Saturday, 10 November 2012

Major Title to R-Type 1 Conversion - Day 2

The conversion of Major Title to R-Type 1


Day 2: De-Solder & Replace the C0, C1, C2 & C3 Roms..


After sorting the Program & Audio ROMs, I thought I might attempt to remove & socket the four background graphic ROMs on the top CPU board.

Following the advice given by a fellow member of Jamma+, I went straight for the wire cutters... as there was no real need to salvage to original ROMs. (Especially as they were of the PROM type and could not be erased to be re-written.)

The pins were snipped along the edge of the four PROMs as far away from the PCB as possible.

Before de-soldering I've found it's always a good idea to flow some new solder into the joints, just to make sure theres some flux running through to the other side of the board.

Since we are talking about a circuit board more than 20 years old.. I would advise using lead-solder with multi-core flux.

I then used a heated de-soldering pump to remove 90% of the solder.. It's a cheap pump (~£15 in Maplin) and to be fair is a good tool - but the tip is prone to cracking around the tips-edge! :(

Looks like a combination of heat-stress & cheap alloy..

Word of advice - keep the receipt, as you're probably not going to get more that a couple of jobs done before it's knackerd (I'm on my second) - Maplin seem cool with replacing it as they dont sell spare tips.

Finger burning time.. Grabbed each pin (by-hand) from underneath and applied my soldering iron (quickly) in such a way as to touch/heat both the pin & the surrounding pad.

The pins should pop right out (with 128 little finger burns) without tearing any of the pcb contacts off the board.  Not using too much heat, or for too long is important!

Might also be a good time to recommend you use a temperature controlled iron.. ;)

Goodbye Mr Golf game..

I then ran a flux pen over the pads and used de-soldering braid (wick) to suck-up the remaining blobs of solder.

Application of flux really helps you get a good solder flow & you get a satisfying little sizzle when you apply the heat. :)

But.. dont forget to clean the flux off with an isopropyl (rubbing) alcohol soaked cotton bud, as flux is quite corrosive and could potencially eat thru stuff over time.

Not bad for a first attempt..

Just have to fit four 32-Pin DIL sockets & were good to go..!

NOTE: I thought i'd be clever and use turned-pin sockets... Talk about square peg in a round hole! (literally) I spent over an hour just trying to fit the chips into the sockets! while listening to Rom pins going "tink-ta-tink-tink" and have two pins bend under a chip! :(

I know these sockets provide the best connection - but mate this is b*ll*cks! For the other four chips I'm seriously thinking about using the cheaper sockets! Much less stress on the chips and me.

Below is a video of the progress so far: The first part is how the board behaved with just fitting the chips.. (graphics are still a mess), and the second part is how it looked after moving the 3 jumpers on the CPU board (to reflect the change from 1 to 2MBit Roms):

As can be seen, the backgrounds are starting to take shape & it's actually quite playable!

(This was actually the first time I'd performed a major de-soldering job on a double-sided board, it took best part of a day.. and was quite nerve racking.)