I am showing the location and the challenge that you will have to appropriately add the 8 pfd ceramic capacitors.
Thanks James. If youâve added the component please post a photo. 
My unit is very intermittent but I noticed it failed regularly with higher humidity so Role could well have the answer, the data sheet indicates these capacitors are required and unless the HT1381 has internal loading capacitors, which I doubt, they should definatly be fitted.
I have PCB REV A 20220402
The correct way to modify the circuit is like this. Loading capacitors and crystal should be mounted as close the RTC IC (U4) as possible with symmetrical PCB track length. Clean a small amount of the black solder mask on the ground plane with a fiber pencil or modeling knife to expose the copper without damaging the copper surface too much. Carefully solder the two smd 8pf capacitors as I have shown in the picture. These PCBâs would(should) have used lead free solder but I would suggest to rework using leaded low temperature solder. Clean any flux residue with alcohol or similar to avoid any chance of electrical leakage. This did drop my clock frequency very slightly as expected but not enough to worry about, the device will occasionally re-synchronise the time over WiFi to keep it accurate (at least it should!). Also check the 5.5v back up cell (EC1) it should read approx 4.7v when the unit is plugged in, it wonât stop the RTC working or give the time-error but you will loose the time if it fails when the unit is unplugged. These cells donât last much more than 6-8 years. Be sure to work on an anti static mat and take all the usual static precautions.
I should know in the next couple of weeks if this modification has fixed the issue.
Clearly this is going to be outside the scope of most people on this forum, but if you know a capable friend with the required tools it is quite simple.
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Iâm awaiting your feedback on the modification. It would be very helpful if someone could share step-by-step pictures showing the âbeforeâ and âafterâ views side by side, as I donât have an electronics background. I plan to get this done at a soldering shop, so detailed pictures would help me explain the work clearly.
This post does contain sufficient detailed information to understand the issue and what steps to take to stabilise units that have issues.
Some electronics back ground will help.
Just to confirm, adding the additional capacitors has fixed the problem with my controller. I did find a deal to get a new IIC-800 and had a look at the PCB. The new products have the capacitors added in the same manor as I did with mine. So it would appear that issue has been resolved. You will need the correct size of capacitor so they fit neatly, search using the following sentence, I buy mine from AliExpress.
0603 SMD capacitor 8pF
Hi. Do you have a picture of the repair you did?
Instead of soldering to the pins of the U4 integrated circuit, couldnât you solder to the crystal pins and connect them to the PCB ground? That way I wouldnât have to solder to U4.
I have the same board as you.
Thanks, Alejandro
Hello. I have an 8.2 pF capacitor, would that work too?
Solder the capacitors as close to the crystal as possible as you can see in my photo. 8.2pf capacitors will be okay.
The following is from a previous reply on this post.
It should answer your question.
I have PCB REV A 20220402
The correct way to modify the circuit is like this. Loading capacitors and crystal should be mounted as close the RTC IC (U4) as possible with symmetrical PCB track length. Clean a small amount of the black solder mask on the ground plane with a fiber pencil or modeling knife to expose the copper without damaging the copper surface too much. Carefully solder the two smd 8pf capacitors as I have shown in the picture. These PCBâs would(should) have used lead free solder but I would suggest to rework using leaded low temperature solder. Clean any flux residue with alcohol or similar to avoid any chance of electrical leakage. This did drop my clock frequency very slightly as expected but not enough to worry about, the device will occasionally re-synchronise the time over WiFi to keep it accurate (at least it should!). Also check the 5.5v back up cell (EC1) it should read approx 4.7v when the unit is plugged in, it wonât stop the RTC working or give the time-error but you will loose the time if it fails when the unit is unplugged. These cells donât last much more than 6-8 years. Be sure to work on an anti static mat and take all the usual static precautions.
Hello. Good morning.
I had ordered SMD capacitors, but they sent me the ones that use PCB holes.
Well, I think I managed it. Iâm sending you photos. I hope theyâre useful.
Thank you very much, Alejandro Castelli
That should be ok and do the trick. Well done!