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Nichibutsu Moon Base sudden blank screen (but alive)


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Hi folks,

 

New here, have come in search of assistance for my beloved Nichibutsu Moon Base Cocktail arcade (black and white with colour panes on screen).

 

I had it repaired quite some years ago in Melbourne (failed board) and it has been running perfectly since for about 8 years now.

 

I had some guests visit over the weekend, and one of them lifted the unlocked top and then dropped it back down again while the game was in play.

 

The screen went immediately blank, but the sounds continued.

 

Here is an image of the CRT output:

IMG20180821161045.jpg

 

I've tested a few things to troubleshoot where the problem may lay, and can confirm the following:

- The board is alive, as inserting a coin runs the usual sound output and logic it seems

- I've turned up the brightness on the CRT controls to check that the CRT is still in action, and I get diagonal lines across the whole surface

- I've carefully reseated the game board socket and also checked the fuses to confirm all are seated and the fuses aren't blown

- I've checked thoroughly for any loose items hanging around and cannot find any

 

I build mechatronic sculptures and often build circuitry and logic with Arduinos, so I know my way around certain things, but I'm very unfamiliar with troubleshooting this kind of circuitry, and haven't worked much with high voltage or CRT based stuff.

 

Can anyone offer any kind of assistance in what are the next steps to check and try to find where the fault lies?

 

I would assume that confirming that the game board is outputting video would be the next step, but I'm unsure how to do that. Is it a standard composite video output from the board with the B/W CRT? I have downloaded some manuals for the machine that I can refer to to find certain pins (pin 26 appears to be video out, pin 19 appears to be color sync, possibly unused with B/W monitor?).

 

How can I check for this video output?

 

Very thankful in advance to learn this, rather than send it off for repair (I now live 2 hours west of Melbourne) as I'm keen on learning for future machines some basic troubleshooting.

 

Jesse

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You should be able to hook the PCB upto a TV, just wire the video to the tip of an RCA connector, and the outer ring to PCB ground. That will test if the board is running properly.

 

If you coin up and hit start do you get all the normal game play noises? That would indicate the board is running, whereas just the "coin up" noises may not, depends how the audio is controlled on these. On early boards it is often totally analogue, so the act of coining up could trigger the coin noise independently of the rest of the system being dead. If the rest of the game play sounds are there then something is clearly alive enough to be controlling that, which would suggest the game is actually running.

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Hi Womble,

 

Thanks for getting back so quickly!

 

All of the sounds happen, the advancing of the aliens, the shooting of the laser - so it does appear to be fully alive internally.

 

I rigged up a couple of probes on an RCA lead and managed to get perfect video output from the board! Thankfully the game board is fully alive!

 

What should I try next?

 

I should mention that whilst I was doing this, I found a tiny light bulb in the bottom of the machine (it's a tabletop). There is no lighting in this machine, is it possible that it is being used as a fuse like what was used on speakers in the sound industry in the 70s/80s? I can't find a socket for it.

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If the game bard is three layers which I believe it should be then it is the same as Taito Space Invaders.

You have composite out on the lower 'T' connector and RGBS on the top 'G' connector.

It seem like you've either lost the input to the CRT or it's lost the input signal on the chassis somewhere.

Do as Womble suggested and you should be able to bring up an image when on the Compisite/AV on any TV (CRT or LCD), it will work fine on a colour TV and display the image b&w.

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Hi Kaizen,

 

I have video out happening well into a CRT monitor, so it appears as though I've lost signal into the chassis - I'll follow the wiring through and try to find the connector/connection point. If I'm seeing the lines in the original image, does that mean the chassis is ok, but is simply lacking video input?

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Update: I've tracked it through and nothing seems to be disconnected (tested with multi-meter either side of the signal connector on the way to the chassis) - it seems to be a problem in the chassis itself.

 

With a lack of signal input, is it common for these CRTs to show an image like above? Or is that a symptom of another problem?

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The retrace (diagonal lines) are normal when you have the screen/brightness turned up too high.

If you only turned the brightness up just back it off until the lines just disappear.

Have you tested the PCB output on a TV yet?

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Ah great - that's handy to know. Will adjust back down again.

 

Yep tested the PCB and got healthy video output from the game board to an external TV.

 

So from what you're saying, it's like the chassis has lost it's video signal input, but I've followed and checked the video leads all the way through to the chassis... so I'm a little stumped

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If you have a good video input and ground then there s most likely an issue with the chassis. @Jomac

These are a rather simple Toei B&W chassis and it may come down to something like a dry solder joint.

I'd see what Joey suggests first before having a go at trying any repairs on it yourself as you can introduce more issues that can make what could have been a simple repair a much more involved/expensive one.

