U72's Galaga

[jonhughes]

This is U72's Galaga PCB I said I would repair. I picked this up from Expo but to be honest it's taken me so long because I'd had other things to do and had 'gone off' repairing. With Christmas holiday of 2 weeks though I had some time on my hands. This is the fix on the graphic board. The CPU board and the graphics board have both been worked on. I'd given up partially on the CPU board since it's been hacked quite a bit. I have found a broken trace, unrepaired, and I'm wondering if all the hacking is to compensate for this. I'll remove it all later and patch the trace. The only reason I'm going to do this is because I now have a spare working CPU board.

After changing a failed custom (07xx) and a RAM at 3H I was getting blocks as characters on the video. Something had been spilled on the board over customs at 1K, 1L & 1N. Decided to replace all the sockets. I didn't photograph this part. This was the board up to know.

And this is what I was getting - rotating characters which were the wrong type. Everything was wrong - shots, explosions, characters.

As mentioned previously, the board had been worked on before - here is some of the handy work. I really don't like working on such boards.

Since the characters were messed up, I decided it would be a good time to replace the character ROM sockets. After pealing off the housings I was greeted with three broken pins. Looking promising.

Removed all the pins - this is my handy work on the top.

And again on the solder side.

New sockets now installed.

and voila, we have cured the video issues.

I'm going to remove all the hacking on the CPU board and fix that trace. There's no pressure in doing this now since I have that working spare CPU board, otherwise I wouldn't want to be removing it. I've had to replace 2 missing customs on this board and a further 51xx custom which was causing issues with the sound.

Will keep you posted.

 

[lesoleil70]

Nice one.

 

[jonhughes]

Update, I have replaced the sockets on the customs. I decided not to remove the hacking from the board. The broken trace is already patched, just not sure about the other 'parts' in there.

The board now boots but there is an issue with one of the ROM sockets on the CPU board. Board re-sets about every minute and I've tracked that down to one or two sockets.

I've removed the amp because it nearly took my skin off when I first tested it. I know there is a broken trace to pin 7 of the amp but it could be another issue. The break is so close to the soldering eye it may have been making contact. I'm going to order a new amp anyway.

Here is the board pre-socket change on the customs ICs.

Here is the trace and other components, notice how scorched the area around the amp is.

Here is the broken trace.

Here it is on a good board. This doesn't feature on other versions of the board. As far as I know there are board versions A to D.

Here is the board on the test rig working but resetting. I'll have to order the amp which will take a while but in the mean time I'll replace all the ROM sockets to make sure the board is a lot more reliable. ROM E needs to be burned also, that one is on loan from my test board - I've order a batch of chips from Germany.

 

[jonhughes]

Both boards are now fully repaired and re-furbished. Andy wanted a board with stability and wasn't particularly bothered what it looked like at the end of the day. All the important sockets have been replaced along with good customs sat in sockets, most have new legs attached.

I have a hunch that galvanic corrosion could be responsible for the corrosion to the custom chips.

Finally, then. Board was re-setting so removed all the ROM sockets.

and replaced them with nice new ones. The board is now solid no re-setting. I hate turned pin sockets BTW don't expect me to recommend them.

After removing the amp months ago, I couldn't find it for about 2 hours. I had stored it somewhere safe, that I couldn't remember. Eventually found it and thought might as well put it back in. Nothing to lose really.

Next though, that broken trace on pin 7 of the amp socket.

Using 2 twined 0.2 copper wires I made a repair over the break rather than solder over. The board is looking a bit fried there.

And that's it, the amp was ok. Last thing though was the explosions were missing. All other sounds are present bar the ship explosion. This took a while to track down. The usual suspects are the polar ROMs at 1D & 5C. After wasting a fair amount of time I eventually discovered it was a faulty custom 54xx. Unfortunately, I'm out of them. However, I know Andy has one in the first board I sold him and this board will be a spare. If anything happens to the first board he can just switch out the custom into this one.

Thanks for reading.

 

[Big Phil]

I love detailed repair threads like this. Thanks!

Wish I had the knowledge.....

 

[jengineer]

good work Jon!!!! love it

 

[jonhughes]

Thanks, it is actually a scaled down version. I didn't photo the first part because I couldn't find the camera. All the chip testing isn't in there either so I knew what was good and what was bad. Just wished I could have photographed the blocked out graphics on the sprites before replacing the sockets on the video board.

 

[jonhughes]

I'll post a funny/educational/embarrassing post for you later on how someone tried to replace a custom socket on another video board I'm working on. They managed to break five or six traces prying the socket of the board but still soldered horrid turned pin socket rows in expecting it to just work.

