Heatpump Controller PSU - Page 1
Forum section: electronics / repair

author: Thalhammer
author_rank: Contributor
timestamp: September 06, 2025, 09:52:02 pm
content: Hi,I registered because I am running out of ideas.I have a Swimmingpool Heatpump that worked fine for about 6 years.Last week I went to turn it on only to notice that the control panel showed an error that it couldn't contact the main unit.I took apart the control board and noticed that none of the mcu power rails had any voltage. Turning the board around showed that all the magic smoke had escaped from the controller chip of the power supply.The chip is a TNY280G, do I ordered a couple of them along with a diode that was clearly burnt.However after replacing it the only thing that happened is another (very impressive tbh) firework and the new chip got obliterated exactly like the old one. It might be worth mentioning, that the low voltage side did spring to live for a very brief time (like half a second or a second) before it died again.The only reason why it would die this fast, that I could think of is a direct short between the high voltage drain and source, however the resistor that's in there measured fine and I while I don't have a lcr meter, the cap definitely wasn't shorted.Is it possible the cap shorts only at higher voltages or frequencies?What other reasons could there be for the chip to explode pretty much instantly ?This is the datasheet of the chip:https://www.power.com/sites/default/files/documents/tinyswitch-iii_family_datasheet.pdfThe circuit on the board is pretty much exactly the same as the datasheet example.Any ideas/help is appreciated.Sincerely,Thalhammer

author: golden_labels
author_rank: Super Contributor
timestamp: September 06, 2025, 10:35:25 pm
content: Welcome tothe TNY explosions club.If you bypass the optocoupler and bind EN/UV to ground by e.g. 1MΩkΩ(errata:1)resistor, does it explode? If it remains silent, I’d look at the output side or the optocoupler itself.See if the output is not shorted, if the optocoupler itself seems fine. If the PSU is as simple as shown in datasheet diagrams (Fig. 1 and Fig. 14), that it it has no additional control circuitry that would control the optocoupler, also check if the zener used to detect voltage is fine.(errata:1)See thepost below. Apparently I was too cautious and chosen a value that does nothing.

author: moffy
author_rank: Super Contributor
timestamp: September 06, 2025, 10:35:52 pm
content: Check the transformer and the secondary side for any shorts, measure all the diodes near the device to make sure they are intact.

author: Thalhammer
author_rank: Contributor
timestamp: September 06, 2025, 11:27:07 pm
content: Quote from: golden_labels on September 06, 2025, 10:35:25 pmA shit, that's not a club I prefer being part ofQuote from: golden_labels on September 06, 2025, 10:35:25 pmWill try that once I have resoldered replacement chip 2/5 😅Quote from: golden_labels on September 06, 2025, 10:35:25 pmFrom what I could tell its pretty much exactly the example circuit in the datasheet, except they changed the zener to make it output 15V instead of 12V (which feeds into a linear reg converting it to 12V).I will check the optocoupler and transformer. Worst case I'll just try replacing everything I can find in the vicinity of the psu. If all things fail I could just buy a external psu and remove the psu from the high voltage side.

author: coppercone2
author_rank: Super Contributor
timestamp: September 07, 2025, 12:13:16 am
content: check for opens, the new failure mode I learned about with power electronics is that the thermal relief via + shape acts like a fuse, so after parts burn out, you might have a open circuit on some pins that are connected to planes. Very hard to spot it on a interior plane.

author: golden_labels
author_rank: Super Contributor
timestamp: September 07, 2025, 07:40:16 am
content: Thalhammer: Trying to be on the safe side with testing, I think I might have overdid it.A 1 MΩ resistor to bypass sensing may be way too high to turn off the chip. 1 kΩ seems more reasonable, though in case of a failure the resistor may get vaporized alongside the TNY. If I still have any, I’ll check that later (EN pin triggering, not vaporization).The rest of my post remains valid.

