This version installs in 11J
Why a different version ?
Diagnostic mode is still available via Player 2 Start + Reset
Differences
Download link
Got a familiar Operation Wolf PCB that I offered to look at for a friend.
I’ve had this board several time over its life and this new fault was “no sound”. The sound actually stopped working when the owner hit the start button but the game could still be played.
I found the fault really quickly. Starting at the CPU I checked all the signals on the Z80.
Everything was doing what it should be doing except for the /NMI pin (pin 17) which was stuck high all the time.
The NMI is used to signal to the sound CPU to start playing a sound. The signal is generated by the custom PC060 chip nearby on pin 12
I transplanted the custom from my Rainbow Islands PCB to test and the sound all came right back.
Here you can see and hear the /NMI pulse as a new sound plays
So now I’ve confirmed the device at fault what do I do for a replacement. I have no scrap boards with one available. Furrtek has recreated the operation of this device and Caius has made a CPLD replacement that uses this code.
I’ve recapped the sound section and Caius is sending me a replacement but for now I’m happy that this is working again.
Lately I’ve gone through all the faulty/untested PCBs I never looked at (tons of them…) to check if there was something that was worth a repair.I found this Sega System 16B motherboard :
I plugged in a Golden Axe (conversion) ROM board and powered up the set.Board booted up, game was playable with good graphics but sound was missing :
The audio hardware is made of Z80 CPU plus a Yamaha YM2151 for music (and a NEC uPD7759 for speeches) :
Looking at schematics the serial data from the YM2151 (pin 21) is sent to the YM3102 DAC (pin 4) which then routes the analog signal to the TL084 OP-AMP :
Probing with the oscilloscope revealed the YM2151 serial data were present on the input of the YM3012 (pin 4) but the output (pin 11) tied to the OP-AMP was silent :
The DAC was likely fault so I replaced it :
This brought the sound back but it was faint and corrupted (except the speeches that was fine) :
The TL084 OP-AMP is the only part between the DAC and the final sound output :
It’s a well known prone to failure part so I went straight to replace it :
The sound was completely restored and board 100% working.End of job.
Got an original Passing Shot PCB for repair, as you may know it’s a tennis game released for System 16B hardware by Sega in 1988.
Board had its ‘FD1094’ battery-backed custom CPU module which was still alive since the board booted but sound was missing at all:
These are the times when an audio probe really comes in handy in diagnosing the fault helping you to figure out the nature of the lack of sound (if digital or analog).So I fired up this tool and started to listem to various points of the audio circuit :
For first I probed the outputs of the YM3812 DAC and I got sound from them, this meant the fault was in the analog circuit.Looking at schematics I followed the path, the sound was still present on the input of the volume potentiometer :
But then it was silent on the output which gives the signal to the Fujitsu MB3733 amplifier :
Schematics shows there is nothing between the output of the potentiometer and the input of the amplifier (apart from a 10uF electrolytic capacitor that was tested as good)
Metering the amplifier I found that pin 1 ( the input which takes the signal from the potentiometer) was almost shorted to pin 11 (+12V supply), there was only 12.4 Ohm of resistance :
The amplifier was likely bad so I removed it :
And replaced it putting also some thermal silicon grease for a better heat dissipation :
I powered the board up again and the sound was back.No other issue found hence I could declare this board 100% fixed and working.
Yet another Operation Wolf repair and this one gave me trouble.
First test we had watchdogging. All ROM’s checked out fine in the programmer and seeing nothing else obvious I removed the work RAM both of which failed.
Now on boot up I got a screen seemingly running game but all the screen was garbage.
Probing the data lines of the screen RAM show pretty much all of them across two RAM chips were dead. I desoldered and replaced them both.
Now I got a running game but the colours were messed up
There are two 74LS245’s attached to the data lines of the colour RAM at location IC78 & IC90. Probing these revealed stuck bits on IC78. Replacing this gave me perfect results on the colour test screen in test mode but dull colours in game. Other issues in-game showed me all the sprites were missing and the screen doesn’t scroll when entering a game.
Stupidly I chose to ignore the colour issue and concentrate on the other two (I will get back to this later).
The sprite and scrolling issue worried me because these areas are related to the PC080SN and PC0900J custom chips.
Paulcan69 sent me a scrapper PCB so I could rob the customs off it if needed so I started out by replacing the PC0900J.
Replacing this brought my sprites back but the scrolling issue was still present.
I didn’t enjoy replacing that IC so I started checking around to see if the scrolling issue could lie somewhere else.
I found nothing wrong so removed the PC080SN custom and replaced it with the spare but it made absolutely no difference. A lot of work time and effort for nothing.
I spent time over the course of the next few days looking into this but found nothing.
Eventually I got sick of looking at the washed out colours on screen and replaced IC90 to fix the last of the colour issues.
I couldn’t really believe it when this fixed my scrolling issue as well.
I still don’t understand why this chip caused the scrolling issue but I’m really glad it did.
All issue are now fixed on this board.
Onto the sound PCB.
The original sound PCB that came with this board was a complete write off. Every chip I pulled from this board was broken and both amps were also burning hot.
Among all the other boards that Paulcan69 had sent me he also kindly sent me a spare sound PCB for Muddymusic to have.
There was a sticker on this board saying “No Sound”.
On first test I found that the music played but the volume was really low. Turning the volume up to the maximum made the sound audible but not nearly enough.
I checked the resistance of the volume pot and found that if you move the pot off maximum setting then it read megaohms. I tried cleaning it but it didn’t work so I replaced it.
This made the sounds much better but like with most of the others I’ve repaired some of the samples were scrambled and didn’t stop playing when they should.
I quickly found another 74LS688 that was dead. Replacing this made the sounds stop when they should but the samples on channel A were scrambled.
Looking at the schematics shows where the sample data goes.
Using an audio probe I checked the output at pin 10 of the 5205. The sound was the same. This ruled out issues caused by bad caps and things like that.
Next I checked the 574 at IC33. Both the input and output looked good so moved onto the 74LS157 at IC 44.
Probing all the outputs with a logic probe showed pin 9 was stuck HIGH
Replacing this fixed all the samples.
That’s the last one fixed
Big thanks to Paulcan69 for the spares board. Without it this board would be scrap too.