Tuesday, 7 May 2019

Sega Choplifter PCB repair

I recently fixed a Sega Choplifter PCB. Its a System 2 board that I picked up a few years back.

From a quick visual inspection it was clear IC 152 & 153 we smashed and needed replacing. I'm not sure what had happened to them, they were half de-soldered on the underside and half missing as if they have be smashed up due to bad storage. I removed the leftovers of the broken bits and fitted two replacements. IC's positions in question, ready for a sockets and new parts.

After fitting replacement parts the self test ran and stopped with and Error for IC91. This is one of the CPU ROM's. After removing the ROM from the socket I could see the socket itself was caked in grime, I cleaned the socket and ROM legs and the game booted. Good news time to play a game...

Well it turned out the There were no sprites in the game, no nothing, couldn't really play a game. I also noticed in attract mode the helicopter and game title on the main screen was missing.

I did a bit of Google Kung-Fu and found a few forum posts about the PCB but nothing specific like the fault my PCB had.

I used the MAME source file to check which ROM's contained sprite data, with my trusty logic probe I went round checking various pins using the schematics. I honed in on the two banks of RAM that I had traced signal for the original Sprite ROM's,

 The fault turned out to be a 74LS32 logic OR gate. which was located at position IC107, this logic is used to control the Write Enable signal for the Sprite RAM. inputs to the Logic gates were happily toggling away but the output was always low and the I could tell by the way my probes LED was lit that something wasn't happy. The output should have been toggling but it wasn't. Piggybacking the IC with a known good chip didn't fix the problem and actually made the screen image worse but  still convinced it was at fault, I removed the suspect IC, fitted a new socket and replacement IC. The sprites were now back looking good!

Well good until the Tanks showed themselves, they came on to the screen with vertical lines running through them as shown below.

I decided to remove the other ROM's that deal with sprites and found pins 14 & 15, (the bottom two on either side) had been bent over when fitted in the socket at some point.

Two minutes later after using some long nose pliers, the legs were straightened and the ROM refitted. This fixed the problem with the lines running through the Tanks. 

The final thing I had already noticed was that the sound was badly distorted and quiet, you could hear all the sounds but something wasn't right. After a closer inspection of the sound section, I could see the audio amplifier has previously popped with a section of IC missing.

A Wonder Boy PCB came to the rescue as a temporary donor for a replacement amplifier. 

Once fitted all sounds and music played fine and that was it PCB fixed.

Sunday, 21 October 2018

Electrohome G05-805 repair and tube swap

G05-805 Tube swap.

From a friends cocktail cab.

The monitor came to me slightly faulty, the Contrast adjuster on the deflection PCB was totally out of spec. and was replaced. Also the Focus adjuster on the HV PCB was bad causing brightness issues on the monitor, this was simply 'worked' back and forth a few times and the issue cleared. The HV and deflection PCB's had previously been repaired and now was all good.

I also the chance to swap the tube over for a NOS one that was sold on the UKVac forums a few years back.

Needless to say the new tube gives a great image and only takes around five seconds from cold to show an image. Here's a few photos of the process. Yoke swap was interesting to see how moving it around altered the screen image.

Monday, 27 August 2018

Bonanza Enterprises Super Breakout Cocktail cabs


Monday, 13 August 2018

Tuesday, 3 July 2018

Sega Hang-On Arcade PCB fix

My Hang-On game failed recently while on, I returned to the game and the monitor was showing a black display and the attract sound appeared to be playing as normal. I re-powered the game and got the same black display with no sounds, test mode didn't work.

I check the PSU voltage and the 5V was steady across the four board stack.

I used my logic probe to quickly scan through some pins on the CPU, Clock and all data or address line were either high or low and not toggling as expected.

I opened the schematics and headed for the clock circuit on the CPU board.

Image below:

I had a good pulsing clock signal passing through the 74112 Flip-Flop, moving along the signal chain pin 4 of the 7404 Inverter was showing no signs of life, from this point on in the circuit the clock signal is divided up and sent to different areas of PCB, with the CPU being an essential component ro receive the clock signal to do anything like run the game.

I 'piggybacked' a new 7404 on top of the suspect one and the game started playing. I removed the IC and checked it in my tester. All 6 Inverter gates were faulty.

With a new IC soldered in place, the game is working fine again. The faulty IC was manufactured by Fujitsu with a date code of 8547, this era of IC's made by Fujitsu have a reputation for failing, Sega arcade PCB's do seem to have a fair amount of them installed...

Friday, 25 May 2018

Revival: Generation X 2018

Had a great weekend as mentioned by all, nice to catch up with old buddies and meet some new forum folk! Here's a few of my photos taken across the weekend.


Off we go... Myself, Alex and Dave Flynn sharing the ride up to Walsall.

Dino fever. No they're not for sale and we can't 'just put them in the back of your car'... ;)
The Nintendo Arcade area.

Nice view from the event hall.

A well deserved beer on Friday Evening with the gang.

Place your bets, how long until the Asteroids stops working.

A few Cabarets.

the British IBM on stage Saturday afternoon.

Pinball Alley

Where the hell did Marty go to, he's an impostor...

Me topping the high score on SHO beginner courses....

Er... Mame on a Vectrex!!!

The Pacman master takes a break to play some T&F.