Sony J30 PSU repair  - Page 1
Forum section: electronics / repair

author: john2021
author_rank: Contributor
timestamp: April 21, 2024, 01:01:16 pm
content: Hello everyone,I am trying to repair an old Sony j30 PSU, which I have no information about or schematics.I am not an expert in electronics, but I would appreciate some help.I recapped the whole PSU and still no output, though I get about 15-24v on the power transistors on the primary side. The MC33262 controller gets about 15v.I get no power on the secondary side.By the shottcky diode, where I think I have a short, as I replaced the component that seemed to be a diode (white like those connected to the power transistors with no marking on it, or the board itself). but it didn't change anything.Any idea how to proceed?Thank you in advance for any helpJoe

author: wasedadoc
author_rank: Super Contributor
timestamp: April 21, 2024, 03:08:02 pm
content: That is a switch mode power supply. The "power transistors" on the primary side are working from the rectified 120 Volt AC input stored on that big 150uF capacitor. Not something that I would advise someone "not an expert in electronics" to be be working on.

author: john2021
author_rank: Contributor
timestamp: April 21, 2024, 04:17:14 pm
content: I very much appreciate the response and the safety advice. I know enough, I think, to try and repair this board with some help.As I said the primary side of the board is working as far as I can tell.I get AC power on the transformer primary side, but not on the secondary. The transformer I refer to is the one, which connects the primary and secondary side of the board – flyback I think is the correct term. Is there a way to test whether the transformer is bad, or the problem is down the secondary side of the board?Thank you

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 21, 2024, 05:23:58 pm
content: Dear Joe,No problem that you don't have circuit diagram. MC33262 is PFC controller. Just open datasheet and you will have information about first stage ofPS.Could you measure votage on the biggest capacitor 150uF@400V. Should be around 380V.

author: Laval
author_rank: Regular Contributor
timestamp: April 21, 2024, 06:28:35 pm
content: It would probably be a good idea to test those power transistors as they do drive the transformer.

author: john2021
author_rank: Contributor
timestamp: April 21, 2024, 06:51:56 pm
content: Thank you for the reply.The voltage was about 320 dcv.However, when I tested the board again, it shorted the k3234 transistor and blew the fuse. I think of replacing the transistor with a k3568 transistor, is that ok?Thanks again

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 21, 2024, 07:18:05 pm
content: Quote from: john2021 on April 21, 2024, 06:51:56 pmWhy did you decide that the transistor had shorted?Is it Q1?Did it fail on its own?

author: john2021
author_rank: Contributor
timestamp: April 21, 2024, 07:28:39 pm
content: Yes, it is Q1. I must have shorted something while measuring voltage.Just my luck.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 21, 2024, 08:51:41 pm
content: Could you answer exactly the questions:1. Is it Short Circuit between D and S of Q1?2. Is it SC between D and G of Q1?3. Check the parts marked in red

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 21, 2024, 09:29:09 pm
content: Check one more resistor near PFC controller under FB.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 22, 2024, 08:05:01 am
content: Joe,meanwhile give me a good quality photo of the back of PCB. It's better to use a camera stand. Pack it in Zip file.

author: john2021
author_rank: Contributor
timestamp: April 22, 2024, 09:05:03 am
content: I attach a photo I took of the back of the board with my phone.If you need better photos let me know, I will try to use a magnifier microscope camera.Q1 pulled out of the board1. All shorted2. All shorted3. diode B3 - shortedR6 47.5 K ΩResistor next to R6 47 ΩFB Resistor at IC 0.5-1 ΩD2 – OKI need to source the damaged parts.Do the rest of the readings look to be OK?Can a ka6 or 5d diode replace the B3 diode?And can 12n60f cs10n60f k3568 be a good replacement for Q1?Thank you very much again

author: john2021
author_rank: Contributor
timestamp: April 22, 2024, 09:06:19 am
content: I attach another photo of the back.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 22, 2024, 12:21:04 pm
content: Please see my comments below:1. All shortedThis is bad. Means MOSFET Q1.2. All shortedThis is very bad. Means that high voltage passed to controller output stage.3. diode B3 - shortedProbably you mean SOT-323 diode marked  (I can't see). Probably it is 1SS184 or Schottky MMBD717LT1G.R6 47.5 K ΩCurrent sense resistor should be ~0.3 ΩResistor next to R6 47 ΩIs is Ok but little bit burned. High voltage passed through this resistor to controller.FB Resistor at IC 0.5-1 ΩThis is short. Ok.D2 – OKThis is Boost PFC diode.Do the rest of the readings look to be OK?Controller also should be changed. Also R6 and  and Q1.Please check resistor marked .Can a ka6 or 5d diode replace the B3 diode?And can 12n60f cs10n60f k3568 be a good replacement for Q1?I will have a look.How did you measure  and R6? Did you unsolder them?

author: john2021
author_rank: Contributor
timestamp: April 22, 2024, 05:04:28 pm
content: R6 is a ceramic resistor marked 0.22I measured R6 and the diode marked as B3 on the board itself.Diode mode on the diode beeps resistance mode on R6.I measured again with a different meter and I got good news R6 is about 0.5.Where is resistor 331 located?Is there a way to test the controller?

