Sometimes it’s just matter of capacitors…We could call this repair log in this way, let’s read why.

I bought this not working  Vapor Trail – Hyper Offence Formation PCB on Ebay:

The board gave a static blank screen on power up:

Like other Data East games, hardware uses as main CPU a custom 68000 marked ’59’ :

Here you can see its pinout figured out by Porchy some time ago:

Data East ’59’ 68000 CPU Info

Probing it revealed static address/data bus, clock was present instead.Since it was not included in the above pinout I spent some time to figure out that pin 59 was the /RESET one.Probing it I found that on power up there was no transition from LOW to HIGH but pin went directly to HIGH state hence CPU didn’t get initialized.RESET circuit is a typical one made of the PST518 voltage monitor IC, a 47uF 50V electrolytic capacitor and a couple of resistors :

Checking in-circuit the ESR of this 47uF 50V capacitor @IC56 gave no reading, value was out of the 100Ohm range of my meter:

I removed it and out-of-circuit testing confirmed this capacitor was bad:

Replacing it restored a proper RESET signal so board successfully booted:

But sound was quiet despite adjusting the potentiometer and some interferences were present on screen too:

I went to measure the impedance of the electrolytic capacitors in analog sound circuit and I found many of them with out-of-specs value:

I replaced them all :

This restored a loud and a clear sound.As said in the beginning, it was only matter of capacitors!

Another Namco System 1 CPU board on the bench after the past one :

Board (coupled with a good ROM board) gave only a black screen with some green lines, watchdog was active :

I checked the three colors outputs and only the green was active, the other two were dead:

We saw in the past repair that there are three 6264 static RAMs, each one for a color, they are addressed by the custom ‘C120’ and data are processed by the custom ‘C116’  which generates the different shades (then formed into a single color and converted to analog signals from some resistor arrays)

Probing the RAMs revealed stuck signals on data pins of the ones @B2 (RED related) and E2 (BLUE).I removed them :

But during desoldering I decided to remove also the GREEN one @D2.They all failed when tested out-of-circuit:

But also with good RAMs I got no improvement, watchdog was no longer active but all three colors still dead.Probing the other RAMs on board, I found no data coming out the two 6264 @D6 and E6 despite address lines were active:

When tested both out-of-circuit actually only the one @E6 failed:

Finally the board booted but with missing sprites and music (ony FXs were present).Here’s a video using a World Stadium ’89 ROM board:

I noticed that if I piggybacked the 6264 RAM @L3 ( used by the custom ’30’ which controls the sound), the rustling sound I had instead of the music disappeared:

So I removed the RAM and it failed the test:

This restored full sound.Now the sprites issue.I noticed that, when using this CPU board with a Galaga88 ROM board, the sprites (that were competely missing when using the World Stadium ’89 one) were visible but garbled and blocky:

The two customs related to objects (the sprites address generator ’48’ and the sprites generator ’39’ ) were good but probing the two 74LS377 @A3 and A4 revealed stuck outputs:

I promptly removed them and they both failed when tested out-of-circuit:

Replacing them restored the sprites and fixed completely the board.Five RAMs and two TTL replaced to achieve this, a nice booty…