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Dead Astrocade, strange motherboard?


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#1 TVisitor OFFLINE  

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Posted Mon Apr 3, 2017 7:19 PM

I purchased an astrocade that was not working and I'm trying to fix it.  I've found internally that once AC power is plugged in, the voltages get dragged *way* down (the 7.5VAC gets dragged down under 3, and the 23 or so VAC gets dragged down under 10VAC). I think that big smoothing caps in the supply are toasted and was going to replace them.  So I started looking over the motherboard, and started looking at it compared t the parts layout on the bally alley website. 

 

All I can say is "Huh?" 

 

First, I did realize that someone did the "Kludge board" modification in this system for video issues.  OK, at least that explained why the video section under the shield was not what the board layout says.  They also did the power modification where there is a jumper wire running from one of the bridge diodes to the + of the C6.

 

However, I see that there are a bunch of components missing.

 

Specifically it appears that the custom roms U1,3,4 are gone, and the associated caps are gone - C88,93,94.  

 

Above the big smoothing caps C1 and C6, it seems that C61, 55, 56 are gone.

 

C58, 59, 60 in the vicinity of U14 towards the bottom of the board are gone.

 

Near the Q1 transistor (with the heat sink, just under where the modulator plugs in), it appears that there is a resistor where the jumper should be.

 

Now that gives me a *tad* of hope is that near U15, there exists C53 and C52 which are missing on my system.  I did a search of motherboard pics, and I saw one person's where those were also missing.  

 

I'm at a loss to describe these issues.  I'm not WTF this is, if someone scavenged this, or it's normal, and if I should continue to fix it.

 

I also noticed that when I took the main cover off, I there were 2 screws that I could not remove until I removed the RF shield.  The service manual seems to indicate that there are punched holes in the shield to do this, mine didn't have them.

 

Does anyone have any photos of working astrocades that they'd be willing to post?  Or better yet, any knowledge of what's in my system?


Edited by TVisitor, Mon Apr 3, 2017 7:19 PM.


#2 ballyalley OFFLINE  

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Posted Mon Apr 3, 2017 7:45 PM

I've not fixed an Astrocade, but I can give you a few hints.  First though, what is the model of your unit? I presume it's he later Astrocade model made by Astrocade, Inc.

 

I'll try to point someone in the direction of this thread to help you out a little bit with the voltage levels.

 

I can help with a few of the topics:

 

1) 8K ROM - On the early Bally Arcade systems, the 8K ROM was made of four 2K ROMs (U1 - U4).  Later revisions ditched three of the ROMs and replaced them with one 8K ROM.  So, that sounds okay.

 

2) Kludge Board - Also, I recently learned that the Kludge board was made an official part of some (or possibly all) of the astrocade units.

 

I can post pictures of my working Astrocade motherboard quite easily, as the top cover just rests on top.  Whenever I use the unit, I take the cover off and expose the motherboard (which has the RF shield removed) so that it gets air.  What kind of pictures are you looking for: specific close-ups of the board, or just a general idea of the whole thing?

 

Adam



#3 TVisitor OFFLINE  

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Posted Mon Apr 3, 2017 9:20 PM

Hi Adam,

 

I've got the one that actually says "Bally Computer System" with the white smiling face and the black face nested inside of it with the gold "star" inside of it as the badge on the front.  Sounds like that's one of the more popular ones.  the board itself is labeled as "A084-90701-B620  A080-90704-B620" in the upper right.

 

I'd love a picture of the board showing the areas I've marked in orange (in addition, the section below the modulator labeled Q1 and "Jumper")  

 

By the way - your site has been a great resource.  

 

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#4 kenzre OFFLINE  

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Posted Mon Apr 3, 2017 9:40 PM

OK,let's start from the top. The 4 2K On-Board Rom chips were replaced by one 8K ROM when the cost was more feasible. Easier to assemble, less parts to go wrong. The bypass caps c88,94,&94 were no longer needed because the chips weren't there. The capacitors C55,56,61 were found to be unnecessary as the chips could handle the small spikes in the signals. The same goes for c58-60. The resistor near Q1 was for the change from +15V to +12V on the DRAM chips. These were more common when all of these changes came about. The +15V DRAMS were no longer made. As like other "wave shaping" capacitors, it was found that they really weren't needed. The digital chips were being made more "bullet proof". Getting to the 2 screws under the shield is common.