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Good news on the board.

 

The fact the chassis died when the lid was slammed would point towards either physical component failure, or a dodgy solder joint(s) that finally cracked through from the shock.

 

Talk to Joey first, the worst case for any repairer is to get a board that someone else has had a go at, and probably introduced dozens more faults, while hiding the one original fault-needle in a haystack of things "touched up".

 

He may be able to point you in the right direction, or it may well be a good opportunity to get the chassis serviced, it is probably running on the last 5% of its service life in its current condition.

 

It is worth getting a B&W serviced to give it another 20 years or so, they aint making those anymore so if it totally destroys itself you have a problem.

Edited by Womble
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If Joey is Jomac from WA, I've already emailed and unfortunately he's said he doesn't service CRTs this old. He has suggested to continue discussing here for help.

 

Is there anyone else who might be able to assist in this? I'm willing to dive into reflowing all of the joints on the CRT chassis board (I do have good soldering skills), but as one of you has said above, sometimes it's better to leave it to someone who knows what's wrong rather than make things worse, and harder to troubleshoot.

 

My main fear is ensuring I've de-energised the tube and capacitors as I'd had to get that heavy duty of a jolt!

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Sorry to drag this one up from the deep. I had to put this project away as I was away touring for much of last year and building new major works (walking humanoid robots with television heads, probably inspired by this!).

 

I'm back on this and have decided to tackle it head on and pull the monitor PCB. I'm unsure of the best way to go about this though. Is it best with these cocktails to pull the game board, then extract the monitor PCB from the side, or should I also pull the tube (it looks daunting to do).

 

Of course I'll discharge the CRT tube, but a quick question on that also, what's the most reliable earth to link the flyback plug to to do so? I've serviced early 90s macs before and have done this, but just not on a cherished, well loved 70s arcade :)

 

Many thanks in advance,

Jesse

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Hi mate, I've worked on a few monitors from this period. You got retrace which is awesome. With black and white monitors, just ONE bad transistor or cap will put it out of action. Are you still struggling with this? I'll try to help, if not fix it for you.

 

Oh... and on discharging the tube. First! Unplug the chassis. Pull the plug from the wall, extension cord, whatever.

There will me a strap on the monitor, AQUADAG, or DAG strap, This is effectively the other side of the very large capacitor that is the tube... collect your wire to that. Then bring your screw driver, I'm presuming that's attached to the other end of the wire, near the anode cap surface, lifting the rubber cap. ((Make sure your aren't handling the metal part of the screwdriver.)) Be careful not to scratch the anode area. Once you hear the crack, do it a few more times, but if it has been sitting around for a while, there's a change you wont hear anything. I just sit the screwdriver in the anode cap for a while as surprisingly it can recharge from surfaces inside the tube. ha! It wont hurt... you but you will cry... "BaJeasssuuss" when it shocks you. ha ha. There's just not enough current to kill you at that stage.

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Well, COVID hit and all the usual shenanigans, loss of work, struggle to survive etc etc happened, so this was on the back burner!

 

I'm back on this, and just spent another day on the problem.

 

So I have retrace when I turn the brightness up, so that's good we have a functional CRT drive happening, we're just not processing the video signal.

 

I've traced the video signal back to the source, and that's fully functional, works when jumpered to an external monitor, so the game board is outputting video.

 

Following these tests, I've gone ahead and recapped the board except for a couple of the bigger high voltage ones that I don't have here. Still the same.

 

I then traced the signal path to the first transistor on the chassis (Q1) which is a C828R - pulled it from the board and put it in my DMM transistor tester and got a zero. Must be dead.

 

So it seems this transistor is an antique and no longer available, so I've replaced it with what seems to be a close match which is a BC547. Still dead.

 

I can start to follow the whole circuit through and pull each transistor out and test it and seek a replacement, but before I go through that long process, does anybody have experience with these Toei black and white GM-120 boards? Is there a common fault that I can look for?

 

I'm still seeking what would cause a failed transistor if the lid was slammed by our lovely visitor - it seems a bit strange to me.

 

I've found the schematic in the manual for the machine from the Internet Archive:

https://ia600501.us.archive.org/19/items/ArcadeGameManualMoonbase/moonbase.pdf

 

From this service manual schematic I can see these transistors:

Q1 = C828

Q2 = C1520

Q3 = A844

Q4 = C458

Q5 = A844

Q6 = D667

Q7 = C681A or C901A

 

This isn't my usual scene, so I'm unfamiliar with these transistors, so I'm going to have to go on a serious hunt to find equivalents. Does anybody have any advice on definite proven replacements for these? I don't want to push the circuit out of spec with too many "close enough" matches if I can help it.

