I bought this pretty rare Exzisus PCB as faulty from our member Corrado:

For the uninitiated it’s horizontal scrolling shooter arcade game released by Taito Corporation in 1987.There are two PCB version, one not JAMMA with separate RGB outputs for background and sprites, the other with a single video outputs and is JAMMA compliant.The one I got was the latter.

Once powered the board up I immediately noticed two issues : all sprites were horizontal lines shifted and repeated on each half of screen :

and  sound was missing at all (although I could hear some noises sign that amplifier was  good).Studying a bit the hardware, I could figure out how sprites were drawed.The four sprite EPROMS are addressed by a custom, marked ‘TC0010VC’ (there is another one for the backgrounds) while the data were written on two 6116 RAMs which were addressed by the same custom but not directly but through two 74LS273 latches and four 74ALS169 counters:

Probing the latter with my logic comparator I got troubles on the outputs of three of them so, although false readings are quite common for this kind of device I decided to remove them.Tested in my BK560A they all failed:

Once replaced these counters, the sprites were correctly restored:

So I could focus on the sound lack.Connecting an external amplifier to the analog output of the YM3012 DAC I could hear all the sound as well as on the input of the near TL074CN OP-AMP but nothing on its output :

This was confimed also on my analog scope (good input on the left, no output on the right):

Fitted a new TL074CN @J21 restored full sound.End of job.

Not a real repair but just a quick “dirty” fix for this Konami Teenage Mutant Hero Turtles PCB :

All was fine but  the music played at the start of a game (when turtles jump from palace) was missing :

A usual I started my troubleshooting with a visual inspection and I found soon the culprit.One of the two 640KHz ceramic resonator was missing:

I took it from a dead donor board :

and once fitted the missing music was restored.End of (small…) job.

Some days ago I bought on Ebay for cheap an untested original Sega Pengo PCB, today it arrived:

Buying a board as untested is always risky, you could ended up to have a not working one on hand and indeed mine was.I was greeted by a solid black screen when I powered it up, the main Z80 CPU didn’t reset properly.As schematics suggested the /RESET is generated by a counter 74LS161 @IC23 so I went to probe it and found it was missing clock signal.At this point I started to suspect some trouble in the timing signals generation.The Pengo manual has a troubleshooting section which suggests to check some iC in case the picture will not appear:

When I went to probe a 74LS74 @IC66 :

I found its outputs pin 5 and 6 were stuck high.I put a my fingers on it and it was really burning hot.Also comparing it against a good one with my HP10529A logic comparator confirmed my suspicions:

Once removed, the IC failed the out-of-circuit test:

Fitted a good IC fixed the board completely, no further issues were found.