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MODNOTE: Not sure if this is the most appropriate location for this as although it refers to a "Pointy end" machine it's more about electronics than anything else.
Apologies in advance, this may be a bit rambly, and will likely not mean a lot to anybody without some electronics knowledge.
So a few weeks ago we had our (one for the whole house) RCBO trip a few times "randomly", this is not an infrequent occurrence as the normal leakage of the gear in my study is quite high, but it occurred two days running which was unusual, so warranted some investigation.
Eventually figured out that there was some water pooling underneath my VBM Domobar Junior, pulled the main cover off to see what the source of the water was, and found that my anti-vac valve was dumping substantial amounts of water at startup and drenching the top of the boiler, which appears to be the cause of the RCBO tripping.
Initially thought the anti-vac valve was stuck, so powered up again holding the valve closed, no leak. Ran it without issue for a few days then we had another power drop, and we were back to tripping the RCBO and this time the unit was behaving generally erratically (pump running continuously on one occasion, element relay pulsing on and off every few hundred milliseconds on another, generally erratic...), so I decided it was time to jump back in and investigate.
This time I noticed what looked distinctly like a scorch mark on the Gicar controller and so the saga begins;
This sort of thing generally tends to suggest something inside got REALLY hot, at this point I confirmed that it was out of warranty, and given the price of replacements I decided to pull the controller and have a go at it myself (I'm a qualified EE).
I pulled the guts out of the controller to check it out, "unfortunately" the controller was 100% pristine, no evidence of any damage and no evidence to suggest that the "scorch" mark was anything to do with the controller internals (no markings on the inside of the casing, no damaged components), the only thing I can think of is that they use thermal paper to print their labels and that end being the end which "points" at the boiler it got hot enough from radiant heat to discolour.
Time to actually test the controller. First rule of electronics troubleshooting "thou shalt check power rails".
The controller has two power rails, there's a 12V rail which drives the relays, and a 5V rail (derived from the 12V rail) that drives the microcontroller (PIC16F627) and all the other interface circuitry.
The 12V rail read 9.5V so I back tracked and checked the output voltage of the transformer, it was ~18VAC which is reasonable for a lightly loaded, unregulated 12V transformer output. Swapped out the 7812 voltage regulator and checked again, no change, typically this suggests something "downstream" is pulling the rail low.
Conveniently enough the Microcontroller is socketed (Gicar are also kind enough to provide an ICSP header if you should be so inclined), so I popped that out to isolate most of the circuitry in the controller. Rails were still low and nothing was getting hot (things that pull rails low will generally get hot as they are dissipating more power than they should be). At this point I basically concluded that the low rail must've been some kind of intentional design choice, perhaps a deliberate attempt to lower the power dissipation of the controller, since it's a rather tight envelope. The relays were still happily able to switch on the 9.5V provided by the 12V rail, and 4.5V (the 5V rail was low due to the 12V rail being low) is well within acceptable limits for the PIC micro.
While the micro was out I had a poke around the socket to confirm I could fire all the relays OK, also the buzzer so it seemed that everything in the controller (other than the micro itself) was hunky dory, which suggested that the micro must have been the problem.
Gicar of course are not going to give you the firmware file for their controllers, and as such if the micro is dead you've got two options, either buy a whole new controller, or write your own... Being that it's based on a PIC micro and a boiler auto-fill is not the most complex thing on the planet to implement I decided I'd go with option 2.
The first step in that option was to reverse-engineer the whole damn controller, the result of that is the full schematics in the attached PDF. These are complete board schematics for the two boards in the controller, including unpopulated parts, the values for the SMD capacitors in there are largely stabs in the dark based on experience (small SMD caps generally don't have value markings on them), where I was unable to make an educated guess I labeled them ??nF. A point to note is that the Buzzer and the strange 2-pin connector (diagnostics of some kind maybe?) on the controller aren't really part of the "full" design (they're using holes which are intended for other things in other versions of the controller) and as such I didn't include those. For reference the buzzer's + terminal connects to FA11 and the - terminal connects to FA12, and the strange 2-pin connector is pins 3 and 4 of CN3.
Now that I knew what was connected to where on the micro, it was time to try to characterise it as much as possible within the erratic functionality it was providing, I got some way through this work when I happened to poke the power rail with my Oscilloscope...
That ain't right... 100Hz tells me it's mains related, so back to the power supply, filter caps looked fine, tested the diode bridge, it checked out, replaced it anyway in case it was some odd on-load type issue, no change.
Next step, feed 15V from a bench power supply to the input of the 12V voltage regulator, et. viola, stable controller... Move it back to the input side of the bridge, still working A-OK, pulled out the filter cap to see if it'd ruptured on the bottom, looked fine, tested it with the meter and it was reading WAAAAAAY low, replace with a nice shiny new Nichicon cap from my stock and it looks like we're back in business.
