Corrado Tomaselli

Jul 012017
 

These system boards from Namco has a common problem: SMD capacitors

These caps expecially the ones produced in the 90s are very unreliable and sooner or later will start to leak

On my boards there isn’t one that has the ESR in a good range.

On Namco system NA ( Emeraldia, Tinkle Pit, Super World Court) or NB ( Point Blank, Nebulas Ray), the problems you will face are sound related ( low sound or scratchy ), on ND system ( Namco Classic Collections), the SMD caps are used also for the RGB amplifier and in addition you will get colour problems.

I will take as an example a Namco Classic Collection I just finished to repair and which had all the problems coming in about one week of intensive use after a while in storage.

 

First of all it started to have trails on the RED component of the image.

The system uses a common RGB amplier LM1203 which for example is used on the majority monitors neckboards

Here are the usual circuit taken from the schematics of the LM1203:

As you can see , on the inputs of each colour component you have to place a 10uF cap.

Namco engineers decided to use a 4,7uF but I tested and there are no differences between the two values.

So, if you have colour quality problems on your Namco Classics Collection pcbs, first thing is to recap the RGB input section using commercial

electrolitic caps.

 

I am not a fan of brute force recap, so with my ESR meter I usually check all the caps and change only the ones that have a very out of range value.

As said before, after few days I get no sound for a while and after about 5 minutes, you could hear it coming up but very scratchy.

The amplifier got also really hot after a short time.

The system uses a LA4705 sound amplifier

 

I probed with the ESR meter all the caps and found out the both the small ones 2,2uF placed on  IN1 and IN2 had a value of more than 99 ohms.

The other ones also were really not in the specification range but to get sound back it was enough to change the small ones.

 

As said the sound section of Namco system NA and NB is the same more or less, therefore if you start to have low sound and you don’t have an ESR meter,

change the 2,2uF, 47uF (33uF on the amp schematics) and 100uF one.

Nintendo Vs System repair log #2

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Jun 282017
 

I bought this system in a lot of faulty pcbs.

Game was booting but it had no sync and the graphic was all corrupted.

The OSC 21.477mhz was giving out around 12mhz

 

After changing it, the game was back to life but it was missing the blue component

Looking at the schematics , I could confirm that the RP004 video chip was giving good signal on the BLUE signal pin, therefore I started

to check the LM324 OP AMPS involved in the DAC circuit.

The output of the LM324 for the BLUE component was dead therefore I proceeded to change it but the game was not fixed yet despite now having a good signal

 

By turning the blue pot I could see briefly some “sparks” of blue ,therefore confirming that the blue component

was working again.

In the end it turned out that the blue pot had some cold joints on the ceramic base.

I reflowed the solder and the game was 100% fixed

Satan Of Saturn repair log

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Jun 282017
 

Got this game cheap for my collection because the seller stated that it has very noisy sound

When powered, the game had a constant white noise while music and the other sound effects were working correctly.

The sound problem was not due to the amplifier or bad caps but it was produced by the logic of the game.

To make a long story short, this game has a similar circuit to what Space Invaders use to produce analog sounds.

It uses a SN76477, which is a programmable sound chip which has a white noise function.

On Space Invaders and in this game, the chip continuosly output the white noise which is switched OFF and ON using operational amplifiers and it is modulated with capacitors and resistors to produce different sounds.

I downloaded the schematics from the US version ( called Zarzon ) where it is shown how the chip is connected to the LM3900 OP AMPS

 

 

Instead of trying to understand which of the two chips are broken, I piggybacked a good one on both chips until

the white noise disappeared.

Problem was fixed by changing the LM3900 Nr.47 on the schematics

Burnin’ Rubber repair log

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Jun 282017
 

I bought this game for my collection some months ago.

 

 

I tested briefly and it was OK. After a few weeks I decided to make a good play but the game developed a strange problem:

 

 

 

 

As you can see from the pics above, the screen was very dark and the brightness was not steady.

Also all the objects left trails of different brightness.

The problem was somewhat similar to when you don’t have video GND connected but as you can see

the text HI SCORE was repeated on top and bottom.

Adjusting the horizontal size of the image with the monitor pots ( vertical on the game) I noticed the screen didn’t shrink, it was like it had no borders.

I had immediately remembered that on the CPS1 hardware , on certain screens of some games ( 3 wonders selection screen for example)

the image is very dark and this is due to a flaw in the video circuit of the CPS1 hardware which doesn’t blank properly the video at the edges

leading to some monitor electronics to loose the black reference and behave strangely.

Charles McDonald on his website  http://www.techno-junk.org/ has a fix but right now the link is missing because he is restructuring the page.

 

Anyway back to the topic, I was convinced that my problem was due to video blanking not working properly, so I downloaded the Bump and Jump

schematics available from Bally (  the japanese ones are impossible to find ) and searched for a video blank signal and tested all the TTLs involved until I found this:

 

Output pin 5 of 74ls74@1B was floating and didn’t clear the 74LS273 connected to the video DAC

 

Therefore the video was not blanked properly on the edges.

Changing the TTL@1B  fixed the problem

 

Unfortunately after a couple of plays,  the pcb developed two other problems:

  1. Car didn’t go left
  2. car crash sound was broken

 

The first problem was fixed by replacing the 74LS367@4E on the sound board ( directly connected to the left direction pin)

Second problem was fixed by replacing one AY8910.

The game, for the moment, is working nicely 😉

May 252017
 

I got for my collection an untested boardset of Defender which was really in great conditions with no battery acid leak.

The boardset is the newer revision of Defender with the red label roms.

The game is very difficult to find it in working conditions nowadays because it has several weak points, expecially the 24 drams 4116 which are very unreliable to due the fact the run very hot and they require +5V, -5V and +12V to be applied at the same time, otherwise they will be damaged.

The old Williams PSU become defective and often they ruin the drams.

After converting it to Jamma and triple checked all the power supply lines I booted it up but the game appeared to be dead.

Fortunately Defender has a lot of bibliography and a very good manual which is also a troubleshooting guide.

I check the clock and it was working correctly, but after checking the reset line I saw it was pulled low all the time.

To make it short, Defender has two +12V power supplies, one regulated and one not.

You have to supply +12V also to the not regulated one because it is needed for the power on reset.

After adding that +12V t, the game booted but as soon as the message ALL UNIT OK was displayed it reset in a never ending loop.

I found out that the problem was caused by the ribbon cable , after reseating it a couple of times, the game booted correctly.

I started the game but the ship kept always going down.

With the test menu , it reported that the down direction was always pushed.

I checked the interface board which has the circuit for the inputs. the hex inverters 4049 were all toggling correctly, the pull up resistors were good therefore there was only one chip to check: the Peripheral Interface adapter 6821P.

I desoldered it and installed another one I had on stock taken from another arcade games.

Since I had no way to test it, I decided to put a 40 pin socket just to be sure I could easily swap it with another one in case it was defective.

Luckily the inputs were now correct, thefore I could declare the board fixed.

In the end I was very lucky because the game had only the input problem and no other issues.