Siemens LOGO PLC repair

[CookieB]

Hy,

I got a Siemens LOGO PLC

It failed in an industrial application and therefore simply got replaced. Normally they would throw it away but due to my interest in such devices I got my hands on it.

It served as a display piece on my shelf for quite a while but recently I was thinking why not try to fix it.

It pops open easily (without any tools) an inside there is are 3 PCB’s.

A close inspection of all components shows only one that is physically damaged.
It is a component on the back, of the biggest PCB so unfortunately there is no silk screen.
The text on the component is small but I managed to read it and it has a Motorola symbol followed by “837B” and “ZP621” on the second line.
Googling this seems to learn me it is a Zener diode.

I’m not very experienced with electronics so that’s why I’m here.
What is the chance of this being the sole problem and what Zener diode can I replace this one with (I can’t find that one for sale anywhere). Any advice for where to get it is welcome to (I live in Belgium).

Here are some Pictures:
https://www.dropbox.com/sh/xpk0zbabswhoa21/AACP053EqfEPnzvUnqVVaqz_a?dl=0

[singapol]

Most probably 1N837...not a zener but a switching diode. The close equivalent is 1N3070 or NTE177.

http://www.farnell.com/datasheets/46802.pdf

[PTR_1275]

I just grabbed one of the logos from our storeroom and it is different internally. We use the 12/24v ones not 240v. I can't see a similar component on ours to even confirm the part number for you.

[bruno_0021]

Hello CookieB

 I have exactly the same problem and I think ZP621 is not a switching diode but a Zener. Do you have found a good diode ?
If yes, can you tell me the reference of your new diode please ?

Bruno.

[kmike]

Hi,

I disassembled one of the oldest working LOGOs that I have here, but it is completely different (0BA3).
That LOGO You have there is one of the first ones (0BA0 at the end of the order number), I would not recommend spendig too much time on it, because the old ones have a very limited memory and very few functions to work with. Also the output relays are likely to be defective at that age, although this depends on the switching count, so I would not rely on those either.

edit:
oops, sorry to have replied to this old thread, did not read the date... 

br,
mike