The game was working fine but you could hear only the sound fx, not the music.
Usually these kind of issues are related to either the DAC or the operational amplifier connected to the FM sound chip.
I used my external amplifier to probe the output of an operation amplifier and I could hear perfectly the music.
After checking for interrupted lines I noticed a missing cap.
Bridging the two pins restored the music.
Easy job!
Maybe the name “Kyohkoh-Toppa” doesn’t say anything to most of arcade collectors/fans but if ,instead,I said “BreakThru” many of you will remember a game whose goal is to drive a dune buggy to “breakthru” the enemy lines of five different areas.So, for those who still have not understood, “Kyohkoh-Toppa” is the japanese version of BreakThru released by Data East in February 1986 for the eastern market.
Here is the PCB:
Board booted fine but it had a graphic issue since sprites were missing some lines:
I noticed that problem went away if I flexed the board so there was some poor contact somewhere.In this kind of hardware all the graphics is generated in the bottom board so I reached it and found this:
Someone (certainly not manufacturer) replaced two TMM2018 300-MIL SRAMs with two 600-MIL equivalent ones adapting them in narrow sockets!For a better understanding of the package dimensions:
Not a neat job, for sure…Anyway, I could pinpoint sprites issue in the SRAM @11E (the one of the left picture) since problem was cleared when I pressed it.As you can see from picture they used some jumper wires on part side while patched some broken tracks on solder side :
So, I decided to remove this hack, check that all the RAM connections were fine and use a proper 300-MIL chip in a new socket :
In this way sprites were stably restored and board 100% fixed.
Another Nova 2001 repair log here after the one from Corrado.Here is the “patient” on the operating table today:
PCB was sent me flagged as “SOUND ERROR”, indeed when I fired it up, the music and sound FXs were only noises.Here is a record for a better understanding of what I mean:
All sound/FXs are generated by two AY-3-8910 chips so I went to probe them and found no activity on all their pins.This was due a missing clock on PIN22 of both (signal is shared) as shown on analog scope:
I could trace the CLOCK signal back to PIN9 of a 7474 @3E and comparing the chip with a good reference one using with my HP10529A confirmed trouble on this output:
It failed miserably when tested out-of-circuit:
Mission accomplished, another arcade PCB preserved!
Got from a friend this The Battle-Road PCB :
Honestly I never heard of this game before.Anyway, it runs on IREM M62 hardware which is the same one of Kung-Fu Master and other games.
My friend said that sprites was completely missing and he was right but comparing what I got with MAME emulation also text/characters colors was incorrect :
So time to investigate and start to study the sprites circuitry which is located on bottom board.Data from the six sprite ROMs are multiplexed by a custom maked “NANAO KNA6034201”, its outputs go to some TTLs (74LS157 and 74LS374) until they hit the RAMs I/O pins (four 2149 DRAMs) which were all stuck HIGH.Probing the custom revealed it did its job, all outputs were correctly toggling as well as piggybacking the four DRAMs didn’t change anything so fault was in the middle.When I probed the 74LS157 @H3 with my HP10529A logic comparator I got this:
So troubles on all its outputs that were confirmed from my logic proble which reported them as stuck HIGH.Obviously IC failed when tested out-of-circuit:
Fitted a new 74LS157 restored sprites but as I said early text/character colors were wrong compared to MAME emulation correct ones.Text colors BPROM was dumped fine so I went to dump the two ROMs containing this part of graphics and I found they were swapped into their respective sockets (on the left the wrong positioning, on the right the correct one) :
This fixed board completely.End of job.
Got this Nitro Ball PCB from my friend Corrado as not working:
When I first fired it up I was greeted by a solid black screen.Hardware uses, like other DATA EAST games, a custom 68000 CPU in QFP package marked “59” whose pinout is unkown since no schematics are available and nobody has yet figured it out.My first intention was to probe the RESET line on main CPU, this is the first thing I usually do when I got a totally dead board (along with CLOCK pin) but since I couldn’t I started with my visual inspection and I found this:
A 4.7uF 50V capacitor @C43 with anode terminal desoldered from its pad.This may seem a minor thing a but not in this case since this capacitor was part of the RESET circuitry along with a voltage monitor transistor (silkscreening suggests a PST518A IC but a generic BC547 transistor was used instead in order to detect a voltage and generate a RESET signal) :
Once replaced this capacitor board properly booted but all screen was red:
A dominant red color means that blue and green ones were missing so I traced them back to three transistors:
As you can see from picture above manifacturer/assembler used three compatible BC547 transistors compared to original silkscreened part adapting their different pinout by rotating them and twisting the base and collector legs.This caused a short circuit between the base and collector of the blue and green (TR2 and TR3 on picture) transistor.After clearing the short colors came back to normality.
No further issues were found on PCB so I could declare this one 100% fixed.