Taito Space Invaders Cocktail Repair

[Lurch666]

Just in case someone reading this doesn't know.

Even when unplugged CRTs carry enough voltage to kill.

There is a sticky in this maintenance thread about discharging a CRT so it's safe but obviously don't touch any part you aren't sure about when it's on.

 

[Clabs]

Just in case someone reading this doesn't know.

Even when unplugged CRTs carry enough voltage to kill.

There is a sticky in this maintenance thread about discharging a CRT so it's safe but obviously don't touch any part you aren't sure about when it's on.

Wise words Lurch and I probably should have expanded on my “be careful when poking about in there” comment.

@Lenty - if you are not comfortable doing that stuff then definitely worth asking someone to do it for you.

 

[patzik]

Hi Mark,

Great advance one the repair, it always best when repairing multiple faults to start with the one that are clearest and easiest to repair. Sometime fixing one fault also fixes another one. I had a hunch about fixing the sounds would also fix some of the other problem when looking at the schematic, good to hear it did indeed.

So you are almost there… can you make a video about the sound of the ufo that has the noise? Also, looking at your previous video the space invaders step sound (the thump sound) doesn’t sound ok, it sounds like the same thump 4x while the tone should go lower each of the 4 times. Is this the video or is it actually like this?

The service switch only works when you have the credit board, does your cab have it?

Regarding the #7900 key, I have one but I don’t think I can make a copy, it’s a bit of an odd key that I haven’t found a place that had blank key. Maybe I’ll try to 3d print one one of these days to see if that would work. You can always replace the lock with one of those barrel locks, or buy a #7900 key on ebay, but they are quite expensive.

I have a cocktail cab too, but after recapping I had to start rewiring it back to original (it was converted to jamma at soem point), and I tried to find a wiring loom instead of doing it all by hand but never found one and then got sidetracked with other projects.. wanted to get the legs re-chromed too, but there is no place here that does this.

Anyhow, back to the sound, maybe you can run the test rom and make a video?

 

[Clabs]

Hi Patzik and thank you for the reply.

Yes - a good jump forward so thank you for all your help and advice. When I bought this thing, I never imagined that those horrible noises it made, together with the corrupt display, would down to faulty chips - it sounded and looked so much like interference from a noisy power supply/duff capacitors etc. So, I have certainly learnt a thing or two. And your tip about breaking the sweat joints when removing chips was a revelation - I would have been completely stuck without that!

Anyway, here are a couple of videos of the sounds. This first one is with the SI game playing. When the invaders advancing VR6 is turned up, the 4 x sounds turn into 1 x thump. When the ufo vr1 is turned up there is hiss in the background all of the time. The actual ufo sound is fine. Hopefully this shows what I mean:

This second video is of the test rom running. There is still some hiss when I turn the ufo VR1 up although not nearly as bad with the SI romset and the ufo sound is loud and clear. Similarly, I can turn the invaders advancing VR6 all the way up and all 4 sounds are loud and distinctive. Here it is:

So, those sounds seem to be getting distorted somewhat when the game is running. For extra info, I already changed out the second 74ls42 @ IC14 & 74ls17 @ic18 that were mentioned previously as I had the chips and sockets, but they made no difference.

Lurch suggested that I try the test rom with the shifter reinstalled, so I installed it before the above rom test. I still don't know how to interpret all of the test rom results but he also suggested trying the original Space War romset to see what happened. Here are the results:

So, as Space Wars apparently depends on the shifter to run, I can assume that the shifter is actually ok? What I forgot to do was try the sounds with Space War running to see if that made a difference. I don't know if that is worth trying?

For the service switch/coining up, I do have the credit board though when I first got the table, this didn't seem to do much. Whether the board was plugged in or not, I was able to coin up via the coin slot. The service switch does nothing.

After all the work on the sound board, coining up stopped working via the slot, with the credit board removed. When I plugged the credit board back in, I was able to coin up again but credits kept counting up to 99. I have adjusted the dip switch this morning and that seems to have resolved the problem. The service switch still doesn't work though. I did quickly check the cables which seem ok and the switch is working properly. I still have those 2 yellow wires that have been stripped and wound together, and the black/white wire that is hanging loose. I haven't had time to investigate those properly but the black/white wire seems to be for a coin lockout coil, according to the schematics I have. Having said that, the schematics I have are for the smaller credit board. My credit board is the larger one with the two banks of DIP switches. I don't know what the lockout coil is - I don't seem to be able to find reference to it anywhere and my coin mech doesn't seem to have anything on it other that the coin switch.

The key for mine is the 7800, NOT the 7900. I did see someone in Australia selling copies but they are really expensive. In the meantime, a company fairly local to me claim they can cut keys from the number. I am not very hopeful but they say I wont have to pay if they don't fit. If they don't fit, I will try and pick up some blanks from them and have a go at cutting my own. I don't know if the 7800's and 7900's have the same basic profile but I could always pop a couple in the post to you and you could try having spares cut for yours?

For refinishing the legs, I do know that chroming is seems to be very expensive. I don't know if it is to do with extra preparation of the surface? Anyway, again, I have found a plating company not too far away and as soon as my back is a bit better, I will remove the legs and take them over for them to quote on.

