Hail to Galaxian... by Namco!

[level42]

Robin and I had a quick look if there would be any life in the Tazz-Mania....

It booted to fixed garbage on the screen and we couldn't get much life in it.

The sockets are pretty bad (also because of the large pins of the daughter boards) so these will probably need replacing.

However first I undid all the mods. This was actually pretty easy. I snipped off all the legs of the piggy-backed chips close to the bodies. This made it much easier to remove them and the pins, using some new solder and my bad-ass Soldapult (love that thing).

Removed the small daughter board and inserted 3 "fresh" 74HCT259's (bought this week, but I noticed the Philips logo and Philips does not make chips anymore since YEARS (NXP is the company name now) and the date is from 94, so these have been waiting in the seller's drawers quite a bit

Anyway, removed the large EPROM daughter board and installed the test ROM, I have no idea if this is the correct spot. Can't seem to find info on where to put it online, only thing I found was someone who inserted it at the first position on the daughter board.....so I have no idea if it will work directly on the board.

Also installed the missing heat sink and of course the two 2101 RAMS, borrowed from the bootleg board.

I found 4 trace cuts so far and fixed them, but I need to go over it again a couple,of times, there's probably more. I put a bright (LED) light behind the PCB and look on the other side for cut traces. Then I measure them and fix them with some tiny wire and solder.

As soon as I complete the track cuts search but before replacing all the sockets I'd like to give it another spin to see if there is more life in this board...

It also need a good wash

[level42]

Pics

[level42]

OK it's washed and I fixed one more cut track that I could find....also replaced the character ROMs with the one's from the bootleg board and burned one (it showed bad during Romidenting it....I guess that's where the stripes came from on the bootleg board )

So now I have this:

[level42]

The garbage is absolutely frozen. No response on the reset button. So I started some probing at the CPU. Clear enough the reset line was going up and down in a "nice" puls, so the watch-dog is barking. Shorted the watch-dog pad to stop the watch-dog...no change.

Started checking each pin at the CPU, this is what the read and write lines looked like:

Even if you don't know much about these kind of things, you are probably aware that digital stuff normally only has two states: high or low. So you expect to see nice block waves....but not this analogue looking kinda shit....

[level42]

So I swapped the Z80 with the one from the bootleg board (known working) and now those lines looked like this:

[level42]

Hurah, yes that's what we want to see !
So I fixed the first big thing on this board, one dead Z80 replaced....

However....the screen didn't change a tiny bit !!

I probed around at all adress and data lines on the CPU and all look active (some need a reset to give a couple of pulses and then go quite, but I figure that's OK).

Checked the buffers and every in and output looks OK.

Checked the 74LS245 and here I have a bit of doubt. The picture looks a bit "sawtoothy" on some pins, not sure if that's OK.......anyone ?

[level42]

Forgot to mention I had replaced the CPU socket too.

I need to do the other ROM sockets too (esp. the one's where the daughterboard with the big fat pins were in....) but I don't have any sockets at the moment, gotta order....

It might be easier to get a working Namco board (or even a Midway board, I know someone who WANTS a working Midway board so that I can get his Namco board ....however, I see this as a good learning case.

I think I could really use the Fluke now. I have probed all over the board (well at a lot of important places) and there is activity everywhere....

However, the Fluke is in storage and I'm not too sure if it works 100%...

[level42]

Hmmm, I found a track that I fixed but the schematics show that this should be going elsewhere....gotta puzzle this out...

[level42]

Ok found two tracks that didn't connect right, fixed those.....still same frozen garbage.

Then I probed around with the oscilloscope on the 3 chips that had the most piggy backed legs and comparing it with the schematics. Soon enough I found another track to be cut that I had missed. Bridged that too and.....we have life !!!

https://youtu.be/wUO1fcP2WRc

This may look like garbage still, but at least it's moving garbage which actually seems to show the messages and patterns of the TEST ROM.

Now Macros guide says that if you get this screen it's probably the RAMs at locations 3F and 3H or the buffer of those. I piggy backed the RAMS and saw some changes, cut out the most suspioucos one and put in socket and RAM from bootleg board.....some difference but not good. Maybe have to do the other too or replace the buffer.....but it's already way too late now

[level42]

For comparison:here is what The test rom routine looks like:

http://youtu.be/vDT1D0-X2Kg


You can see the pattern of the blinking text, some fixed text and then the scanning of the VRAM on my board too, just garbled.

Need to order the buffer IC, 74LS245 and will order all the other already socketed TTLs too....they cost close to nothing so replacing them (and the sockets) will at least make it more reliable.....some of those chips have really weak and corroded looking pins.

[Luigi]

I can not help in any way here.....but keep going!!

[level42]

I Will !!

Replaced both RAMs....no improvement......I was working too late obviously as I had put the single RAM in backwards  

Somehow it seems it didn't fry though as I have swapped both VRAMs with the program RAMs and the tests still run OK but same garbage. I guess it's the buffer IC then.

[Franzy21]

For the info, I think there's one NAMCO GALAXIAN pcb on Yahoo! Auctions...

http://page7.auctions.yahoo.co.jp/jp/auction/g153826591

[Etienne MacGyver]

I think its impressive and you are making progress.
you'll get it fixed, i am sure 

[level42]

For the info, I think there's one NAMCO GALAXIAN pcb on Yahoo! Auctions...

http://page7.auctions.yahoo.co.jp/jp/auction/g153826591

Thanks, great tip ! However 20000 yen is about 150 euro and that's without pretty expensive shipping I'm sure.

They sure did a thorough DC conversion on that one, they even removed the filter caps, which is OK, but it doesn't hurt to keep them there if they are OK.

I found some more TTLs I already had yesterday and swapped those, but no result. Also found some 2114s I had on stock and to be sure swapped those for the VRAM. Results look different but still garbage.

I also found a 74HCT245 so I removed the original buffer chip for the VRAM and installed this.....no joy.
The waveforms on this buffer look weird, maybe the other buffer is dead, I'll have to wait for the parts, they got shipped this morning from Germany (Reichelt).

I have a feeling it's time to get out the Fluke.

Also: having a working (loaned) board to compare things would be a great help.............anyone ?