Burco boiler power problem

[CuriousJohn]

Burco BCPLSAFWM5L 5 Litre Wall Mounted Automatic Water Boiler With Filtration UK 240v

Does anybody have any experience with these Burco units at all there is no record of them on the forum lol and a proper service manual would be nice. I invite you all to pesuade me not to botch repair it with a 5v relay, read on.

This unit was rescued from a skip 3 years ago, the only fault it had then was no backight display (plus it wanted a new probe set and top seal) but the screen was never an issue you can still see the screen as is and I just use it to get 5 Litres of very hot water once or twice a week to do my washing up and cleaning as its much cheaper than attempting to use the 60L immersion boiler in the cupboard which is very redundant these days given we have a shower wet room so no bath and no will to pay a fiver to heat 60L up to temp.

So the last few months the unit has been intermittantly going into fault mode as it appears the heating element is not getting switched on so it times out giving pcb fault but when you tap the screen area very gently the relay will switch on and heat the water so i thought it was sticky relay contacts on the HF152F-12v power relay that drives the heating element but just replaced the relay with china supplied new one of same spec and that relay will not even switch with the gentle tap now so a step back!

See video 1

https://www.youtube.com/shorts/7m8MLHi7KtU



So just replaced the relay and it seems I was wrong on the relay issue although upon opening the old relay up the contacts are very crusty, not suprising it has 16A 240V coursing through it so anyway.

Further investigation has revealed the voltage to the coil is only 5v and it should be more like 12v so not enough to energise the coil properly. The Relay coils are turned on from a STM8L MCU into the base of a npn transistor inside a sot363 package, BCR48PN (NPN/PNP Silicon Digital Transistor Array) which derives its Vcc from the op of what looks like a full wave rectifier but no transformer here. This board i think uses some capacitors in series to drop the mains voltage but big clive knows way more about that than me at ths time lol.

I wonder with my rudimentary knowledge if the FW rectifier has faulted so its only doing half wave dropping the voltage across the board which might explain the lack of backlight as when tested with led tester the backlight seems fine so it fits but i dont have a scope at present to check. Could be the transistor as well but that wouldnt effect the backlight fault as the BL is driven from a different npn transistor that acts as a cathode sink, i need to measure that backlight supply next really but i dont need it. Suppose its worth noting the relay for the solenoid valve that fills it with water works fine tho does seem to buzz a bit.

So, im torn really i just want the thing working as tired of having to wait around tapping it when its clean up day lol so toying with the idea of sticking a 5v coil relay in it instead as it is available in this power relay range, its cheap enough to do but i have to wait for china man to bring it and that is just a quick nasty bodge fix. Talk me out of it, or dont lol.

See video 2

https://www.youtube.com/shorts/Jlled0yA90o

[CuriousJohn]

Burco BCPLSAFWM5L control board photos

[redwire]

The board appears to use a dropper cap to make up the 12V power rail. That is the large grey rectangle cap next to the relays, with the "M" Matsushita/Panasonic logo. It must have failed low value. Check it.
Or the electrolytic capacitors C14, C15 have dried out and gone low value.
Hopefully replacing the relay did not cause a new problem like a poor connection or broken PCB trace.
HF152 12V coil needs only 30mA.

edit: or the (string?) of SMC size diodes might have a dud zener there. I can't read their part numbers but they seem to have two in series with a middle take off point.

[CuriousJohn]

The board appears to use a dropper cap to make up the 12V power rail. That is the large grey rectangle cap next to the relays, with the "M" Matsushita/Panasonic logo. It must have failed low value. Check it.
Or the electrolytic capacitors C14, C15 have dried out and gone low value.
Hopefully replacing the relay did not cause a new problem like a poor connection or broken PCB trace.
HF152 12V coil needs only 30mA.

edit: or the (string?) of SMC size diodes might have a dud zener there. I can't read their part numbers but they seem to have two in series with a middle take off point.

Thanks for the reply Redwire and merry Christmas.

Was careful removing the relay and checked the traces as this board is double layerd they wander off all over so used a heated solder sucker gadget its a great thing. The HF152 comes in a range of coil voltages i have tested these with AA and coin cell batterys and cant get them to switch on anything lower than 6v.

Have just replaced the electrolytic caps (Lelon) C13,C14 & C11 having tested them and found C13 had an V loss of 24% in circuit but when tested out it was ok. C20 tests low so removed to double check and its reading 237nF supposed to be 680nF X2 Class 275V ac and it does appear to be across the mains supply. Not sure if its low value would cause this fault but if it is a dropper then actually the ratio is in same region: 12v rail sitting at 5v = 59% drop and that cap is down in value by 65% ish.

All diodes seem ok with the exception of the little zener below the 4 and my DTU-1701 tranny tester will not see it and i havent tested it off (yet) its weird tho as it sits across the coils of the other relay yet those pins measure around 400 ohms with my meter same as big relay. That zener also seems to be on the op point i think you mention might well be the 12v rail (this feeds into a voltage regulator which supplies the led backlight so getting closer.) but that small zener sits across the relay coil of the smaller relay that drives the water valve and this works fine tho i noticed it buzzing a bit.