author: golden_labels
author_rank: Super Contributor
timestamp: September 09, 2025, 02:04:32 am
content: Just reporting back: 1 MΩ is indeed way too big value. But pulling EN/UV down with a 1 kΩ resistor is enough to make it stop switching. Tested with a TNY279P.I couldn’t build the full setup, so just used a resistive load on a barely 85 V supply. Instead of an inductor at 300 V. TNY appeard unhappy about that, when trying to drive the inductor. But turning off works as expected: it draws only stand-by current.

author: Thalhammer
author_rank: Contributor
timestamp: September 12, 2025, 07:49:23 pm
content: Just a quick update.I did not yet try the resistor test.The reason for this is that I noticed a second 15V line from the winding thats used for the feedback circuit.I didn't notice it initially because its traces where on the underside of the transformer.It's used for the Mosfet drivers and indeed it had a short. It took me a while but I traced the short to a schottky diode right next to the transformer.I desoldered it and tested the circuit with a bench supply and it seems to be still intact.The diode I desoldered is a SK3B5A* (3A,150V Schottky Barrier Rectifier) that got conductive in both directions (no idea why).Sadly I don't have anything similar in my parts drawer and its really hard to get them in germany (only found them on ebay and lcsc).I'll check if I can find something close enough at one of the stores here (reichelt/mouserconrad).*https://www.goodark.com/specification/SK3B5A.pdf

author: golden_labels
author_rank: Super Contributor
timestamp: September 13, 2025, 08:13:16 am
content: Below I assume we’re talking about D6 (in Fig. 14, page 8 of the datasheet)--- edit 2025-10-04:theschematic added laterindicates wedo nottalk about D6!If this diode died, consider the capacitor it charged. It must have been battered severely, if the diode is short.As for finding a replacement for SK3B5A, maybe SS315 or SS320? But it doesn’t seem the diode has to be that specific one. Its only function is to charge C6.If the circuit is designed per datasheet, following recommendations,the difference in diode’s forward voltage is irrelevant. It changes the output by single percents. I can’t imagine to what extent would the designers of this PSU need to deviate from the Power Integrations’ reference to make it matter.Power Integrations themselves use UF4001–UF4007 series in the example circuit. Which differs from jellybean 4001–4007 in recovery time guarantees (plain 400x have none) and in I-V curve being smoother.(1)Also, SK3B5A don’t have that huge advantage at medium currents, while where it seems to be better shouldn’t matter here. Except for the initial C6 charge, there should be no significant current present. At the same time its reverse voltage rating is low.So, if you can’t find a suitable replacement, perhaps just go for some UF4004 (or higher) equivalent in SMD package? Like US1G?(1)Vishay UF400x vs 1N400x IV curves; taken from datasheets, pp. 3:

author: Thalhammer
author_rank: Contributor
timestamp: September 13, 2025, 01:55:07 pm
content: I had planed on getting the SK3B5A directly from LCSC, however it looks like you can no longer order from there as a private individual in germany (they ask for a Umsatzsteuer-ID, which is only handed out to companies).Since I couldn't find it at any retailer I'll probably order a SS320 instead (which I did find).I do have ceramic and electrolyte capacitors in my parts drawer, they are not the exact same, but should be close enough if those are bad as well, but I only had signal level shottky's (BAT43).I'll report back again once they arrived and I got a chance to try.

author: Thalhammer
author_rank: Contributor
timestamp: September 17, 2025, 02:54:58 pm
content: After finally managing to put the new diode in (it's footprint is larger) I can at least report a partial success.It no longer explodes and powers the output for a short time. Then the MCU tries to turn on a relay and the power collapses. I suspect this is because some of the secondary side caps went bad due to the shorted diode, so I'll try to change those next.Are there other reasons that might cause this behaviour/things I should check ?PS: I am already thankfull for all the tips so far, even though it still doesn't work yet.

