Porchy

Arkanoid repair log #2

Jun 012018

I recently borrowed this Arkanoid PCB from NES4Life. I wanted it as part of a project to recreate the 28 pin custom chip that found on this, Darius and probably a couple of other Taito games of the same era.
He kindly loaned me this but knew it had issues so I agreed to look at this one rather than poke around on one of his workers.

First up the game would not boot, just watchdogged.
Using the schematics available in the download section I could easily track down a stuck bit on the data bus.

IC42 was to blame for this. Replacing it let the game boot but with all new issues.

You can see the game has booted straight into test mode and the colours are messed up.
One of the DIP switches is for test mode and the DIP’s are handled by the YM2149 chip. Looking at the databus when this chip is supposed to be active showed all data bits stuck.
Replacing this chip let the game boot.

Colours are still messed up so lets look into that. I chose to start at the 3 colour PROM’s

Probing the address pins revealed most were floating. Going backwards we come to a 74LS298 at location IC38. Replacing this then gave me this:

You can see now the screen is doubled up.
The graphics are contained within 3 EPROM’s. These EPROM’s are all addressed by 74LS298 chips before outputting their data to the custom bit shifters.
Checking these 298’s showed some stuck output pins on IC50.

Replacing this gave me a more normal screen but the bat sprite is being drawn half way up the screen and is doubled up.

Horizontal position has its own bus on the schematics

I confirmed the operation of the 74LS157’s first so moved onto the 74LS669’s. I’ve not dealt with these before and had none to hand either but I was fairly certain id narrowed it down to IC65 so I ordered some new ones up, desoldered the old one and tested it. Thankfully it failed.

Got the new chips a couple of days later and fitted.

Just the double bat issue to go.
The schematics also have a bus identified as OBJ which Im taking stands for Object. It made sense to me that the issue was somewhere along the same path as the previous positioning fault so armed with my best guess going from schematics I carried on following the path first of all checking the other 74LS669. This appeared to be OK and the RAM didn’t have any unusual looking signals on so I carried on. After these there is a 74LS374 on the OBJ bus. Probing the outputs of this found a single stuck bit. Replacing this gave me a seemingly fully operation game.
I cannot check the spinner inputs but all the sounds, DIP’s and regular inputs are working.

Sky Skipper repair log

PCB Repair Logs Comments Off

May 052018

Recently I was sent a TNX1 Sky Skipper PCB for repair from my friend, Whitney.
It had developed a sprite fault which looked like this

As you can see in some places the sprites look fine but as it scrolls they start to disappear and flash etc.
I had already done quite a bit of work with these PCB’s and the regular Popeye PCB too so was fairly familiar with the whole setup.
I knew the main RAM also held the sprite data too which the DMA circuit then pushed out to sprite RAM during VBLANK.
With this in mind I was sure the main RAM was OK and enabling the test mode also backed this up.
I checked most of the DMA circuit out which is mainly just counters and they all seemed fine too..

I moved onto the RAM PCB next. I could rule out the 82S09 SRAM chips straight away as they are all socketed and I have spares.
The 5501 sprite buffer RAM was a little more difficult to check. While I was probing about these RAM’s with the scope I found the voltage wasnt stable and fluctuated every few seconds a little and also there was a big volt drop compared to the output of the PSU.
I confirmed that with this RAM PCB unplugged that the volt drop went away as did the fluctuation of voltage.
I hooked up this PCB to my bench PSU on its own and monitored the current draw and voltage. I later pinpointed these issues to the RAM that I had swapped in to test. They were older ceramic types and clearly they were drawing a lot more current than the original. Swapping them back cleared this issue but obviously was not going to solve my problem.

Moving on the whats seems to be getting called the “timing” PCB I started probing the counters and found a 74LS161 which had weak looking outputs.

*note this picture was taken after being changed hence its in a socket

I piggybacked a new 161 on top but with the output legs bent out so as not to make connection then probed again.

I didn’t really think it would clear the problem but as there was such a difference I swapped it out anyway

After checking the game I had this

Game is all fixed.
Going to do some minor servicing on this and then send it on its way home.

HP 10529A reference card gerbers

Reproductions Comments Off

Apr 252018

Recently Bad_Ad84 had the need for more reference cards for his HP 10529A logic comparator so decided to make his own.
He kindly sent the gerbers to me to be hosted and they can be uploaded to the usual PCB fab places like OSHPark and DirtyPCB

ZIP file can be downloaded HERE
Massive thanks to Bad_Ad84 for these, I know ill be using them.

Chopper I PAL dumps added

PAL Updates Comments Off

Apr 082018

Muddymusic sent me a Chopper I PCB to look at.
There were 5 PAL’s on this board and all were soldered in so I had to desolder them to dump.
All the PAL’s were unlocked so these are native dumps in their native format.
They will need converted to GAL format to use in a GAL chip.

Cruisin USA link PAL, Commodore C16 PLS100 & Shadow Dancer PAL added

PAL Updates Comments Off

Apr 022018

Here is something a little more special than normal.
A quick google search for “Cruisin USA link PAL” shows that a few people have been searching for this for a while now. I personally bought a PCB a few years ago in an attempt to dump it only to find the link up version uses a different PAL chip.
Recently TheDrunkenArcade bought the correct PCB and gave the PAL to JROK to reverse.
Massive thanks to TheDrunkenArcade and JROK for doing this and also allowing us to add it.

Next up is the Commodore C16 PLA. I made a post showing the method I used to recreate this to allow it to be programmed to an original PLS100 device. After much testing I have uploaded the file.

Finally my good friend Banjo Guy Ollie sent me IC48 PAL chip from his Shadow Dancer bootleg. The device seems to be operational but the PCB it came from is not yet 100% so we cannot test it right now.
There is another PAL on this PCB that he will be sending my way when he can.
Thanks to Ollie for this

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