 

Now, about your voltage problem. try clipping the + side of the 10KuF cap, attach your meter to the pins on the light pen connector on opposite sides. Don't touch the center one and either side. To do so may fry your custom I/O chip. You should see + or - 5V depending on which lead is on which pin. The one closest to the hand control port #3 is the +5V, the other is ground.

turn the power on MOMENTARILY. If you voltage doesn't come up, try the 1500uF after resoldering the 10KuF. If you don't see any significant change, you probably have a short on the PCB. Maybe an IC or a bypass capacitor are usually the culprit. I found one bad cap by accident once. I was feeling around for a hot chip when I felt a hot part. It was a bypass cap. I cut it loose, and things were OK. There have been times that I had cut every bypass out, and started pulling chips until I found the culprit. I replaced most of the chips I pulled with CMOS equivalent. They work find.

 

Another tip, pull the custom chips (the 3 40 pin socketed chips) one at a time to see if one of them is bad. They use +10V and +5V. If one of them is shorted, that will bring down all of your supplies. Last, but not least, check the 3 diode bridges. If one of the diodes is shorted, you'll be introducing AC onto the DC lines, lowering their voltage.

 

If you have any more problems write me back. We can do this!



#5 kenzre OFFLINE  

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Posted Mon Apr 3, 2017 9:53 PM

The order of testing s/b

1 pulling the custom chips

clipping the 10K uF

   "          "  1500 "

clipping any HOT parts.

The custom DATA (under the keypad) normally gets real hot as does Q1 and the +10V regulator. The +12V gets warm but not hot. The 2 watt resistor at the front of the PCB gets hot also. It is on the +10V line. The custom address chip may get warm but never HOT. and the custom I/O (closest to the hand control ports) usually runs pretty cool.

Try to clip parts so that a little solder will put it back in the circuit if it it not the culprit.

Clip bypass caps, the chips. If you just clip VCC or GND pins on a chip, the rest of the chip could be shorted, so removal is usually the best deal.

 

REMEMBER these PC boards are over 30 years old and the glue uded to attach the copper may be dried out and will lift if too much heat is applied.



#6 128Kgames OFFLINE  

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Posted Tue Apr 4, 2017 11:29 AM

I purchased an astrocade that was not working and I'm trying to fix it.  I've found internally that once AC power is plugged in, the voltages get dragged *way* down (the 7.5VAC gets dragged down under 3, and the 23 or so VAC gets dragged down under 10VAC). I think that big smoothing caps in the supply are toasted and was going to replace them.  So I started looking over the motherboard, and started looking at it compared t the parts layout on the bally alley website. 

 

All I can say is "Huh?" 

 

 

Just an FYI but a picture is worth a thousand words...



#7 ballyalley OFFLINE  

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Posted Tue Apr 4, 2017 12:33 PM

I've got the one that actually says "Bally Computer System" with the white smiling face and the black face nested inside of it with the gold "star" inside of it as the badge on the front.  Sounds like that's one of the more popular ones.  the board itself is labeled as "A084-90701-B620  A080-90704-B620" in the upper right.

 
The dust cover that you describe is one of the more popular ones, but (as Lance Squire mentions in his Astrocade FAQ), you can't tell which Bally Arcade/Astrocade system that you have from this.  Try using the label on the bottom of the console.  My console is an "Astrovision Arcade."  Model ABA-1000-2.  Serial # 049240.  All of this information came from this label:
 
Astrovision Bottom Label.jpg
 
I'm not sure what those number that you describe from the upper-left of the Astrocade's PCB mean.  Our number almost match.  My board says: "A084-90701-B620  A080-90701-B620" (notice that my fifth five digit number is 90701, while yours is 90704).  Check out the picture:
 
Astrocade (Top-Left)(Cropped).jpg

@Kenze: Do you know what these six sets of numbers means?
 

