Astro wars / galaxy ii repair

bobmoo79 · Posted: Sun Jan 20, 2019 5:58 am Post subject:

Thanks for the reply TokyoBatman!

Yes it would have been a wrap but I jumped the gun with the 32v zener idea.

I connected it in circuit and nothing worked and the transitor D882 got very hot. Quickly switched the power off and had a rethink.

So I set about measuring the working unit again but this time using my scope.

The cathode of the S06 (assumed 'diode') connects to pin1 on the transformer.
I disconnected the other end of the diode from the circuit to see what's going on here.

I was surprised, but I'll report what I saw.

According to my scope the Transformer is providing an ac signal, 200v pk-pk, period 10us, 140vdc offset. It's a very basic self-build scope and this signal is actually above its rating, so is probably not entirely accurate, but I hope it gives the general idea - big ac signal in to the diode.

at the other end of the diode, which is disconnected from the circuit I see a -39v dc signal with ripple of 1v pk-pk.

So I now assume I need a 39v zener diode.

I splashed another 99p on ebay and will have to wait a few days before I can try again.

If the new diode doesn't work then I'll have to seek help from somebody who knows more about electronics than I do. I have continued to develop the schematic, correcting it as I worked so I hope it's near enough correct now, except obviously a few diodes remain unidentified, but it may be good enough to give somebody an idea of what this circuit is actually doing. I also added key voltages measured in the working system (e.g. Transformer outputs, Transistors - gate, base, collector and other points) which may be good as a reference if I ever decided to fix another one of these.

Neutral

TokyoBatman · Posted: Tue Jan 22, 2019 5:15 pm Post subject:

It seems like you have crossed your t's and dotted your i's. I believe the 39v zener diode should do the trick, but I have no real knowledge in this area, just based on what you've reported/found.

We are all looking forward to seeing the video of the working unit. You've put a lot of effort into this one!

Hope all works out as planned Smile

mmackin · Posted: Wed Jan 23, 2019 3:27 pm Post subject:

Thank you for posting the details of your repair. As this can be helpful to others trying to repair and solve issues with their own machines. I've been able to repair machines from the details others have shared here. This is entertaining for those of us who like to repair and fix up these little machines. Also to see the success of bringing it back to working condition. I wish you success.

bobmoo79 · Posted: Fri Jan 25, 2019 1:09 am Post subject:

Thanks guys.

After installing the 39v zener the unit powers up and the game appears to work fine, although the zener is getting incredibly hot (it shouldn't be), so I'm not quite there yet.

My first thought is I need some added series resistance, but I'll have another look at the circuit and the spec for the zener to see what's going on. Obviously if I had the right component I wouldn't need to do anything so I got it wrong somehow.

I'm not giving up though, and hopefully at the end of all this I'll be able to tell you guys exactly what component you need to fix this particular fault and it'll benefit others.

mmackin · Posted: Fri Jan 25, 2019 9:23 am Post subject:

Usually when you have a component that gets very hot is usually an indication of a short in another location. Have you changed out all the transistors? You could have a faulty working transistor.

Those transistors are fairly inexpensive to replace, and they are the biggest culprit of shorts.

A bad transistor is probably the original cause of the zener failing.

bobmoo79 · Posted: Mon Jan 28, 2019 1:37 am Post subject:

Thanks.
Yes I replaced all the transistors previously and so they're all working well.

It's definitely a problem with S06 because I have ruled everything else out. Also, when I take a working S06 component from my working machine and place it in this broken one everything works perfectly. In that situation the working S06 does not get hot, so I know the only problem is with my replacement S06 (39v zener diode).

This is frustrating because I know which component is faulty but can't quite figure out the spec.

I have considered using a diode with a higher power rating, but I don't really think that is going to help in this case.

With the good S06 in place and with the circuit operating normally I measure 10mA current by placing the DVM in series with the diode.

The output voltage is 39v (i.e. measured between the anode of the diode and gnd)

Therefore I calculate the power is 39*0.01= 0.39W.

so my 1.3W zener should be man enough for the job.

bobmoo79 · Posted: Fri Feb 08, 2019 1:20 am Post subject:

I went to the pound shop and bought four 9v PP3 batteries, so over the weekend I'll connect them in series with a resistor (and a 5th PP3 battery I already had) to generate 45v and test the zener that way.