Repair Logs – Page 97 – JAMMArcade.net

NANAO MS9-29T chassis repair log #1

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Apr 222015

Recently I finally got my first arcade cabinet from my friend ‘robotype’;

For the uninitiated the Astro City is a compact sitdown cabinet released from Sega in the 1993.It’s by far the most popular cabinet in Japan.It mounts a wide 29″ 15/24KHz monitor (Nanao MS8, some have Nanao MS9), its interface is JAMMA so widely compatible with most arcade PCBs.

After redone all the internal wiring and adapted the powering to 100V (main electricity in my country is 230V), I turned it on for the first time and I got a vertically crushed screen:

First thing I done was trying to adjust the vertical size through the pot on the remote board:

but I was not able since the pot was jammed.When I desoldered it, it fell off in pieces.The exact part is a 10KOhm manifactured by ALPS quite impossible to find nowadays so I opted for a generic trimmer:

With the new pot fitted I was able to correctly stretch the image vertically:

But the image was not stable, sometimes it crushed to become a horizontal line so I decided to furher investigate taking apart the chassis (NANAO MS9-29T model).First thing I’ve done was checking all the capacitors in-circuit with an ESR meter and I was able to found one bad which was clearly leaking and whose ESR was out of range of my meter (0-99 Ohms) :

Replaced it fixed all issues.

P.S.

For those interested I compiled a capacitor list of the NANAO MS9-29T chassis.You can view it from here (or download from site)

Nanao MS9-29 Arcade Chassis Capacitor List

Twin Cobra Repair Log

Apr 212015

Recently, I picked up an ‘untested’ Twin Cobra PCB off of eBay. As most of us are aware, when something is advertised as ‘untested’, 9 times out of 10 its completely broken. This Twin Cobra was no exception to this rule.

Out of the box, the game booted up to a flat black screen, zero activity at all. When I see this on unknown condition boards, the first thing I do is give it a thorough visual inspection. I generally look for rust/corrosion, deep scrapes and gouges severing traces, physically damaged capacitors and IC’s, etc. Right off the bat, I noticed the the Koyo 28mhz crystal at X1 was hanging on by a thread! The other three had snapped off at the base of the crystal, so it was time to find a replacement. I was able to find a donor crystal in my parts boards.

I desoldered what was left of the original crystal, and then I installed the donor. The donor is slightly faster than the original, but it should be OK until a proper replacement arrives in the mail.

The rest of the board looked good – no gouges, no other damage so to speak. At this point when I powered it up, the game sprang to life!

Everything appeared to be working as expected, so I coined up and tried a game. Almost instantly, the next fault presented itself. Some (not all) of the sprite layers were incorrect. When the tanks aimed at towards 7:00, their turret would disappear completely. When larger tanks were destroyed, their remnants would take priority over my helicopter.

I knew something was at fault either with the ram or layer priority sections of the video board. From here, I started reading up on the mame driver, as well as the memory map for Twin Cobra posted on Toaplan.org. From what I could tell, it looks like sprite priority is controlled by the bipolar roms present on the TP-011 SUB (graphics) pcb.

I gave the 82S123’s a closer look, the bipolar rom marked B30-22 on the parts side of the PCB had a factory defect! There was a small solder bridge connecting pins 5 and 6. I fired up my soldering iron and removed the bridge.

Fired the board up, all faults were cleared! Game now works 100%. It’s mind-blowing to think that a game manufactured in 1987 has only played properly some 28 years later. This Toaplan masterpiece lives to fight another day! Until next time…

Vendetta repair log #3

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Apr 142015

Had this board for a while now but hadn’t looked at it.

On booting the board up I got completely messed up graphics.

On my pre power up visual inspection I somehow missed the damage and solder blob on the 052109 tilemap generator.

I removed the solder using solder braid and straightened the legs up best I could with some fine tweezers. It took a while as I didn’t want to snap the legs off but I ended up with something I was happy with.

Fixing that gave me the graphics back but there were jailbars present.

Jailbars are usually a sign of a failed ROM and as the two MASKROM’s have previously been replaced for a pair of 27C400 EPROM’s I thought it was best I check these out first.
Both turned out to be fine so the next step was to check the address and data line to see if they were active.
Again I could find no problems here.

I then found the test menu which runs a self test on these ROM’s. The ROM at location 16I gave a different checksum each time I ran the test. A changing checksum can be a sign of a floating data pin. I already knew the data pins were active and that the ROM’s were good so I set to work with the multimeter checking continuity between the EPROM and the 051962 tilemap generator which these data line go to.
Eventually I found data pin 8 did not make it to the 051962.

I was able to patch this underneath the EPROM so it would be hidden (and protected).

On powering up all the jailbars were gone and the board is fixed.

Commodore 1084S-P1 repair log (part 1)

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Apr 052015

This was a quick fix .

Whilst testing the stereo sound of one of my CPS2 games I noticed the monitor display went blank all of a sudden. I thought there was a problem with the RGB connector but this was not to be the case.

I wasn’t getting a signal through the RGB connector or through composite on the back. Power led was on and neck glow was present so that was a good sign.

I opened up the monitor and discharged the tube using a flat-head screwdriver, a heavy gauge wire with two alligator clips on each end is also required.

Warning: Please don’t attempt to discharge a CRT unless you know what you’re doing!

See the following video from John’s Arcade for info on safely discharging CRT monitors.

Once discharged first thing I checked were the switches on the back of the monitor which gives the 1084 its various operating modes. Switches which handle those were fine & were set correctly. I recently re-flowed the solder to the connectors on the back which are notorious for creating intermittent problems.

I then began an inspection inside of the chassis, I was looking for bad capacitors in particular. I immediately spotted 1 really bad looking electrolytic that has seen better days.

I had a spare Panasonic/Matsushita 50v 4.7mf capacitor in my parts bin which I happily replaced the bad one with. This seems to have done the trick and my display is back again.

A few other caps are budging slightly at their tops but I don’t have the right values yet.

In the near future I am going to recap the entire chassis since it shouldn’t be too long before another one fails completely.

Lei Shen Zhuan Thunder Deity Biography (Chinese hack of Battle Garegga) repair log

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Mar 292015

First of all, my apologies for the kilometric title but this seems be the correct one according to MAME which has emulated this game after my dumps 🙂

A friend of mine sent me this Battle Garegga bootleg PCB for a repair :

saying it had bad sound.Infact it was scratchy and noisy:

Besides, sometimes it muted completely.Regarding this last issue, I traced it to a bad YM2151 FM (actually a rebadged version marked ‘PD2001’) sound synthesis chip, once replaced it I got no more mutings.As for noisy sound, connecting the analog output (PIN12) of the YM3012 DAC (a ‘KA3002’ rebadged chip also here) to an external amplifier revealed that sound came out distorted.

Replaced it fixed the sound completely

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