BYOC 27v Boost Help Needed

[shicks255]

Hello everybody.

First time noob poster here.  Completed my first build about a week ago, but have been trying to troubleshoot it to no avail.

It's the BYOC 27v boost kit, a link to the schematic can be found here: http://byocelectronics.com/27vboostschematic.pdf

I have not done any modifications or part substitutions and have followed the directions.

The signal comes through and works fine in bypass mode, but when engaged, there's sort of a farty crunch sound, and you only hear anything when the notes are strummed pretty hard.  And the notes die off quickly, almost like there is some sort of gate.

What I have done so far is checking all the joints and connections, making sure there are no bridges, double checking the correct resistors are in the correct slots.  Ive gone through with an audio probe and the signal seems fine up until it gets into IC1 on pin 3.  The signal coming out of IC1 pin 1 & pin 2 is the bad sound.


Here are the voltages I am seeing

IC1 TL072
P1=7.85
P2=7.56
P3=7.11
P4=7.56
P5=7.85
P6=7.87
P7=7.88
P8=8.66

IC2 7660S
P1=9.45
P2=8.99
P3=0
P4=seemed to fluctuate from about 8.3 -> 6.05
P5=7.56
P6=6.3
P7=9
P8=9.45


The 2 Diodes

D1
A=9.45
K=9.05

D2
A=9.05
K=8.66


9.45 Volts from the positive power circuit board connection.


Hoping someone can give me a little assistance.  Would really love to get this thing working.
As mentioned earlier, this is my first build and my first post so apologies if I missed anything, and please go easy! 

Ive included images of the board and the schematic

Thanks
Steven

[antonis]

Hi & Welcome..

First of all, check for -9V on IC2 pin 5..
Then check for 4.5V on IC1 pin 3..

On a second glance, somewhere should be a major grounding issue..

P.S.
Although never dealt with particular circuitt, it seems to me a bit odd for bi-polar supply the 4.5V bias..
(but I presume circuit design might specifically count on that..)

edit: Didn't realize +18 / -9V supply, hence +4.5v actually is mid-supply bias..

[antonis]

For OP convenience..

ALL TL072 pins ( except 4 & 8 ) should read around 4.5V DC..
Pin 4 should read -9V (as long as IC2 pin 5 does the same) and pin 8 should read +9V..

[shicks255]

Thanks Antonis for quickly jumping in

Yeah, i thought it was strange how i'm not seeing any negative voltages at all, as from what I have researched the opamps need a negative source

Do you think there may be something wrong with my ICs or something with other components/wiring?

You said major grounding issue? 

Double checking again all my pin voltages seem the same, definitely not seeing the -9v on TL072 pin 4 :/  Not seeing any negative voltages anywhere

[zesak]

Start with max1044; check for correct polarity (the plus sign) of capacitor C10.

[antonis]

Start with max1044; check for correct polarity (the plus sign) of capacitor C10.

Good suggestion but not critical, IMHO..

Correct polarity ensures good -9V regulation and C10 long live happiness..
It should make trouble for -9V output only in case of C10 shorted..
(bown up open should create minor issues, like voltage regulation..)

[shicks255]

Thanks for the suggestion.

I did check the polarity for C10 and from what I can tell, it is correct.  The - is connected to pin 5, and the + goes to ground.

[antonis]

The - is connected to pin 5, and the + goes to ground.

Which ground should be checked for proper connection to IN/OUT/ Power supply ground..

Could you check for +4.5V on R10/R11/C6 joint..??

[shicks255]

Ok, just did a quick check,

The R10 is reading 9v on one side and 4.7ish on the other side, r11 and c6 both seeing 4.7v

[idy]

Welcome to the forum!

The charge pump is not doing anything. It is not making -9 or +18. Until that is solved, nothing else matters. Pin 5 should be about -9. The "striped" end of the diode furthest from the chip should show about +18.


Unfortunate you have not used sockets for the ICs. BYOC used to emphasize that. Your instructions don't mention it. They are hard to remove without destruction. Cheap to replace, but a hassle if you don't have spares.