 

[Alpha1]

Awesome tech thread - amazed how much that amp burnt the PCB.

 

[TonyElyod]

Awesome Video...

I too wish I had the Know how,

..a steady Hand,..

..clear vision,

..a cleanTable....

.,a soldering iron..

... & SODDER ???..!!

ALL THE BREAST FOR 2015

GAME ON................................

 

[RGP]

Awesome tech thread - amazed how much that amp burnt the PCB.

I've seen a few of those MB3730's do that.

IIRC, they are self-referenced for the speaker return so if you get a ground short they go supernova very quickly and pop, if you have an intermittent leak to ground or the return trace is bad they will superheat but stay working and do that to the board.

 

[david_orton_2000]

Nice write-up John, and WOW...that is a lot of socket replacements!
Out of interest, why are are you so against the turned/rolled pin sockets?
-I find them very reliable, ok yes, a little more expensive.

MB3730 amps, agreed as James mentioned, seen a few other boards with the over-heat issue.. :-(

All the best,
David.

 

[jonhughes]

Hi David, using chips with numerous legs in the rows which are slightly iffy is a problem on turned pin sockets. Everything has to line up correctly otherwise it's too easy to break the legs off the chips particularly at the frequency I'm changing them out to do testing.

They're installed on the Sega 16 CPU socket and are a nightmare to install the chip. On good chips they're ok.

Just my experiences.

 

[jonhughes]

Just when I believed I had this conquered.

Fixed this board over the Christmas holidays and placed it in secure storage in the loft, ready to be taken to Play Blackpool in May. On the Saturday morning of Play Blackpool, I take the PCB out of storage to test and disastrously the board refuses to boot.

I feel like the board has committed treason.

I perform some trouble shooting on the board, all customs are good, all chips appear fine. The graphics board is solid, but it's the CPU board that's giving me the problem.

To cut a long story short, I've been on and off with this for over 2 months and was about ready to take a hammer to it. Given up, had another go, given up, etc, etc. It's booted, then not booted.

To fix the board I've had to replace every socket on the CPU board, every single one and all were bad (23 in total on the CPU board). I replaced the final 2 this afternoon and the PCB is finally stable. Couple this with having a brand new Z80A packing in immediately and it's been quite a journey and one I won't be doing again. This is the only board I've repaired for someone else and from now on I'll be sticking to what I've always down, repairing only my own. I don't have the equipment, yet, do to this sort of thing properly. I'm still after a Fluke in the wanted section. I'll just keep wanting and waiting.

Bad pins.

More bad pins.

Finally got 4.93 volts in it.

And working again.

 

[Hurray Banana]

jon sounds a nightmare. good job you've done there though,well done mate

 

[chuckles1001]

WOW Great work, hopefully I will not have that many problems with my Gaplus PCB

 

[Alpha1]

Well done for persevering dude! Top work.

 

[u72]

Amazing work Jon - I wasn't aware it was so bad - its the board that came with the cocktail I won off ebay,
the other one I got off you has been working perfectly in Arcade Club (and at Events) for almost a year!

It's a very popular game and is played many times every weekend!

Thank You!

P.S. I'll hold off sending you this pile of Scramble Boards....

u722015-06-30 18:23:49

 

[RGP]

Jon, I feel your pain, i'm working on a Missile Command PCB which has a weird issue around the CPU so every time you flip the board over to desolder/replace something and then flip it back, it comes up with a yellow screen and halts.

Whomever the previous repairer (i'm not saying owner as often through history its not their fault) has done some interesting attempts at repair on it including trying to replace a 7442 with a 138 and some strip-board.

Still, can't be as bad as the other board next to it which was dropped off inside a cocktail as working but has socketed parts and its 10mhz crystal missing but not in the cabinet anywhere.

 

[jonhughes]

Amazing work Jon - I wasn't aware it was so bad - its the board that came with the cocktail I won off ebay,
the other one I got off you has been working perfectly in Arcade Club (and at Events) for almost a year!

It's a very popular game and is played many times every weekend!

Thank You!

P.S. I'll hold off sending you this pile of Scramble Boards....

Hi Andy,

Something was spilled on the board, that I do know, was the issue. I think the only reason I wouldn't give up on this is to keep my 100% repair rate on Galaga. This was purely the only motivation.

I can sell you a Stern Scramble PCB if you need one. I'm having a break from the repairing for a bit, there's not a lot I'm on the lookout for. Let me know if you need one.

Cheers