[redwire]

Merry Christmas as well.
I would say the dropper cap C20 needs to be replaced, it's in series with the zeners and mains to make 12V for the relays, as well I think the second zener is a tap to provide maybe 5V for the logic and backlight.
These caps don't last long and as they fade away low value, a controller gets starved of power.

[CuriousJohn]

Some Christmas photos lol.

Have reversed engineered the circuit about 80% now massive breakthrough last night lol next post may well reveal the circuit diagram.

There are two zeners in series with the output of bridge rectifier i think holding up the 12v rail (this point is tapped for both relay coils cathode sunk by two Sot363 BCR48PN) or at least dropping it for the next set of two series zeners fed from the first two but first split by C13+C14, output of second pair of zeners feeds at the least a 5v regulator that runs the MCU and yet another zener providing 3.2v for the led backlight. C20 is before the BR across the mains it could be dropping or filtering maybe both I sadly dont know yet still got a few more bits to check though C20 is well out of tolerance so replacement ordered as couldn't find anything in ma junk pile.

The MCU seems happy it can operate down to 1.8v according to the datasheet but it will fail if C20 keeps going lower i suppose lol and also think the low volts is affecting the level probes as well.





Well out of spec! Supposed to be 680nF!

[CuriousJohn]

Merry Christmas as well.
I would say the dropper cap C20 needs to be replaced, it's in series with the zeners and mains to make 12V for the relays, as well I think the second zener is a tap to provide maybe 5V for the logic and backlight.
These caps don't last long and as they fade away low value, a controller gets starved of power.

Finally received the replacement capacitor in the post today and glad to report you where right C20 replaced and the boiler now functions perfectly and i might have actually learned a bit about how modern power supplies are being designed. Very interesting deployment of a 30v varistor here, appears to provide a 30v pulse into the rectifier by blocking the neutral path above 30v in both directions. Happy to be corrected..


https://www.youtube.com/shorts/3ZIG8dtHelk

[stj]

i'm just stunned how much shit is now involved in boiling some water!
i remember the older generation of those and they just used a bimetal switch!
can it play doom on the display?

[CuriousJohn]

i'm just stunned how much shit is now involved in boiling some water!
i remember the older generation of those and they just used a bimetal switch!
can it play doom on the display?

haha Yeah! Later on tonight im going to see if the firmware is locked, its a STM8L MCU, can they do doom probably to little RAM?

It is very efficient boiler though it seems to fill a bit then heat so a cup of boiling lava is available very quick suppsoed to be in commercial kitchen or some gift shop selling overpriced instant coffee ha!

[stj]

STM8 is pretty unusual to see - very cheap but usually if it can do the job a pic chip or AVR can do it cheaper

[redwire]

The original dropper cap was a Kemet R46 "Not for use in "series with mains" type applications." I thought they were a bit better polyprop.

There likely is a functional safety aspect to one of these controllers so choice of MCU includes the special watchdog, clock monitoring and CPU self-test functions to meet IEC60730/61508. ST offers a bunch of stuff for that. AVR and PIC don't have it.
Although there should ultimately be a high-high temp cutoff to prevent calamity if the MCU crashed leaving the heat on.

One of the magic tricks with this controller, is the board (power supply) is not isolated from mains.
You can see this is a problem for the buttons I think so people don't get a shock or for whatever connects to the F1-F3 terminals. This explains the array of high voltage Y-caps C3 etc. I think it's to do that.
Deffo a low cost board.

[stj]

does it use buttons?
i see a bunch of springs - last time i saw that it was "antenna's" for a touch panel.

[CuriousJohn]

The original dropper cap was a Kemet R46 "Not for use in "series with mains" type applications." I thought they were a bit better polyprop.

There likely is a functional safety aspect to one of these controllers so choice of MCU includes the special watchdog, clock monitoring and CPU self-test functions to meet IEC60730/61508. ST offers a bunch of stuff for that. AVR and PIC don't have it.
Although there should ultimately be a high-high temp cutoff to prevent calamity if the MCU crashed leaving the heat on.

One of the magic tricks with this controller, is the board (power supply) is not isolated from mains.
You can see this is a problem for the buttons I think so people don't get a shock or for whatever connects to the F1-F3 terminals. This explains the array of high voltage Y-caps C3 etc. I think it's to do that.
Deffo a low cost board.

This is a very interesting board to me its new ways, i was educated long ago on real old ways now lol also never worked in the industry just keep my hand in for fun mostly.

Still puzzling over the 30v varistor its the blue disc thing next to the 1w resistor, i think that it seems to prevent a neutral path above 30v each way from the rectifier so a 30v pulse gets rectified and divided to generate a 6v rail plus zeners galore limiting both current and voltage but thats not even talking about the 12 rail lol, i have drawn a ropey diagram if you like. might have to get a scope at this rate or just be happy its working again and leave it alone.

For safety there are two thermal switches inline with the heating element, one of them is screwed onto the boiler base to detect boil dry temp its a 135 Deg C affair, the second is on the overflow/steam off pipe.

