Mar 132021
 

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.

 

 

 Posted by at 4:10 pm

PLD Archive domain update

 General  Comments Off on PLD Archive domain update
Feb 232021
 

As of yesterday the PLD Archive wiki was locked for editing and it has been moved to the new domain of wiki.pldarchive.co.uk.
The link on this site has been updated but if you have bookmarks saved or whatever then these will need updated too.
As usual there will likely be broken links and errors so if you happen to find any then please do let me know. There is an email link on the main page of the new wiki. Likewise, if anyone has any PLD dumps or recreations, PCB pictures or IC pictures to contribute please also use that new email address to send them in.

Thank you

 Posted by at 5:41 pm

Taito PC080 & PC090 info

 Technical Info  Comments Off on Taito PC080 & PC090 info
Dec 302020
 

Channelmaniac has put together a couple of drawings to show the pinouts for the Taito PC080 and PC090 customs

Thanks again to Channelmaniac

 Posted by at 4:16 pm

Konami 054539 info

 Technical Info  Comments Off on Konami 054539 info
Dec 062020
 

Channelmaniac kindly sent me some tech info he made up recently for the 054539 custom found on some Konami boards.
Here we have the pinout for the chip and also the circuit conenctions
Thanks to Channelmaniac for sharing these

 Posted by at 6:43 am

Passing Shot (Sega System 16B) repair log

 PCB Repair Logs  Comments Off on Passing Shot (Sega System 16B) repair log
Oct 122020
 

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.

 

 Posted by at 3:51 pm