I'd love a picture of the board showing the areas I've marked in orange (in addition, the section below the modulator labeled Q1 and "Jumper")

 
I realized that some of the areas that you want pictures of will require me to remove the keypad, which I'm not willing to do right now.  Maybe "Kenze" can provide a picture of these areas.  Here are two pictures that I can provide for now.  I hope that these provide the details that you're looking for.
 
This first picture is from the upper-left of the board.  The cap that you want (C10) is in this picture, along with U17 and U19:
 
Astrocade (C10 - U17 - U19).jpg
 
This second picture is from the top-middle of the board.  It shows U8, U9 and U15:
 
Astrocade (U15 - U8 - U9).jpg
 
I hope these pictures show you some of what you need.  I actually had to pull out a portable light and shine it on the PCB to get good color and details from the pictures.  Hopefully, if you need additional pictures, someone can remove their keypad/cart slot to get you the additional pictures that you want.
 

By the way - your site has been a great resource.

 

I'm glad that you like the BallyAlley website. It's not very easy to navigate, so if there is specific information that you're looking for, then just ask about it.

Adam



#8 ballyalley OFFLINE  

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Posted Tue Apr 4, 2017 12:43 PM

It just occurred to me that I do have a picture of an Astrocade motherboard that should be able to provide the details that you're looking for on the PCB.  This PCB belongs to "Kenzre."  When he and I met at the beginning of March at the Louisville Arcade Expo, he brought along some equipment with him.  I took some pictures of some (most?) of it.  The six sets of five digit numbers on this PCB are the exact numbers on my own Astrocade PCB.  I know that the board in this picture didn't work (it gets a gray screen on startup). I'm not sure if Ken did any sorts of modifications to this board-- but he'd be able to explain that better than me.

 

Astrocade (March 03 2017)(Astrovision Arcade).jpg

 

When I took this picture, I didn't expect it to be examined carefully.  Does it provide the details that you need?

 

Adam

 



#9 TVisitor OFFLINE  

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Posted Tue Apr 4, 2017 7:41 PM

1) 8K ROM - On the early Bally Arcade systems, the 8K ROM was made of four 2K ROMs (U1 - U4).  Later revisions ditched three of the ROMs and replaced them with one 8K ROM.  So, that sounds okay.

 

Certainly looks like that's the case with mine.

 

If you have any more problems write me back. We can do this!

 

Thanks kenzre!  I will follow up with this this weekend when I have some time for more troubeshooting.

 

Just an FYI but a picture is worth a thousand words...

 

Indeed they are - I did post a picture of what seemed like it was missing, though later pictures people have posted seem to confirm what looked to be missing are just later board revs and it's not an issue.

 

 

 The dust cover that you describe is one of the more popular ones, but (as Lance Squire mentions in his Astrocade FAQ), you can't tell which Bally Arcade/Astrocade system that you have from this.  Try using the label on the bottom of the console.  My console is an "Astrovision Arcade."  Model ABA-1000-2.  Serial # 049240.  All of this information came from this label:

 

Mine says "Bally Arcade" model # ABA-1000-2, Serial D 47263.  It's Patent Pending Astro Vision Inc, PO Box 133, Garner Iowa 50438.

 

Oh as well, the pictures you provided were really useful.  Looks like the parts that are missing on mine are definitely not on yours either.  I was worried that once I found it wasn't working and then opened it, that it was possible someone hacked it up for parts.

 

Now as a further questions, I know these units run hot, and the wall-wart runs hot itself.  I realize it's subjective, but how hot would you say that wall-wart gets?  Warm?  "Damn, that's hot" or "don't freaking touch that, you'll burn your fingers" hot?

 

It's interesting as the parts lists on the newer astrocades don't quite seem up to date with the original service manual, such as U24-U31 are 4027 chips, where th manual says they're 4096.  Of course, I can just read the part #'s on the actual board to replace, but I"m wondering if there's any other documentation that's further up to date?

 

By the way - I know you said the website can be hard to get around and such, but I'm not complaining.  You're one of the few resources out there.  That's how I went from "WTF is this board?" to "Oh, that's the (video) kludge board!"  



