I was told the fault was with the sprites not being visible.
Visual inspection showed a pretty grubby looking PCB that has clearly had some work done before by the looks of it.
It also had this wiring harness soldered directly onto two pads of the edge connector. It was only 2 but I really hate this.
I fired the PCB up and sure enough I had the exact issue
Before receiving this board I had decided where I was going to look for the fault. After probing for a few minutes I was sure I was in the right place.
All these outputs were barely toggling so I went ahead an removed it.
As I had similar issue on my last Arkanoid repair I had a decent stock of spare 669 IC’s. New one fitted and another Arkanoid fixed.
Some months bought for my collection Vasara and Vasara 2 in bundle from an american guy.
From the beginning Inoticed that Vasara had very dimmed colours and required to adjust monitor constrast to the maximum in comparison to Vasara 2.
Since I was not familiar with this system I thought it was due to the motherboard revision which is earlier on Vasara ( and there is a factory mod to make it compatible)
After some months I decided to check on internet if someone had a similar problem and I found mentioned on system11 blog about Cave CV1000 colour problems.
According to him it’s a very common problems on SSV games and I found also mentioned on japanese blog sites afterward.
I checked with the oscilloscope the signals coming out from the 4 2sc1674 transistors ( RGB ans SYNC) and indeed all of them very about 2volts, same intensity of the inputs.
Signals in Vasara 2 in comparison were about 3,5V
I decided to change all of them and indeed it fixed the dimmed colours which are now very bright and crisp
What I find really curious is that all of them went faulty, I think probably the transistors choosen by Seta are not correct for this kind of load.
Maybe someone with a good electronic background can shed a light
PCB Repair LogsComments Off on The New Zealand Story repair log #5
Aug022019
Received for repair from New Zealand this The New Zealand Story PCB (sorry for the wordplay…), the one layer hardware revision :
Board booted up but graphics were totally wrong :
GFX data are stored in eight 28 pin 1Mbit MASK ROMs whose pinout is pretty identical to 32 pin 1Mbit non-JEDEC EPROM (extra pins apart)
Before dumping them I used my logic probe and found stuck upper address lines (pin 12-13-14-15)
I traced the address lines back to outputs of a 74LS174 @U9 whose inputs were floating, these came from a Fujitsu 74LS374 @U41:
Inputs of it were toggling but all outputs were stuck at undefined voltage level of 1.48V, this is the typical way of failure of Fujitsu TTLs :
The chip failed the out-of-circuit testing, all outputs were indeed in ‘Z’ (or high-impedance if you prefer) state :
Once replaced the IC the graphics were restored but I noticed some corruption on title screen :
I dumped the 1Mbit MASK ROMs and my programmer complained about the one @U7 :
This was a good chance to use one of my adapters I designed some time ago for replacing the 28 pin 1Mbit MASK ROMs with a TSSOP Flash ROM
But suddenly during power cycling the graphics went bad again :
I quickly pinpointed the fault to another 74LS374 @U10 with floating outputs, another Fujitsu one obviously :
Chip totally failed the out-of-circuit testing:
Graphics were now perfect so I started a game but controls didn’t work, the main character of both players moved by itself:
Looking at hardware I figured out the I/O circuit.The inputs from JAMMA connector go to some custom resistor arrays marked ‘X2-005’ and then signals are routed to a 52 pin SDIP custom chip marked ‘X1-004’ that handles them :
Resistor arrays did their job by pulling-up the signals and then routing them to the custom so most likely the ‘X1-004’ was bad.I played the card of replacing it but I had to struggle before finding a good spare as it seems this custom is quite prone to failure.I tried two donor parts but they were faulty until I caught the good one:
This fixed the controls and board completely.Repair accomplished.
