Diode k2k2 replacement

[Mote]

I am working on an older amp, which had zero resistance between + and GND terminals. Found one small diode which was shorted. Writing on it says: "K2K2". Tried googling it, fairchild cross reference search but found nothing.

[Perry Babin]

The only diode that should be directly connected across the B+ and ground is the reverse protection diode. That's not a critical part and can be replaced by any diode with equal or greater current rating. If you don't know the current rating, the size is generally a fair indicator of the current rating.

[Mote]

I think it is not reverse protection diode.
I will add pictures tomorrow, it is 01:50 in the night at the moment here.
Remote terminal connects to a wire, wire is connected to somewhere in the middle of the board. Connected to that wire is this diode. Other damage was two blown power supply mosfets, which I replaced already.

Reverse protection diode is near the + and GND terminals? It is not shorted. I removed components one by one to see removing which would make resistance between + and GND more than zero. Removing this diode helped and it checked out shorted.

[Mote]

Borrowed 1N4004 diode from another amp, without rectifiers i have no current draw anymore. When I installed rectifiers I got maximum current draw, removed output transistors and got rid of the current draw. All output transistors are good. 3300uF caps look like they are a bit swollen but testing them with MM and LC meter shows similar results to other 3300uF caps I have lying around here.
On PS FETs I get very weird readings: gate 7,7V, drain and source 0.
PS chip is SG2525AN, so I dont know if gate is supposed to have 7,7V on it.

I did not measure voltages on SG2525 yet. Try to do it tomorrow, anyway very strange stuff.
Pictures: rectifiers are out, this diode is also out. I noticed that there are some resistors missing from audio section but I did not have time to figure out are they removed by someone or are they not supposed to be there.

[Mote]

Obviously amp does not power up, no protection LED, no Power LED, nothing.

[eyoung]

pc board in first picture has a slot cut through it looks like several components are severed as i bet traces on the back side of board are severed as well, looks intentional may be a warranty unit that was rendered unusable at the factory.

BTW, what make is the amp???

Best of luck , Elwood

[Mote]

Sorry, this is Intersonic Maxound MX 220
Where do you see the slot? Between R130 and Q507?
That is not a slot but a big metal jumper.

[Mote]

+, GND and remote terminals are connected to a small board, and from there + goes through fuse and through wire to main pcb, there was bad connection and 12V never made it to board. Only remote and GND were actually connected to amp.

Fixed the connection, disconnected remote and measured voltages on FETs. Two had 0V, 12,5V, 0V other two (Q504, Q503) 0,4V, 12,5V 0V. Cant figure out where this 0,4 is coming from. FETs are good but with them out of the board I have no 0,4V on the gate pad. With only Q504 on board and Q503 out I get 0,02V on gate pads.

With remote connected the amp draws some current, 50W current limiting lamp glows a bit.
Voltages on FETs: 3,6V, 9,3V 0V, Q504 and Q503: 4,0V, 9,3V, 0V.
Voltages on SG2525AN:
01:0
02:6,57
03:3,57
04:5,75
05:4,49
06:5,07
07:4,41
08:6,39
09:7,08
10:0
11:3,68
12:0
13:8,13
14:3,67
15:8,13
16:6,53

[Perry Babin]

Is Q502 being used as a driver for the FETs in this amp?

[Mote]

Yes, there are two transistors like this, one for each side. With remote disconnected Q502s partner from the other side had 0,4V on first leg but 0V on the other two legs. Switched Q502 to other side and vice versa, no effect, 0,4V stayed on Q504 and Q503.