author: golden_labels
author_rank: Super Contributor
timestamp: September 22, 2025, 06:04:32 am
content: I was preoccupied IRL and couldn’t give any reasonable answer. But I also have no opinion on that.TNY2xx itself doesn’t check the output voltage directly. It only receives two kinds of feedback:Through the optoisolator.The output side turns on the optoisolator, when it detects the voltage rises above the minimum level. This tells TNY2xx to skip charging cycles until the voltage falls back below the minimum level. This is how the output voltage is maintained at a reasonably stable level.Through the feedback winding.An additional coil on the primary side is present, with no connection to the secondary or output. You may think of it as “emulated output,” though with different voltages. It works in such a way, that if TNY2xx pumps too much energy, the “emulated output” goes too high and TNY2xx stops. But it has no knowledge of the actual overvoltage condition on the secondary. It may be a bit confusing, since in Fig. 14 that feedback system is drawn on the same side as secondary. This circuit is where you replaced the diode.From that it’s hard for me to guess, what really happens.

author: Thalhammer
author_rank: Contributor
timestamp: September 25, 2025, 06:37:21 am
content: I still didn't have time to look at it again, but from what I remember my circuit is a bit a mix of both.They use a optocoupler for the control signal (which tested fine with a multimeter, but I'll test it incircuit to ensure it actually outputs anything) but the feedback side is not isolated, it's relative to the High Voltage DC Negative. It's also used to power the Mosfet/IGBT drive circuits. According to the test points on the pcb both the "main" secondary and feedback secondary are designed for 15V so the winding numbers are probably identical.When measuring I measured 0 volts on the feedback side, but maybe I measured wrong. The entire board is conformal coated which makes measuring stuff a pain in the a**.I know for a fact that both secondary side circuits are fine and not shorted, because when I solder wires to the testpoints and power them up using a bench supply various relays click, the debug led's are blinking and the controlpanel reports errors about missing sensors (which is fine because I unplugged them).However when I let it power by the tny supply I can hear the first relay click and then it seems like the voltage collapses.

author: Thalhammer
author_rank: Contributor
timestamp: October 03, 2025, 08:48:30 pm
content: Sorry for the long delay for updates, I was busy with work and couldn't really proceed with the repair.I have now removed the PCB from the actual heatpump and took it inside to my workbench. I am now also powering the whole thing with a benchsupply from the TNY HV side (thankfully the tny starts switching waaay below the designed voltage - I am using 40V and the chips seems to be fine).I measured the voltage on BP/M and its 5.8V, which seems to be fine.I also measured the voltage on EN/UV and its around 1V, I am not entirely sure if thats ok, but I think it should be.I have also drawn a circuit diagram of the whole supply part and have to revise my earlier statement that it follows the datasheet example. It does in fact not.There are two secondaries, both power loads.Secondary 1 is rectified and feeds into a chain of linear regulators to generate +12V, +5V and +3.3V for powering the controll circuit and communications ports. There is no feedback from this one.Secondary 2 is rectified, feeds through a inductor and provides the 15V supply for all the high voltage IGBT switching circuits. Unlike Secondary 1, this oneis not actually isolated, because the negative side is connected to HV negative. It does however provide the feedback using a PC817 optocoupler to the TNY in order to regulate it to roughly 15V. It uses an SOT-89 ic to drive the optocoupler. The marking on it is "3B 815" and according to google it should be a RH5RL23AA voltage regulator, however the pinout makes no sense in the circuit.I tested the optocoupler with the labsupply and it seems to work fine.Now that the voltages are sane and the board is powered by a isolated lab supply I can also attach my saleae and check what happens at various points in the circuit (I don't have a scope).Below is the circuit diagram I came up with (It's not pretty, I know...). D1 is the diode I replaced. I am mostly sure about the resistor values and the value of C21 (I desoldered that before and measured it), however all other ceramic values are just placeholders. The identifiers match the ones on the board.I hope this helps. I suspect that U2 might be bad, but I am not sure what chip it might be (probably a voltage reg or something like that).Any ideas for next steps / things to check ?

author: golden_labels
author_rank: Super Contributor
timestamp: October 04, 2025, 08:19:34 am
content: The most important part:assuming the circuit diagram you show is correct, they don’t use BP/M pin! The damaged and replaced diode is not D6 from Figure 14.I see you noticed this yourself, but making it clear in case somebody else reads this thread later. I also added a warning in the earlier post.That 3B815, could it be something from Torex’s XC6227 series (datasheet attached)? I can’t imagine how it would be connected in this circuit to provide feedback, given pin 3 of U2 needs to be driven low to indicate reaching correct voltage. But let’s try it nonetheless.Careful with connecting any test gear, in particular grounded one. Not because of your own safety (it’s only 40 V), but to avoid blowing up the equipment. A DMM is floating and designed to face harsh tretment. A logic analyzer is not.In this version, D1 being a Schottky diode makes much more sense and its lower voltage drop may in fact be needed. Earlier I was assuming we’re talking about the overvoltage feature on the BP/M pin.⁂Here is my line of thought. Mostly going through the schematic and comparing it with what the datasheet says.BP/M is only used to stabilize voltage, and 5.8 V is correct.(s:1)The overvoltage protection feature, discussed in the earlier post, is not used.EN/UV seems to be fine. It’s nominal 1.2 V - VGS, and is expected to be kept around 1 V.(s:2)The optoisolator should pull EN/UV down to indicate the expected output voltage has been reached. If I understand correctly, it has to do this within 64 ms.(s:3)They do use line undervoltage detection, with 4 MΩ resistors from positive rail to EN/UV. Here confusion starts. With 40 V supply and 4 MΩ resistors, the current into EN/UV is about 9 µA. This is enough to enable the undervoltage function (> 2 µA), but not enough to enable switching (> 25 mA).(s:4)I have no advice or opinion on that, just noting something is off here. However, if the chip detects this as undervoltage, there will be no attempts to do charging.Let’s ignore the first secondary (5-6) feeding GND-CON/+15V-CON. It is not in the feedback loop of the TNY, and if I understand correctly it supplies a controller that is powered just right.The +15V-DRIVE is what feeds back through the optoisolator. But that feedback is not referenced to HV-. At least not on this board. It’s referenced to something connected through pin 3 of U2 connector.D3, C3, R8 are just a snubber network.(s:1)Datasheet, upper part of Fig. 2 on p. 2; and “5.85 V Regulator and 6.4 V Shunt Voltage Clamp” on p. 3.(s:2)Datasheet p. 3, “Enable Input and Current Limit State Machine”; and left side of Fig. 12 on p. 2.(s:3)Datasheet p. 4, “Auto-Restart”.(s:4)Datasheet p. 4, “Line Undervoltage Sense Circuit”

author: Thalhammer
author_rank: Contributor
timestamp: October 04, 2025, 11:50:06 am
content: > I have no advice or opinion on that, just noting something is off here.Yes, I forgot to mention that. I broke the trace between the HV Caps and the circuit to safely power it from the bench supply without also having to charge the massive caps. The sense line is connected to the other side meaning it has no connection to the supply anymore and thus behaved as if its not there from the chips pov.Regardless I figured it out. Turns out my botched in diode replacement didn't make good contact. It was sufficient to trigger the continuity check of the multimeter but not enough to carry significant current. As a result the voltage on the rectified secondary never reached more than ~3V and the TNY entered reboot mode because it never got the ok through the optocoupler. U2 might be what you listed, but after fixing the diode soldering (I moved it to the back of the board) it started working. I only noticed this because I was probing the voltage there on the bench.The diodes I replaced are D3 (I replaced with the identical type), but I don't think it was actually bad, just chared due to the proximity to the tny that exploded, and D1 which I replaced with a SS320, which as far as I can tell is only used to rectify the output. The SS320 should be close enough for that purpose, its just a bit larger so it didn't fit on the original pads.I am aware that logic analysers are not isolated, but mine is because I have a USB isolator between the PC and the analyser, so it should be fine.I have the board reassembled and it's running in the heatpump right now and everything seems to work fine. I'll let it run for a couple hours to check that it's stable and then I will probably close it for the winter because heating the pool back up at these temps is not viable at my electricity cost.I thought about ordering the correct replacement for D1, now that LCSC fixed its order form, but if the SS320 works (and it should since its very similar) I don't think I'll go through the effort of disassembling the whole pump again.I am very glad for the help in here, I don't think I would have figured it out without (or at least it would have taken much longer).