Wrong transistor  - Page 1
Forum section: electronics / repair

author: debi
author_rank: Contributor
timestamp: March 29, 2020, 01:21:51 pm
content: Hi guys,im actually repairing an air conditionner MFP1280 (no name chinese brand), regarding to the error code on the screen, i had to order new sensors.. but nothing changed. Even though i dont have any Error code on the screen anymore i couldn't turn on the differents modes. I checked the main pcb connected to the front commands and i noticed a S8050 had the collector leg cut by rust... i decided to replace them all (3x S8050) but as im an idiot i didn't read well and i picked the wrong NPN in the box to put some S8550 on the pcb...which is PNP transistors... my skills are limited (i start a 2years school training in Electronic repair in August, i can't wait) but from what i read they are completly dfferents... before noticing my mistake i obviously turned on the air conditionner... the differents modes turned on by themselves like the machine was reinitializing then completly turned off and no power at all... I checked the pcb then i understood my mistake..I put the good transistors this time and checked the resistors (all good).From now, the machine turn on but no way to select the different modes on the front panel or with the remote control....On this board there is a Samsung IC (S3F84I9XZZ-QZ89).... do you think its possible i damaged it by putting PNP instead of NPN transistors ?Thanks for your timeand excuse my french !

author: debi
author_rank: Contributor
timestamp: March 29, 2020, 01:25:05 pm
content: the back of the pcb

author: cnqhdszq
author_rank: Regular Contributor
timestamp: March 29, 2020, 01:44:21 pm
content: Normally the working volts of the board is 5V(guess).so this volts can not damage the IC.my suggestion ：check the diodes and the resistors with DMM .

author: debi
author_rank: Contributor
timestamp: March 29, 2020, 02:50:42 pm
content: Hi, thank you for your reply,unfortunatly i checked the resistors on the front panel pcb and also on the power supply pcb and they are ok, Diodes also...I checked the 10uf and 100uf capacitors on the front panel board also..it's really strange, i m going to check the power relays just in case..Im trying to find the datasheet of the samsung ic i mentioned..Im disappointed because i don't know if the wrong transistors i put are guilty in this situation..

author: Zero999
author_rank: Super Contributor
timestamp: March 29, 2020, 04:15:49 pm
content: No one can say for sure you haven't damaged it by using the wrong transistors. It's possible but unlikely.It's more likely the transistors you put into the circuit have been damaged and should be discarded, rather than saved for future projects.What error code was displayed in the first place?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 29, 2020, 04:50:07 pm
content: I think you're overfocused on the transistors as being the cause for the problems. The one near the corrosion is responsible for making the beeper beep. Another is responsible for turning on the numeric display and the third is responsible for turning on the row of LEDs near it. Are the LEDs lighting? If not, perhaps your replacement transistors have a different pin order (pinout) than the originals.I can't see any way that putting in PNP transistors would have damaged anything. Nor do I see how the original damaged transistor could have caused anything other than the beeper not to sound.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 29, 2020, 05:00:47 pm
content: Looking a bit more closely, I would be checking the continuity of that thin track that runs along the bottom of the board. It seems to run all the way around in a loop and then back into the controller chip. It's hard to say what it does since your thumb covers part of the track, but perhaps it's a designed-in failure point.

author: debi
author_rank: Contributor
timestamp: March 29, 2020, 05:14:35 pm
content: Hi Paul,i can hear the beeper once i plug the air conditionner, the numeric display is working (once turned on it shows room temperature), and leds are working fine.. otherwise i touched the ic while working and it s not overheating.Hi Zero999, Before i replaced 2 sensors (E2 and E3 error code), i couldn't turn on the device. Since i changed the sensors (5K sensors, one has copper head, one has a rubber head) i can turn on the device then the fan starts as it should, the numeric display show me the temperature but after that the only reactive button is the ON/OFF from the front panel.. the other ones do nothing, so i do not have the other functionalities : deshumidifier, heater,.... as far as i remember, i could heard clics (coming from the relays i guess?) when switching between modes...I m going to have a look at the PSU board just in case. i do have 3 relays (JZC 32F) and a big one (Hongfa HF2160).. im going to check them, also there is a cable from the psu board to the ic board with several pins out : GND, +5V, 4WAY, PUMP, L,M,H, HEAT, COMP. (L,M,H for the fan)i check it again right now

author: debi
author_rank: Contributor
timestamp: March 29, 2020, 05:21:32 pm
content: Hi again Paul,The continuity test is a success.

author: debi
author_rank: Contributor
timestamp: March 29, 2020, 06:56:12 pm
content: I test the voltage from the psu to the IC board.. and i think problems keep coming.I have 9 pins on the strip cable (Ground, +5V, 4WAY, Pump, L, M, H, Heat, Comp)... and i have 63 Volt on each pin...I think im going to leave it because i cannot improvise myself as an electronician.I have to learn how to test the comp off the circuit first... and check the relays as well... so im going to spend time on internet before doing anything else.

author: debi
author_rank: Contributor
timestamp: March 30, 2020, 11:45:54 am
content: Hi guys,i keep digging. I found that the voltage regulator LM78L05 catch 72 V and delivers 72 V as well... when the pin out goes to the +5V in direction to the IC PCB board...As previously said, the strip cable going to the IC PCB board delivers on each pins out 72 V (Ground, +5V, 4WAY, PUMP, FAN L, FAN M, FAN H, Heat, COMP)... In this scenario, is it possible the Samsung IC died which still give the possiblity to turn ON the air con without being able to turn ON the differents modes ?I also found something which i did not understand at the first place. It s from the Power Relay, when i start the Air Con, i can hear a "clic" noise coming from this relay, there is 2 PINS on top of it, the bottom PIN collect the 220V, the one on the top is supposed to bring current to 2 types of capacitors (a CBB61 and a motor capacitor)... At this PIN, i do not have any voltage. Am i right saying its normal because to deliver the current its controlled by the samsung IC while pushing the right buttons on the front panel ?I keep searchingThanks for your time

author: debi
author_rank: Contributor
timestamp: March 30, 2020, 03:51:29 pm
content: Hello !! i fixed it !!!All the push buttons on the front panel were dead ! While the On/Off was working great (which makes me not thinking of something else), all the others (exactly same reference) had dead contacts inside. I replaced them by push buttons from an old VHS player and TADA !! Everything works great again !Regarding to the remote control, i checked the PCB and found again a S8050 transistor with leg cutted and rust... replaced it, but nothing changed.. i finally replaced the receiver diode with the one coming from the old VHS player and now i can use the remote control again !!!So glad i found what was wrong on this machine,Never give up !Cheers and thanks to everyone who ve been part of this repair.

author: Zero999
author_rank: Super Contributor
timestamp: March 30, 2020, 07:42:03 pm
content: Thanks for posting the update.I'm not surprised about the switches being dead. Mechanical parts like that are more prone to failure, than electronic components, such as transistors. Ideally the switches should be replaced with brand new ones, of a reputable brand, from a reliable distributor, as second hand ones are more likely to fail in the near future.Does the receive have three or two legs? If it has three, it's most likely an IC, rather than a diode and you're lucky it was the right one, with the correct pin-out.

author: debi
author_rank: Contributor
timestamp: April 01, 2020, 09:20:20 am
content: Hi Zero999yes it has actually 3 legs so calling it a diode is wrong.thank you for your help