Thermozyklus ZE5 Heating Controller. Bus error

[redwire]

For the power mosfet, does the drain or source go to power(+)? Maybe to R42 then power. That will confirm if a clown changed the part.
What part number is T2?
I think R45 is bus current-sense resistor and likely 0.1Ω and maybe goes to op-amp IC7. Where does the far end of R45 go to? Power (-)?
Why does IC7 have no markings, no pin 1 dot on the bad board? Same for D2 where is the stripe? What some Aliexpress junk or a dark picture?

D2 protects against reverse-polarity, unless he connected power to the bus by accident. Customer must not be totally honest about the board's history.

[edugimeno]

For the power mosfet, does the drain or source go to power(+)? Maybe to R42 then power. That will confirm if a clown changed the part.
What part number is T2?
I think R45 is bus current-sense resistor and likely 0.1Ω and maybe goes to op-amp IC7. Where does the far end of R45 go to? Power (-)?
Why does IC7 have no markings, no pin 1 dot on the bad board? Same for D2 where is the stripe? What some Aliexpress junk or a dark picture?

D2 protects against reverse-polarity, unless he connected power to the bus by accident. Customer must not be totally honest about the board's history.

Thanks for your time!
My comments:
Yes power+ goes straight (after a protection Diode in series D1) to the mosfet Source pin
Large top resistor (R42, 330Ohm)) goes from Drain of mosfet, to SMD Q T3 pin 2 (I believe collector of a PNP Q labeled 2F)
T2 is also labeled 2F so it should be a PNP transistor
Yes, the far end of R45 goes straight to a ground plane in the back side thru a via. The right end connects thru the coil directly into the BUS. Also the right side of BUS goes to D2 for reverse protection and also to R52 and T7
The left bus side goes to mosfet Drain and R42 like above
Sorry the picture had a bad light angle so IC7 didt show its marking, Im attaching here a better angle and it shows MC34071 which is a single Op Amp, and power and Vss matches the datasheet, output is leg 6 driven to R36

I don't believe user connected power to BUS as the power he is using is a round barrel connector, that can't fit anything else. Yes, there is an alternate power plug that matches tha same socket as BUS but he doesn't have that option in his power adapters

Hope this helps!!
Thanks again!

[redwire]

Your customer is full of it. Reverse-polarity would damage other parts, and the tech in here was sloppy.
High-side control needs a P-ch mosfet, so I would say somebody was careless and put the wrong part in.
An N-ch part would always be putting almost full power to the bus because of the body-diode being on and possibly give bus error because it is stuck high. 17N40 is a bit silly 400V rated on an 18V bus 😝

Try putting in a 17P06 (P-ch 60V) and replacing R45 to 0.100Ω, and see where that takes you.

[edugimeno]

Thanks!! Yes I will try the right mosfet in place first. My only question is... 10 Ohm (as it is now after I replaced it) or 0,1 Ohm as the second board has? Or maybe try both, but I need to travel to the place where it is to be installed for each try...

Thanks!!

[redwire]

If the wrong mosfet was put in, the wrong resistor could also have been put in.
I think the resistor is current-sense for the bus, and not sure how much power it provides. Let's say 0.5A; if the resistor goes to op-amp then I would guess 0.1Ω to amplify the 50mV. But 10Ω would drop 5V and dissipate 2.5W !

[edugimeno]

I talked to the guy, he's the manager at a large student housing. He said he claimed this to the shop where it was (wrongly) repaired and they sent back a long audio in which they explained that they changed several parts (and attached a picture with the mosfet and 3 small IC's) and saying first they needed to fix the receiving part and then it was ok and then they realized it wouldn't send so they replaced the transistor and then tested it in their bus and found it working correctly... He asked then because he had been charged 300€ for this repair, and when he called back saying it wasn't working, they said they woudl return part of the cost if he was buying a new replacement, which he did, assuming it was the only option at that time...

Anyway, I don't believe the sense resistor was replaced...I don't see traces of desoldering/resoldering/flux but depending of the quality of that shop, that could have been done with no marks...
I will probably test it with the new mosfet when it arrives, and then if it doesn't work, try a second time with the other sense resistor

Thanks!

[edugimeno]

Final update on this. I replaced the mosfet by the correct model, and took it to be tested before I tried with the the resistor. It failed, "shorcut in bus" message right away.
Took it back home, put a 0,1 ohm resistor in the bus sense R and this tested perfectly now, with no errors and controlling heating correctly.
So this board had basically fallen into the wrong hands when it was sent to the shop to be repaired in the first instance. Thanks everyone who replied here!