![]() I decided to test with the logic comparator the which is mixing the bits from the rams : it reported some bad pins. So it was clear that these stripes where the “scattered” colours which should have been combined to make the ship correctly coloured. Tested with the logic probe they were pulsing correctly.Īt this time it was clear that the problem came from around there because shorting some pins changed the coloured stripes.ĭisabling the CS line of the rams, restored good backdrop, stars and enemies but your ship and missiles disappeared. 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. Worth of note is the score part of the display that was good. So I fixed the clock problem installing a 7402 and lifting provvisorily the resistance.Īfter booting up, unfortunately the game had another issue:Īfter some studying of the pcb schematics and some short circuiting I discovered that beneath these stripes there was the black background with the ![]() In the end the guys at SIDAM made this “modification” on purpose to the original Namco design! 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. 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. I then discovered that this 74128 is not common at all and it is used only on early namco pcbs. 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.īad luck, someone put wrong TTL as a place holder…. Traced back to a dead output of a The input coming from custom 07xx was OK. I checked the clock on the 3x z80s and it was missing. 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). I got this original namco untested pcb as a part of a deal.Īs always happens, untested =not working and infact upon booting up it was totally dead with only a fixed static screen.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |