SOLVED Pharmacist pedal lights no effect

[johnzero0]

Hi guys

I wonder if you can help, i just built a pharmacist pedal and after painstakingly ordering the individual components im getting lights but an almost inaudible low volume output with pedal engaged. pass through is working fine.

 

[johnzero0]

i too noticed those you have circled in red as possible shorts but there is no continuity between the 2 points within the circles i tested which were the bottom 2 in the picture.
i will follow your advice and check the rest of you helpful suggestions later.

 

[johnzero0]

Ok
Q4 which is 3rd from the left on the underside of the board S or Pin 2 is definitely reading 1.2v

Q2 p3 (im calling it C)and Q3 p2 are reading the same 4.3v and do have continuity, sorry for the discrepancy and red herring in my reading of 0 on Q2 pin3 / C yesterday

to be clear these are the pin outs on diagram are what i am referring to as p1 p2 and p3 or C,B,E in my list of readings of my 2n2222a which are plastic TO92 shell not the metal TO18

edit: can confirm no continuity to ground from Q4 p2

 

[eh là bas ma]

can confirm no continuity to ground from Q4 p2

Thats to be expected, pin 2 should have continuity with one side or R25, and the other side of R25 should have continuity with ground, according to schematics.

https://docs.pedalpcb.com/project/Pharmacist-PedalPCB.pdf

Can you confirm that there are no mistakes in designations on your last complete list of readings ? Can you update the list with your last good readings ?

 

[johnzero0]

Thats to be expected, pin 2 should have continuity with one side or R25, and the other side of R25 should have continuity with ground, according to schematics.

Confirmed after testing this is true

I will take measurements again and post tommorow.

 

[johnzero0]

Please see latest readings in volts
Q1
3C 8.4
2B 2.7
1E 2.3

Q2
3C 4.3
2B 0.6
1E 0.05

Q3
3C 8
2B 4.3
1E 3.7

Q5
G 2.7
S 16.9
D 17

Q4
G 0
S 1.29
D 16.9

Q7
G 2.6
S 16.3
D 17

Q6
G 0
S 0.6
D 16.3

Edit: The wires from the board to the 2 switches proved to be a bit problematic for me during the build i had to replace the wires, however the soldering points on each are solid and pressing the switch lights the corresponding LED. Is there a diagram i can use to test continuity from each of the pads on the switch to the board? specifically the effect on/bypass switch.

 

[eh là bas ma]

Is there a diagram i can use to test continuity from each of the pads on the switch to the board? specifically the effect on/bypass switch.

It's usually often the same thing, Input Jack's pad gets grounded when you switch off, it's connected to Board IN when you switch on :


You can also test for continuity between all ground points, starting with the jacks, the on/off 3PDT, the DC 9V jack...

But now that you mention it, I wonder if you didn't soldered the switchboard on the wrong side... Aren't there some writtings on the other side? With markers for each pads ?

If so, this would be a wiring issue. You'd have to take off the switchboard without melting the fragile 3PDT, which is a bit tricky (most builders would just take a new one, or carefully break the switchboard with cutting pliers), and start over the switch wiring. Can you confirm both switches are soldered with the right side toward the 3PDT ?

Be that as it may, your transistors are getting power, that's a good sign. I can't say for sure that's there's something odd... I am sure an audio probe test will tell you what's working and what's not. See reply #16.

 

[johnzero0]

The grounds continuity checks out fine and the switch is fine there is continuity where there should be and tested with off and on.
The pads are i believe the right way around as compared with other builds and are printed on reverse " this side down"

Parts are on order for audio probe....

can an incorrect value component cause weak signal or clipped audio i have noticed the boosted signal has some clipping going on.

Thanks for your
perserverance and patience!

 

[eh là bas ma]

can an incorrect value component cause weak signal or clipped audio

Yes, depending on where it is located in the signal chain, its function in the circuit, etc. It's always a good idea to carefully triple check and measure each component, first thing at the beginning, when you populate the board : before soldering.

Experts are telling us that levels of dexterity and caution can greatly vary, according to the hour in the night, rage and stamina levels, digestion, individual's mindsets, etc.

 

[johnzero0]

I have a audio probe and im looking at the signal path you have kindly drawn out i tested at the circuit in with pedal engaged as i assume this is the signal start then move on to the volume pot ? which i believe to be the next component in the path? But im not getting any signal on any lug

edit i am comparing your path to the circuit diagram supplied in the documentation now makes sense i can see “in“ on left and “out” on the right i was reading it right to left!

 

[eh là bas ma]

Signal path starts at R1, Volume pot is in the end of the signal path. After Volume, the signal goes to the 3PDT switchboard, and finally to the jack Out.

Volume's Pin 1 is grounded (no signal), so you should have a signal on pin 2 and 3. If there isn't, it means the signal stops somewhere betweeen R1 and Volume. Check R1, C1, Q1 (one of its legs should have a signal), etc.

You should follow the signal starting at the beginning of the circuit (R1), and keep probing the pads all the way through the signal path, looking closely tro the schematics. Each time you notice something weird with the signal on some pad, try to reflow the pad, look for a short, and check the component's value, it's orientation and continuity.

After C14 and R23, the signal splits in two :
The part going to R24 is the normal signal path working without the boost. The other part going to R32 is the boost section : You won't have a signal unless the boost is engaged.

Edit : More precisely, the signal enters the box on the jack In tip, it goes to the 3PDT switchboard Jack In (J IN), then to the switchboard Board In, wired to the main pcb's pad In, and then to R1.

 

[Chillums]

Just thought I would chime in about something I saw in one of your pictures. It's around the charge pump IC, the electrolytic caps look bulging to me although it could be an optical illusion from the angle but if they are roasted might try replacing them with a higher voltage rating. Again, I could be wrong...

 

[johnzero0]

Thanks for chiming in Chillums, the caps are rated for 50v but i think i have traced thr problem to a cap as there is no signal after C16, i have reflowed Q4 just in case and also C16 but no joy, should i try to replace the 10u cap or bridge the connection?

edit: just to note that there is continuity between the last leg of Q4 and C16
edit i meant no signal from C16 onwards

 

[eh là bas ma]

should i try to replace the 10u cap or bridge the connection?

Bridging the connections will tell you if the signal can be easily restaured, but you will probably need to fix C16 cap.

Unsolder C16 and take it off the pcb, perform a capacitor test with your multimeter to confirm it's working and its value. Replace it with a new one if necessary.
While C16 is off the board, you can do a continuity test between C16 pads and R29, to make sure the empty pads are correctly connected to the next component. If there is an issue with C16 and R29 connection (because the pcb's trace is damaged for exemple), you can try to solder a jumper between C16 negative side and R29 correct pad, the side not connected to the Volume pot.

 

[johnzero0]

Ok have replaced C16 audio probe now gets a nice clear sound signal at C16! and at one side of R29 the side pointing to C16 but the other side of R29 and at the volume pot there is barely any signal on any of the 3 terminals on the pot. Volume pot doesn't seem to do much and the value of R29 looks fine to me = 57k6

Edit at Q4 legs 2&3 source and gate I'm getting a much louder overdriven sound more in line with how I expect the effect to be but at C16 it is much cleaner and much lower in volume.

Edit there is continuity between c16 and r29 and i have replaced Q4 but still the same legs 2 and 3 have a overdriven loud guitar sound affected by the gain control pot. But leg 1 and C16 have a clean low volume sound.

 

[Chillums]

I'm not sure if anyone suggested this yet but could it be the volume pot?

 

[johnzero0]

I'm not sure if anyone suggested this yet but could it be the volume pot?

Not sure the volume pot would affect the signal / anything "upstream" from it

 

[eh là bas ma]

at Q4 legs 2&3 source and gate I'm getting a much louder overdriven sound more in line with how I expect the effect to be but at C16 it is much cleaner and much lower in volume.

Can you confirm, with continuity tests and following schematics, that everything is ok with R28, C17, R26 and Q5 ? (circuit switched off and power unplugged).

Not sure the volume pot would affect the signal / anything "upstream" from it

It could be the issue, if there's a short or if the pot isn't correctly soldered to the pads. Make sure the pot's legs and body aren't touching anything in the enclosure.
You can also check if the pot is working by measuring, with a multimeter on resistor test, if the value is changing when you turn it. Probes on Volume pin 2 and 3 (middle one and the lug connected to R29).

Looks like progress, you are narrowing it down...

 

[johnzero0]

Can you confirm, with continuity tests and following schematics, that everything is ok with R28, C17, R26 and Q5 ? (circuit switched off and power unplugged).

There is continuity in those places and the values of those components are correct however Not sure where to test continuity for q5 to vcc and r26 to vref though.

The vol pot also checks out in resistance check and moving does change value between p2 and 3

 

[eh là bas ma]

Not sure where to test continuity for q5 to vcc and r26 to vref though.

Any other Vcc and Vref points on schematics will do.

For exemple C20 + side is Vref, C24 + side or R30 are Vcc, according to schematics.

 

[johnzero0]

Any other Vcc and Vref points on schematics will do.

For exemple C20 + side is Vref, C24 + side or R30 are Vcc, according to schematics.

Unfortunately after checking continuity these check out as well

Edit: with the gain control at full i can hear some audio signal on the volume pot and at c16 hence my earlier post about detecting a signal at this point. But vol pot is at full and it is nothing compared to the sound at q4 points 2&3