I'll throw it back in the VBM over the next few days and with luck I'll be able to move the ISOMAC Zaffiro back to the garage and push my single-boiler management mojo back to auxiliary storage
Apologies in advance, this may be a bit rambly, and will likely not mean a lot to anybody without some electronics knowledge.
So a few weeks ago we had our (one for the whole house) RCBO trip a few times "randomly", this is not an infrequent occurrence as the normal leakage of the gear in my study is quite high, but it occurred two days running which was unusual, so warranted some investigation.
Eventually figured out that there was some water pooling underneath my VBM Domobar Junior, pulled the main cover off to see what the source of the water was, and found that my anti-vac valve was dumping substantial amounts of water at startup and drenching the top of the boiler, which appears to be the cause of the RCBO tripping.
Initially thought the anti-vac valve was stuck, so powered up again holding the valve closed, no leak. Ran it without issue for a few days then we had another power drop, and we were back to tripping the RCBO and this time the unit was behaving generally erratically (pump running continuously on one occasion, element relay pulsing on and off every few hundred milliseconds on another, generally erratic...), so I decided it was time to jump back in and investigate.
This time I noticed what looked distinctly like a scorch mark on the Gicar controller and so the saga begins;
This sort of thing generally tends to suggest something inside got REALLY hot, at this point I confirmed that it was out of warranty, and given the price of replacements I decided to pull the controller and have a go at it myself (I'm a qualified EE).
I pulled the guts out of the controller to check it out, "unfortunately" the controller was 100% pristine, no evidence of any damage and no evidence to suggest that the "scorch" mark was anything to do with the controller internals (no markings on the inside of the casing, no damaged components), the only thing I can think of is that they use thermal paper to print their labels and that end being the end which "points" at the boiler it got hot enough from radiant heat to discolour.
Time to actually test the controller. First rule of electronics troubleshooting "thou shalt check power rails".
The controller has two power rails, there's a 12V rail which drives the relays, and a 5V rail (derived from the 12V rail) that drives the microcontroller (PIC16F627) and all the other interface circuitry.
The 12V rail read 9.5V so I back tracked and checked the output voltage of the transformer, it was ~18VAC which is reasonable for a lightly loaded, unregulated 12V transformer output. Swapped out the 7812 voltage regulator and checked again, no change, typically this suggests something "downstream" is pulling the rail low.
Conveniently enough the Microcontroller is socketed (Gicar are also kind enough to provide an ICSP header if you should be so inclined), so I popped that out to isolate most of the circuitry in the controller. Rails were still low and nothing was getting hot (things that pull rails low will generally get hot as they are dissipating more power than they should be). At this point I basically concluded that the low rail must've been some kind of intentional design choice, perhaps a deliberate attempt to lower the power dissipation of the controller, since it's a rather tight envelope. The relays were still happily able to switch on the 9.5V provided by the 12V rail, and 4.5V (the 5V rail was low due to the 12V rail being low) is well within acceptable limits for the PIC micro.
While the micro was out I had a poke around the socket to confirm I could fire all the relays OK, also the buzzer so it seemed that everything in the controller (other than the micro itself) was hunky dory, which suggested that the micro must have been the problem.
Gicar of course are not going to give you the firmware file for their controllers, and as such if the micro is dead you've got two options, either buy a whole new controller, or write your own... Being that it's based on a PIC micro and a boiler auto-fill is not the most complex thing on the planet to implement I decided I'd go with option 2.
The first step in that option was to reverse-engineer the whole damn controller, the result of that is the full schematics in the attached PDF. These are complete board schematics for the two boards in the controller, including unpopulated parts, the values for the SMD capacitors in there are largely stabs in the dark based on experience (small SMD caps generally don't have value markings on them), where I was unable to make an educated guess I labeled them ??nF. A point to note is that the Buzzer and the strange 2-pin connector (diagnostics of some kind maybe?) on the controller aren't really part of the "full" design (they're using holes which are intended for other things in other versions of the controller) and as such I didn't include those. For reference the buzzer's + terminal connects to FA11 and the - terminal connects to FA12, and the strange 2-pin connector is pins 3 and 4 of CN3.
Now that I knew what was connected to where on the micro, it was time to try to characterise it as much as possible within the erratic functionality it was providing, I got some way through this work when I happened to poke the power rail with my Oscilloscope...
That ain't right... 100Hz tells me it's mains related, so back to the power supply, filter caps looked fine, tested the diode bridge, it checked out, replaced it anyway in case it was some odd on-load type issue, no change.
Next step, feed 15V from a bench power supply to the input of the 12V voltage regulator, et. viola, stable controller... Move it back to the input side of the bridge, still working A-OK, pulled out the filter cap to see if it'd ruptured on the bottom, looked fine, tested it with the meter and it was reading WAAAAAAY low, replace with a nice shiny new Nichicon cap from my stock and it looks like we're back in business.
I'll throw it back in the VBM over the next few days and with luck I'll be able to move the ISOMAC Zaffiro back to the garage and push my single-boiler management mojo back to auxiliary storage
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