#10 ballyalley OFFLINE  

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Posted Tue Apr 4, 2017 9:27 PM

how hot would you say that wall-wart gets?  Warm?  "Damn, that's hot" or "don't freaking touch that, you'll burn your fingers" hot?


I'd say that mine gets warm.  I could run it for a while tomorrow and check.  I don't recall my unit's AC adapter getting so hot that it felt like it would burn me.  Then again, my AC adapter is plugged into a power strip that I turn on and off; I rarely, if ever, touch it after I've used it.
 

I'm wondering if there's any other documentation that's further up to date?


The PA-1 Service Manual is the most up-to-date manual that I'm aware-- and it's from very early-in in the products life-cycle.  From reading letter written to the Arcadian, I know that Bally sent these out to customers as early as 1978.  I've had a few original PA-1 Service Manuals, and I've never noticed any differences between them (i.e. different revisions of the same manual).
 

By the way - I know you said the website can be hard to get around and such, but I'm not complaining.  You're one of the few resources out there.  That's how I went from "WTF is this board?" to "Oh, that's the (video) kludge board!"


I'm glad that you don't find BallyAlley.com too hard to navigate. The site has been around since 2001.  Many of the files have been on the website for a long time.  This is useful if you know approximately what you're looking for and then use the Google Search bar on the first page of the BallyAlley.com website.  You'll usually come across something useful.

 

So, what made you pick an Astrocade?

 

Adam

 

 



#11 kenzre OFFLINE  

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Posted Tue Apr 4, 2017 10:23 PM

This unit is only slightly modified. I replaces the 10KuF lytic and moved it to where it wants to be electrically, nearer The diodes. Every chip socketed. The keypad PCB is missing. the rest looks the same as any Astrocade unit and the late Bally units.If you check the documentation on the Kludge board in the Arcadian newsletter, you will see that it also has most of the changes discussed. Also the power switch is missing the top/contacts.


Edited by kenzre, Tue Apr 4, 2017 10:25 PM.


#12 128Kgames OFFLINE  

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Posted Wed Apr 5, 2017 3:37 PM

Indeed they are - I did post a picture of what seemed like it was missing, though later pictures people have posted seem to confirm what looked to be missing are just later board revs and it's not an issue.

 

Really? All I see is a picture of a schematic; posting a picture of your actual motherboard would make things a lot easier, especially for people to match up to what they have, is what I was implying.  

 

As the boards and the revisions may not be 100% accurate or the same across the line with the system and various suppliers, possible in house repairs etc.  I have some spare motherboards I can look at but it would make things easier if I knew what I was looking for, visually. 



#13 ballyalley OFFLINE  

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Posted Wed Apr 5, 2017 4:07 PM

 

As the boards and the revisions may not be 100% accurate or the same across the line with the system and various suppliers, possible in house repairs etc.  I have some spare motherboards I can look at but it would make things easier if I knew what I was looking for, visually. 

 

What's interesting about this thread is that it brings up a major weakness of the BallyAlley website.  I've had the website for over fifteen years, yet there are no quality pictures/scans of the various Bally Arcade PCB boards.  I should make that a project, although I can't really do it alone (I don't have all the needed hardware).  It wasn't until this thread came along that I realized just how different some of the various motherboards are from one another.  This is no surprise, but it's weird that this subject seems to have been ignored until now.

 

Maybe I'll try to get some high-quality pictures of one of my two working motherboards.  I've always wanted high-quality pictures of some of the various hi-res arcade boards (especially Sea Wolf II, since it's supposed to be very similar to the first release of the Bally Arcade PCB).

 

@Michael: Maybe you and I can compare our PCBs, take pictures of them (or maybe even scan them) and then try to get a page on BallyAlley.com that can show some good pictures of the hardware that we both have.

 

Adam



#14 128Kgames OFFLINE  

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Posted Wed Apr 5, 2017 4:21 PM

 

What's interesting about this thread is that it brings up a major weakness of the BallyAlley website.  I've had the website for over fifteen years, yet there are no quality pictures/scans of the various Bally Arcade PCB boards.  I should make that a project, although I can't really do it alone (I don't have all the needed hardware).  It wasn't until this thread came along that I realized just how different some of the various motherboards are from one another.  This is no surprise, but it's weird that this subject seems to have been ignored until now.

