Aug 142019
 

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.

Repair – 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

Aug 132019
 

Got another Pacmania faulty.

This time the sprites were glitchy with some black lines

 

Custom 39 is usually involved in sprites generation but after testing with a good one problem remained.

There are two 74ls377 connected to it and one @A3 has one missing output.

Changing it fixed the board

 

 

Aug 132019
 

Received this board from a friend which booted to a static screen

 

Decided to have a look immediately to the 2k work ram which was a Toshiba which is normally prone to faults.

Changed with an Hitachi 2k

And game 100% fixed with no other errors

Aug 112019
 

Another custom IC successfully reproduced, it’s the Irem ‘KNA6032701’ , a 42 pin DIP 600mil IC used on M62 (Kung-Fu Master, Lode Runner, Spelunker and other), M75 (Vigilante) and M72 (on some  type of ‘M72-B-D board) hardwares

As usual I reproduced it my way by observing how it was reverse-engineered on bootleg boards obtaining in a board layout with same dimensions of original part :

Testing on a Kung-Fu Master PCB :

 Posted by at 10:26 am
Aug 022019
 

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.

 Posted by at 9:25 am