Identify ST chip / Agilent N6700 mainframe powersupply

[ahakman]

Hi. I have a few Agilent N6700 Modular power supplies where the primary power supply (3rd party Cherokee International SP547, 48VDC, >600W) has failed. All of them seem to have failed in a similar fashion with the failure being after the PFC circuit, and on the primary side of the main switcher. Being very high wattage supplies, they seem to have quite a complicated design vs most normal switchmode supplies. All of these have failed in somewhat spectacular fashion (traces vaporized off the board, chips with the top completely blown open, one of the main switcher fets shorted and one of the DC bus capacitors exploded from the resulting short). I'm not having a problem finding shorted parts, resistors with holes in them, etc, but I'd like to reverse engineer the controller circuit a bit to at least slightly understand it and check for less obvious component failures in order to repair them.

A problem I've run into is a chip on the daughter board I can't identify. It's clearly an ST part, but I can't seem to find a datasheet for it. On the board from one power supply, it's labeled 339 GZG3349 (I think those are G's, they might be 6's too), and on the board from another power supply, it's labeled 339 eZMY815. I can't find a datasheet for this part with either of these part numbers. The 339 being common between the 2 would seem to mean this is part of the part number, and the rest is factory or date code?? Does anyone know what these are?



The board also has a PFC controller ST L4981AD datasheet https://www.st.com/resource/en/datasheet/l4981.pdf, a UC 3842B Current Mode PWM controller datasheet https://www.st.com/resource/en/datasheet/uc3842b.pdf if that at all helps.

Has anyone repaired any of these power supplies from an N6700 in the past?

I'm having to draw out a schematic for parts of this to keep things straight for myself - as I mentioned, these are quite complicated supplies. If I get these figured out and I think the schematic is good enough to help others repair their units, I will post it.

[CJay]

LM339.

[ahakman]

Yes! They would appear to be that. Not sure how I missed the obvious. I googled "ST 339 datasheet" and it came right up! Now I feel even dumber than trying to reverse engineer this switcher is making me feel!

[CJay]

Yes! They would appear to be that. Not sure how I missed the obvious. I googled "ST 339 datasheet" and it came right up! Now I feel even dumber than trying to reverse engineer this switcher is making me feel!

Heh, no worries, we all do it sometimes, real easy to overthink stuff.