PCB Repair Logs – Page 85

Ashura Blaster repair log

Jun 242015

Got this pcb from ebay marked with “cracking sound problems”

The game sounded like an old LP with a lot of scratches and missed some sounds.

On this board, the YM2610 handle FM synthesis and PCM samples.

Given the fact that it is very difficult that the sound chip will fail, I started to probe the smd stereo DAC YM3016.

I could hear the same cracked sound coming out and I was sure that changing it would fix the issues.

I found a donor board and soldered a new DAC.

Retested the pcb and same problems.

At this time I was quite sure that the sound chip itself was broken.

Suddendly I remembered the most obvious thing to test first: the sound rom C43-01!

It was a maskrom….marked Taito….they had the most unreliable supplier ever.

In the past, I found many Taito maskroms which caused gfx faults because of internal faults.

After cheking the maskrom on my eprom programmer one pin was not making contact and it was clear that is was an internal break.

Burning a 4mbit eprom with maskrom pinout (like a 27c4100) restored the sound.

Robocop 2 repair log

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Jun 242015

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!

Kyohkoh-Toppa (BreakThru) repair log

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Jun 232015

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.

Nova 2001 repair log #2

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Jun 232015

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!

The Battle-Road repair log

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Jun 232015

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.

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