 

Maybe I'll try to get some high-quality pictures of one of my two working motherboards.  I've always wanted high-quality pictures of some of the various hi-res arcade boards (especially Sea Wolf II, since it's supposed to be very similar to the first release of the Bally Arcade PCB).

 

@Michael: Maybe you and I can compare our PCBs, take pictures of them (or maybe even scan them) and then try to get a page on BallyAlley.com that can show some good pictures of the hardware that we both have.

 

Adam

 

Hmm, how does one scan a motherboard?  Actually lay it on the scanner?  Like a book?  Does that work?  I've only ever scanned flat things I'm afraid. 



#15 ballyalley OFFLINE  

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Posted Wed Apr 5, 2017 4:32 PM

 

Hmm, how does one scan a motherboard?  Actually lay it on the scanner?  Like a book?  Does that work?  I've only ever scanned flat things I'm afraid. 

 

I've never scanned a motherboard before, but I've scanned smaller PCBs (cartridges), and that works good.  I think putting the Bally motherboard on a flatbed scanner would work (although it might have to be scanned in sections and then stitched back together).  Maybe you can try it and find out.

 

My Canon Power Shot SX60 HS 16.1 megapixel camera takes 180dpi pictures.  I can even set it to take RAW pictures, which don't suffer from jpg lossy compression.  Although, to use the RAW setting, I can't use "auto" mode, which forces me to set all the settings manually-- which can be a chore for a point-and-click guy like myself.

 

The issue with using a camera to take quality pictures of PCBs, in my experience, is that you might get a really good overall "feel" for the motherboard, but you can't read the chips, which a scan might allow.  The reason that the camera doesn't work good may be because of poor lighting.  I've been told that taking pictures in natural sunlight (i.e. outside) works best.

 

Am I getting to far off the topic of this thread now that I'm talking about getting pictures of the Bally's motherboard?

 

Adam



#16 TVisitor OFFLINE  

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Posted Wed Apr 5, 2017 7:17 PM

Maybe I'll try to get some high-quality pictures of one of my two working motherboards.  I've always wanted high-quality pictures of some of the various hi-res arcade boards (especially Sea Wolf II, since it's supposed to be very similar to the first release of the Bally Arcade PCB).

 

I certainly can take some pictures of mine and try to stitch them together or get my friend to take a picture of mine with his DSLR.

 

 

Really? All I see is a picture of a schematic; posting a picture of your actual motherboard would make things a lot easier, especially for people to match up to what they have, is what I was implying.  

 

As the boards and the revisions may not be 100% accurate or the same across the line with the system and various suppliers, possible in house repairs etc.  I have some spare motherboards I can look at but it would make things easier if I knew what I was looking for, visually. 

 

Ah Ok.  I had taken the component layout picture from the manual and marked up what was (mostly) missing in orange figuring someone could say "whoa, that's not right..."  However, from what I've read within this post I can garner that it's not a result of someone using my board for parts.  However, I can still take a picture and post it up (at least since Adam also would like to get some pics of the boards for the site).

 

 

So, what made you pick an Astrocade?

 

Like a lot of people, nostalgia is a driving factor.  I didn't have one when I was a kid, but growing up I remember going to Crazy Eddie's and seeing their display with an Atari 2600, Colecovision, Astrocade, and one or two other systems that I can't remember.  I remember that the Astrocade just had this cool look to it.  I also enjoy tinkering with older hardware.  A friend had one growing up and I think it would be fun to have a walk down memory lane with him when I get this one running.

 

By the way - on a separate note - I remember reading that the 3 custom chips in the Astrocade were also used on several of their arcade games, Gorf being one of them.  What were the others?


Edited by TVisitor, Wed Apr 5, 2017 7:19 PM.


#17 128Kgames OFFLINE  

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Posted Wed Apr 5, 2017 8:14 PM

Ah Ok.  I had taken the component layout picture from the manual and marked up what was (mostly) missing in orange figuring someone could say "whoa, that's not right..."  However, from what I've read within this post I can garner that it's not a result of someone using my board for parts.  However, I can still take a picture and post it up (at least since Adam also would like to get some pics of the boards for the site).

