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Grandstand "Astro Wars" / Epoch "Galaxy II" Repair.

Thread starter #1
Hello all, new member here!

Please forgive me for the massive dump of information I am about to drop on you all.

when I was a child I owned a game released by Grandstand in the UK called 'Astro Wars' (also known as 'Galaxy II' and released by Epoch in other countries). It was awesome, at least that's my recollection of it, but unfortunately the unit I have no longer works and so I am trying to repair it with ever decreasing optimism!
Nonetheless for now I am persevering and wondering whether any of the kind folk on this board would be interested in helping...

This is what I'm talking about!


Astro Wars Manual

The system takes +6vdc either from batteries or dc adapter and uses a custom 4bit microcontroller to drive a VFD display.

Pictures:
Epoch Galaxy II PCB Back.jpg Epoch Galaxy II PCB Front no CPU or VFD.jpg 20181205-204125.jpg

UPD553-153 datasheet and manual.

nec-1981-175-s6-upd553.jpg

uCOM-43 manual (including UPD553)


Symptoms:

When power is connected the system shows no signs of life. No sound. no display.





Draft Schematic:
I have not managed to find a schematic for this game online anywhere and so I set about buzzing out the circuit board manually and created something that I hoped would help me, but it doesn't. My electronics knowledge has well and truly lapsed and I can't make any sense of the power section. Of course given my own lack of skill in this area, and despite me being as methodical as I could, it almost certainly contains errors, and definitely could be laid out more professionally. Some of you may find it a little confusing but I'll post it in the hope that it could help the discussion.

Ignore the VFD symbol. I used EasyEDA to create the schematic and was unable to find the correct symbol, or even edit the one I used.

Schematic_Astro-Wars_Sheet-1_20190109112110.png

Draft Parts list:
This is the parts list I created by inspection and measurement.

Astro Wars Parts List.png

Fault finding:

I have opened the unit for inspection and noticed that the Transistor (S02 - a D882 npn transistor) gets very hot very quickly when power is applied. When switched on the voltage (when measured at the supply) drops to around 2.5v and the current is high - 1.5A(!).

On pins 41 and 6 of the microcontoller I only measure -5v but have been told it should be -10v.

Initially I thought the problem might be a faulty transistor or a shorted capacitor but think I have ruled that out now.

These are the things I have tried so far:

Replaced all transistors.
checked all caps for shorts. There are none.
Replaced all electrolytic capacitors.
Measured and confirmed all resistor values.
Tested some diodes. (Identified zener voltage in a couple of cases).


Because I hit a brickwall and because I thought it would be interesting do so, I removed the VFD and fully tested it and it works perfectly.

Question 1: Can anybody provide any guidance on what I can try next?

I thought about taking the removing the controller and using a simple breadboard circuit to power it up, perhaps with oscillator and speaker (and associated components) just to confirm whether it would do anything (i.e. does it play any sound when powered up) but I got confused about how to supply it.

Pins 41 and 6 need -10v with respect to pins 20 and 21. I can set that up by reversing the + and - leads from the power supply, but that leaves me with a question about how to connect the GND connections to the pull down resistor packs etc.


Known issues:

Transformer TY-33:
This is a 10pin transistor that I have so far been unable to test because I don't have access to a low voltage Ac supply and can't find any useful information about it online. I think it unlikely this has failed but this is what I have managed to learn by inspecting the PCB.

Pins 1, 2, and 5 are GND.
Pins 7 and 9 are not connected to anything on the PCB.
Pin 3 = +6vdc (from the batteries/mains adapter).
Pin 4 = Collector S02 (measured +6vdc when tested in circuit)
Pin 10 = VFD filament (Pin30)
Pin 6 = VFD filament (pin 1)
Pin 8 = I'm not sure but assume it could supply the microcontroller with -10v.

I would expect this transformer to provide the different voltages to the circuit.
From my research into VFDs I assume that pin 10 and 6 should output 3vac to the VFD filament (although I was successfully able to test it by using 3vdc).
I have been told the microcontroller should receive -10vdc (although the datasheet says anything from +0.3v to -15v should work), and I assume that would be from pin 8 because I can't find any place for it to come from.
Many pages discuss VFDs (the grid pins and phosphor plates) being driven by as much as 40+v, but I got this one to work fine with only 10v applied. I assumed that as each pin is driven by the micro it should be 10v in this case.

(Example VFD power supply circuit attached)


Question 1: Any ideas on how I can test this transformer?


S06:
I presume this is a diode to protect reverse current to pin (via the speaker and resistor), but I haven't tested it to confirm. There are no markings printed on the glass casing.

20181205-204026 markedup s06s08.jpg


Question 2: Can anyone help identify this component?


S08:
I initially presumed this was a zener diode but using the max voltage my supply could provide (31.5v) I didn't reach a point where voltage was being limited in my simple test circuit. There are no markings printed on the glass casing.


Question 3: Can anyone help identify this component?