Sorry for all my rambling

Cheers, Mark

Clabs2022-05-28 10:20:38

 

[Lurch666]

For the shifter check on the test rom it plays all the sounds one by one then plays them all again. After that it should show 'shifter ok' or a grid of numbers if the shifter isn't working properly.

The numbers help figure out what part of the shifter is faulty but since you got the space wars running your shifter appears to be OK anyway.

The sound FX would be exactly the same for space wars.

Lurch6662022-05-28 14:26:02

 

[patzik]

Listening to the game running and especially the test rom, I hear the advance sound goes lower each time so the circuitry is running fine. The hiss in the background of the ufo sound, just sounds to me like the sound is turned up too high, just like a radio or anything other with an amplifier when you turn it up high, you will get a hiss sound. I think you will have to look at a balance between the sounds with the VR1 through 7 and then turn the volume up as required with VR8. If there is still background hiss, all I can think of is changing the caps in the sound circuitry, although I think they should still be ok. there are a few caps in the circuit where the ufo sound is generated, and VR1 through 7 have a 1uf at the input and the output, and then the main amp also has some caps. Just look at the schematic and you'll find them.
Still I think you should be able to get a nice balance without too much hiss without changing the caps.

So board wise, I think it's up and running fine.

Regarding the coin, service switch and coin lockout. "Fixing" them is depending on how you want the game to run, basically the credit board is there just for using a coin counter, the credit switch on the coin mech could be wired directly to the pcb. The service switch should be connected directly to the pcb and actually all it does is add a credit bypassing the credit mech. The lockout coil is there on the coin mech so that when the machine is off, the coins don't go into the machine, but are redirected to the return chute. It is off when the machine is off, and turns on and stays on while the machine is powered.

If you have a way to coin up the machine and it works for you, I wouldn't bother with it personally.

 

[Clabs]

Thanks for the replies chaps - appreciate it.

Lurch - I am embarrassed because I think you already told me before that to test the shifter, I should wait till after the second sound test when running the test rom. I will give this a go as soon as I have the control panels back in - I am giving them a clean up.

Patzik - It is odd about the sounds because I can turn the volume right up on each one when they are playing individually via the sound test, even the invaders advancing sound good up loud. It is when all the sounds are combined together that some of them seem to degrade. As I said before though, perhaps I am expecting too much from this thing and I can at least reach a reasonable compromise if I juggle the pots. When I get some spare time, I will look at those caps. I already changed the electrolytics around the power amp.

For the credit switch, yeah, it is not a big deal and I will probably wire it up as you say. For the lockout coil, my coin mechanism definitely doesn't have one because I took the whole thing out to give it a clean today. My mechanism does look like it has been messed about with a bit in the past so maybe it has been removed. Same thing though, now I know what it does, I think I can live without it!

The only other thing I did today was to actually remove the coin box completely - Ah, so THAT is where the coin counter is! Mine wasn't working so I traced the wiring back and what do you know? That is what the two yellow wires are for that I have, that have been cut then wound together. And now it works. It is odd, because I have seen quite a few posts on various forums that show those same two cut and then twisted together wires. I wonder what people were trying to achieve by cutting them? Anyway, I do like as much as possible working, even if don't need them so it is nice to check something else off the list

Thanks again for helping me along the way.

Cheers, Mark

 

[Clabs]

Here is a quick update from me. The table was more or less working well and I have been waiting on the legs being refinished and new CPO's from Olly so not even switched the thing on for a while.

I had an idea to see if I could get Space Invaders Part II roms working but for some reason, the game refuses to start so I have put that on the back burner for now and replaced the Part I roms which got it all back working again.

So, the next time I go to switch the game on, it was randomly crashing/hanging/resetting itself. I did some voltage measurements and it looks like the +5v has become a bit unstable, jumping around by 0.3 - 0.4v.

Whilst measuring, I had a bit of a disaster: I thought I would get some voltage readings with the board stack installed and in moving the board stack around, I managed to touch one of the long board stack support rails against the monitor board which blew the 1A fuse on the monitor board. I replaced the fuse and powered on again and it looks like this has caused some damage to other component(s) on the monitor board and the picture is now stretched somewhat so that Player 1 & 2 does not fit on the screen.

The monitor has never been recapped by the look of things so hopefully, Gunblade is going to take a look for me and hopefully sort that out.

Back to the power supply. It looks like this has never been touched either so yesterday, I replaced all the electrolytic caps. I say all, because I was short of one capacitor so I removed the remaining one and it tested in spec with my cheap component tester. I put it back in circuit till a replacement arrives. The +5v is just the same - still jumping around with a bit of ripple too.

The only other thing I did was to reflow some of the bigger pins like the connector header though everything looks fine under a magnifying glass anyway.

Here is a picture of my PSU board:

You can see the Cap with the blue top is the one I didn't replace. I also replaced the big axial cap (top left) but that one is the largest physical one I could find. I included the old axial cap in the picture for comparison. Is that going to cause problems or should I use a radial cap and run fly leads?