 

Awesome, I'll try and match yours up to some of the spare boards I have. 

 

Like a lot of people, nostalgia is a driving factor.  I didn't have one when I was a kid, but growing up I remember going to Crazy Eddie's and seeing their display with an Atari 2600, Colecovision, Astrocade, and one or two other systems that I can't remember.  I remember that the Astrocade just had this cool look to it.  I also enjoy tinkering with older hardware.  A friend had one growing up and I think it would be fun to have a walk down memory lane with him when I get this one running.

 

Ah, good old Crazy Eddie: his prices were I-N-S-A-N-E-!!!  (So apparently, were his business practices).  I practically lived at the Syosset location on Jericho Turnpike back in those days, always trying to see what new games came in and what was on the horizon.  They had the games and computers (Atari, Commodore etc.) right in front when you walked in.  

 

For me though my "first time" with the Astrocade was across the street at PlayWorld, and I agree the look of it was something else: the cartridge bay, the controllers, the keypad etc. Plus the fact that all the games displayed at the time were all arcade ports, and who wasn't an arcade junkie back in the day? (games, not drugs, cause drugs are bad, m'kay?).  

 

The system was still the Bally Computer System at that time but it still looked sooo sexy!  I would have loved a future console revision to be an all black design, like the 2600 'Vader, that would have been sweet.  I've often toyed with the idea of sanding down a spare console cover and getting rid of the faux woodgrain...

 

Maybe this will help jog your Crazy Eddie memories:

 



#18 ballyalley OFFLINE  

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Posted Wed Apr 5, 2017 8:36 PM

I certainly can take some pictures of mine [...] or get my friend to take a picture of mine with his DSLR.


Wait a minute. You have (that is, you own) a full-size Sea Wolf II arcade cabinet with the periscope?!?
 

Like a lot of people, nostalgia is a driving factor.

 

I never knew anyone who had an Astrocade when I was growing up in the late 70s and early 80s.  I never saw an Astroade until the mid-90s, when I used to find them on a fairly regular basis at thrift ships.

 

I like the Astrocade for different reasons depending upon when I am asked about it.  If you ask me this right now, then I have to say I like the Bally Arcade because I can browse through the Bob Fabris Collection and still find new things to scan in for BallyAlley.com.  Today, I was scanning-in material from a box and I came across the original letter that Fred Cornett sent to potential subscribers of his upcoming newsletter Cursor.  I'd never seen that before, so it was pretty cool.  Happily it arrived in Bob Fabris' mailbox in the Fall of 1979.  It is mentioned in the October 31, 1979 of Arcadian, which Paul and I will be discussing in the next episode of the Astrocast podcast.
 

By the way - on a separate note - I remember reading that the 3 custom chips in the Astrocade were also used on several of their arcade games, Gorf being one of them.  What were the others?

 

The six main games that use what is usually called the "Astrocade chipset" are:

 

Seawolf II (1978)
Extra Bases (1980)
Space Zap (1980)
Wizard of Wor (1980)
Gorf (1981)
The Adventures of Robby Roto (1981)

 

There are a few other games that use it too, including an interesting prototype that's obviously inspired by Dungeons and Dragons.  Back in 2001, I wrote an "article" about the Astrocade arcade games; you can read it here:

 

http://www.ballyalle...rcade_games.txt

 

I've been in contact lately with someone who upgraded his Astrocade in the mid-1980s to be able to access hi-res (320x204) mode.  This is the resolution that the arcade games used, which is four-times higher than the Astrocade's "consumer" mode, which is 160x102.  This person wrote a detailed set of articles that he sent to Bob Fabris in 1986.  This was either right at the tail-end or after the Arcadian newsletter stopped publishing, so it was never mentioned in print.  Luckily, I've scanned these documents, and you can read detailed instructions on how to upgrade your Astrocade to hi-res mode here:

 

http://www.ballyalle...s_packages.html

 

I've always thought that it would be neat to see a new game written for the Astrocade's chipset that used hi-res mode.

 

Adam



#19 128Kgames OFFLINE  

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Posted Wed Apr 5, 2017 9:54 PM

I've always thought that it would be neat to see a new game written for the Astrocade's chipset that used hi-res mode.