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 22, 2024, 05:42:00 pm
content: Please unsolder B3 and check it. Also check R6 at PCB.331 is near the controller.You can supply the controller with 15 volt (pin8) and look for signal at pin 7 (Gate).

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 22, 2024, 07:41:45 pm
content: Here is PCB views for Paint.nethttps://drive.google.com/file/d/1o8F8PD_h3s2HAJLKBaQ9ABi1_6qN4PEE/view?usp=sharing

author: john2021
author_rank: Contributor
timestamp: April 23, 2024, 08:14:35 am
content: I de-soldered B3 and tested it seems OK.The board traces at B3 seems to be shorted so maybe that is the design, I don’t understand that.There is a short in diode mode Anode to cathode and the between cathodes.Then I took out Q1 and measured again.Resistor 331 measured 331 ΩR6 measured 0.5 ΩResistor next to R6 47 ΩFB Resistor at IC 0.5-1 Ω

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 09:17:35 am
content: and R6 are in parallel (pls see the picture).So you have to change Q1 and may be controller MC33262.You can use MOSFET K3568 or CS10N60F as analog of K3234. Of course you may to solder Q1 change fuse and switch PS on. But it is bad way.Check the controller fist then connect external DC power supply as mains. Most PFC work from 60 VDC. This is safe way.

author: john2021
author_rank: Contributor
timestamp: April 23, 2024, 12:10:05 pm
content: Replaced Q1 and now I get 313v on the biggest capacitor.I get 12v on Vcc of the ic controller.I took out the rectifier schotcky diode on the secondary side.What should I check next?

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 02:14:07 pm
content: If your mains 110VAC this is perfect!Schottky  is required to cut a back spark on R6 parasitic inductance. Put it back. Just measure it in diode mode. It should be 0.25V in forward direction and "OL" back (means overload).Please provide me the name of the second controller.

author: john2021
author_rank: Contributor
timestamp: April 23, 2024, 03:50:13 pm
content: The second controller markings are hard to read, but I believe it is ST L6574D.The last measurements were with B3 installed.I said I had took out the rectifier schotcky diode TRANSISTOR FCH30A04 on the secondary side, so there will be no load there.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 04:58:19 pm
content: Please check following parts and measure the voltage.What is the left one?PSFor what reason did you remove this rectifier diode?

author: john2021
author_rank: Contributor
timestamp: April 23, 2024, 06:05:50 pm
content: Q7 - G TO D 311V G TO S 0VQ8 – G TO D 1.8V G TO S 1.5VG TO V_C53 1VI know this is not good it was higher voltage before.The initial problem was there was no power at the schotcky diode TRANSISTOR FCH30A04.In diode mode it was shorted in all direction and to a white diode connected to the left anode that was also shorted.So I also removed the diode (that looks like the one connected to Q7 Q8 collector).Now when removed it reads open. I don’t know what kind of diode this is.The other transistor is a regulator PQ1CG21H – no power

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 07:57:24 pm
content: Dear John, please check Q7 and Q8 by diode tester. Don't switch PS power on.See to face of MOSFET. Plus (red probe) to right leg minus to central. Should be around 600mV. Then change + and -. Should be OL. And also OL between left leg and any other.Where was higher voltage before? Please explain.The "white diode". Do you mean a part that was in green oval (pls see the picture)?Apparently the problem was in Schottky barrier diode FCH30A04. Is it has zero voltage between any leg? Please check again by tester in diode mode.Do you have any to replace it (40V @ 30A)?

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 08:30:27 pm
content: Next connect DC power supply +12,5V to central pin of FCH30A04 (red circle on PCB). And check the rest voltages (in circles).

author: john2021
author_rank: Contributor
timestamp: April 24, 2024, 09:32:07 am
content: I tested Q7 and Q8 I think they are OK.I meant that the higher voltage was on these transistors Q7 and Q8. They are K3233. Now I get 12-14v from their legs to ground.FCH30A04 had zero voltage between any legs and shorted between any legs and also with the white diode. Where can I test for input voltage for it?I will look for a replacement for it.What you circled green oval is exactly where there was a white diode I removed. What type is it?I connected 12.5v as you suggested and tested all the points they are all OK. THAT IS GREAT BECAUSE SECONDARY IS WORKING.Thank you again very much

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 24, 2024, 11:08:42 am
content: Good!Please send me the photo of "white diode".Please try to check again the controller name seems it is not L6574D. Try to look at it from different angles to the light.

author: john2021
author_rank: Contributor
timestamp: April 24, 2024, 01:18:53 pm
content: The white diode looks like the white diodes on Q7 Q8 (see photo).The ST L6574D is visible in the photos I took and see also a stock photo.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 24, 2024, 02:21:35 pm
content: White diode is a capacitor. It is required for RC snabber for resonance suppression.Please check it and if it is not shorted put it back.