[mrg2783]

Hello EEC Family,

I’ve searched high and low for a A9L computer schematic. I am getting zener diodes replaced on the circuit board and the repair shop was hoping I can find a schematic to make sure they are replacing them correctly.

Does anyone have an A9L schematic? Or can anyone tell me what the Orange zener diodes are rated at? Looks like a couple have a white and blue line and a couple have a white and green line.

Any guidance is appreciated.

[wwhite]

I don't think those are diodes, I may be wrong.
They don't have leads on them.

Looks like someone already went in there and did something. Pretty poor soldering on those.

I wouldn't trust your repair shop if they don't know how to figure it out.
I do not have A9L on hand at the moment. Should be easy enough to take one out, measure and get the specs.

[wwhite]

A little research shows they are SMD Diodes.

The color band can mean cathode end.
Also can mean zener or shotkey depending on manufacturer.

So, basically, you would need to pull one or all, and setup up a test bench and figure it out.

[Jman]

Insomnia got me and I unsoldered the leadless glass diodes off of an A9S and measured them. Physically they are 2.62m OD around the glass and 5mm long end to end. I pulled off six of them and they are all identical. I tested the forward bias voltage with two different bench meters and got .59 on one meter and .60 on the other. I compared the A9S glass leadless diodes with the ones in an A9U2 I'm working on, and they appear to be the same. They have a single-color stripe to mark the cathode side that looks white; however it almost seems yellow, but I think it may just be aged or the conformal coating on the PCB changed it to be slightly yellow. There is a clear area in the middle that almost looks like a color band but if you look closely when they are soldered down you see the PCB color thru this area, and it looks blueish green depending on the angle you look from. If you look dead on you see the silver metal of the diode inside the glass tube.

I also used a power supply and a 1k 1/2watt resistor to try reverse biasing the diodes to see if they are Zeners. I went all the way up to 42VDC and they did not bias in reverse, so they are definitely NOT Zener diodes. I think with the slightly low forward voltage they are probably Schottky diodes. I found what is my best guess (1N5819UR-1) so if you try this remember this was my GUESS not an absolute.

I'd try testing these more if someone can suggest other good tests to be more certain. I would even consider a destructive test if it would prove something.

Thank you
J.W.S.