 

Adam

 

Hi-res mode + 64K expanded RAM + 512K bankswitched cart = WORLD DOMINATION!!!



#20 TVisitor OFFLINE  

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Posted Thu Apr 6, 2017 7:44 PM

Wait a minute. You have (that is, you own) a full-size Sea Wolf II arcade cabinet with the periscope?!?

 

Sorry I meant I could scan my board meaning the one in my Astrocade :)

 

You know I'm getting way ahead of myself, but it seems that the 7.5VAC part of the supply is ONLY used to derive the +5V internally.  I'm not sure why the regulator VR3 can't be dumped and a one like a LM7805 can't be used to take the input voltage and derive +5 off it.  It looks like VR1 can be substituted by a LM7815, VR2 by a LM7810, and VR4 by a LM7905 as direct replacements though.  24VAC supplies can be much more readily found given that they find application in the HVAC world.

 

I guess I should get the damn thing running first before I screw around.



#21 kenzre OFFLINE  

kenzre

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Posted Mon Jun 19, 2017 8:07 PM

The 7.5VAC (which is actually low, it S/B around 8.3) is ONLY going to the +5VDC circuit.

As far as regulators, the 78 / 79 series are direct replacements for the LM324 regulators.

There are 2 reasons for the "different" way of doing the +5v circuit the way they did originally:

   1) the Pass Transistor configuration was the best way to acquire a high current. The new regulators can go as high as 3.0A with the proper heat sink.

   2) the switch they used was only a DPST configuration. So by controlling a regulator that drove the pass transistor, they could shut off the +5V supply to the PCB. This design is very poor 

      because : A) the bridge diodes are still conducting and

      B) the 10,000uFd Lytic is still across them. I had one of those 10K caps blow out on me with the switch off. I was glad I was right there so it couldn't start a fire.

 

If you have a scope or a frequency counter capable of handling a 10V P-P signal, check pins 9 & 10 on the custom data (under the keypad) to should get a clock signal approx 7Mhz ( double color burst) and @ pin 16 you should get approx 3.5 MHz clock. If you don't get the signal @ pins 9 & 10, the culprit may be the 74S74 under the Kludge board. I have found that goes bad on occasion. If the signal is there, then check pin 40. (DATEN) if you get nothing there, NOW the trouble comes. Almost anything on the PCB can cause that signal to not appear. Ask me how I know THAT!



#22 nanochess OFFLINE  

nanochess

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Posted Tue Jun 20, 2017 7:21 AM

I would remove the chip in socket to check if the voltages still drop. It would mean the chip went bad.

Also I would use a high-technology device to check for failures, the FOC or Finger-Over-Chip ™ to check for too hot chips that are draining voltage and socket them for further testing. ;)

#23 CatPix OFFLINE  

CatPix

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Posted Tue Jun 20, 2017 9:25 AM

Tho, the fingertest on a Bally is anything but accurate. All "big package" chips (the Z80, the "Astrocade chip" and the two others that I do'nt remember right now) get frigging hot. On mine, I glued radioators to help them cooling, and it helped my Astrocade to run better. But still, it's near impossible to put a finger on the Astrocade chip and even the Z80 get excessively hot (especially knowing how widespread it was, but heh, most ofther Z80 computers I know and use are from 82/84 so they improved them by then I imagine)



#24 nanochess OFFLINE  

nanochess

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Posted Tue Jun 20, 2017 10:00 AM

Tho, the fingertest on a Bally is anything but accurate. All "big package" chips (the Z80, the "Astrocade chip" and the two others that I do'nt remember right now) get frigging hot. On mine, I glued radioators to help them cooling, and it helped my Astrocade to run better. But still, it's near impossible to put a finger on the Astrocade chip and even the Z80 get excessively hot (especially knowing how widespread it was, but heh, most ofther Z80 computers I know and use are from 82/84 so they improved them by then I imagine)


The original NMOS Z80 burns as hell after a while.

But anyway the test is to be done as soon the Bally is powered on. Any chip going hot too soon (less than 10 seconds) is pretty suspicious.




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