Porchy

I have no background in electronics or programming. Everything I have learnt over the years has been through self teaching and the help from other kind people willing to lend a hand.

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.

 Posted by at 2:59 pm

HP 10529A reference card gerbers

 Reproductions  Comments Off on HP 10529A reference card gerbers
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.

 Posted by at 5:17 pm

Chopper I PAL dumps added

 PAL Updates  Comments Off on Chopper I PAL dumps added
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.

 Posted by at 2:58 pm

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

 PAL Updates  Comments Off on Cruisin USA link PAL, Commodore C16 PLS100 & Shadow Dancer PAL added
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

 Posted by at 12:40 pm

Recreating the Commodore 16 PLA

 General  Comments Off on Recreating the Commodore 16 PLA
Mar 132018
 

I recently picked up a nice boxed Commodore 16 for not too bad a price.
The PLA found in this is a MOS variant of the PLS100 PLA chip. I don’t believe it can natively be dumped as it seems to have its connection on pin 1 severed internally and decapping done some time ago revealed it was neither a PLS100 or 82S100 device either despite the pinout being the same.

I wanted to make a replacement using the NOS PLS100 chips I have because some people like that sort of thing and there doesn’t seem to be anything out there publically already.

I hooked up the PLA to an Arduino MEGA and wrote a small program to count through all combinations of the address pins and log the outputs to a 64KB binary file.
From here I wrote a program that converted the file to a truth table

and finally into equations which I could compile to a PLS100 fusemap using the old easyABEL program.

From here I could program a blank PLS100 and test in a real machine.

Still need to do some testing but early signs are looking good.

 Posted by at 7:39 pm