Sega Hang-On PCB repairs

[smarty]

Having a working PCB set, it was easy to isolate the four boards that comprise of a complete set to find the faulty board. Repairs made as follows.

Sound Board 1 - Silent no audio.

No clock signal at Sound CPU. Traced back to the Oscillator, this feed a 74ALS109 at 12J, Clock signal present at the input. Nothing coming from the output pins 6&7. Removed IC, fitted socket and Replaced IC with new part. The clock signal now propagated through the board and there was lots of logic activity across the board. Very faint game audio could be heard, it certainly didn't sound right though. After a careful listen it was clear that lot of sounds were missing from the game... I used MAME and its ability to change the different channels of game audio to work out that the PCM sounds were completely missing and thee of the sound channels from the YM2203 we missing...

The PCM sound fault was traced back to a faulty Fujitsu LS157 at location 10D/E/F I can't really explain the fault finding process here, the available schematics are scanned and its difficult to follow them along and read pin numbers. Once I had a suspect IC I piggybacked a new IC and a I did have some of the PCM sound return, they were still mixed and garbled. Once replaced all PCM sound came back and sounded normal.

The final art of this fix was getting the missing sound channels back from the Yamaha sound generator. Using an O'scope on a working board I could clearly 'see' these sound channels moving with the game tune I could hear from the speakers. Moving back to the faulty board I could still see these channels coming out of the Sound IC. These analog audio channels propagate through some resistors and then feed into a TL084 Op amp IC at 12J and then hit the output connector, so again a quick piggyback of a new IC and Boom! We have sounds back. After replacing the IC and having a play test everything is sounding as it should.



More Hang-On repairs to follow in the near future, I have more Sound boards, CPU, Control and ROM boards that need looking at.

To be continued...

smarty2016-09-23 16:33:27

 

[dj_yt]

Good work!

I have a Hang-On board set knocking about that's on my todo list and an Enduro Racer that I need to fix and convert to a Space Harrier. God knows when I'll get round to doing them, but I look forward to reading your progress.

I noticed you picked up a System 24 based machine recently. Did you get it working?

 

[smarty]

Cheers Chris!

Yes I have the system 24 game working. I purchased a floppy disk emulator box of tricks that has the game ROM image on an SD card, after lots of teeth pulling I got it working.

 

[smarty]

My Hang On cab broke down when I loaned it to the last Revival show earlier in the year.... The game had been totally reliable for approximately 15 years prior to its journey to the show, well after being powered on for the morning the monitor image turned to garbage, foreground text was still visible, but the majority of graphics were a garbled mess and the game wouldn't actually start.





Tonight I fixed the game. First I confirmed the fault was on the CPU board, Hang-On comprises of a four board set which includes the mention CPU board, a Control/Video board and a ROM and Sound board. The game will run with Just the CPU and Control board connected, this makes it slightly easier to test whilst hanging out of that back of my cab! There are sprites and graphics missing and no sound but the game will run.

I knew the CPU ROM's and CPU RAM were working OK, The ROMS were verified and the RAM had previously been socketed so it was easy to confirm they were good.

Using my trusty logic probe I could see there was plenty of active logic across the CPU board, After looking the board over I homed in on a bank of Fujitsu 74LS157's, The Fujitsu IC's from this era of games have a reputation for going bad. Reading the schematic my understanding is that these bank of five 157's control the Address bus between the Main and Sub CPU's. All the inputs and output had active logic signals but select signal on pin 1 which decides which address bus signal should be active was stuck in a high state.



Tracing this back in the schematic, the signal comes from an LS109, Pin 3 the 'K' input was not showing as having any signal, again this was traced back to a 74LS32 at 8J (Labelled as 8H on the schematic!) Input pins 4 and 5 were active and pulsing away with data but the Output pin was showing no signs of life.. A quick piggyback test with a new 74LS32 proved this was the fault as the game screen came back good.

I removed and replaced the IC and the game is back in action.

Brmmmmm Brmmmmmmm!!!



smarty2016-09-27 19:46:33

 

[bonehead]

That's a cool fix.

You are getting good at these fixes now.
Keep up the good work smarty.

 

[Milky]

Most cabs are bullet proof until I stand near them.

 

[cosine]

Glad you got it running fella, I was gutted when it broke down at Revival lol

 

[smarty]

I was gutted when it broke down at Revival

So was I... Happy to have it working again though

Mart your boards are next on my list

 

[philmurr]

Excellent stuff again Smarty.

Great to see another board being brought back to life

 

[dj_yt]

Well done. Did you manage to fix this with the PCB hanging out of the cab with just a logic probe then? That's good work if so.

 

[smarty]

Chris,

Yes PCB hanging from the cab, crossed legs in a cramped space!

I need to make a test loom for HO as I have loads more boards that need looking at. Another thing to add to the list

 

[smarty]

I was O'scoping the analog audio circuits, but generally a logic probe is getting me by for most fixes I've made so far.