 

I see there is also at least one IC on the board (hopefully this is correct, hard to read from the hand-drawn schematic):

- MPC-1031M (seems to handle refresh drawing)

 

How likely is it that this could be blown, being that we're getting redraw showing when brightness is turned up?

 

Deeper down the rabbit hole!

 

Thanks in advance

Jesse

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Hi, it's good that you do have a raster, so the high voltage and deflection are working.

 

I don't think it's necessary to be replacing virtually every component though, if the monitor was working well prior to the problem the capacitors are unlikely to have suddenly failed.

 

More likely there is a mechanical fault of some kind such as a 'dry' solder joint or cracked trace on the PCB or CRT socket board. It might be worth examining them closely with a magnifier and looking for those.

 

Are there any solder joints which are not completely smooth or appear to have any defect between the component lead and the PCB? sometimes a hairline fracture can be spotted, appearing as a faint circle around the lead in the middle of the solder 'blob'. Also, check soldering between the input connectors and the PCB as these are often subject to vibration or mechanical stress. If you can, and are suspicious of any, carefully remove some of the old solder with a soldering iron and some solder wick braid or a suction desoldering tool and then resolder them.

 

Looking at your circuit, on the chassis you can concentrate on the video amplifier which is really only the area around Q1 and Q2 and if that doesn't reveal anything look further around Q3 and Q4 which are sync and clamping. beyond that are the oscillators and deflection which are known to work as you have a raster so the fault won't be in those areas anyway.

 

Also, have you tried adjusting the contrast pot, just in case it is dirty or has a dead spot?

 

Hope this helps, regards John

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Hi, just following up on the transistor information you were after for your monitor, there's datasheets and cross reference info available on this site if you need them:-

 

https://alltransistors.com/transisto...ansistor=17175

 

Japanese transistors marked as A or C something are usually 2SA or 2SC

 

Does your C828 look like the one in this datasheet? The BC547 should work as a substitute but I was a bit sceptical whether the original one is really dead, make sure you note which pin is which when you connect your transistor tester. The pin connections are shown on the data sheet.

 

If you want to double check, does your meter have a 'diode' test which shows the forward voltage across a device, if so select that and make sure your meter leads are plugged into the correct sockets on the multimeter.

 

Touching the leads together should display 0V, leaving them apart should display OL or open circuit

 

With an NPN transistor such as the 2SC828 put your Red lead on the Base of the transistor (do this with the transistor removed from the PCB or try with a loose new transistor)

 

Then touch your black lead to the Emitter, then the Collector.

 

Base to Emitter and Base to Collector should each give a reading of around 500 or 600 milliVolt or 0.5 to 0.6 Volt. Anything around that is fine but they should not be 0Volt or open circuit.

 

Now put your black lead to the Base and try your red lead on the emitter, then the collector. Both should read open circuit.

 

Finally Red lead to collector, black lead to emitter then again with the leads swapped, both ways should read open circuit.

 

If any of those measurements are 0V your transistor is short circuit. If Base to Emitter or Base to Collector are open circuit your transistor is also blown.

 

If all the readings were as expected that transistor should be OK.

 

To test any diodes, Red lead on Anode, black lead on cathode (usually indicated by a line or stripe) should read around 0.5V, reverse measurement should be open circuit (when the diode is removed from PCB) neither way should read 0V or short circuit.

 

Hope that helps too, regards John

Edited by jbtech
Fixing typo
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Thanks so much John!

 

This is great info - I ran through your method of testing the transistor and it tested fine (although the numbers I was getting from base to emitter and collector were more like 720mV or so. All the other tests were fine, so I'll put it back in circuit.

 

I did have a good look over the board and touched up a few joints but couldn't find any faults, but I'll go over it again now with the sun shining over my desk to help me see it. I might even just solder suck and redo most of the joints in the Q1 Q2 area and see if that helps.

 

I think the difficult thing for me here is the testing and removal of the board is such a complex little process that it's slow to test my changes. I build mechanical and robotic sculptures and never work normally outside of 48VDC max, so I'm having to keep reminding myself of the dangers of playing in the land of CRT. I'm also very familiar with any kind of CRT drive, and how composite signals get broken up and turned into sync for the HV side.

 

I'll keep plugging and testing and see what comes up today!

 

Thanks again,

 

Jesse

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With an NPN transistor such as the 2SC828 put your Red lead on the Base of the transistor (do this with the transistor removed from the PCB or try with a loose new transistor)

 

Then touch your black lead to the Emitter, then the Collector.

 

Base to Emitter and Base to Collector should each give a reading of around 500 or 600 milliVolt or 0.5 to 0.6 Volt. Anything around that is fine but they should not be 0Volt or open circuit.

