transistor o.k., or does the "40 BU" mean something incompatible?
The letter following the designation won't matter much in the context.
You need also to check that you're not going to blow the next one.
thanks, djazz! can you point me in the direction of how to check i'm not going to blow the next one? is it a matter of visually inspecting all the soldering, or is there a process to follow around the circuit with a multimeter or something like that?
The -25 and -40 are references to the amount of gain the transistor has. You can find it in the datasheet. I don't know what the other letters mean.
But, like djaaz said, it doesn't matter much here.
One thing to check, is the voltage rating on C5 and C6.
Also, you could pull both trannies and the IC and check voltages on the sockets. Post them here.
Also, this:
QuoteI would say in the meanwhile, check your wiring. Check the obvious thing that should not be connected to each other (no continuity between 9v & ground for instance). Make a visual inspection of the different components.
And: I looked at your pic and C5 and C6 look like they are physically over the top of some resistors, you might want to check that they are not touching those components. For example, is C5 touching R8 and R9? That's the first thing I'd check.
Is there any solder on lug 3 of your potentiometer?
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Quote from: NorthCoast on January 14, 2024, 07:55:49 PM
And: I looked at your pic and C5 and C6 look like they are physically over the top of some resistors, you might want to check that they are not touching those components. For example, is C5 touching R8 and R9? That's the first thing I'd check.
Just looked at the other pic and C5 doesn't look like it is touching R8 and R9 at all. Hmm.
Thank you all so much for your patience and help here.
@jimilee: do you mean where the wire from lug 3 goes to on the circuit board? from the top side, there isn't much solder there, alright, but from underneath it looks good. i checked for continuity between the top side of those pads and the lugs on the potentiometer itself, and all have continuity.
@NorthCoast:
- Thanks re the transistor naming sleuthing!
- re voltage rating on C5 and C6, apologies again here for the newbie question, but do you mean de-solder them from the board first and then check the voltage (as described here, for instance: https://www.electrical4u.com/how-to-test-capacitors/)? Or visually verify what's written on the capacitor? (in which case, it's 35V)
- i had a look at any potential physical contact between C5/C6 and neighbouring resistors, but there's clear daylight between everything.
- i've measured those voltages (to be clear, all measured without any of the IC, Q1 or Q2 in the circuit, rather than removing a single component at a time):
Q1:
Left: 2.9V
Middle: 0.91V
Right: 8.9V
Q2:
Left: 2.9V
Middle: 0.86V
Right: 0V
IC: (anti-clockwise, starting from bottom right, as per this graphic: https://startingelectronics.org/beginners/components/IC/8-pin-IC-outline.png)
1: 0.82V
2: 0.8V
3: 4.47V
4: 0V
5: 0.78V
6: 0.01V
7: 0.01V
8: 8.9V
I've also realised initially mixed up the placement of Q1 and Q2. I thought they were identical components, but obviously one is a PNP and the other a NPN. If I'm very fortunate, maybe nothing else will have blown, and getting replacement transistors in the *correct* place might solve the issue. I'll order a spare TL072 while I'm at it, in case I've fried the IC too.
I can't thank you all enough for your help with this. Good to be learning on this learning curve!
Quote from: dicey_reilly on January 14, 2024, 09:16:33 PM
Q1:
Left: 2.9V
Middle: 0.91V
Right: 8.9V
All your transistor legs are to the right of something. Look at the schematic, look at the transistor, google your transistor datasheet or at least pinout
(https://components101.com/sites/default/files/component_pin/BC327-Pinout.jpg)
And then post something like:
E: 2.9V
B: 0.86V
C: 0V
Before powering up, in case of doubts, better remove all active components that you socketed and make voltage measurement.
Once you are confident that you have the correct voltage per the schematic (9v on the collector of Q1 and 0V on the collector of Q2 for instance), socket and power up.
Quote from: dicey_reilly on January 14, 2024, 09:16:33 PM
Or visually verify what's written on the capacitor? (in which case, it's 35V)
Yes, that is what I was wondering. 35v is plenty.
Quote
I've also realised initially mixed up the placement of Q1 and Q2. I thought they were identical components, but obviously one is a PNP and the other a NPN. If I'm very fortunate, maybe nothing else will have blown, and getting replacement transistors in the *correct* place might solve the issue. I'll order a spare TL072 while I'm at it, in case I've fried the IC too.
Yeah, that makes a big difference. Those transistors are apples and oranges.
Thanks, djaaz, that would be much clearer alright - apologies.
So, I think it should be:
Q1:
E: 2.9V
B: 0.91V
C: 8.9V
Q2:
E: 2.9V
B: 0.86V
C: 0V
And thanks NorthCoast, I'll get replacements for those transistors and post an update here one way or the other. Thank you for all the help!
An update here: I had blown the BC337 transistor, so with that replaced, I am at least getting audio through the circuit now. Woohoo!
However rather than boosting the signal, it's giving me a signal that's quieter than the original.
The pot does work, and turning clockwise increases the signal from inaudible to a max of just very quiet.
I've tried replacing the BC327 transistor and the IC chip too, but no improvement, still the same behaviour.
Any ideas on what I've done wrong?
You really need to post that in the right section, now, to get the attention it deserves.
As of now, you need to look at the schematic and understand the different sections of it even if you don't need to understand everything about it.
Retake the voltage and post them.
Also, you might need to build a few very simple tool to help you troubleshoot further.
o.k., much appreciated djazz, i'll do that. once again, thanks to yourself and all here for the help getting me this far.
You're very much welcome. Someone far more knowledged than i am will probably pickup the ball in the THcustom support section.