Moon Cresta bootleg PCB

[mattp]

Hi folks, been reading your forums and hoping I might get some thoughts as to what might be wrong with my 2 faulty bootleg Moon Cresta PCBs (both with a display fault).
I am new to arcade boards and can see these 80s designs are complicated and could really do with pointing in the right direction.

So, my MC stopped working and I couldn't mend it so I did the sensible thing and bought another identical faulty one for comparison. It's good to have a reference. After some further "mending" they now both have identical faults.
I have tried all the normal easy fixes eg PSU, changing EPROM and CPU sockets, testing the various RAMs (by swapping them into my Galaxian board) , checking the EProms have good CRC, changing the colour PROM, scoping the video signals etc and sorted a few things out. I have run the MC test EPROM and can see flashing, corrupted something on the screen which makes me think it's saying "testing RAM" (like the Galaxian test ROM does) and so probably running code.If I install the MC EProm set there are stars in the background with garbage overlaid (see pic) and the watchdog triggers at 120ms intervals. My hunch is there is a software issue and I would rather not start changing ICs wholesale
If anyone can help I would be super-grateful

 

[TheDaddy]

Welcome , I think that's a monitor issue not a PCB fault personally. Could be a board fault as well , Have you got another cab or setup you can try it in ?

Dave.

 

[mattp]

Thanks Dave, I am thinking the monitor is ok because the star field is showing correctly in the background.
I could wire the board up to my Galaxian table though and check it. Worth a try do you think ?

 

[TheDaddy]

Thanks Dave, I am thinking the monitor is ok because the star field is showing correctly in the background.
I could wire the board up to my Galaxian table though and check it. Worth a try do you think ?

Its hard to tell just from pic but it does look like the screen is scrolling. Its wirth trying , again just a matter of trying to rule things out. I am viewing on crappy phone so will have s proper look at the pictures you posted tomoz.

Dave.

 

[Georgian2]

Did you try adjusting the H Sync potentiometer on the monitor? Could be marked as H Freq aswell.

 

[mattp]

I tweaked the V and H hold pots and like magic got a good startup screen…
As promised I’m super-grateful, thanks people for your advice. I was over thinking the problem. Not finished yet though

 

[mattp]

The board is in a reset loop. I will make a Jamma adapter and try my boards in another table to see what happens.
Also, during my fixing somebody 😀 put the colour proms in backwards and killed them both ( one on each board). The pic above shows the groovy colors that result when a Galaxian colour prom is installed instead. Can anyone program a 82S123 ? Or unused programmed 8S123 for me to play with ( I made a DIY one bit at a time programmer that should do the job, slowly ). I will need a couple of 2101 SRams (22 pin job) too and have ready money to spend.

 

[NivagSwerdna]

The board is in a reset loop. I will make a Jamma adapter and try my boards in another table to see what happens.
Also, during my fixing somebody 😀 put the colour proms in backwards and killed them both ( one on each board). The pic above shows the groovy colors that result when a Galaxian colour prom is installed instead. Can anyone program a 82S123 ? Or unused programmed 8S123 for me to play with ( I made a DIY one bit at a time programmer that should do the job, slowly ). I will need a couple of 2101 SRams (22 pin job) too and have ready money to spend.

a Colour PROM replacement.

Maybe I should take your money?

There are a number of people here who will program Colour PROMs if you provide a blank and ask nicely.

PS

I've bought these before https://www.ebay.co.uk/itm/123928377802 but I have no connection with seller so at your own risk etc.

 

[mattp]

Thanks for the Ebay link, I missed that they are a good price. The flash ROM in your picture doesn’t have the necessary tri state outputs unless I am missing something ?

 

[mattp]

So I read a datasheet and I guess your solution looks good! Can you program these ? Got price for two please ?

 

[NivagSwerdna]

The flash ROM in your picture doesn’t have the necessary tri state outputs unless I am missing something ?

OK... I'll try and play nicely.... 82S123 is Tri-state; 633-1 is Tri-state; ... Tri-state is easy with modern parts... just use chip enable. Open Collector... now that's a different story. But here we are probably looking at 82S123 or equiv.

