Help identifying an old diode

[tryppyr]

I am in the process of restoring a 1984 solid state bingo pinball machine. Until recently I had it in full working mode using what I will discretely refer to as inferior restoration methods. When I decided to clean up my work and do it more "properly" things went downhill fast.

One thing I did on this board was to replace an old broken ceramic capacitor. My concern is when I did so I damaged one or both of the diodes nearest one of the capacitors I replaced. Now, for the sake of completeness, I would like to replace both.

My chief problem is I cannot identify the diodes in question and don't know what I need to install to replace them. Having not removed them from the board yet, I read the markings as saying:
6V8 PH BZY (or BZX)

15 PH AAZ

The pictures may be more revealing than my attempt to read what is on them.

Can anyone tell me what I need to buy to replace these?

 

[Six_Shooter]

That looks like 8A9 to me.

I believe the other diode is a germanium based diode, but, don't take my word on that.

 

[davenn]

That looks like 8A9 to me.

I believe the other diode is a germanium based diode, but, don't take my word on that.

think you will find you are reading it upside down
its really a 6V8 = 6.8V Zener diode

Dave

 

[(*steve*)]

It would be very useful to see a little more of the board around this, and both sides of it as well.

There are other things you might have done.

Do you still have the old broken component? If not, are there other similar (although perhaps not broken) components on the board?

 

[tryppyr]

I do have lots of photos. I've been taking them since I started this project.

First one is a shot of that area of the board before the capacitor got replaced. You'll note the two legs of the capacitor are all that was left and they were bent to touch each other.

Second shot shows the ceramic part of one of the capacitors after it fell off.

As you can see, there were a lot of these capacitors on the board.
My initial repair involved wire wrapping the replacement caps on the posts. That worked fine but was ugly.

 

[tryppyr]

Here is a shot of the underside showing my solder work. I've since gone back and redone this to make it even tidier.

 

[tryppyr]

Incidentally, thanks to your help I think I have identified the components as 1N4736 (for the 6.8V Zener) and 1N5245B (a 15V Zener)

 

[(*steve*)]

Are you saying it worked with the legs of that capacitor twisted together?

If so, then the problem is more likely to be a fault in the design of the board and that this component should either be a link (or possibly a series resistor for the zener)

 

[tryppyr]

I did not observe the machine working with the legs twisted together. I had replaced two of the broken capacitors and the memory battery before the machine successfully fired up for the first time. The other capacitor I replaced initially can also be seen in the "before" picture, right beside the daughter board (random number generator), just to the left of the unlabeled EPROM.

 

[(*steve*)]

Your soldering is pretty average... (poor)

I recommend you practice before you work on the board any more.

The first capacitor you've shown us looks like the pad on the top side of the board has been removed. That may break the circuit (it looks like it has), possibly removing power from something.

I see the same sort of soldering on the reverse side of the board. I also see scratch marks that look like you've been using the tip of the soldering iron to unbend leads to make them easier to get out.

A solder joint should look smooth and bright and flow over the pad. The original ones are examples. You should be able to do almost as well yourself (and yours should look shinier!).

It would be best to look at every solder joint you've made and check to see if you have damaged the board. The good news is that boards like this are easy to repair.

Remember that if you are holding your soldering iron on a joint for longer than a couple of seconds, you are taking WAY too long.

 

[tryppyr]

I appreciate your candor. I'll check on the pad and the trace. It is pretty obvious to me that it (and some around it) have been corroded, so it is possible I've damaged it in trying to restore contact with the top pad.

 

[tryppyr]

Just wanted to let you folks know that I got the machine working again.

I removed the capacitor that was between the two diodes, and also removed the 6.8v diode. I cleaned up the pads for both, and made certain they were intact. I then installed the new parts, added a little flux and soldered (from the top this time) both parts very carefully. Then I put the board back into the machine and powered it up. Came up clean the first time.

Now I can rest easier knowing I didn't screw things up permanently.

 

[(*steve*)]

Congratulations. A poor solder joint is an easier repair than a damaged pad