🎵One of these things is not like the other! 🎶

[Pauleo1214]

Don't you love when your combo build works the first time, 75% of the time?

I am currently on a hot mess streak. My last four pcbs (of which I built successfully before) produce dry signal but no modulation.
I decided to focus on another weird build, four HAARPs in parallel. A QUAARP if you will. Except one of them doesn't produce any modulation. The PCB in question is the one on the upper left (component side up), upper right (pot side up).

So far i checked all my resistors, reflowed all my solder joints, checked that the ICs are getting proper voltage (they are), swapped the regulator and tl072's, and swapped one of the EEPROMs. No dice. Could anyone who is an eagle eye with resistor color bands see if I possibly subbed a wrong value? My next guess besides that is a broken trace.

 

[Pauleo1214]

Maybe the crystal?

How do you tell that the crystal's bad? Just my luck that I have to order more if it has to be replaced.

 

[fig]

A scope, or if your DMM has a frequency function. There may be other ways?

 

[peccary]

How do you tell that the crystal's bad? Just my luck that I have to order more if it has to be replaced.

If you find that it's the crystal and need one drop me a line, I believe I have a few from when I did a HAARP.

 

[zgrav]

you could swap in temporarily a crystal from one of the others to see if it brings the pedal to life. if so, consider adding in the clock module to get another odd variation for your monster build.

 

[Pauleo1214]

I found I had a spare bag of the crystals and swapped one. Definitely not the crystal. Given all the values are correct, there's a severed trace somewhere. Looks like I'll be hunting it down tonight with a probe.

you could swap in temporarily a crystal from one of the others to see if it brings the pedal to life. if so, consider adding in the clock module to get another odd variation for your monster build.

Hmmmmm.....

 

[fig]

I found I had a spare bag of the crystals and swapped one. Definitely not the crystal. Given all the values are correct, there's a severed trace somewhere. Looks like I'll be hunting it down tonight with a probe.

Hmmmmm.....

Bummer...sorry Paul. I'm as much help as Fig in the troubleshoo....well you get the idea.

 

[music6000]

I found I had a spare bag of the crystals and swapped one. Definitely not the crystal. Given all the values are correct, there's a severed trace somewhere. Looks like I'll be hunting it down tonight with a probe.

Hmmmmm.....

Do you recall removing any components from this Build?
I would look at the traces around the area you may have done ie just like the crystal you just replaced ????

 

[Pauleo1214]

Do you recall removing any components from this Build?
I would look at the traces around the area you may have done ie just like the crystal you just replaced ????

Only other component i removed was R22. The pads and traces for both that and the crystal appear fine. I am going to have a go with a probe shortly

 

[JamieJ]

 

[music6000]

Only other component i removed was R22. The pads and traces for both that and the crystal appear fine. I am going to have a go with a probe shortly

Do you have Continuity between R22 & Pin 17 on FV-1, R22 opposite pad goes to Ground.

 

[Pauleo1214]

Do you have Continuity between R22 & Pin 17 on FV-1, R22 opposite pad goes to Ground.

There is continuity between R22 and Pin 17.

Commencing probing.

 

[Pauleo1214]

Sad news, everyone.

I am about ready to conclude that the FV-1 might be bad. I followed the schematic from the output back to the input and test continuity at every point. What that search turned up was a broken trace between R4 and R18. Both read their regular component values and not the parallel value of 6.8K. A jumper between those two points did not fix the issue.

At this point, it will be quicker and more cost effective to populate a new board.

 

[Pauleo1214]

broken trace between R4 and R18.
NOTE: Trace also goes to Pin 6 of IC1 & R19:
View attachment 25352

I did not junk the board yet. Let me give this a shot.

The curious thing I did not issue for fear of being looked at as a noob is I did not get any continuity reading across the 22K resistor on R4. A resistance reading always showed the correct value but no continuity between the two traces of R4 itself, nor the point between R18 and R4.

 

[music6000]

These 4 Red Circles should all have Continuity:

 

[Pauleo1214]

The four points in red circles have continuity. What I found that is very curious is there is NO continuity across R4 itself.

A continuity reading across R4 on the bad board reads 0L and gives a resistance reading of 22K.

A continuity reading across R4 on all other boards reads 1.3L and gives a resistance reading of 6.8K (parallel with R18 at 10k).

There is continuity between lug #2 of both the Wet and Dry pots on all boards except the bad one.

There is continuity between the left side of R4 and lug 2 of the Dry pot but no contiuity between lug 2 of the dry pot and the right side of R4. That is where my readings came to a stop. I'm baffled to what is actually occurring.

Green line on the image indicates contiuty, red line indicates none.

 

[music6000]

The four points in red circles have continuity. What I found that is very curious is there is NO continuity across R4 itself.

A continuity reading across R4 on the bad board reads 0L and gives a resistance reading of 22K.

A continuity reading across R4 on all other boards reads 1.3L and gives a resistance reading of 6.8K (parallel with R18 at 10k).

There is continuity between lug #2 of both the Wet and Dry pots on all boards except the bad one.

There is continuity between the left side of R4 and lug 2 of the Dry pot but no contiuity between lug 2 of the dry pot and the right side of R4. That is where my readings came to a stop. I'm baffled to what is actually occurring.

Green line on the image indicates contiuty, red line indicates none.

View attachment 25356

There should not be Continuity across R4!!!
You should not have Continuity across lug #2 of both the Wet and Dry pots!
When I do Continuity Test with DMM, I use the function that BEEEEEEEEEEEEEEBS!
If no BEEEEEEEEEEEEEEBS!, something is Broken or I have it on the wrong pads!!!

 

[Pauleo1214]

I apologize if I am trying your patience. I am just trying to get an understanding of the problem of this board vs. the others

I realize I am applying the term continuity incorrectly too. The schematic shows the output lugs of the wet and dry controls are connected by the junction of R4 and R18.

That said, the resistance reading of those resistors gives off their normal values showing they are not in parallel.

 

[music6000]

I apologize if I am trying your patience. I am just trying to get an understanding of the problem of this board vs. the others

I realize I am applying the term continuity incorrectly too. The schematic shows the output lugs of the wet and dry controls are connected by the junction of R4 and R18.

That said, the resistance reading of those resistors gives off their normal values showing they are not in parallel.

View attachment 25358

It's all Good, did you jumper the R4 & R18 or was it OK to begin with????

 

[Pauleo1214]

It's all Good, did you jumper the R4 & R18 or was it OK to begin with????

Last night i jumpered the left side of R4 the right side of right of R18 which the incorrect sides to jumper.

I was going to jumper the other sides but had to mow, pick up my car from service, run an errand, drive my car back to service because the charge piping on my intercooler uncoupled, take an uber home, get groceries, and now make dinner.

I'll solder the jumper on tonight.

 

[music6000]

Last night i jumpered the left side of R4 the right side of right of R18 which the incorrect sides to jumper.

I was going to jumper the other sides but had to mow, pick up my car from service, run an errand, drive my car back to service because the charge piping on my intercooler uncoupled, take an uber home, get groceries, and now make dinner.

I'll solder the jumper on tonight.

If you have the Beep function on your DMM & the 4 red circles all Beep, you don't need the jumper!