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Entex Stargate repair and restoration

 
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lordsardonyx
Coleco Pac Man


Joined: 04 Feb 2010
Last Visit: 05 Sep 2019
Posts: 36

PostPosted: Mon Jan 25, 2016 12:10 pm    Post subject: Entex Stargate repair and restoration Reply with quote

OK, so I paid WAY too much on EBAy for this non-working Entex Startgate. BUT, I have been keeping my eye open for one of these for quite some time and they don't show up TOO often. Hardly ever, non-working. It's always more fun to fix them, especially if I've never played them before. There's a great reward at the end of the repair job. Hopefully, I didn't outbid any of you...

Here is the photo of the original item taken by the seller:


I have many of the other Entex games and they are so well designed and built that it is always a pleasure to work on them. They are my favorite manufacturer of these games. Even though the company is no longer, their products are still making people happy over 30 years later! Not many electronics companies can say that. This time, I had the foresight to take some photos as I was working on it. I usually don't care, but I'm particularly happy with the way this one turned out and was determined to share it with someone who cared. Especially since it was a rather easy fix which I'll get to later. My main reason for sharing all this is so I can get some input in my troubleshooting practice. Anyone, please feel free to correct me, I'm always trying to learn.

Other than not turning on when I put in the batteries, it was actually in really good shape, but as you can see, rather filthy. This machine was really cool to work on since it had no hidden screws and all the screws were the same size. When I take a game apart, I try to wash as many of the parts as possible. Unless there are stickers that you should not get wet. I take everything apart and wash the plastic case in the sink with an old toothbrush and dish soap. Then I use Goo Gone on any sticker residue. Yes, I'm that much of a geek.

A very special thank you to the very awesome dude at 2KBoffun who shared the schematic they drew up:

https://www.facebook.com/2kboffun/photos/a.346524368807969.1073741832.326426274151112/842380632555671/?type=3&permPage=1

Now, this is really cool, since this is the first tabletop/handheld game i've seen with actually audio IC circuitry. The speaker (not buzzer) is huge for a game like this. I was blown away by the amount of stuff in this machine. The power goes from the batteries, to a little board with the headphone jack and AC jack, then through the crinkly ribbon cable to the main pcb. As far as I could tell, the long ribbon cable carried the power / ground and audio signals to the speaker.



I was able to use my digital multimeter to check for proper voltages. So I checked the transistors and the 6 volts from the batteries was there. I checked all the diodes and they all showed low resistance one direction and high resistance in the other direction. I always have a bunch of capacitors around, so I replaced all the big electrolytic caps with new ones, even though none of them looked bulging or leaky.





This game had nice long ribbon cables connecting the boards, but each end of the cables was just soldered to each board - no connectors! I saw a nasty rust/erosion/alien blood where the ribbon cables were soldered to the boards, so I thought this was the problem. But, my digital meter tested continuity through these connections to various components on the board. The ribbon cables were made of this weird crinkly clear plastic covering stranded wires. Not sure if the crinkliness was because of the age, or just an early manufacturing experiment, but the plastic sucked because the cables were really stiff and creased alot while moving the parts.



The only really annoying part of disassembling this machine was how the display was attached. If you can see this photo:



The screws holding the main board to the front of the cabinet we under the board. The board was mounted on these industrial-strength steel L-shaped mounting brackets made to survive interdimensional space travel. The four corners of the board have slots for these brackets, then the board is held in place by some strange twist-to-hold-in-place plastic thingys that appeared to have half-melted to the brackets and board. I tried to turn them to remove, but they just squished like hardened wax. So, I just ripped them off with pliers and they fell apart. Later, when remounting the board, I used hot glue where those plastic thingys were. Worked like a chiz-arm.



Of course, after flipping the main board over twice to check voltages, the braided wires of the crinkly ribbon cable broke away from the board. Looking closely, they appeared to be rusted away. I replaced this cable entirely with five new copper wires, so it would never happen again. I thought, just maybe, it would start working again after this, but to no avail.