To switch the heating element relay the MCU sends high signal out to a BCR48PN sot363 digital transistor array (1npn & 1pnp) and uses the npn transistor to switch on the pnp transistor that sinks the relay coil energizing it turning on the heating element. Also this board has a lot of self testing points feeding into the mcu so it defo watches itself a lot very next generation stuff, it can log and record its own faults in a basic way as well that the user can clear but it also can disable the boiler when certain events occur like heating element not on within a minute of its relay being switched, if the mcu sees no volts tapped from the element it shuts down and beeps at you to call the service centre and power cycle to reset it.

4 springs for 4 buttons, its basic 4 button capacitive touch screen stuff via springs lol when turned onto those springs its like soldering on a mini trampoline! There is probably less than 1mm of clear plastic between button and user finger on the front so totally electrically isolated other than the case which is earthed obv. I did note the thermister that the mcu reads uses the earth wire as ground, i wonder if that would disable to heating side of things if there was an earth fault. Clever stuff and cheap to do.

Today i managed to dump the firmware hex file out of it as well but binwalk has failed to find anything at all after conversion to bin but really surprised and delighted Burco didnt lock it down, plan to share it imminently. Haven't tried writing the dump back yet, intend to practice not breaking my boiler needlessly for a month or two at the least.

[CuriousJohn]

does it use buttons?
i see a bunch of springs - last time i saw that it was "antenna's" for a touch panel.

Yeah 4 capacitive touch spring buttons that sit behind less than 1mm of clear plastic, the springs are hidden by the black insert with the button symbols printed on it. This keeps the user electrically isolated i guess but there metal behind the panel has very sharp edges and there are live wires running back there its not great.

[CuriousJohn]

C20 removed shows better view of mains path.The neutral sits behind C20 which has 2 x 270K series resistors in parallel with it smd on underneath and there appears only to be a path to neutral via C20 when the live voltage is less than varistor voltage of 30v in each direction giving a 30v RMS pulse?? The live rail goes to the underside of the board by relay 2 label straight into the bridge rectifier. The 12 v rail comes from the mains side of the rectifier on the 1 Watt resistor line theres zeners in series with it to the ground reference of the rectifier ill post the diagram at some point its late.

[CuriousJohn]

Burco BCPLSAFWM5L 5L auto fill wall mounted water boiler power distribution diagram (likely to contain errors) + notes.

Have checked mains neutral path on this loads, that 30v varistor defo does not sit across the mains (why would it lol) so must be blocking neutral path above 30v ether way?? I need a scope now its time lol but DC measurement on other side of rectifier sort of confirms max 30v DC








Varistor Epcos "S07K30" = 30v RMS 38v DC

[CuriousJohn]

does it use buttons?
i see a bunch of springs - last time i saw that it was "antenna's" for a touch panel.

Black insert with white printed buttons hides the suspension springs of the board

[CuriousJohn]

STM8 is pretty unusual to see - very cheap but usually if it can do the job a pic chip or AVR can do it cheaper

was scanning through the data sheet and saw this MCU chip has: Active-halt with full RTC!
I seen a Pic32MX use a separate RTC so wondered if they dont have them embedded but datasheet of pic says they have RTCC. Dunno then lol

The time can be set but i never have, I also now gunna set it and power cycle to see if it sticks as this boiler also has eco mode but again i never leave it on for that as I am captain eco mode lol



From the boilers manual:

Set Time:
Press Menu and the SET CLOCK will be highlighted. Press MENU to enter the SET CLOCK menu. The
time will be displayed and the hour values will be flashing. Use the scroll buttons to select the correct
value and press MENU. The minute values will now be flashing. Use the scroll buttons again to select
the correct values. To store the new set time press the MENU button, this will also take you back to
the SET UP menu. To exit the SET UP menu press the standby button.

Eco Mode (Auto Fill Only):
When no water is drawn from the boiler in 2 hours, the eco mode is engaged. The backlight turns
off and the only data displayed is the Burco logo along with the time and the status indicator. Water
should be drawn off to resume normal operation. To set the Eco mode timer, simply scroll down to ‘ON'
to set the desired time. Once you are happy with the time that has been set, press the menu button to
confirm this. This will then take you to ‘OFF', where you can then set the time that you want the Eco

[CuriousJohn]

Burco 5L boiler autofill boiler firmware fun

After repairing the faulty control board of this Burco BCPLSAFWM5L 5 Litre Wall Mounted Automatic Water Boiler With Filtration it was time to see if the firmware was unlocked for backup and learning STM8 stuff.

Video 1 - connecting saving firmware hex files.
https://youtube.com/shorts/lB_quEeCop4

video 2 - Writing saved Hex files back.
https://youtube.com/shorts/_r7AXijnhyY

Video 3 - Erase and restore MCU
https://youtube.com/shorts/NQV_1N2GkF4

Warning if planning this work then isolate boiler from mains power before and during connection to the debuger. The debuger can power the boiler control panel as shown when only plugged into USB port on laptop and leaving mains on risks heater element switching during MCU reset operations.