Thanks in advance for any input you can provide!Manual
 

Attachments

Last edited:
Thread starter #2
So I had the good fortune to pick up another Astro Wars (first edition with red text) that was sold as faulty (broken VFD) but when it arrived it works perfectly! I have started taking measurements around the circuit and will use that information to guide my investigations.

On the faulty unit:

I mentioned before that I was unable to figure out what S06 is supposed to be, but it looks like this:



(it is a glass case, with red band at one end, thinner gold band just in from that, no text printed on the case.)

It measures 20ohms in both directions when tested with a DVM.

Yesterday I discovered that when it is disconnected from circuit the supply to the microcontroller is -10v as it should be. With S06 connected the supply voltage drops right down.

I still need to remove the good 'S06' from the new unit and test it.


What's the best procedure to test it?
 
Last edited:
#3
Is there anything else connected across S06? It may not be that device, but something else across the same terminals/traces. Is it still 20 ohms when disconnected?
By the designations of other "S" components, it seems they call their diodes "S". It could be that this was a zener or some other diode that is shot, and shorted.
Without a schematic, hard to tell for sure. Where do the pins of S06 go to? Does one go to the power supply directly? Does it look like S07, S08, etc? Other diodes look like regular 1N4148 types.
 
Thread starter #4
Thanks for your reply.

I agree the naming convention makes it seem as though S06 should be a type of diode. Indeed I have measured the zener voltage of S09 (11.5v) and S10 (7.5v) but not any others.

Yes S06 is 20ohms when disconnected, regardless of which the DVM probes are connected.

I wish I had a schematic that was known to be good because the one I have put together is incomplete and probably contains errors. I haven't yet had the energy to check it all again as it was quite time consuming.

I have added my own draft schematic above and it shows S06 as a zener diode (may be incorrect)

I have confirmed the resistance of the series-connected resistor (R07) is 620ohm and matches the colour code on its casing.
 
#5
Something not right with the schematic. S06 shows it setting a voltage across C3 (negative?)between ground and the -ve side of the cap. But, that line goes off to the R01 network where you show it going to ground.
I also doubt that transformer pins 1,2 and 5 all go to ground, though it may be possible if each is from a separate secondary winding.
Try to check those traces, If S06 is indeed across C3 like in the diagram, it would be creating (somehow) a negative voltage.

Now, if C6 was also a 47uF like C3, then I would say S06 is a 7.5V zener like S10, and both are used to create negative voltage supply.

This all said, the fact that the part sheets clearly labels Zeners, but not S06 as such, I tend to lean back to assuming it is just a regular small signal diode. This all depends on how accurate that parts list is...
 
Thread starter #6
Yes sorry, I did a few quick checks last night and noticed that on my working unit pin 1 of resistor packs R01, R02, and R03 actually goes to -32v, not ground.

So it's clear I need to go and check all points currently marked as GND on the circuit to update the schematic.

I also checked the transformer and you're correct pins 1, 2, and 5 are not all GND. I'm not going to try to document it here from memory but will updated later when I've got my notes to hand.

The parts sheet in my first post is only my working draft, based on my own work so where it says "diode?" it's because I'm not sure exactly what it is. Don't read anything into that.


I only had a few minutes last night so I took the plunge. Because I knew I had supply (-10vdc) on the micro I decided to investigate whether it was actually operational or not. So I applied a few (-ve) volts to the VFD filament and found that yes, the micro is still operational. See video.


So this really is just a problem with the power circuit.

From measuring the working unit I know the power circuit takes +6vdc from the supply and converts that to -10v for the microcontroller supply and -32v for the VFD (the latter voltage not being present on the faulty unit).

The Microcontroller, oscillator and VFD all work. The transistors have all been replaced. Resistors have all been measured and confirmed to be correct. caps have been checked for shorts (there are none).

That only really leaves a few diodes untested and unidentified, one of which I'm quite confident is faulty. Oh and the transformer itself.



This must be fixable, even if I don't understand the circuit and I feel like I'm 95% there now.
 
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Thread starter #7
I managed to pull the s06 from the working unit and put it into the faulty one and it sprang to life.

I put the working s06 in my test circuit to find the zener voltage put my power supply only goes up to 31.5v. I assume it is a 32v zener so I'll order one and try it.
 
Thread starter #10
I took another look at this when I got home and realised something using my (very basic) handheld 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.


The Transformer is providing an ac signal, 200v pk-pk, period 10us, 140vdc offset.
at the other end of the diode, which is disconnected I see a -39v dc signal with only minor ripple of 1v pk-pk.

So do you think it's safe to assume this is indeed a 39v zener diode?
 
Thread starter #11
I ordered one just in case.

Only 99p on ebay for a pack so it's cheap. 39v, 1.3W zener diode. According to my supply the circuit draws about 1.3W so it should be just about ok I think, though in hindsight I maybe it would have been better to order something with a little headroom.

If it doesn't work then I've completely run out of ideas.
 

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