As I was resoldering the wires replacing the ribbon cable to the little AC/headphone jack board, I looked closely at the AC jack and noticed the little copper tongue thing inside the jack. I noticed it was possibly not touching the top of the jack. So, I flipped over the board and shorted across the jack so the board acted like the tongue was touching the top, making connection. I turned on the game and YAY, it worked. So, I used a dental hook to pull up on the copper tongue so it stayed connected. I guess, when you plug in AC, the jack pushes this tongue away, disabling the batteries? The tongue was warped from age, so I guess the game never got battery power until I bent it back.



Lastly, I took apart the control panel and washed the rubber button inserts and used the silver button/contact repair stuff on all the contacts.

So there you have it, another game saved from the trash for a few more years.
And this game is amazing and LOUD. I soldered a resistor in series with the speaker to lower the volume and now it is perfect. The sound effects are really cool and the gameplay is astonishingly similar to the arcade game. Anyone have any wisdom to throw at me? Other than: get outside for some fresh air.



Particularly, I can't understand why I could measure 6 volts at the power transistors before I fixed the copper AC tongue thing. Looking at the schematic, I don't see anything about an AC jack there. How would that be represented?
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Rik
Site Admin


Joined: 07 Oct 2005
Last Visit: 25 Mar 2024
Posts: 1932
Location: California

PostPosted: Mon Jan 25, 2016 8:27 pm    Post subject: Reply with quote

Nice work. If the game isn't working at all, the best start is to just trace power from batteries to the board with the CPU on it... Switches can get weak or oxidated, same with the AC adapter plug. The little tongue in the adapter plug is basically a switch that prevents the AC power from going back to the batteries (can cause them to leak or 'explode'). Over time, that tongue can loose it's flexibility, even if the jack isn't used.

They are usually easily replaceable parts, if you can find an exact new replacement, I'd replace the jack. It may come loose in it's own, and it will probably quickly fail again if you actually try to used it. Modern ones (and maybe even 'better' vintage ones) actually have a little spring behind it so it won't get weak...

But at least it's working... Cool
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blanka
Atari Cosmos


Joined: 14 Dec 2010
Last Visit: 13 Oct 2022
Posts: 561
Location: Eindhoven, the Netherlands

PostPosted: Mon Jan 25, 2016 9:51 pm    Post subject: Reply with quote

The AC plug in the scheme is represented by the circles with + and - symbols, they usually are connected to the battery clamps and sometimes have an extra diode.
Here the plug contains a switch that uncouples the battery when a plug is inserted. These in-plug switches are prone to failure and first thing to watch (always try to power with BOTH batteries and adapter). I could put that switch in the scheme...
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lordsardonyx
Coleco Pac Man


Joined: 04 Feb 2010
Last Visit: 05 Sep 2019
Posts: 36

PostPosted: Tue Jan 26, 2016 7:41 am    Post subject: Reply with quote

Thanks very much for the feedback! It is really appreciated. When I learned about the copper tongue thing, I immediately looked at the Astro Command I was trying to fix recently, hoping that was the problem, but that appears to be a slightly different thing. Is this sort of "protect the batteries from the AC power" circuitry dealt with in different manners sometimes? So, you're saying sometimes just a diode takes care of this function?
I will probably beg for schematics in the future as this was the first time I learned that anyone had the knowledge/patience to trace out a schematic for these games. I'm guessing that is what is done, anyway, since I suppose the companies probably never released them to the public. Without the schematic, I've always had to just guess at many of the components since I'd look them up and not find info on some of them. In the future, I will try an adapter and batteries to test. Since I wasn't certain on the adapter details for this one, I didn't want to experiment. So, if the polarity isn't marked on the machine, can you determine it by measuring continuity from the battery terminal to the AC jack parts? Also, I have one of those universal adapters that allows switching the voltage and tips, are these safe for these old machines? I always use batteries, since at one time I bought a bunch of rechargeables and have been using them for years. I will also use your method of tracing from the AC to the main ICs. A heckuva lot easier with a schematic available, haha! Thanks for listening and the help!
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lordsardonyx
Coleco Pac Man