 

Now put your black lead to the Base and try your red lead on the emitter, then the collector. Both should read open circuit.

 

Finally Red lead to collector, black lead to emitter then again with the leads swapped, both ways should read open circuit.

 

If any of those measurements are 0V your transistor is short circuit. If Base to Emitter or Base to Collector are open circuit your transistor is also blown.

 

 

Aha!

 

So I've pulled Q2 from the circuit and run through testing it (it's a C1514, not a C1520 as per the schematic) and here's the results:

- Red lead base, black to collector = 582mv

- Red lead base, black to emitter = 5mv (!!)

- Black lead to base, red to collector = open circuit

- Black lead to base, red to emitter = 5mv (!!)

 

So it would seem to me that this is the fault. And am I right in thinking that this has to do with chroma? The datasheet for the transistor says that's its common use. And if this is the case, that's why we're getting just a black video image.

 

So if I'm correct in diagnosing this transistor as being faulty, then what would be a common replacement that should work in its place?

 

Currently it's a C1514, schematic mentions C1520 (perhaps they're interchangeable?)

 

Thanks again John

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So reading some datasheets vs what's immediately available from my local electronics shop in stock I have found the 2SC2335.

 

As far as I can see it's just a higher rated newer version of this - am I right in my comparison against the 2SC1514?

 

I know I can order the exact replacement, but it'll take quite some time (plus I'm in the country, things take days longer!)

 

Any advice would be great thanks

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Hi Jesse, great work! that transistor is definitely faulty.

 

There could be other issues but that alone would cause the symptoms you mentioned.

 

Yes, I agree it's difficult to access the chassis in the cocktail machine and just about impossible to take any measurements in-situ.

 

The transistor tester part of the meter should work too but I find them a bit fiddly and sometimes inconclusive. They are very good for matching up working transistors, selecting an exact pair etc.

 

In a colour TV system Chroma refers to the combined colour information while Luminance is the 'Black and White' component of the signal

 

so in this monitor Q1 and Q2 form a 2 stage video amplifier, dealing with the luminance and boosting the signal to a sufficient level to drive the CRT while the sync goes off via Q3 and Q4 to control the oscillators, high voltage and deflection stages.

 

The 2SC2335 isn't an ideal substitute for the 2SC1514 as the gain is a bit lower but it would probably work in a pinch.

 

The Voltage and current ratings are all higher which is fine but generally with transistors as these values increase the gain is typically lower. That's partly why we don't just use the highest power rating for all applications.

 

The Hfe specification is a sort of open loop current gain rating - transistors use a small current flowing from base to emitter to control a larger current which flows from collector to emitter (in a PNP transistor direction of current flows is the reverse of that)

 

It's not absolutely critical as the overall Voltage gain of a transistor amplifier depends largely upon the component values around the transistors but it is a factor so for best results we try and find a substitute which is in the ball park.

 

The originally specified 2SC1520 had a 230V 0.2A rating with a hFE of 70 or more and the manufacturer apparently changed that to the 2SC1514 with a higher voltage rating of 300V, only 0.1A and the hFE down to at least 30.

 

The 2SC2335 apparently has a voltage rating of 400V, max. current 7A (!) but hFE down to 20 or more. The datasheet suggests the L or K versions 2SC2335L etc. have higher gain which may be more suitable if those are available.

 

Apart from that it should be fine, the package is fairly similar and the pins in the correct order. So if you can't find anything closer it would be worth a try especially if you're in a hurry. You could always order the original part to have on hand later, just in case.

 

Hope that answers some questions, regards John

 

 

 

 

 

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John thanks so so much for being so helpful - that's all been great info and I'm learning so much here at high speed!

I ended up just waiting for the exact replacement to come in (somehow Wiltronics found NOS for me and ordered it in) and just dropped it in - we're back in business!

There's definitely some oddity going on, but I didn't recap the whole thing, so there's probably just some dud power going on around the place, but it's back to better than it was before. In fact it's much MUCH brighter than it was.

I'll probably start another thread when I start troubleshooting that side of things, but for now after some adjustment it's back in order.

I'd forgotten that the player one button was stuck in when it was last used (yet another visitor broke it) and I can't seem to figure out how it's removed, so I might start another thread for that. Also I'm missing the sounds for the ship being shot, which I'm assuming will just be one of the oscillator channels.

But right now I'm super happy and had forgotten how difficult this game was!

Thanks again for your assistance, and for the nice simple method for testing NPN transistors. Like I said I've never really used BJT in my work much, usually opting for MOSFET so it's been good to learn about these fellas.

Now for a few victory laps (games) and begin to clean it up a little more. Definitely a far more intense kind of repair than I'm used to.

What a great forum!

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