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Be prepared to face many challenges that you'd never expect...I actually wouldn't recommend it haha...

I've helped launch a fair amount of successful projects and also do some high volume building.

You need to charge more than you would expect...always!

Get everything in writing with whoever you are working with.

If you plan on doing anything more than 100 units, start with an SMD hybrid design to begin with, there are a few companies now that do small SMD batch runs for a reasonable fee.

I do recall making a modulation board using the H11F1 once.
It was a one-off that I was just playing with and ended up using it in a build for someone.
It's not a commercial product, it was just a prototype I had laying around at the time.
From what I recall it worked well but it required some tweaking.  I'm fairly certain it used the same oscillator found in most of the pt2399 modulation circuits but it had maybe a 1M resistor in series with the H11F1 on the "resistance" side.  There really wasn't any secret sauce.
I think at the time I didn't make any further PCBs because the fate of the H11Fx series was uncertain with ROHS compliance.
I don't really remember much more than that as it was maybe +5 years ago?
Josh

The modulation shouldn't be weak at all so there is definitely a problem somewhere.  Make sure that the vactrol polarity is correct and/or that the LDR an LED side of the vactrol is correct.

If you were measuring the resistor in the circuit it won't give you a proper reading.  The chance of an open circuit resistor is slim to none unless it gave up smoke.  Reflow the applicable solder joints.  If you work methodically using the schematic you should find where you are losing signal.  One check you can do is with R20 out you can measure the Ldr side legs of the vactrol and you should have a varying resistance when the modulation is on.  Once you confirm that move onward.

Reflow the depth pot as well.  Maybe a bad joint is causing the weak signal.

Oh, well that is clearer then and good news.

Something is amiss from the vactrol onward.  Check every spot from the vactrol to the delay time pot by following the schematic.  Check your value of R20 too, as if you have an incorrect higher value there it will reduce the modulation.  Use your continuity setting on your DMM to make sure you have continuity where you should.  It's likely something simple as there really is not much between the indicator LED and the delay pot.

You don't need to worry about jumpering the switch pins.  That was before you mentioned it was blinking in time with the speed pot.

Josh

If you bridge the SW1 pads do you have the same effect?
Does the LED light?
If not double check the LED polarity.
if not that check R20 etc and the depth pot for any weak solder joints.

Your voltages look good assuming that the PT2399 was just read as pin 9 being pin 1...
IC2 is the oscillator for the modulation, hence the voltage swing.

Josh

Also, be aware of MLCCs and voltage derating.  Something to just familiarize yourself with in the SMD world.

Not really sure what your definition of low profile is, but most SMDs electros 100uF and under are less than 7mm Z height.  For lower value electros the diameter can be had in 4mm packages.  Kinda a dime a dozen and quantity is your friend.  They do take up more space than TH even in the 4mm diameter packages when you take into account the bottom footprint.  If you're doing SMD by hand just pick your poison   There is no reason to use SMD tant caps which are low ESR unless you have something like a charge pump, to avoid voltage losses.  They are big and expensive.

Josh

Here is another via thing for 4+ layer PCBs

You'll need to set up the DRC for the inner layers for the vias.

You'll need to uncheck the box to eliminate the non-functional pads (NFP) if you have any diameter set other than "auto".

There is much debate about NFP, but for analog, they are fine to leave if you don't want to mess with the DRC.

I believe the pad size for vias is set in the design rules. And you can always select the via and adjust the drill diameter on a layout. There's got to be a way to set it globally, but I've not figure it out (nor have I tried).

You update the eagle.scr

Mine is heavily modified now over the years.  I have custom menus and scripts for my entire workflow.  Sadly, all the workaround time spent I could have just migrated to Altium.  Especially doing 3D mocks.  I know the new version is more streamlined but I paid for 7 and am not moving into the contant update subscription model.

Anyhow, add this to your eagle.scr anywhere in the BRD portion of the script (change to whatever size via you want, use in instead of mm if using Imperial)

Set drill 0.4mm; #Make vias 0.4mm;
Set diameter 0.7mm; #Make diameter 0.7mm
Change Shape Round; #Make vias round

Josh

#2 8.5" x 10", they lay flat and are under the 3/4" requirement, but....if they contain something that doesn't bend or feel like anything but a document they are considered a package as flats are only for documents.  So domestic flats are out and as a result the global processing center.
I am a regular at the post and they already know I ship merch for years so passing a flat is impossible.

All my "drop boxes" go to the local post offices that won't accept my "flats".  Drop and pray isn't really a viable way to run a business.

At this point, I've exhausted all my options and contacts.  There is conflicting information and at this point, I can only offer the international package rates.  I apologize to my international friends, it hurts me as much as it hurts you...

On the plus side my international packages have been arriving much faster to there destinations than the previous international flat.

I've contacted shipstation, read the guidelines, and talked to two different USPS employees now.

You can't use the US first class flat in the U.S. to send to the processing facility if it contains anything other than documents.  Domestic flats cannot contain anything other than docs.  It has to be uniform, so if it can bend and it's apparent that there is something inconsistent it will not be processed.

Is that from contacting Shipstation/reading the guidelines, or do you mean that's what both of the postal workers were saying?

I've been using flats within the US for single-board orders for four or five years now... at 1oz it's much cheaper than standard first class, but at 2oz it's pretty much the same so I switch to regular first class at that point.

Both, but the shipstation rep I have emailed with doesn't really understand to be fair.  I think it really depends on who you talk to.

All the USPS employees I have spoken to have said US flats are not for anything other than documents.
If it bends inconsistently or feels like something other than a document it will be rejected.  (this is US only)
I have shipped flats in the US previously for a few random orders (replacements or one offs) but now I cannot get US flats through.

I will travel to the other post office in my area and see what they say next or call USPS directly.

I've contacted shipstation, read the guidelines, and talked to two different USPS employees now.

You can't use the US first class flat in the U.S. to send to the processing facility if it contains anything other than documents.  Domestic flats cannot contain anything other than docs.  It has to be uniform, so if it can bend and it's apparent that there is something inconsistent it will not be processed.  The last postal worker recommended placing uniform cardboard on each side of the PCBs to make a consistent envelope.  It won't work for shipping any parts that I sell and she isn't sure if it will even go through or not.

I have a feeling some post offices/workers might just pass them through, but mine does not.  I have yet to try another post office but the main one in my area is less forgiving than the one I always use.

It has nothing to do with the new rules.  I've run into it before.  They say you cannot ship an envelope with anything in it as an envelope / flat and that it must be a package.  I've also gotten the opposite, that I can't ship it as a package because it's too thin.  It all depends on who is manning it.

You may be right and I cannot find anything from restricting anything that isn't a document but unfortunately I'm at the will of the local post office and while I explained they do not agree.

I will contact shipstation and see what they say.  I will need to take a loss and get these orders out in the meantime.

This may be the beginning of the end for pcb wrangling for me.  I can't sustain if I don't have international orders