Rolling Thunder repair log #2

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Feb 042017
 

While I was playing this game from my collection  ,I discovered it was missing all the samples (gun shots, walk and so on).

The game is a Namco system86 with an additional daughter board used for the samples

Before beginning the troubleshooting I searched on Internet for a similar problem and found a repair log

where all the caps on the daughter board weere changed , restoring the samples.

I am not a fan of changing caps randomly so thanks to Atari I checked the schematics and

found that the on the daughterboard there is a little circuit which produce 24V out of the 5V for the op amp.

Around that circuit there was a hissing noise therfore I checked if the 24 volts were present which was confirmed.

I proceeded with my sound probe to see if from the op amp I could hear the samples but when I turned on the game,

it continued to reset itself….the watchdog was active.

At this point I was a little puzzled and tried to disconnect the daughterboard which granted me with the game that booted

but with missing background and crashed as soon as the attract mode began.

I took some customs from various Namco games and checked if the game booted but no luck.

Also I hadn’t another Rolling Thunder to check the two customs on the daughter board therefore I put the pcb apart for sometime.

After some weeks i resumed the pcb and without much hope I checked various TTLs until I found a 74LS244@A1 on the daughterboard

which had pin 12 not oscillating properly while the input was healthy (Fujistu part….)

 

I piggybacked it with a good one and the game booted briefly correctly.

After changing it, I returned to the original state with the gameplay without samples.

I tested the output of the op amp TL074 with the sound probe and I could hear the samples.

Ttherefore there could only be one cause which was the capacitor @C1 placed between the output and the daughterboard connector, which infact was tested as open with an ESR meter

Changing it restored all the samples.

 

 

Gaplus repair log

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Jul 022016
 

The game belonging to my personal collection didn’t boot anymore after several years kept in storage.

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Game was in mint condition but the address decoder custom 34 had lot of oxidation on the pins (common problem on these custom chips) so I proceeded to clean and reseat it paying particular attention to avoid breaking pins which generally are really weak.

Game booted but it developed the following problem

 

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After probing around on the rams and TTL for suspicious signals with no luck I decided to dig up my dead Gaplus board which I kept in my garage for Namco customs spare parts and checked one by one each custom.

After changing the CUS20 (tilemap and sprie address generator) the problem was fixed

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Foto 02-07-16 10 26 38

Foto 02-07-16 17 33 44Foto 02-07-16 17 34 11

 

Another Fujitsu chip left our world.

Super World Court repair log

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Jan 312016
 

Another pcb which was part of the cheap deal.

It was completely dead. Given that it is not an interesting game I was about to use it for spare parts when I asked my friend Caius if he ever repaired a Namco NA-1

He told me he once repaired one with a capacitor connected to the reset circuit of the 68000 which faulty and didn’t produce the reset signal.

I tested mine and to my surprise the reset was stuck low.

I changed the capacitor smd 22uF @C5 with one 1uF which I had available and the game booted.

Unfortunately the sound was completely missing, so I probed with my portable amplifier some smd capacitors which are know to be leaking very easily and I found one which interrupted the sound to the main ampli.

After changing it, the sound was very low with lot of background noise.

To end a long story short, I recapped many small smd caps with new ones and restored full volume.

This is a common problem with Namco NA-1 pcbs

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Bosconian repair log

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Dec 282015
 

I got this original namco untested pcb as a part of a deal.

As always happens, untested =not working and infact upon booting up it was totally dead with only a fixed static screen.

I was not too worried because I had a Dig Dug by Sidam which I use for spare parts and there are also schematics available (by Midway).

So I began my troubleshooting.

I checked the clock on the 3x z80s and it was missing.

Traced back to a dead output of a 74128@6B. The input coming from custom 07xx was OK.

clock

I started to search for a replacement and I took my Dig Dug pcb but in place of the 74128 there was a socketed 7402.

Bad luck, someone put wrong TTL as a place holder….

I then discovered that this 74128 is not common at all and it is used only on early namco pcbs.

I decided to contact my friend Charles Mcdonald to have a suggestion how to make the pcb boot just at least to see if it hadn’t other faults.

He told me that this 74128 is a really weird choice because it is used to drive signals over long distances and a 7402 is the equivalent to drive lower mA,  but I had to disconnect the R5 100ohm resistance.

In the end the guys at SIDAM made this “modification” on purpose to the original Namco design!

So I fixed the clock problem installing a 7402 and lifting provvisorily the resistance.

Foto 26-12-15 12 20 49

After booting up, unfortunately the game had another issue:

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After some studying of the pcb schematics and some short circuiting I discovered that beneath these stripes there was the black background with the

stars correctly generated by the custom.

Worth of note is the score part of the display that was good.

On the video pcb there were 4x 4kx1bit rams 2147 which I didn’t have as spares (Dig Dug uses another video board) , two of them were running very hot .

Tested with the logic probe they were pulsing correctly.

At this time it was clear that the problem came from around there because shorting some pins changed the coloured stripes.

Disabling the CS line of the rams, restored good backdrop, stars and enemies but your ship and missiles disappeared.

So it was clear that these stripes where the “scattered” colours which should have been combined to make the ship correctly coloured.

I decided to test with the logic comparator the 74174@7D which is mixing the bits from the rams : it reported some bad pins.

 

mixing

When I changed it I got no better results, but I got another positive feedback that the problems came from the circuit near the rams.

If I left out completely the chip from the socket I got good backdround and no ship.

The enemies and bases are part of the background circuit.

All the TTL which were used to address the rams were good so it was clear that some or all the 4x 2147 rams were bad.

At this time I decided to give up and to order some new rams in the hope that the problem was really there.

Just before placing the order I decided to take another look at the 2148 ram @4J which on my pcb was not placed and I thought of a schematic mistake.

rams

 

Now everything was clear : Namco prepared already the pcb to accept one 2148 ram which is 1k x 4bit instead of 4x 2147 rams, 4 k x 1bit !

The highest addr lines are not used so it can really be used as a replacement!

I had a lot of 2148 rams so I immediately desoldered all 4x 2147 rams and placed @4J the 2148 ram

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Finger crossed and when the game booted up I was finally welcomed with correct colours!

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