Power off, you will want to test for continuity from 1044 pin 3 and ground. Either your 1044 is bad or something around it is, maybe a broken trace or bad solder connection...

[idy]

Maybe show us a photo of the back of the board too. And make sure the ground wire to the board is good. It won't help if pin3 is connected to pcb ground but the wire attaching the pcb to ground is not soldered in. And even joints that look swell can be lousy.

Soldering looks suspicious on the ground to out jack, and also on the ICs. If they aren't soldered in at all I would put sockets in...but if you have soldered them give them a touch up. There are videos show good soldering technique. And the wiki on this forum has tips. Best is temperature controlled iron...

Power off, check continuity 1044 pin 3 to the pads on the board marked with a ground sign, and the one marked - where the power comes in.

[duck_arse]

....
edit: Didn't realize +18 / -9V supply, hence +4.5v actually is mid-supply bias..

ALL TL072 pins ( except 4 & 8 ) should read around 4.5V DC..
Pin 4 should read -9V (as long as IC2 pin 5 does the same) and pin 8 should read +9V..

as Antonis always sez, hello, welcome, and pin 8 should read +18V.

[shicks255]

Big thankful shoutout to everyone chiming in thus far to assist!


Did a few more checks,

Pin 3 on 1044 has continuity to ground, including to the board, the output jack and the power supply ground.

The second diode is NOT reading +18v, still reading around 9v.

None of the voltages have changed, still not seeing any +18 or -9 :/

I touched up the joints on the ICs, except for 1044 pin 6 & 7 because from the schematic they dont appear to be used.

I've also included a few more pictures below

[idy]

Assuming you have the right chip in the right place (I can't read any print on the ICs)?

About soldering: the good joints have that "chocolate chip" shape. The component lead or wire and there eyelet get hot and "wick" the solder up and all over. Globs are bad, wires that  haven't drawn a thin coat up the sides are suspect.

I visited the BYOC forum and found a handful of threads like yours; 27v boost, nothing happening, voltages like yours. The answer was bad 1044. I hate to say it because bad components are the last thing to suspect usually, and I discourage new folks from blaming components and going crazy with the soldering iron. And desoldering chips is a hassle/likely to damage the board. Don't do it in anger...

Get some more input from others first. But if you go there you probably would cut all eight legs and remove them one by one...

I didn't notice how much recent action there is at the BYOC form, but its worth while to post there. They are/were pretty generous about sending odd replacement parts to beginners up a tree.

[zesak]

Do yourself a favor and build your voltage doubler and inverter on breadboard first.
Verify the output voltages are correct. Then move on with the rest. Just what i would do.

[PRR]

MAX1044 ABSOLUTE MAXIMUM supply voltage is 10.5V.

I have heard this is a no-fooling limit.

Lots of "9V" supplies exceed that.

[zesak]

@antonis,
IMO the caps are integral part of charge-pump doubler and inverter function.
Caps external to the chip are getting charged and discharged by chip's internal switches, so no filtering function here.
But thats beyond the point anyway if he has a crapy chip or Vin too high.

[antonis]

@antonis,
IMO the caps are integral part of charge-pump doubler and inverter function.
Caps external to the chip are getting charged and discharged by chip's internal switches, so no filtering function here.

Honestly, I never studied in depth neither 1044 nor 7660 innards..

But, as far as I remember from respective datasheets, charge-pump (switched) cap is the one connected between pins 2 & 4 while pin 5 to GND cap is clearly stated as "reservoir" cap..

https://www.ti.com/lit/ds/symlink/lmc7660.pdf?ts=1653852887821&ref_url=https%253A%252F%252Fwww.google.com%252F

https://datasheets.maximintegrated.com/en/ds/ICL7660-MAX1044.pdf
(page 6, Pin Description Table)

[amptramp]

Am I missing something here?  It looks like the DC adapter centre pin terminal is connected directly to the audio input of the device.

[duck_arse]

Am I missing something here?  It looks like the DC adapter centre pin terminal is connected directly to the audio input of the device.

considering the way they have drawn the circuit diagram w/ the bypass switch showing mixed sense at in and out, I'd say no, you aren't missing something. it would be nice to see a shot of the board showing the traces.