Help identify blown diode in Trace/Xantrex SW4024 inverter

[halfwalker]

Some years ago I bought an old Xantrex/Trace SW4024 off fleabay to work as a partner with an existing one I already have in place and working (for 15 years).  It was bought with the understanding that it was not fully working, and in fact had taken a fall ...  But boy was it cheap 

So I'm finally getting around to trying to get it working again.  On the main control board in one corner is a row of 7 diodes, 5 of one kind (probably 1n4004 or similar) and 2 of another, unknown.  What I can see of the part number is 628-130 - you can see the 130 easily, the 628 bit is more underneath.  I think it's 628 ...  One of the unknown ones is blown - D12 - see the attached pic.

I was told by someone else that it's a 1N5262 - but that's a 51V zener.  Seems like a weird value, but who knows.

The board is PN10-066 rev 8, dated 6/12/14.

Can anyone help identify the diode ?  Also, what might have caused it to blow ?  I've examined the board closely, and I don't see any other signs of damage, not even the transistor next to the blown diode (Q6).  The traces underneath the diode show no signs of heating or damage.

https://ibb.co/MgpX6gm


The idea is to get a split feed off the two SW4024s for a full 220V

[fzabkar]

Can you test the adjacent diode with a Zener tester?

[halfwalker]

If I had a zener tester ...

Hmm, I have an old RSR 926 multimeter that has transistor checking - hFE for npn/pnp.

[DaJMasta]

Not gonna get much info from that diode debris, but since you have a working inverter - why not reference it?

51V is not too uncommon for a zener, but it may not be common for your device.  The other diodes being small signal, there's a chance it could be one of those as well, but with the opposite polarity on the board a zener makes more sense.  A zener and transistor in that configuration is a low current voltage regulator, so if you can find out what voltage is supposed to be on the pin it goes to, you may be in luck that way.  Otherwise, to test a zener you need a psu with a current limit (protection) and a multimeter.  Measure the voltage across, turn it up gradually until it starts carrying current - that's your zener voltage.

[halfwalker]

So put reverse voltage across the existing diode, current-limited to say 20ma.  Multimeter in series showing current.  Turn up voltage until we see current.  Can do that with board out and just right across the diode ends.

Heh, and hope that D12 is/was the same as D13.  Trace/Xantrex/Schneider were notorious for NOT releasing information like circuit diagrams or repair docs.

[DaJMasta]

Also can limit current and measure voltage - when the supply is in constant current mode the voltage will drop right beyond the zener voltage.  Probably best to pull the diode from the circuit in advance, but the rating is just where that zener breakdown point is, so it should be a reliable way to test it.  You just want to make sure it's current limited one way or another - otherwise you'll end up with a second that looks like that.

I mean that if you have a functional SW4024, you can open it up and try to determine the diode used in the working one, then just match it for the second - from the initial post it sounded like you had two and that one likely had the diodes intact.