7898 Power Module

[playmate]

I have a 7898 power board with a bad ZD1 (zener diode) on it but don't have a schematic to find the right value to replace it.

Does anybody have some technical data on this board or info on how to get a replacement board? I would rather fix it if possible but would get another one if need be....thanks.

[Fugazi]

Hi playmate, welcome to EB! I will move your topic to the Train Tech forum where it's more likely that you fill find expert help.

[peterab]

I don't have any specs for you but Briclink will help you find a replacement. I assume you mean This Part, if not the inventory should help.

[playmate]

Yes, that is the whole assembly in which the power board is in. Do you think anyone here would have the schematic for the board so I can fix the one I have that is not working?

I'm a tech and have a variety of parts available but need to know what the value of ZD1 is because it is defective.

Thanks for the help.

[JopieK]

Well, since you are a tech you could guess it couldn't you? Low drop, at least 9V I would suggest.

[lightningtiger]

Are you able to read the numbers on the diode body ?

Plus are you also able to trace out the circuit from the pcb layout and from that you might be able to work out the voltage of the zener.

Question is why did a zener fail ?

[JopieK]

He is a tech, so likely he applied some juice to it (read: more than he should have ;)).

[1974]

Question is why did a zener fail ?

It's an electronic component. Components fail

Replace it with a 5V6 minimelf zenerdiode

It's most likely a part of a reference voltage/Vreg for the potted mystery module/IR recievers as all the other components (LED + resistor, transistors and the 1930 H-bridge motor driver) will handle up to 11V

I could trace it out but there's not much more to it than that, I reckon

Edited August 16, 2012 by 1974

[playmate]

Thanks for all the help-

To answer some questions:

Are you able to read the numbers on the diode body? No, it was damaged by battery corrosion.

I could trace it out also but I thought I would ask here first for a schematic - nice sight for Lego enthusiast!

JopieK said: "He is a tech, so likely he applied some juice to it (read: more than he should have ;))." JopieK is a real JoKer!

[1974]

No, I didn't read the numbers on the component, I measured it. I 've been too long in this game to trust numbers on a component - measurement is what I trust

It's five point six, trust me Just put it in the right way If you can't get a minimelf, it wouldn't be too hard to fit in a regular 0,6W leaded zenerdiode ..

[JopieK]

JopieK said: "He is a tech, so likely he applied some juice to it (read: more than he should have ;))." JopieK is a real JoKer!

Well, since I used to teach tech students and still teach other students, I know myself and my kind a little ;) Lecturing keeps you remembering your own faults ;)