Repair Logs – Page 94 – JAMMArcade.net

Nova 2001 repair log #2

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

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.

Nitro Ball repair log

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Jun 212015

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.

Pang repair log #2

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Jun 162015

Got a friends Pang PCB here for repair.
He had carried out the ROM swap (made by ArcadeHacker) to desuicide it but he had no output although we could hear it playing blind.
The board is very clean and a visual check revealed nothing.
On powering the board up I got this screen

I could also hear the board did play blind so that’s a good sign.
I like to make little schematics for boards when I’m working on them and they don’t have any available and I quickly came up with this.

I started probing back from the RED pin on the JAMMA edge connector and soon came to a RAM chip at location 8C. Probing this chip and its counterpart gave me some odd looking signals which I got suspicious about.
These chips are CXK5814 SRAM chips and they seem the be the most unreliable RAM by comparison.
One of the RAM’s had all its data lines stuck LOW while the other chips data lines were all dead despite all the enable lines working as they should and the address lines active.
At this point I was certain they were dead but one last test was to ‘piggyback’ a known good RAM chip on top of the suspected bad one. I chose the one with the dead data lines to avoid potential contention and I got a partial image on screen.

I desoldered both the RAM chips and replaced them. I didnt have any spares in my RAM bin but found a couple of skinny 6116 RAM’s on a scrap bootleg board.

Fitting these I now got this wonderful sight.

Job done.

Major Title repair log

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Jun 072015

Many of you may think that repairing arcade boards is a difficult task but sometimes it’s not so (well, few times though…).Here is an example.

Got an IREM Major Title PCB (M82 hardware) from my friend Corrado (who is part of JAMMArcade team as contributor):

When I powered it up I was greeted from this rolling screen:

There was no SYNC at all.I traced this signal back to a 74LS32 @IC14 on video board but, after checked its logic, it seemed good.I noticed there were some socketed ICs both on CPU and video board.Two of them were TBP24S10 PROMs manifactured byTexas Instruments (you can read its specifications in our “datasheet” section).When I pulled of the socket the one @IC47 I got this:

PIN16 (VCC) was broken so IC was not powered at all.A little bit of “reconstructive surgery” on this (other adiacent wobbly ones) pin was enough to restore the correct video syncronism (later I found that outputs of this PROM were connected to a couple of custom ICs involved in video timing generation).

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