PC Engine Core Grafx II

Originally this was going to be a repair as it was sold as not working, but it turned out the included power supply had the wrong polarity. After cutting the plug off and soldering on a new one with the correct polarity it powered right up.

It doesn't stop there though, the system had a hole drilled in the side and a scart cable wired directly to the motherboard. Not only is this ugly it isn't very practical when you want to pack it away or move it. I forgot to take a before picture but here is one from the auction.

I never drill extra holes or add switches etc if I can avoid it because I think it looks ugly and like to keep things original looking as possible. However since there was already a hole drilled in the side and there's not really any neat way to fill it or cover it up, I decided to widen it slightly and fit a 8 pin mini din connector for the scart cable.

Now all I had to do was fit a mini din plug to the scart lead and fit a RGB amplifier pcb inside the system, the company that did the mod (Raven Games London) just soldered directly to RGB so the image was quite dark.

They also made the mistake of wiring the 5v pin to pin 16 instead of pin 8 and didn't have a resistor joining the two. This put the TV in RGB mode but didn't auto change the channel, a minor issue but worth it for the cost of a resistor.

They also only wired a single ground in the scart plug to audio ground, all the ground pins *should* be connected on the TV but this isn't always the case so after adding jumper wires to all the ground pins I fired it up and....

It looks great, if only I had a better game to play on it. :)

Capcom System 1 (CPS1) Fitting a heatsink to the A01

By far the most common failure on CPS1 motherboards is the Capcom A01 custom chip followed by rams. Unlike rams the A01 cannot be easily replaced and can only be found on other CPS1 (and CPS2) motherboards.

To help try and get as much more life out of these chips as possible I decided to order some heatsinks and fit them to all my working boards (thanks to Winklepicker on J+ for the idea).

As you can see from this bad A01 I took a dremel to the die is quite small (1 cm x 1 cm).

I then went on RS looking for a suitable heatsink, there are 1 cm x 1 cm copper heatsinks on ebay sold for raspberry pi's but they would look a bit silly on a chip this size, they are also very short. It's my understanding that the bigger the better when it comes to heatsinks as they disperse heat better.

So I ended up ordering one of these http://uk.rs-online.com/web/p/heatsinks/7500885/ which covers the majority of the chip without blocking access to the pins (they may need reflowing in future) and is tall but not too tall to hit the B board that plugs in above it.

The sticky backing these heatsinks came with is pretty poor so I removed it and instead used Phobya which is a 2 part thermal compound you mix and it dries like glue. I already had this on hand from fitting heatsinks to ULA (zx spectrum) and SID (c64) chips in the past.

The finished result (yes I need to clean that flux up).

ABI Boardmaster Keyboard

My boardmaster 4000 didn't come with a keyboard so ever since it arrived I've been on the look out for one. You cannot really make the most of the system without it, anyway it is a rather unique 65 key serial 3 pin connector keyboard.

I wasn't bothered about having an original one and didn't think it would be much of an issue getting a old ps/2 keyboard running on the system as two different people have made adapters. Unfortunately the first one wasn't ever released publicly and the other one is available but at a price of $100 or $125 if you want a used ps/2 keyboard too.

As much of a bargain as that is I went looking for an alterative, ABI didn't help matters by using a top quality cherry made keyboard. As now in 2016 you've got keyboard collectors (yes that's a thing apparently) buying them up. Not only are they driving prices up but they butcher them by pulling off all keycaps, don't ask me what they do with them I have no idea.

While waiting to hear back from a keyboard collector who had one (minus all the keycaps of course) I came across this keyboard listed as a 'vintage studio keyboard' on ebay. As it had the correct layout and number of keys I took a chance on it and ended up winning it dirt cheap.

After receiving it and cracking it open I confirmed it had the correct cherry pcb. As this keyboard was used for different equipment I had to make a few changes, two 74LS08 needed to be populated along with a 1k resistor and a couple of jumpers needed to be changed to change it to serial from parallel. Also the data on the 8749 mcu had some incorrect character data compared to the original keyboard.

A big thanks to my friend Equites on ukvac who was willing to dump the 8749 in his original keyboard and I now have a fully working boardmaster keyboard for less than £10.

While searching I came across this pdf datasheet which has all the info you'd need to replicate the keyboard if anyone else happens to need one and aren't lucky enough to stumble across a cheap one on ebay. :)

Burnin' Rubber (Bump 'N Jump) repair

This was bought in a job lot and listed as untested, I thought there was a good chance it would work after making a jamma adapter for it but no such luck.

