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.

Got this untested Konami Salamander from the UK

It was a little bit dirty, but still in good nick. No previous repair work and no broken traces.

First startup showed that the game was stuck in watchdog, so program code was not loaded correctly by the main 68000 CPU. But sometimes it would take longer to reset the watchdog and sometimes it also shouted out one of the speech samples.

So I first took out the program ROMs, shown below, and re-inserted them:

Now the game booted into ROM/RAM test. The screen is a bit garbled, but I could see when comparing to the test screen in MAME, that ROM6 was reported as BAD

I first verified the EPROMs against MAME and they were ok. So unfortunately there was a fault in one of the MASK ROMs. I had a Salamander board since before, so I just stuck the MASK ROMs from that pcb into this one to see if it booted up and sure enough it worked. The MASK ROM printed with 6108 was indeed not working.

As this is a MASK ROM, 1Mbit 28-pin, and not a standard EPROM, I remembered that system11 made a blog post about converting Salamander to the japanese version of Life Force. I have made that conversion as well, and still had some of the pcbs and flash roms.

So I just made one with the Salamander ROM.

And voila, the game is resurrected from the dead 🙂

 

No other issues, job done!

Received from Germany some faulty boards to repair.There was this Prehistoric Isle in 1930 PCB, an horizontal  shoot ’em up game developed by SNK and released in 1989.

Game boots up but some foreground graphics had vertical lines through them:

Relevant GFX data are stored in a 2Mbit MASK ROM located on video board:

I dumped the device and it was good.The data of the MASK ROM are read by the near custom silkscreened ‘SNKCG’.A visual inspection in this area reveleaed some corrosion on a trace :

Trace was connected to pin 17 of the custom, it  was silent when I put on it my logic probe so either it was a dead output or an input not receiving any signal

I was not able to find where this pin was connected to so the trace was really broken due corrosion.Looking at the other near pins, they were all connected to data lines of the MASK ROM, I found corrispondance for all of them except pin 26 (D6).I run a jumper wire and foreground graphics were restored:

Happy with result I was about to close this repair when, during testing, I noticed that voice samples were missing, I could hear only some crackling noise instead of them:

Looking at sound section on CPU board I quickly found the culprit:

The 640MHz ceramic resonator (which provides clock the uPD7759C speech synthesizer IC) was missing, this a common issue on all boards that use it, it’s very easy that it comes off

I took the spare from a dead Sega System 16B motherboard:

Repair finally completed.