Joined: 04 Feb 2010
Last Visit: 05 Sep 2019
Posts: 36

PostPosted: Tue Jan 26, 2016 7:43 am    Post subject: Reply with quote

Oh yeah, I thought it was pretty amazing that Stargate had what appears to be a surface mount IC on the back of the board. Wasn't that pretty rare in the 80's?
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blanka
Atari Cosmos


Joined: 14 Dec 2010
Last Visit: 13 Oct 2022
Posts: 561
Location: Eindhoven, the Netherlands

PostPosted: Tue Jan 26, 2016 7:51 pm    Post subject: Reply with quote

Your best information on polarity is in the main capacitor. That one easily identifies what is + and what is -. Don't rely on the plugs, they are often used in both ways. Only the mini-jacks are pretty reliable in that the tip is always +.
And yes I traced all the PCB's.
I have right now:
Gakken/Coleco Frogger (same)
Gakken Amidar
Bandai Burger Time
Epoch Astro Thunder 7/Firefox 7 (second sound chip)
Tomy Kingman
Entex Stargate (second sound chip and amp)
Coleco Zaxxon (nice open-gate noise generator!)
Gakken Dig Dug
Gakken Puck Monster
Romtec Frog Prince
Gakken Crazy Kong
Bambino Safari
Parker Brothers Q*bert
Entex 3D Grand Prix.

Surface mount was rare, but strange thing: first microchip game Auto Race in 1976 is surface mount!
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Lukasz604
Mattel Football


Joined: 18 Jan 2016
Last Visit: 01 Feb 2016
Posts: 12
Location: Burnaby BC Canada

PostPosted: Wed Jan 27, 2016 11:04 pm    Post subject: Reply with quote

Excellent work. And an amazing tabletop game for sure.
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Rik
Site Admin


Joined: 07 Oct 2005
Last Visit: 25 Mar 2024
Posts: 1932
Location: California

PostPosted: Thu Jan 28, 2016 5:34 am    Post subject: Reply with quote

blanka wrote:
Surface mount was rare, but strange thing: first microchip game Auto Race in 1976 is surface mount!


Auto Race isn't actually a surface-mount chip. The Rockwell chips just have weirdly shaped legs. They are still mounted through the circuit board and soldered on the opposite side.

The Hitachi HD38820 was widely used in the VFD games, as you can see here also in Coleco Pac-Man:
http://www.handheldmuseum.com/Coleco/ColecoRepair/index2.html
The HD38800 is a normal-looking chip, but the 20 came out in 1981 or so (at least, maybe earlier), and got a fair amount of use in handheld gaming.

lordsardonyx wrote:
Since I wasn't certain on the adapter details for this one, I didn't want to experiment. So, if the polarity isn't marked on the machine, can you determine it by measuring continuity from the battery terminal to the AC jack parts? Also, I have one of those universal adapters that allows switching the voltage and tips, are these safe for these old machines?


If you have the game open, it's easy to see the polarity of the AC port just by following the wires from the battery compartment. Both positive and negative pass through it, so whichever part the + wire is connected to is what the + of the adapter should be set to.

Universal adapters are fine, set them for 6-9 volts for any game that uses 4 batteries. You want at least 100ma for one game (if you want to wire several games into one power adapter, add 100 per game at least, a little more is a good idea. I run 8-10 games off a 1000ma adapter, but if all 10 are on at once, sometimes they don't play right, and adapter gets hot Cool ). 200ma or higher is probably more recommended, depending on the demands of the game (like Stargate or Coleco Zaxxon or something). You can't have too much amperage, the game just pulls what it needs. Too little and you can burn out the adapter.

This may sound scary, but a quick-and-dirty way to figure out voltage for the AC adapter is to just plug it in, and turn on the game FOR AN INSTANT. If it doesn't respond instantly, turn it off and switch the polarity. It takes a second or so for reverse polarity to cause damage, so you can use this technique if you are desperate... But I wouldn't do it on any game that you consider valuable, just in case. Best to just open it and following the wiring. Cool (But I have done this before without harming the game...)

You can also ask here, most games are owned by me and several others, so someone can probably chime in. That's also information I need to update the website with Rolling Eyes , but some games have it listed already...
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