Powered it on and got nothing but a black screen, I could coin up and there was music so it was mostly working. Checking with a logic probe I had sync but no red, green or blue, all three pins were floating.

I decided to check the bottom pcb with the trusty hp logic comparator, this was a little tricky as the top board covers most of the bottom one. I was able to flip the top pcb to the right being careful not to short anything to the jamma adapter. I eventually found a bad 74LS74 at B11.

Bad 74LS74 removed.

New one fitted.

 Repair complete.

ABI Boardmaster 4000 repair

Another new toy to play with, this is a very useful bit of test equipment that can test chips not only out of circuit but also when they are still in circuit. I bought this knowing it had some issues but they are very rare and sought after so you cannot be too picky.

First I wanted to fix the lcd backlight which would flash on for a second then go off, this is a common problem with these things. It also made it hard to read the self test fail messages so looking on UKVAC forum there is a thread explaining how to wire a generic laptop inverter in place of the old one. I was impatient though and did not want to wait 2 weeks or more for one to arrive from China. The two surface mount capacitors looked like they had leaked which I've seen many times repairing Sega Game Gears.

I replaced them with high quality radials and the screen was now nice and clear and made it easy to read the 14! fail messages. I won't go over all the error messages again here but if you want to read more check this thread on UKVAC.

Twelve of the error messages gave part numbers to six different relays which from reading in circuit with a multi meter I could see were bad. The other two error messages didn't point to any parts but I was able to find them by metering every relay, it turned out to be two on the out of circuit testing pcb.

After replacing the eight bad relays...

the repair is complete.

Suitable replacement relays can be found here. - Thanks trm.

Taito AA017751 cocktail power supply repair

I am very slowly restoring a Taito black & white Space Invaders in between other projects. The time has come to rebuild the power supply, I fully recapped it including all the tantalums. One of the resistors was burnt out but there's no documentation online for this exact power supply, so I had to hope that the reading of 33 ohms was correct and replaced it with another 33 ohms.

I then tested it in the cabinet and the 12v, 18v and -5v were all spot on but the 5v was putting out 8.5v! luckily I didn't have the board hooked up at the time or it would have gone up in smoke.

Adjusting the 5v pot made no difference to the voltage. I went looking for documentation online again, backflipper on ukvac pointed me to a schematic in the moon alien manual but after looking it over my power supply is very different.

Then I found a very old newsgroup post by John from John's Jukes (www.flippers.com) that mentioned he had schematics for the AA017741 power supply. I sent an email and got a reply and a copy of the schematics almost instantly, thanks again John. The layout is slightly different but otherwise looks the same as the 51 version.

I looked over both the schematics and the board again and I narrowed the problem down to the TA7089P voltage regulator. A chip that hasn't been made for years and can be hard / expensive to find.

For a new old stock one anyway, I went the utsource route which basically means used pulls that have had their legs sanded and dipped in solder to make them look new again. I don't like this as it makes the legs extremely fragile but they are cheap and everything I've had from them has always worked.

The TA7089's arrived after about two weeks, I fitted a 'new' one to the power supply fired it up, 5.05v on the 5v line, success!.

I replaced the 555 timer too as chances are the 8.5v killed it.

Next the monitor speaking of which, TC if you're reading this I might have a spare chassis available at the end of this project.

My cap map is famous.

 

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CPS1 B Board repair

This capcom CPS1 B board (middle board) was running but the video output would not sync, usually this would be a C or A board fault but I'd already ruled them out by swapping them.

I went around the board checking the connection between the A and B board was solid with a multi meter and found two pins not making contact near the C board. This part of the board had taken a nasty knock at some point and cracked the near by resistor array in half, but one problem at a time.

First I desoldered the connector that had the two missing connections.

Now I could clearly see the two broken pins.

Once I replaced the connector with one from a scrap board sync was restored but there was a graphics glitch, most sprites had vertical lines going through them.

I replaced the two resistor arrays next to the c board as one was broken in half and one had a leg broken off. This made no difference.

I was convinced the issue was in this area since I'd already found so many other issues there. Running the board without the C board means the game won't work but it's the only way to access that area and probe around while the board is running.

I checked every pin on the two resistor arrays and noticed one was high while the others were all toggling. A closer look I could see the through hole had come away from the trace and probing the trace it was toggling away.

A tiny piece of kynar wire to repair the trace and the repair was complete.