Dreamcast PSU with bad diode?

[pentium]

I never really figured out why my Dreamcast kicks out under the load of the GD-ROM drive. If it's installed, the system comes on and then kicks out but when it's removed the system fires up fine (but hangs wile trying to find the drive). Unless an IC on the GD-ROM drive has shorted out the board/assembly is fine.

The other day I was bored and I started going over the power supply in the dreamcast. When I was testing diodes I found that one was acting funny.
With my diode tester I know if a diode is good if it reads one direction but if it reads both ways or not at all I know it's bad. Only difference here is that this is one of those clear diodes and I have never seen one that was bad. Because of that, I don't know if it really is bad.
If it is bad, it might explain why the system cuts out when the drive is installed.
Is it dead or is it okay? I have attached a photo for reference. We are looking at D6 which the probe is pointing at.

[Harvey]

Re: Dreamcast PSU with bad diode?

Without taking it out of circuit you'll never know for sure. Testing diodes in circuit is never reliable.

As to what it is... your guess is probably as good as anyone else's. Diodes that look like that are generally just small signal diodes, 1N4148 or similar... but in a switch mode PSU it could be a Schottky diode or even a Zener....

[linuxguru]

Re: Dreamcast PSU with bad diode?

That's an extremely high quality Japanese assembly, probably Matsushita (Panasonic) OEM. I'd be surprised if anything failed prematurely in that unit.

The glass diode is probably a zener, and most probably OK. Most glass-package zeners are only used as voltage references and are not stressed much by large currents (some exceptions exist in AT/ATX PSUs).

[pentium]

Re: Dreamcast PSU with bad diode?

Okay. Next time I have the time I'll desolder and pull one side of it off the PCB and try again.

[999999999]

Re: Dreamcast PSU with bad diode?

It might be helpful if you supplied more details of this circuit area.

For example, what is that KA7**** chip? What is the circuit connection to it, and the diode, based on the copper traces on the bottom? A good straight-forward (not angle) shot of the top, and a corresponding picture of the bottom, is a beginning in understanding how this is set up.

[pentium]

Re: Dreamcast PSU with bad diode?

I don't have the time to do something like that right now.