CTEK MXS 3.8 repair

I also spoke to Mantech about the 04N60C3 and was given two alternatives:
http://www.mantech.co.za/Stock.aspx?Query=15m6130and
http://www.mantech.co.za/Stock.aspx?Query=35M5114and

The 04N60C3 is 4.5A/650V
The 15m6130 code above is 4.5A/600V
The 35M5114 code above is 11A/650V

Do I need to be looking at RDS values as well?

Please help me select the best match

 

Wowee! St Edd. Right on the money as always.

Pin 7 of the NCP1271 is indeed missing.

There is a complimentary set of transistors, 2fe and a6w. Pin 5 is connected to the connected bases of these two.

The gate of the mosfet is connected to the emitter of the 2FE. From emitter of the 2FE the connection runs through a 22 resistor to the common of the a6w.

Thank you thank you

 

Here's a photo of that area:

 

When I search for that A6W transistor I get to a MMBTA05 Gen Purpose NPN transistor. Is this it?

 

@73's de Edd

St. Edd, hopefully this helps. Attached is a LTSpice file showing the circuit from power in through rectifiers and mosfet and to the 2 tandem transistors and their connection to NCP1271.

Please excuse any errors as I battle with LTSpice and it's tricky plotting an unnumbered pcb. Diodes could be pointing the wrong way etc. Please ignore the two unattached inductors on the right. I am trying draw the transformer with it's 4 primaries and 5 secondaries.

 

Bit of an oddball question: I pulled the 04N60C3 mosfet and then powered up to check some voltages. Instantly blew fuse on power up. On checking I notice a dead short between the drain and source holes on pcb. Is this how it's meant to be or have I got a short somewhere else?

 

Sorted this particular problem. 3 of the 4 rectifier diodes blown.

 

I want to replace the two tandem transistors marked 2FE and A6W. On closer inspection of my photo in post #44 the 2FE could actually be a 2F.
Searching for this transistor brought up this: https://www.google.com/url?sa=t&rct...MBT2907A.pdf&usg=AOvVaw0h21C5BkliR-WwIFQC51Pn
This could be correct but could somebody please confirm.

The A6W is a bit more tricky. Downloaded all the smd code lists in our resources section and some others. Various components come up but I have no way of saying which one is correct. Can somebody please help me to find the correct replacement transistor.

 

Thanks a mill St Edd

Pocket sized? No, not for many years

But I have this:


Hope this can work.

 

St Edd, I am quite happy soldering smd components on. Is there a specific reason for going with leaded components? If something like higher reliability, etc then I will go with leaded components but if not I would prefer to go with smd components

 

Me and my soldering iron have walked a long road since then.

How about the AM radio?

 

St Edd
I found another forum post where you describe the usage of the AM Radio and tried it. Couldn't hear anything above the crackling of the AM radio no matter how I rotated it.

I had previously measured voltages on the NCP1271
FB pin 2 = 3.6V
Vcc pin 6 = 9V
HV pin8 = 328V
No reading on the other pins (which I suppose is logical)

I decided to recheck those readings and while I was reading pin 8 a 1.5kΩ resistor decided to fry itself and depart for the happy hunting ground. No idea why this happened, pin 8 is conveniently freestanding with no pin 7, so short caused by probe unlikely. Ground used for measurement was neg of big cap.

It's the 152 resistor shown by the left most arrow.



I must also add that the NCP 1271 was running pretty hot when switched on through dim bulb tester

 

I replaced the 04N60C3 fet and the blown 1.5k resistor.
Readings I'm getting now: (All relative to neg of big cap)

Voltage on big cap: 336V DC

04N60C3: g: 0V
d: Jumping around in the 200, 300V DC
s: 0V

NCP1271 (7 leg chip)
1 0V
2 0V
3 0V
4 0V
5 0V
6 14V Vcc
8 334V HV

Are there any other readings I can take which might lead us to the problem
I have got replacements for the NCP1271 chip and the 2 complementary transistors, 2N2907 and 2N2222

 

Thanks St. Edd

Yes, it is still the original 1271.
I am trying to find correlation between your application note and my board's reality.
Three posts up is a photo with a red arrow pointing to the blown resistor. Now, is that a 152 resistor or a 251 resistor? If I measure the unblown identical resistor next to it it measures 1.5K

 

@73's de Edd
I have attached a portion of my LTSpice file showing relation between NCP1271 and the 2 driver transistors. No guarantees that is correct. Helluva job creating the LTSpice simulation for the CTEK

 

I have nearly finished the LTSpice simulation. Still some components at the top of the board to do. So I decided to start taking some voltages on the board.
Voltages are shown in dotted rectangles.As can be seen on the simulation voltage on big C5 cap fine (331V) But when I go to the next component in line R4 (0.47Ω) I get no voltage. Although the same voltage arrives at the transformer as can be seen.

I don't understand this, am I missing something.

Please help