It is looking likely that the problem lies elsewhere so any pointers/suggestions as to where to look next would be very welcome.

Cheers, Mark

Clabs2022-08-26 20:14:44

 

[ArcadePCB]

A little bit off topic - but I'm looking for a connector for position 'B' on the PSU pictured above. Does anyone know what this kind of connector is named or where to purchse this?

By the way: I'm very impressed how clean this boardset is. It doesn't look like 40 year old...

When replacing capacitors of a switching power supply, make sure to use low ESR types only because of the repetitive high currents while charging / discharging. Using (cheaper) standard capacitors may cause problems in function or they may become faulty very soon.

And you also should have a look on the voltage capability of the capacitors. If you're using one with less voltage capability than the one that has to be replaced, you should double check this before using the schematics.

 

[Clabs]

Hi ArcadePCB

I am pretty sure that connector is from the AMP Commercial mate-n-lok range. I don't know if this one is the correct one size-wise etc but it looks identical to mine. Hopefully this puts you on the right track:

https://www.arcadepartsandrepair.com/store/connectors-sockets-pins/amp-commercial-mate-n-lok-products-connectors/amp-16-pin-commercial-mate-n-lok-pcb-vertical-female-pin-header-cf1016/

Thanks for the info about the capacitors - appreciate it. I should have mentioned in my previous post, but whenever I replace capacitors, I always try to go for Nichicon wherever possible as they seem to be highly regarded. I always always try to up the voltage and temp rating too. The only one that gave me a problem this time was the big axial cap - Nichicon don't seem to do anything that big.

I actually found the last missing electrolytic so I popped that in this afternoon but that has made no difference.

What I have found though over the last couple of days is if I switch the machine on first thing in the morning when it is cooler, it boots up straight away. It runs for about 20 mins or so then starts rebooting. I will have to dig out my can of freeze spray and see if that helps narrow down where the problem is.

 

[ArcadePCB]

Hello Clabs,

Thank you very much for this link. I didn't know this shop yet, but it seems to be a very good source for all kind of arcade connectors. Unfortunately, it's located in the U.S. which means extremely high shipping costs, but I've already found more connetors there I'm looking for for a while.

For the reset problem: I would try to watch the reset line first. If possible, using an oscilloscope (helpful for detecting glitches etc.), but for the first step a multimeter should do the job, too. I would check the level on the reset line first when just powered on and monitor this until the machine resets. Once directely measured at the reset pin of the CPU and once again at the reset output of the power supply. Is there any drifting towards the threshold level visible? Is there a difference between these two test points? Maybe it's just a bad connection. What's the condition of the CPU socket? Nice and shiny or black / corroded? What's the condition of the solder juctions at the CPU socket? Just a few ideas where I would look at first.

Because the reset circuit is on the power supply, the problem can be either there or on the main board.

 

[Clabs]

Thanks for your suggestions, Arcade - appreciate your input.

I already addressed all of the points you highlighted but I do know that unstable voltages are a no-no. Luckily, a power supply came up on fleabay so I bought that. It is grubby and a bit rusty but the voltages are all spot on. I installed it yesterday and I am back up and running again. I was so worried I may have damaged something on one of the boards, so that is a relief.

I would really like to get the original power supply working again but still don't seem to be able to get to the bottom of the unstable +5. I did a lot of google searching and found everything but fluctuating +5v. In view of that, its probably best if I start a new thread as it might be easier for anyone else with the same problem, to find in the future.

Cheers, Mark

Clabs2022-09-08 20:14:43

 

[bones]

Glad you're up and running. I can't offer the technical advice like some of the others on here but... Many years back I remember that a lot of JPM fruit machines started to suffer with resetting problems. For months the arcade insisted on just sending them up the road to another arcades engineer to repair. After a while he let on that the problem was just the 5v pot,he said all he done was slightly tweak it so the wiper was on a different part of its internal carbon track. He didn't even have to open them up as the case was perforated metal so he could get a terminal screwdriver on it. He said that the pots wiper had deteriorated the carbon track at the point of contact. The 5v read ok but still reset the machine and by moving it the tiniest amount regained the full contact. I tried this after and yes it worked, but many of the components could be suffering under load in your case and may not even be heat related.

 

[Clabs]

Hi Bones and thanks very much for your input - appreciated as always.

That is a good shout about the the 5v pot and it had crossed my mind as I have read quite a few threads where those pots have become unstable. I did already give it a good few quirts of switch cleaner and turned it back and forth lots of times to try and clean the track but it made no difference. I thought the best way to check it definitively was to swap it out with the one from the working board. No difference.

I have to say that I am so glad I bought this Hakko desoldeing gun. It makes jobs like this so quick and easy and puts the minimal amount of stress on the PCB/components you are working on.

I will keep looking!

Cheers, Mark

 

[RaveN]

When replacing capacitors of a switching power supply, make sure to use low ESR types only because of the repetitive high currents while charging / discharging. Using (cheaper) standard capacitors may cause problems in function or they may become faulty very soon.

It's the ripple current you want to look at, not ESR. ANY cap produced today is going to have infinitely better ESR than the ones in the pcbs 40 years ago. Plus it's not a SMPS.