 

[NivagSwerdna]

Got price for two please ?

It's cheaper to use the one time programable PROM that I attached the EBAY link for. I'll program them for free as long as you pay postage; I know others here have done the same for me in the past so they may also offer if you ask nicely. (NOTE: There is always a risk with older parts so... no liability accepted)

 

[mattp]

That’s a very kind offer that I would like to accept. Although I could use my DIY programmer to program the Prom it would take some time to set each bit individually and probably end in catastrophe. I have ordered 2 82S123s and am pretty sure I have an image file for the contents so that lot should be ready to go in the post later this week.
Here’s my email address so you can send your details privately matthewianprime@gmail.com
Many thanks

 

[Georgian2]

That’s a very kind offer that I would like to accept. Although I could use my DIY programmer to program the Prom it would take some time to set each bit individually and probably end in catastrophe. I have ordered 2 82S123s and am pretty sure I have an image file for the contents so that lot should be ready to go in the post later this week.
Here’s my email address so you can send your details privately matthewianprime@gmail.com
Many thanks

You can find the binary files on the internet for almost all games.

 

[NivagSwerdna]

That’s a very kind offer that I would like to accept. Although I could use my DIY programmer to program the Prom it would take some time to set each bit individually and probably end in catastrophe. I have ordered 2 82S123s and am pretty sure I have an image file for the contents so that lot should be ready to go in the post later this week.
Here’s my email address so you can send your details privately *************
Many thanks

They are only 256 bits... shouldn't take long.
Just PM me here and I'll respond with a postal address. You do need to be reasonably confident with which image you want... as these are One Time Programmable and if you get it wrong the colours will be wonky. I would recommend programming a single unit and seeing what it looks like.
PS
Quite a lot of the time you can get away with putting chips in upside down... but maybe not advisable.

 

[NivagSwerdna]

FWIW The popular choice is probably...


SHA-1: 140335D85C67C75B65689D4E76D29863C209CF32



but it's really for you to choose... since it depends on your hardware.

 

[grobda]

you can also use a gal for a prom

REPROGRAMMABLE 82S123

Using GALs to replace small, sparse and/or redundant bipolar PROMs (Galaga bootleg)

If you've done repairs on some of the earlier arcade games (Galaga, Donkey Kong, Pac-Land etc.), you're likely to have encountered the typ...

elgensrepairs.blogspot.com

pretty sure phil murray did some adaptors too but cant find the thread

or an flash eprom

82s126 82s129 82s131 adapter board and 82s123

I read in another post that someone needed replacement proms and so I decided to share the gerbers for an adapter board I designed a while ago. The adapter board takes a winbond 27c512 eeprom, that can be burned with the prom file, no need to adjust the size of the file. On the back of the board...

www.ukvac.com

https://www.arcade-cabinets.com/board_hacks/82S123-to-27512/

both cheap and reusable

 

[mattp]

Thanks Nivag, yes I found an image of a romset and colour proms somewhere on the internet. I need to take a look to see if they look ok. Thanks for the one you posted I have no way of knowing if it is the right one for moon cresta so programming one at a time would be the best plan. I wondered how these got blown and reverse placement doesn’t feel like the answer. Maybe when I put on the edge connector upside down ? Lessons have been learnt.

 

[mattp]

Good and wholesome response Grobda, flash and GAL are both flexible options but I can’t program these due to misguided purchase of vintage eprom programmer where I could have bought a USB thingy from China for less.
For now, the plan is to replace known duff parts as cheap as possible and get back to diagnosing why the boards are watchdogging.

 

[NivagSwerdna]

Do you have a Logic Probe? Is the Watchdog counter getting nVBLANK?

I think you had a stable picture so most of the video circuitry should be OK.

If your board is like a Galaxian then...



You want to know what is going on at pins 1,2 and 6 of the 74393

It's just a counter... causes a reset (on pin 6) if it doesn't see a CLR (on pin2) before too many nVBLANKs on pin 1.

PS
You can consider disabling the Watchdog... but obviously if you have a CPU, ROM or main Memory issue it won't help.