Are these two components interchangeable?

[gintama]

I have an old PCI video card that I keep around for testing - it still works OK except there is no Green output. This makes it extremely difficult to read things in BIOS screens, etc. So I figured I would do a little poking around and see if I could figure out what's causing the problem.

Lo and behold, the green output pin is shorted to ground. I started tracing the circuit back towards the GPU chip (a Creative Riva TNT, in case you're wondering), and didn't get far before I found that the tiny SOT-23 MOSFET on the green output is fried (Gate shorted to Source):



I believe this may be an AO3407 from Alpha & Omega Semiconductor (datasheet here).

Looking though my junk box, I have a dead ATi PCI-e card of some sort, which has some MOSFETs of the same size labelled RKS 46, which I believe might be the ROHM RK7002A (datasheet here).

I need some help figuring out whether this is a suitable replacement part... Looking at the schematics, it stands out that the integrated diodes are facing different directions, but I assume that doesn't change the outward function of the chip, otherwise the pins would no longer be in the same configuration?

[rievax_60]

Re: Are these two components interchangeable?

I cant open those 2 links, MalwareBytes blocks them.
As long as the 2 parts are of the same polarity, like N-Channel and the pin out is the same which it always is for that package as far as I have seen, It will be ok to try.

EXTRA: Ok, I closed MalwareBytes and had a look at the 2 links, nothing bad happened. Those 2 MOSFETs are opposite polarities or complements of each other.

[gintama]

Re: Are these two components interchangeable?

Thanks for looking, I guess I'll keep hunting...

On the other hand, is it possible the mosfets aren't necessary? Another dead video card I pulled out has the same-ish layout to the VGA header and has the solder points for mosfets, but they're unpopulated...

[rievax_60]

Re: Are these two components interchangeable?

Thanks for looking, I guess I'll keep hunting...

On the other hand, is it possible the mosfets aren't necessary? Another dead video card I pulled out has the same-ish layout to the VGA header and has the solder points for mosfets, but they're unpopulated...

Its possible they are there to protect the outputs from high voltage spikes.
It was a real problem when plugging in a CRT monitor because of the possible static build up on the screen.
Try it with the MOSFET removed.

I used to solder 5.6v zenners from the outputs to ground on cards that I would use alot for testing CRT monitors.

[gintama]

Re: Are these two components interchangeable?

Well... The site above also lists "A7p" as a switching diode, so I may not have even identified the part properly... I still haven't found any confirmation of who the manufacturer might be, but as the card is from 1998 that's not completely surprising. I guess I'll try removing this part that acts differently from the other ones and see what happens.

[rievax_60]

Re: Are these two components interchangeable?

Well... The site above also lists "A7p" as a switching diode, so I may not have even identified the part properly... I still haven't found any confirmation of who the manufacturer might be, but as the card is from 1998 that's not completely surprising. I guess I'll try removing this part that acts differently from the other ones and see what happens.

That would make sense. Each middle pin looks like it connects to a signal path. I would be curious to know if all the left pins all connect to the same rail. And if all of the right pins all connect to another rail.

[gintama]

Re: Are these two components interchangeable?

Looking at it from the orientation in the photo, the left pins all lead to ground. The right pins are also tied together for each group (R/G/B, and then Vsync/Hsync/?), R=~20 Ohms.

[rievax_60]

Re: Are these two components interchangeable?

Im suspecting its something like this but protecting outputs insted of inputs,
http://www.radio-electronics.com/inf...guidelines.php

[gintama]

Re: Are these two components interchangeable?

That site doesn't respond for me, but I think I get the usage here if it is a diode - basically, voltage goes out OK but is shunted to ground if it's coming in from whatever's plugged in?

At any rate, I removed the part and nothing changed. Guess I'll have to live with it, or find a scrap PCIe card somewhere. Thanks again for your input rievax_60.

[selldoor]

Re: Are these two components interchangeable?

Could be a BAV99 - see here
https://cdn.badcaps-static.com/pdfs/...ddbe71062e.pdf

[budm]

Re: Are these two components interchangeable?

This is the typical way the VGA and DVI inputs are protected. The Monitor will function if they are removed, just will be no protection.

[gintama]

Re: Are these two components interchangeable?

@selldoor: That's what I was referring to in post #5. I fiddled around with my dmm's diode detection setting trying to come up with a way discern a diode vs a mosfet and couldn't see any real pattern, which is why I gave up and just removed it.

@budm: Hello again, and thanks for the link - the diagram looks very similar to this PCB's layout. There are very few parts between the GPU chip and the output pin: the diode(?), a few small caps, and a resistor... I guess I could try replacing or removing the other ones as well.